Treating hepatitis B virus infections by administering receptor associated protein (RAP)
1. A method of treating a subject against hepatitis B virus (HBV) infection, the method comprisingidentifying the subject in need of being treated against HBV infection;
- andadministering to the subject a therapeutically effective amount of purified receptor associated protein (RAP) that binds to low density lipoprotein receptor related protein (LRP) and a HBV vaccine,wherein the subject is not diagnosed of having liver cancer, and the RAP comprises an amino acid sequence that has at least 90% identity to SEQ ID NO;
6,thereby treating the subject against HBV infection.
The specification provides compositions and methods of reducing a risk of a HBV infection in a subject and of treating a subject infected with HBV.
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- 1. A method of treating a subject against hepatitis B virus (HBV) infection, the method comprising
identifying the subject in need of being treated against HBV infection;
administering to the subject a therapeutically effective amount of purified receptor associated protein (RAP) that binds to low density lipoprotein receptor related protein (LRP) and a HBV vaccine, wherein the subject is not diagnosed of having liver cancer, and the RAP comprises an amino acid sequence that has at least 90% identity to SEQ ID NO;
thereby treating the subject against HBV infection.
- View Dependent Claims (2)
- 3. A method of treating a subject against HBV infection, the method comprising administering to the subject a therapeutically effective amount of an anti-HBV agent consisting of receptor associated protein (RAP), thereby treating the subject against HBV infection, wherein the RAP comprises an amino acid sequence that has at least 90% identity to SEQ ID NO:
- 6 and the RAP binds to low density lipoprotein receptor related protein (LRP).
- View Dependent Claims (4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
- 18. A method of inhibiting HBV infection of a liver cell, the method comprising contacting the liver cell with an effective amount of an anti-HBV agent consisting of receptor associated protein (RAP), wherein the RAP comprises an amino acid sequence that has at least 90% identity to SEQ ID NO:
- 6 and the RAP binds to low density lipoprotein receptor related protein (LRP), thereby inhibiting HBV infection of the liver cell.
- View Dependent Claims (19, 20, 21, 22)
This application is a U.S. National Phase Application under 35 U.S.C. § 371 of International Patent Application No. PCT/US2014/025788, filed on Mar. 13, 2014, which claims priority to U.S. Patent Application Ser. No. 61/783,327, filed Mar. 14, 2013, the disclosure of which is incorporated herein by reference in its entirety.
The claimed methods relate to reducing a risk of a hepatitis B virus (HBV) infection in a subject and to treating a subject infected with HBV.
Hepatitis B is an infectious inflammatory illness of the liver caused by HBV. The disease has caused epidemics in parts of Asia and Africa, and hepatitis B is highly endemic in China. About a third of the world population has been infected with HBV at one point in their lives, and approximately 300 million people worldwide are chronically infected with HBV. Hepatitis B is a major global health problem and the most serious type of viral hepatitis as it puts people at high risk of death from cirrhosis of the liver and hepatocellular carcinoma.
A vaccine against hepatitis B has been available since 1982. The hepatitis B vaccine, which is made from inactivated HBV, is about 95% effective in preventing infection and its chronic consequences. Once infected with HBV, however, there are only two types of agents approved to treat a chronic HBV infection. Pegylated interferons are effective in only a small fraction of patients, have serious side effects, and are expensive. Nucleoside or nucleotide analogues are potent inhibitors of HBV DNA replication, but they fail to clear the covalently closed circular (ccc) DNA, the template of viral DNA replication and protein expression. They also fail to block the expression of viral proteins. For example, hepatitis B surface antigen (HBsAg) is believed to promote viral persistent infection by inducing immune tolerance. Nucleoside analogue therapy rarely promotes the loss of HBsAg followed by the rise of corresponding antibody (called HBsAg seroconversion), a marker of sustained virological response. In this regard, targeting host factors for HBV entry may block the viral lifecycle at the first step. Targeting HBsAg secretion may also promote HBsAg seroconversion.
Chronic infection with HBV greatly increases the risk to develop liver cancer. Current therapies with interferons and nucleoside or nucleotide analogues suffer from low response rate or induction of drug resistance. Maintenance of a persistent infection in the liver requires continuous release of infectious virions from infected hepatocytes for de novo infection of regenerated cells.
Despite decades of extensive search, host factors required for HBV entry into hepatocytes remain ill defined. At present, heparan sulfate proteoglycan (HSPG) has been identified as a low-affinity HBV receptor. A high-affinity, proteineous HBV receptor remains obscure, although a sodium-dependent, co-transporting polypeptide (NTCP) has recently been proposed as a HBV receptor (Yang H et al., eLife 1: e00049). HBV expresses three envelope proteins: large (L), middle (M), and small (S). These three proteins are translated from the same gene through alternative, in-frame start codons, with the M protein comprising extra N-terminal sequence (preS2 domain) over the S protein, and the L protein comprising extra N-terminal sequence (preS1 domain) over the M protein. The envelope proteins, especially the L protein, are believed to mediate HBV attachment to the high-affinity HBV receptor. Many proteins have been identified that bind to a HBV envelope protein, but none of them are receptors for HBV on hepatocytes.
The present disclosure is based, in part, on the discovery that low density lipoprotein receptor (LDLR), low density lipoprotein receptor related protein (LRP), and Factor Xa (FXa), interact with HBV, e.g., as components of a HBV receptor complex, on hepatocytes. Accordingly, the present specification provides methods of treating a subject against a HBV infection, e.g., reducing a risk of a HBV infection in a subject and treating a subject infected with HBV.
In some aspects, the present disclosure provides methods of treating a subject infected with HBV, the method comprising administering to a subject infected with HBV a therapeutically effective amount of LDLR, LRP, receptor associated protein (RAP), LDLR inhibitor, LRP inhibitor, FXa inhibitor, or any combination thereof, to thereby treat the subject infected with HBV. The LDLR, LRP, and/or RAP can be, e.g., in a purified form, e.g., as a component of a pharmaceutical composition. In one embodiment, the methods include administering to the subject a pegylated interferon or a nucleoside or nucleotide analogue.
The present disclosure also features methods of reducing a risk of a HBV infection in a subject, the method comprising administering to a subject at risk of a HBV infection a therapeutically effective amount of LDLR, LRP, RAP, LDLR inhibitor, LRP inhibitor, FXa inhibitor, or any combination thereof, to thereby reduce the risk of a HBV infection in the subject. The LDLR, LRP, and/or RAP can be, e.g., in a purified form, e.g., as a component of a pharmaceutical composition. In some embodiments, the method includes administering to the subject a HBV vaccine.
In some aspects, the present disclosure provides uses of LDLR, LRP, RAP, LDLR inhibitor, LRP inhibitor, FXa inhibitor, or any combination thereof, to treat a subject against a HBV infection, e.g., reduce a risk of a HBV infection in a subject and treat a subject infected with HBV, the use comprising administering to the subject a therapeutically effective amount of LDLR, LRP, RAP, LDLR inhibitor, LRP inhibitor, FXa inhibitor, or any combination thereof. The LDLR, LRP, and/or RAP can be, e.g., in a purified form, e.g., as a component of a pharmaceutical composition.
In some embodiments, the LDLR comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:2. In one embodiment, the LRP comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:4. In some embodiments, the RAP comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:6.
In one embodiment, the LDLR inhibitor comprises an anti-LDLR antibody or antigen-binding fragment thereof, e.g., a monoclonal antibody, polyclonal antibody, chimeric antibody, humanized antibody, single chain antibody, Fab fragment, or F(ab′)2 fragment. In some embodiments, the LDLR inhibitor comprises an inhibitory nucleic acid effective to specifically reduce expression of LDLR, e.g., a LDLR expression reducing small interfering RNA molecule or antisense nucleic acid.
In one embodiment, the LRP inhibitor comprises an anti-LRP antibody or antigen-binding fragment thereof, e.g., a monoclonal antibody, polyclonal antibody, chimeric antibody, humanized antibody, single chain antibody, Fab fragment, or F(ab′)2 fragment. In some embodiments, the LRP inhibitor comprises an inhibitory nucleic acid effective to specifically reduce expression of LRP, e.g., a LRP expression reducing small interfering RNA molecule or antisense nucleic acid.
In some embodiments, the FXa inhibitor comprises an anti-FXa antibody or antigen binding fragment thereof, e.g., a monoclonal antibody, polyclonal antibody, chimeric antibody, humanized antibody, single chain antibody, Fab fragment, or F(ab′)2 fragment. In one embodiment, the FXa inhibitor is selected from the group consisting of antistasin, antistasin-related peptides, tick anticoagulant peptide (TAP), fondaparinux, draparinux, rivaroxaban, apixaban, betrixaban, edoxaban, and otamixaban.
In one embodiment, two or more of LDLR, LRP, RAP, LDLR inhibitor, LRP inhibitor, and FXa inhibitor are administered, e.g., orally, intravenously, or by injection, to the subject, e.g., a mammal, a human. The LDLR, LRP, and/or RAP can be, e.g., in a purified form, e.g., as a component of a pharmaceutical composition.
The present disclosure also features methods of identifying a candidate anti-HBV agent, the method comprising providing a cell expressing a polypeptide comprising an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:2 and/or 4; providing a HBV; contacting the cell with the HBV in the presence of a test compound; determining a level of HBsAg secretion; and comparing the level of HBsAg secretion in the presence of the test compound with the level of HBsAg secretion in the absence of the test compound, wherein a reduced level of HBsAg secretion in the presence of the test compound than in its absence indicates that the test compound is a candidate anti-HBV agent.
In some embodiments, the cell expresses a polypeptide comprising an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:2. In one embodiment, the cell expresses a polypeptide comprising an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:4. In some embodiments, the test compound is selected from the group consisting of deoxyribonucleic acids, ribonucleic acids, polypeptides, and small molecules.
In one aspect of the disclosure, pharmaceutical compositions are provided that comprise a compound that inhibits or reduces interaction between HBV and HBV receptor complex, wherein HBV receptor complex comprises LDLR, LRP, and FXa; and a pharmaceutically acceptable carrier. In some embodiments, the compound is selected from the group consisting of deoxyribonucleic acids, ribonucleic acids, polypeptides, and small molecules.
In yet a further aspect of the disclosure, compositions comprising a therapeutically effective amount of LDLR, LRP, RAP (e.g., in purified form), or any combination thereof; and a pharmaceutically acceptable carrier, are provided. In some embodiments, the LDLR comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:2. In one embodiment, the LRP comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:4. In some embodiments, the RAP comprises an amino acid sequence that has at least 90% identity, e.g., at least 92%, 95%, 96%, 97%, 98%, or 99% identity, to SEQ ID NO:6. In some embodiments, the composition comprises a combination of two or more of LDLR, LRP, and RAP. In some embodiments, the composition comprises a FXa inhibitor, a pegylated interferon, a nucleoside or nucleotide analogue, a HBV vaccine, or any combination thereof.
As used herein, the term “hepatitis B” refers to an infectious inflammatory illness of the liver caused by the HBV. This disease and its symptoms are well-known in the art and are described herein.
As used herein, “treatment” or “treating” is an approach for obtaining beneficial or desired results, including clinical results. For purposes of this invention, beneficial or desired clinical results include, but are not limited to, one or more of the following: alleviating one or more symptoms resulting from the disease, diminishing the extent of the disease, stabilizing the disease (e.g., preventing or delaying the worsening of the disease), preventing, reducing risk, or delaying the spread (e.g., reinfection) of the disease, preventing or delaying the recurrence of the disease, delay or slowing the progression of the disease, ameliorating the disease state, providing a remission (partial or total) of the disease, decreasing the dose of one or more other medications required to treat the disease, delaying the progression of the disease, increasing the quality of life, and/or prolonging survival. Also encompassed by “treatment” is a reduction of pathological consequence of HBV infection. The methods of the invention contemplate any one or more of these aspects of treatment.
Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Methods and materials are described herein for use in the present invention; other, suitable methods and materials known in the art can also be used. The materials, methods, and examples are illustrative only and not intended to be limiting. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. Other features and advantages of the invention will be apparent from the following detailed description and figures, and from the claims.
The methods and uses described herein are based, at least in part, on the discovery that LDLR, LRP, and FXa interact with HBV, e.g., as components of a HBV receptor complex, on hepatocytes and that HBV infection of liver cells can be suppressed by a LDLR inhibitor, a LRP inhibitor, RAP, a FXa inhibitor, antistasin and/or antistasin-related peptides (Tuszynski et al., J Biol Chem 262:9718-23, 1987; Nutt et al., J Biol Chem 263:10162-7, 1988), as well as by silencing the expression of LRP or LDLR by small interfering RNA (siRNA) or short hairpin RNA (shRNA). Accordingly, a therapeutic strategy provided herein involves inhibiting interaction between LDLR and LRP on hepatocytes and HBV, thereby inhibiting HBV infection. Inhibiting this interaction can be performed in a number of ways, e.g., by administering RAP to sequester both LDLR and LRP, or antistasin or antistasin-related peptides to inhibit L protein cleavage. Alternatively, or in combination, soluble LDLR and/or LRP proteins, or fragments thereof, could compete with cognate proteins on the surface of a hepatocyte to bind HBV particles in circulation. Another option is to silence the expression of LRP and/or LDLR on hepatocytes by RNA interference.
Accordingly, provided herein are compositions and methods for treating a subject infected with HBV by administering a therapeutically effective amount of a LDLR inhibitor, LRP inhibitor, RAP, LDLR, LRP, and/or a FXa inhibitor such as antistasin or an antistasin-related peptide (Tuszynski et al., J Biol Chem 262:9718-23, 1987; Nutt et al., J Biol Chem 263:10162-7, 1988). Also provided herein are compositions and methods of reducing a risk of a HBV infection, which include administering to a subject at risk of a HBV infection a therapeutically effective amount of LDLR inhibitor, LRP inhibitor, RAP, LDLR, LRP, and/or a FXa inhibitor such as antistasin or an antistasin-related peptide. In some embodiments, the methods described herein include administering a combination of two or more, e.g., three or more, four or more, five or more, or all six, of a LDLR inhibitor, LRP inhibitor, RAP, LDLR, LRP, and/or FXa inhibitor such as antistasin or an antistasin-related peptide. The methods described herein can further include administering to the subject a HBV vaccine, a pegylated interferon, or a nucleoside or nucleotide analogue. Such an approach is highly recommended for infants born to HBV infected mothers, especially if the mother is HBeAg positive.
A subject can be selected on the basis that they are infected with HBV, are suspected to be infected with HBV, and/or are at risk of a HBV infection. It is well within the skills of an ordinary practitioner to recognize a subject that is infected with HBV, suspected to be infected with HBV, or at risk of a HBV infection. A subject that is infected with HBV, suspected to be infected with HBV, or at risk of a HBV infection is, for example, one having one or more symptoms of the condition or one or more risk factors for developing the condition. Symptoms of HBV infection are known to those of skill in the art and include, without limitation, general ill-health, extreme fatigue, loss of appetite, nausea, vomiting, body aches, mild fever, dark urine, jaundice, serum-sickness-like syndrome, acute necrotizing vasculitis (polyarteritis nodosa), membranous glomerulonephritis, papular acrodermatitis of childhood (Gianotti-Crosti syndrome), inflammation of the liver, cirrhosis, and hepatocellular carcinoma. A subject that has or is at risk of a HBV infection is one with known risk factors such as infants born to infected mothers, people with high-risk sexual behavior (e.g., people who have sexual contact with an infected person, have multiple sex partners, have a sexually transmitted disease, and men who have sexual encounters with other men), partners and household contacts of infected people, injecting drug users, people who frequently require blood or blood products, recipients of solid organ transplantation, people at occupational risk of HBV infection, including health-care workers, and travellers to countries with high rates of hepatitis B. The methods are effective for a variety of subjects including mammals, e.g., humans. The subject can be an adult or child.
The LDLR is well known in the art and is a mosaic protein that mediates the endocytosis of cholesterol-rich LDL. LDLR is a cell-surface receptor that recognizes apoprotein B 100, which is embedded in the phospholipid outer layer of LDL particles. The LDLR also recognizes the apoE protein found in chylomicron remnants and VLDL remnants (IDL). In humans, the LDLR protein is encoded by the LDLR gene. It is the prototype of the LDLR gene family, which also includes LRP, LRP-1b, megalin, very low density lipoprotein receptor (VLDLR), apoE receptor 2 (or LRP8), and multiple epidermal growth factor repeat containing protein (MEGF7). Several examples of LDLR are highlighted below in Table 1.
In one example, LDLR can be encoded by a 2583 base pair sequence found on chromosome 19 of the human genome (SEQ ID NO:1). The protein, as shown below, is 860 residues long (SEQ ID NO:2).
LDLR Nucleic Acid Sequence
LDLR Protein Sequence
LRP, also known as LRP1, alpha-2-macroglobulin receptor (A2MR), apolipoprotein E receptor (APOER), and cluster of differentiation 91 (CD91), is a protein forming a receptor found in the plasma membrane of cells involved in receptor-mediated endocytosis. In humans, the LRP protein is encoded by the LRP1 gene. LRP is highly expressed in the liver, the target of HBV infection. Moreover, LRP shows polarized distribution on basolateral membrane of hepatocytes (facing blood). Several examples of LRP are highlighted below in Table 2.
In one example, LRP can be encoded by a 13635 base pair sequence found on chromosome 12 of the human genome (SEQ ID NO:3). The protein, as shown below, is 4544 residues long (SEQ ID NO:4).
LRP Nucleic Acid Sequence
LRP Protein Sequence
Receptor associated protein (RAP) or low density lipoprotein receptor-related protein associated protein 1 (LRPAP1) is a chaperone protein that is encoded in humans by the LRPAP1 gene. LRPAP1 is involved with trafficking of certain members of the LDL receptor family including LRP and LRP2. It is a glycoprotein that binds to LRP, as well as to other members of the LDLR family. It acts to inhibit binding of all known ligands for these receptors, and may prevent receptor aggregation and degradation in the endoplasmic reticulum, thereby acting as a molecular chaperone. It may be under the regulatory control of calmodulin, since it is able to bind calmodulin and be phosphorylated by calmodulin-dependent kinase II. Several examples of RAP are highlighted below in Table 3.
In one example, RAP can be encoded by a 1074 base pair sequence found on chromosome 4 of the human genome (SEQ ID NO:5). The protein, as shown below, is 357 residues long (SEQ ID NO:6).
RAP Nucleic Acid Sequence
RAP Protein Sequence
Factor Xa (thrombokinase, known eponymously as Stuart-Prower factor) is the activated form of the coagulation factor X (FX). Factor Xa (FXa) is an enzyme, a serine endopeptidase, which plays a key role at several stages of the coagulation system. Factor X is synthesized in the liver. The most commonly used anticoagulants in clinical practice, warfarin and the heparin series of anticoagulants and fondaparinux, act to inhibit the action of FXa in various degrees. Several examples of FX are highlighted below in Table 4.
FXa can cleave the L envelope protein present on the surface of HBV. Moreover, a 7-aa antistasin-related peptide (Tuszynski et al., J Biol Chem 262:9718-23, 1987; Nutt et al., J Biol Chem 263:10162-7, 1988), a direct FXa inhihbitor, can block HBV infection of HepaRG cells, demonstrating that L protein cleavage by FXa is critical for HBV infectivity. Cleavage of the L protein switches HBV binding from HSPG, the low-affinity HBV receptor, to a high-affinity HBV receptor, e.g., LDLR or LRP.
Accordingly, FXa inhibitors can be used to treat HBV infection or to reduce a risk of a HBV infection. In some aspects of the methods described herein, the 7-aa antistasin related peptide (or antistasin itself) can be used to inhibit or reduce HBV infection. Since FXa is a key enzyme in the blood coagulation cascade, many small molecular inhibitors exist that can be utilized in the present methods. For example, tick anticoagulant peptide (TAP), fondaparinux, draparinux, rivaroxaban, apixaban, betrixaban, edoxaban, otamixaban, or any combination thereof can be used in the methods described herein.
Therapeutic Proteins, Nucleic Acids, Vectors, and Host Cells
In one aspect, the invention includes nucleic acids encoding LDLR, LRP, and RAP polypeptides, fragments, and variants thereof. A nucleic acid sequence encoding an exemplary LDLR polypeptide is provided in SEQ ID NO:1. The amino acid sequence encoded by SEQ ID NO:1 is provided in SEQ ID NO:2. A nucleic acid sequence encoding an exemplary LRP is provided in SEQ ID NO:3. The amino acid sequence encoded by SEQ ID NO:3 is provided in SEQ ID NO:4. A nucleic acid sequence encoding an exemplary RAP is provided in SEQ ID NO:5. The amino acid sequence encoded by SEQ ID NO:5 is provided in SEQ ID NO:6.
LDLR, LRP, and RAP nucleic acids described herein include both RNA and DNA, including genomic DNA and synthetic (e.g., chemically synthesized) DNA. Nucleic acids can be double-stranded or single-stranded. Where single-stranded, the nucleic acid can be a sense strand or an antisense strand. Nucleic acids can be synthesized using oligonucleotide analogs or derivatives (e.g., inosine or phosphorothioate nucleotides). Such oligonucleotides can be used, for example, to prepare nucleic acids that have altered base-pairing abilities or increased resistance to nucleases.
The term “isolated nucleic acid” means a nucleic acid, e.g., DNA or RNA, that is not immediately contiguous with both of the coding sequences with which it is immediately contiguous (one on the 5′ end and one on the 3′ end) in the naturally occurring genome of the organism from which it is derived. Thus, in one embodiment, an isolated LDLR, LRP, or RAP nucleic acid includes some or all of the 5′ non-coding (e.g., promoter) sequences that are immediately contiguous to the LDLR, LRP, or RAP nucleic acid coding sequence, respectively. The term includes, for example, recombinant DNA that is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule (e.g., a genomic DNA fragment produced by PCR or restriction endonuclease treatment) independent of other sequences. It also includes a recombinant DNA that is part of a hybrid gene encoding an additional polypeptide sequence.
The invention includes vectors, preferably expression vectors, containing a nucleic acid that encodes the proteins described herein. As used herein, the term “vector” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked and can include, e.g., a plasmid, cosmid, or viral vector. The vector can autonomously replicate or it can integrate into a host cell'"'"'s DNA. Viral vectors include, e.g., replication-defective retroviruses, adenoviruses, and adeno-associated viruses.
A vector can include a LDLR, LRP, or RAP nucleic acid in a form suitable for expression of the nucleic acid in a host cell. Preferably a recombinant expression vector includes one or more regulatory sequences operatively linked to the nucleic acid sequence to be expressed. The term “regulatory sequence” includes promoters, enhancers and other expression control elements (e.g., polyadenylation signals). Regulatory sequences include those that direct constitutive expression of a nucleotide sequence, as well as tissue-specific regulatory and/or inducible sequences. The design of the expression vector can depend on such factors as the choice of the host cell to be transformed, the level of expression of protein desired, and the like. The expression vectors of the invention can be introduced into host cells to thereby produce LDLR, LRP, or RAP polypeptides encoded by nucleic acids as described herein.
The recombinant expression vectors of the invention can be designed for expression of LDLR, LRP, or RAP polypeptides in prokaryotic or eukaryotic cells. For example, polypeptides of the invention can be expressed in E. coli, insect cells (e.g., using baculovirus expression vectors), yeast cells, or mammalian cells (e.g., CHO or COS cells). Suitable host cells are discussed further in Goeddel (1990) Gene Expression Technology: Methods in Enzymology 185, Academic Press, San Diego, Calif. Alternatively, the recombinant expression vector can be transcribed and translated in vitro, for example using T7 promoter regulatory sequences and T7 polymerase.
Expression of proteins in prokaryotes is most often carried out in E. coli with vectors containing constitutive or inducible promoters directing the expression of either fusion or non-fusion proteins. Fusion vectors add a number of amino acids to a protein encoded therein, usually to the amino terminus of the recombinant protein. Such fusion vectors typically serve three purposes: 1) to increase expression of recombinant protein; 2) to increase the solubility of the recombinant protein; and 3) to aid in the purification of the recombinant protein by acting as a ligand in affinity purification. Often, a proteolytic cleavage site is introduced at the junction of the fusion moiety and the recombinant protein to enable separation of the recombinant protein from the fusion moiety subsequent to purification of the fusion protein. Such enzymes, and their cognate recognition sequences, include Factor Xa, thrombin and enterokinase. Typical fusion expression vectors include pGEX (Pharmacia Biotech Inc; Smith and Johnson, Gene 67:31-40, 1988), pMAL (New England Biolabs, Beverly, Mass.) and pRIT5 (Pharmacia, Piscataway, N.J.) that fuse glutathione S-transferase (GST), maltose E binding protein, or protein A, respectively, to the target recombinant protein.
One can maximize recombinant protein expression in E. coli by expressing the protein in host bacteria with an impaired capacity to proteolytically cleave the recombinant protein (Gottesman (1990) Gene Expression Technology: Methods in Enzymology 185:119-128, Academic Press, San Diego, Calif.). Another strategy is to alter the nucleic acid sequence of the nucleic acid to be inserted into an expression vector so that the individual codons for each amino acid are those preferentially utilized in E. coli (Wada et al., Nucleic Acids Res 20:2111-2118, 1992). Such alteration of nucleic acid sequences of the invention can be carried out by standard DNA synthesis techniques.
Modified versions of peptides disclosed herein are referred to as “peptide derivatives,” and they can also be used in the new methods. For example, peptide derivatives of a peptide can be used instead of that peptide in therapeutic methods described herein. Peptides disclosed herein can be modified according to the methods known in the art for producing peptidomimetics. See, e.g., Kazmierski, W. M., ed., Peptidomimetics Protocols, Human Press (Totowa N.J. 1998); Goodman et al., eds., Houben-Wevl Methods of Organic Chemistry: Synthesis of Peptides and Peptidomimetics, Thiele Verlag (New York 2003); and Mayo et al., J. Biol. Chem. 278:45746, 2003. In some cases, these modified peptidomimetic versions of the peptides and fragments disclosed herein exhibit enhanced stability in vivo, relative to the non-peptidomimetic peptides.
Methods for creating a peptidomimetic include substituting one or more, e.g., all, of the amino acids in a peptide sequence with D-amino acid enantiomers. Such sequences are referred to herein as “retro” sequences. In another method, the N-terminal to C-terminal order of the amino acid residues is reversed, such that the order of amino acid residues from the N-terminus to the C-terminus of the original peptide becomes the order of amino acid residues from the C-terminus to the N-terminus in the modified peptidomimetic. Such sequences can be referred to as “inverso” sequences.
Peptidomimetics can be both the retro and inverso versions, i.e., the “retro-inverso” version of a peptide disclosed herein. The new peptidomimetics can be composed of D-amino acids arranged so that the order of amino acid residues from the N-terminus to the C-terminus in the peptidomimetic corresponds to the order of amino acid residues from the C-terminus to the N-terminus in the original peptide.
Other methods for making a peptidomimetics include replacing one or more amino acid residues in a peptide with a chemically distinct but recognized functional analog of the amino acid, i.e., an artificial amino acid analog. Artificial amino acid analogs include β-amino acids, β-substituted β-amino acids (“β3-amino acids”), phosphorous analogs of amino acids, such as α-amino phosphonic acids and α-amino phosphinic acids, and amino acids having non-peptide linkages. Artificial amino acids can be used to create peptidomimetics, such as peptoid oligomers (e.g., peptoid amide or ester analogues), β-peptides, cyclic peptides, oligourea or oligocarbamate peptides; or heterocyclic ring molecules.
Nucleic acids disclosed herein also include both RNA and DNA, including genomic DNA and synthetic (e.g., chemically synthesized) DNA. Nucleic acids can be double-stranded or single-stranded. Nucleic acids can be synthesized using oligonucleotide analogs or derivatives (e.g., inosine or phosphorothioate nucleotides). Such oligonucleotides can be used, for example, to prepare nucleic acids with increased resistance to nucleases.
The term “purified” refers to a LDLR, LRP, or RAP nucleic acid (or LDLR, LRP, or RAP polypeptide) that is substantially free of cellular or viral material with which it is naturally associated, or culture medium (when produced by recombinant DNA techniques), or chemical precursors or other chemicals (when chemically synthesized). Moreover, an isolated nucleic acid fragment is a nucleic acid fragment that is not naturally occurring as a fragment and would not be found in the natural state.
In some embodiments, the invention includes nucleic acid sequences that are substantially identical to a LDLR, LRP, or RAP nucleic acid. A nucleic acid sequence that is “substantially identical” to a LDLR nucleic acid has at least 90% identity (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or identical) to the LDLR nucleic acid sequence represented by SEQ ID NO:1. A nucleic acid sequence that is “substantially identical” to a LRP nucleic acid has at least 90% identity (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or identical) to the LRP nucleic acid sequence represented by SEQ ID NO:3. A nucleic acid sequence that is “substantially identical” to a RAP nucleic acid has at least 90% identity (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or identical) to the RAP nucleic acid sequence represented by SEQ ID NO:5. For purposes of comparison of nucleic acids, the length of the reference nucleic acid sequence will be at least 50 nucleotides, but can be longer, e.g., at least 60 or more nucleotides.
To determine the percent identity of two amino acid or nucleic acid sequences, the sequences are aligned for optimal comparison purposes (i.e., gaps can be introduced as required in the sequence of a first amino acid or nucleic acid sequence for optimal alignment with a second amino or nucleic acid sequence). The amino acid residues or nucleotides at corresponding amino acid positions or nucleotide positions are then compared. When a position in the first sequence is occupied by the same amino acid residue or nucleotide as the corresponding position in the second sequence, then the molecules are identical at that position. The percent identity between the two sequences is a function of the number of identical positions shared by the sequences (i.e., % identity=# of identical positions/total # of overlapping positions×100). The two sequences may be of the same length.
The percent identity or homology between two sequences can be determined using a mathematical algorithm. A non-limiting example of a mathematical algorithm utilized for the comparison of two sequences is the algorithm of Karlin and Altschul, Proc. Natl. Acad. Sci. USA 87:2264-2268, 1990, modified as in Karlin and Altschul, Proc. Natl. Acad. Sci. USA 90:5873-5877, 1993. Such an algorithm is incorporated into the NBLAST and XBLAST programs of Altschul et al., J Mol Biol 215:403-410, 1990. BLAST nucleotide searches can be performed with the NBLAST program, score=100, wordlength=12 to obtain nucleotide sequences homologous to LDLR, LRP, or RAP nucleic acid molecules of the invention. BLAST protein searches can be performed with the XBLAST program, score=50, wordlength=3 to obtain amino acid sequences homologous to LDLR, LRP, and RAP protein molecules of the invention. To obtain gapped alignments for comparison purposes, Gapped BLAST can be utilized as described in Altschul et al., Nucleic Acids Res. 25:3389-3402, 1997. When utilizing BLAST and Gapped BLAST programs, the default parameters of the respective programs (e.g., XBLAST and NBLAST) can be used. See online at ncbi.nlm.nih.gov.
In other embodiments, the invention includes variants, homologs, and/or fragments of certain LDLR, LRP, or RAP nucleic acids, e.g., variants, homologs, and/or fragments of the LDLR, LRP, or RAP nucleic acid sequences represented by SEQ ID NOs:1, 3, and 5, respectively. The terms “variant” or “homolog” in relation to LDLR, LRP, or RAP nucleic acids include any substitution, variation, modification, replacement, deletion, or addition of one (or more) nucleotides from or to the sequence of a LDLR, LRP, or RAP nucleic acid. The resultant nucleotide sequence may encode an LDLR, LRP, or RAP polypeptide that has at least 50% of a biological activity (e.g., binding to histone mRNAs) of the referenced LDLR, LRP, or RAP polypeptides, respectively (e.g., SEQ ID NOs:2, 4, and 6, respectively). In particular, the term “homolog” covers homology with respect to structure and/or function as long as the resultant nucleotide sequence encodes or is capable of encoding a LDLR, LRP, or RAP polypeptide that has at least 50% of the biological activity of LDLR, LRP, or RAP encoded by a sequence shown herein as SEQ ID NO:1, 3, and 5, respectively. With respect to sequence homology, there is at least about 90% (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or 100%) homology to the sequence shown as SEQ ID NO:1, 3, and 5, respectively. The term “homology” as used herein can be equated with the term “identity.”
“Substantial homology” or “substantially homologous,” where homology indicates sequence identity, means at least 90% identical (e.g., at least about 92%, 95%, 96%, 97%, 98%, or 99%) sequence identity, as judged by direct sequence alignment and comparison. “Substantial homology” when assessed by the BLAST algorithm equates to sequences which match with an EXPECT value of at least about 7, e.g., at least about 9, 10, or more. The default threshold for EXPECT in BLAST searching is usually 10.
Also included within the scope of the present invention are certain alleles of certain LDLR, LRP, or RAP genes. As used herein, an “allele” or “allelic sequence” is an alternative form of LDLR, LRP, or RAP. Alleles can result from changes in the nucleotide sequence, and generally produce altered mRNAs or polypeptides whose structure or function may or may not be altered. Any given gene can have none, one, or more than one allelic form. Common changes that give rise to alleles are generally ascribed to deletions, additions, or substitutions of amino acids. Each of these types of changes can occur alone, or in combination with the others, one or more times in a given sequence.
The invention also includes nucleic acids that hybridize, e.g., under stringent hybridization conditions (as defined herein) to all or a portion of the nucleotide sequences represented by SEQ ID NOs:1, 3, and 5, or complements thereof. The hybridizing portion of the hybridizing nucleic acids is typically at least 15 (e.g., 20, 30, or 50) nucleotides in length. The hybridizing portion of the hybridizing nucleic acid is at least about 90%, e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or 100%, identical to the sequence of a portion or all of a nucleic acid encoding a LDLR, LRP, or RAP polypeptide, or to its complement. Hybridizing nucleic acids of the type described herein can be used as a cloning probe, a primer (e.g., a PCR primer), or a diagnostic probe. Nucleic acids that hybridize to the nucleotide sequence represented by SEQ ID NO:1, 3, or 5, are considered “antisense oligonucleotides.”
High stringency conditions are hybridizing at 68° C. in 5×SSC/5×Denhardt'"'"'s solution/1.0% SDS, or in 0.5 M NaHPO4 (pH 7.2)/1 mM EDTA/7% SDS, or in 50% formamide/0.25 M NaHPO4 (pH 7.2)/0.25 M NaCl/1 mM EDTA/7% SDS; and washing in 0.2×SSC/0.1% SDS at room temperature or at 42° C., or in 0.1×SSC/0.1% SDS at 68° C., or in 40 mM NaHPO4 (pH 7.2)/1 mM EDTA/5% SDS at 50° C., or in 40 mM NaHPO4 (pH 7.2) 1 mM EDTA/1% SDS at 50° C. Stringent conditions include washing in 3×SSC at 42° C. The parameters of salt concentration and temperature can be varied to achieve the optimal level of identity between the probe and the target nucleic acid. Additional guidance regarding such conditions is available in the art, for example, by Sambrook et al., 1989, Molecular Cloning, A Laboratory Manual, Cold Spring Harbor Press, N.Y.; and Ausubel et al. (eds.), 1995, Current Protocols in Molecular Biology, (John Wiley & Sons, N.Y.) at Unit 2.10.
Also included in the invention are genetic constructs (e.g., vectors and plasmids) that include a LDLR, LRP, or RAP nucleic acid described herein, operably linked to a transcription and/or translation sequence to enable expression, e.g., expression vectors. A selected nucleic acid, e.g., a DNA molecule encoding a LDLR, LRP, or RAP polypeptide, is “operably linked” to another nucleic acid molecule, e.g., a promoter, when it is positioned either adjacent to the other molecule or in the same or other location such that the other molecule can control transcription and/or translation of the selected nucleic acid. Such constructs are useful for, for example, gene therapy to treat a subject against HBV infection, e.g., reduce a risk of a HBV infection in a subject and treat a subject infected with HBV. Skilled practitioners will understand that soluble forms of LDLR, LRP, and RAP can be expressed and secreted from cells to interact with HBV.
Also included in the invention are various engineered cells, e.g., transformed host cells, which contain a LDLR, LRP, or RAP nucleic acid described herein. A transformed cell is a cell into which (or into an ancestor of which) has been introduced, by means of recombinant DNA techniques, a nucleic acid encoding a LDLR, LRP, or RAP polypeptide. Both prokaryotic and eukaryotic cells are included. Mammalian cells transformed with a LDLR, LRP, or RAP nucleic acid can include host cells for an attaching enteric organism, e.g., intestinal cells, HeLa cells, and mouse embryonic fibroblasts. Prokaryotic cells can include bacteria, e.g., Escherichia coli. An engineered cell exemplary of the type included in the invention is an E. coli strain that expresses LDLR, LRP, or RAP.
Certain LDLR, LRP, and RAP polypeptides are also included within the present invention. Examples of such polypeptides are LDLR, LRP, and RAP polypeptides and fragments, such as the one shown as SEQ ID NOs:2, 4, and 6. Also included within the present invention are certain fragments of LDLR, LRP, and RAP polypeptides, e.g., fragments of LDLR, LRP, and RAP polypeptides may include at least one mRNA binding domain, or other useful portion of a full-length LDLR, LRP, or RAP polypeptide. For example, useful fragments of LDLR, LRP, or RAP polypeptides include, but are not limited to, fragments having mRNA binding activity, and portions of such fragments.
The terms “protein” and “polypeptide” both refer to any chain of amino acids, regardless of length or post-translational modification (e.g., glycosylation or phosphorylation). Thus, the terms “protein” and “polypeptide” include full-length naturally occurring isolated proteins, as well as recombinantly or synthetically produced polypeptides that correspond to the full-length naturally occurring proteins, or to a fragment of the full-length naturally occurring or synthetic polypeptide.
Fragments of a protein can be produced by any of a variety of methods known to those skilled in the art, e.g., recombinantly, by proteolytic digestion, and/or by chemical synthesis. Internal or terminal fragments of a polypeptide can be generated by removing one or more nucleotides from one end (for a terminal fragment) or both ends (for an internal fragment) of a nucleic acid that encodes the polypeptide. Expression of such mutagenized DNA can produce polypeptide fragments. Digestion with “end-nibbling” endonucleases can thus generate DNAs that encode an array of fragments. DNAs that encode fragments of a protein can also be generated, e.g., by random shearing, restriction digestion, chemical synthesis of oligonucleotides, amplification of DNA using the polymerase chain reaction, or a combination of the above-discussed methods. Fragments can also be chemically synthesized using techniques known in the art, e.g., conventional Merrifield solid phase FMOC or t-Boc chemistry. For example, peptides of the present invention can be arbitrarily divided into fragments of desired length with no overlap of the fragments, or divided into overlapping fragments of a desired length.
A purified or isolated compound is a composition that is at least 80% by weight the compound of interest, e.g., a LDLR, LRP, or RAP polypeptide. In general, the preparation is at least 90% (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or 100%) by weight the compound of interest. Purity can be measured by any appropriate standard method, e.g., column chromatography, polyacrylamide gel electrophoresis, or HPLC analysis.
In certain embodiments, LDLR, LRP, and RAP polypeptides include sequences substantially identical to all or portions of naturally occurring LDLR, LRP, and RAP polypeptides. Polypeptides “substantially identical” to the LDLR, LRP, and RAP polypeptide sequences described herein have an amino acid sequence that is at least 90% (e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or 100%), identical to the amino acid sequences of the LDLR, LRP, and RAP polypeptides represented by SEQ ID NOs:2, 4, and 6, respectively (measured as described herein). For purposes of comparison, the length of the reference LDLR, LRP, and RAP polypeptide sequence is at least 50 amino acids, e.g., at least 60 or 80 amino acids, or the entire length of the wild-type sequence.
In the case of polypeptide sequences that are less than 100% identical to a reference sequence, the non-identical positions are preferably, but not necessarily, conservative substitutions for the reference sequence. A “conservative amino acid substitution” is one in which the amino acid residue is replaced with an amino acid residue having a similar side chain. Families of amino acid residues having similar side chains have been defined in the art. These families include amino acids with basic side chains (e.g., lysine, arginine, histidine), acidic side chains (e.g., aspartic acid, glutamic acid), uncharged polar side chains (e.g., glycine, asparagine, glutamine, serine, threonine, tyrosine, cysteine), nonpolar side chains (e.g., alanine, valine, leucine, isoleucine, proline, phenylalanine, methionine, tryptophan), beta-branched side chains (e.g., threonine, valine, isoleucine) and aromatic side chains (e.g., tyrosine, phenylalanine, tryptophan, histidine).
Where a particular polypeptide is said to have a specific percent identity to a reference polypeptide of a defined length, the percent identity is relative to the reference polypeptide. Thus, a polypeptide that is 50% identical to a reference polypeptide that is 100 amino acids long can be a 50 amino acid polypeptide that is completely identical to a 50 amino acid long portion of the reference polypeptide. It also might be a 100 amino acid long polypeptide that is 50% identical to the reference polypeptide over its entire length.
LDLR, LRP, and RAP polypeptides of the invention include, but are not limited to, recombinant polypeptides and natural polypeptides. Also included are nucleic acid sequences that encode forms of LDLR, LRP, or RAP polypeptides in which naturally occurring amino acid sequences are altered or deleted. Certain nucleic acids of the present invention may encode polypeptides that are soluble under normal physiological conditions.
Antibodies to LDLR, LRP, and FXa
Antibodies can be produced that bind to LDLR, LRP, or FXa. For example, an antibody can bind to LDLR, LRP, or FXa and reduce or inhibit LDLR, LRP, and FXa activity. The term “antibody” as used herein refers to an immunoglobulin molecule or immunologically active portion thereof, i.e., an antigen-binding fragment. Examples of immunologically active portions of immunoglobulin molecules include F(ab′) and F(ab′)2 fragments, which retain the ability to bind antigen. Such fragments can be obtained commercially, or using methods known in the art. For example, F(ab′)2 fragments can be generated by treating the antibody with an enzyme such as pepsin, a non-specific endopeptidase that normally produces one F(ab′)2 fragment and numerous small peptides of the Fc portion. The resulting F(ab′)2 fragment is composed of two disulfide-connected Fab units. The Fc fragment is extensively degraded and can be separated from the F(ab′)2 by dialysis, gel filtration or ion exchange chromatography. F(ab′) fragments can be generated using papain, a non-specific thiol-endopeptidase that digests IgG molecules, in the presence of a reducing agent, into three fragments of similar size: two Fab fragments and one Fc fragment. When Fc fragments are of interest, papain is the enzyme of choice because it yields a 50,000 Dalton Fc fragment; to isolate the F(ab′) fragments, the Fc fragments can be removed, e.g., by affinity purification using protein A/G. A number of kits are available commercially for generating F(ab′) fragments, including the ImmunoPure IgG1 Fab and F(ab′)2 Preparation Kit (Pierce Biotechnology, Rockford, Ill.). In addition, commercially available services for generating antigen-binding fragments can be used, e.g., Bio Express, West Lebanon, N.H.
The antibody can be a polyclonal, monoclonal, recombinant, e.g., a chimeric, de-immunized or humanized, fully human, non-human, e.g., murine, or single chain antibody. In some embodiments the antibody has effector function and can fix complement. In some embodiments, the antibody has reduced or no ability to bind an Fc receptor. For example, the antibody can be an isotype or subtype, fragment or other mutant, which does not support binding to a Fc receptor, e.g., it has a mutagenized or deleted Fc receptor binding region. The antibody can be coupled to a toxin or imaging agent.
Methods for making suitable antibodies are known in the art. A full-length protein or antigenic peptide fragment thereof can be used as an immunogen, or can be used to identify antibodies made with other immunogens, e.g., cells, membrane preparations, and the like, e.g., E rosette positive purified normal human peripheral T cells, as described in U.S. Pat. Nos. 4,361,549 and 4,654,210.
Methods for making monoclonal antibodies are known in the art. Basically, the process involves obtaining antibody-secreting immune cells (lymphocytes) from the spleen of a mammal (e.g., mouse) that has been previously immunized with the antigen of interest (e.g., a cancer-related antigen) either in vivo or in vitro. The antibody-secreting lymphocytes are then fused with myeloma cells or transformed cells that are capable of replicating indefinitely in cell culture, thereby producing an immortal, immunoglobulin-secreting cell line. The resulting fused cells, or hybridomas, are cultured, and the resulting colonies screened for the production of the desired monoclonal antibodies. Colonies producing such antibodies are cloned, and grown either in vivo or in vitro to produce large quantities of antibody. A description of the theoretical basis and practical methodology of fusing such cells is set forth in Kohler and Milstein (Nature 256:495, 1975), which is hereby incorporated by reference.
Mammalian lymphocytes are immunized by in vivo immunization of the animal (e.g., a mouse) with a cancer-related antigen. Such immunizations are repeated as necessary at intervals of up to several weeks to obtain a sufficient titer of antibodies. Following the last antigen boost, the animals are sacrificed and spleen cells removed.
Fusion with mammalian myeloma cells or other fusion partners capable of replicating indefinitely in cell culture is effected by known techniques, for example, using polyethylene glycol (“PEG”) or other fusing agents (See, Milstein and Kohler, Eur J Immunol 6:511, 1976, which is hereby incorporated by reference). This immortal cell line, which is preferably murine, but can also be derived from cells of other mammalian species, including but not limited to rats and humans, is selected to be deficient in enzymes necessary for the utilization of certain nutrients, to be capable of rapid growth, and to have good fusion capability. Many such cell lines are known to those skilled in the art, and others are regularly described.
Procedures for raising polyclonal antibodies are also known. Typically, such antibodies can be raised by administering the protein or polypeptide of the present invention subcutaneously to New Zealand white rabbits that have first been bled to obtain pre-immune serum. The antigens can be injected at a total volume of 100:1 per site at six different sites. Each injected material will contain synthetic surfactant adjuvant pluronic polyols, or pulverized acrylamide gel containing the protein or polypeptide after SDS-polyacrylamide gel electrophoresis. The rabbits are then bled two weeks after the first injection and periodically boosted with the same antigen three times every six weeks. A sample of serum is then collected 10 days after each boost. Polyclonal antibodies are then recovered from the serum by affinity chromatography using the corresponding antigen to capture the antibody. Ultimately, the rabbits are euthanized, e.g., with pentobarbital 150 mg/kg IV. This and other procedures for raising polyclonal antibodies are disclosed in E. Harlow, et. al., editors, Antibodies: A Laboratory Manual (1988).
In addition to utilizing whole antibodies, the invention encompasses the use of binding portions of such antibodies. Such binding portions include Fab fragments, F(ab′)2 fragments, and Fv fragments. These antibody fragments can be made by conventional procedures, such as proteolytic fragmentation procedures, as described in J. Goding, Monoclonal Antibodies: Principles and Practice, pp. 98-118 (N.Y. Academic Press 1983).
Chimeric, humanized, de-immunized, or completely human antibodies are desirable for applications which include repeated administration, e.g., therapeutic treatment of human subjects.
Chimeric antibodies generally contain portions of two different antibodies, typically of two different species. Generally, such antibodies contain human constant regions and variable regions from another species, e.g., murine variable regions. For example, mouse/human chimeric antibodies have been reported which exhibit binding characteristics of the parental mouse antibody, and effector functions associated with the human constant region. See, e.g., Cabilly et al., U.S. Pat. No. 4,816,567; Shoemaker et al., U.S. Pat. No. 4,978,745; Beavers et al., U.S. Pat. No. 4,975,369; and Boss et al., U.S. Pat. No. 4,816,397, all of which are incorporated by reference herein. Generally, these chimeric antibodies are constructed by preparing a genomic gene library from DNA extracted from pre-existing murine hybridomas (Nishimura et al., Cancer Research, 47:999, 1987). The library is then screened for variable region genes from both heavy and light chains exhibiting the correct antibody fragment rearrangement patterns. Alternatively, cDNA libraries are prepared from RNA extracted from the hybridomas and screened, or the variable regions are obtained by polymerase chain reaction. The cloned variable region genes are then ligated into an expression vector containing cloned cassettes of the appropriate heavy or light chain human constant region gene. The chimeric genes can then be expressed in a cell line of choice, e.g., a murine myeloma line. Such chimeric antibodies have been used in human therapy.
Humanized antibodies are known in the art. Typically, “humanization” results in an antibody that is less immunogenic, with complete retention of the antigen-binding properties of the original molecule. In order to retain all the antigen-binding properties of the original antibody, the structure of its combining-site has to be faithfully reproduced in the “humanized” version. This can potentially be achieved by transplanting the combining site of the nonhuman antibody onto a human framework, either (a) by grafting the entire nonhuman variable domains onto human constant regions to generate a chimeric antibody (Morrison et al., Proc Natl Acad Sci USA 81:6801, 1984; Morrison and Oi, Adv Immunol 44:65, 1988) (which preserves the ligand-binding properties, but which also retains the immunogenicity of the nonhuman variable domains); (b) by grafting only the nonhuman CDRs onto human framework and constant regions with or without retention of critical framework residues (Jones et al., Nature 321:522, 1986; Verhoeyen et al., Science 239:1539, 1988); or (c) by transplanting the entire nonhuman variable domains (to preserve ligand-binding properties) but also “cloaking” them with a human-like surface through judicious replacement of exposed residues (to reduce antigenicity) (Padlan, Molec Immunol 28:489, 1991).
Humanization by CDR grafting typically involves transplanting only the CDRs onto human fragment onto human framework and constant regions. Theoretically, this should substantially eliminate immunogenicity (except if allotypic or idiotypic differences exist). However, it has been reported that some framework residues of the original antibody also need to be preserved (Riechmann et al., Nature 332:323, 1988; Queen et al., Proc Natl Acad Sci USA 86:10,029, 1989). The framework residues which need to be preserved can be identified by computer modeling. Alternatively, critical framework residues may potentially be identified by comparing known antibody combining site structures (Padlan, Mol Immun 31(3):169-217, 1994). The invention also includes partially humanized antibodies, in which the 6 CDRs of the heavy and light chains and a limited number of structural amino acids of the murine monoclonal antibody are grafted by recombinant technology to the CDR-depleted human IgG scaffold (Jones et al., Nature 321:522-525, 1986).
Deimmunized antibodies are made by replacing immunogenic epitopes in the murine variable domains with benign amino acid sequences, resulting in a deimmunized variable domain. The deimmunized variable domains are linked genetically to human IgG constant domains to yield a deimmunized antibody (Biovation, Aberdeen, Scotland).
The antibody can also be a single chain antibody. A single-chain antibody (scFV) can be engineered (see, for example, Colcher et al., Ann NY Acad Sci 880:263-80, 1999; and Reiter, Clin Cancer Res 2:245-52, 1996). The single chain antibody can be dimerized or multimerized to generate multivalent antibodies having specificities for different epitopes of the same target protein. In some embodiments, the antibody is monovalent, e.g., as described in Abbs et al., Ther Immunol 1(6):325-31, 1994, incorporated herein by reference.
Antibodies to LDLR, LRP, and FXa are also commercially available. For example, antibodies to LDLR are available from Santa Cruz Biotechnology (sc-20744). Anti-LRP antibodies are available from EMD Millipore (438192, 438190); and R&D (AF2369). Antibodies to FXa are available from R&D (MAB1063). These antibodies can be modified as known in the art and disclosed herein, e.g., humanized or deimmunized.
Inhibitory Nucleic Acids
Nucleic acid molecules (e.g., RNA molecules) can be used to inhibit (i.e., reduce) LDLR and/or LRP expression or activity. A LDLR inhibitor or LRP inhibitor can be a siRNA, antisense RNA, a ribozyme, or aptamer that can specifically reduce the expression of LDLR or LRP, respectively. In some aspects, a cell or subject can be treated with a compound that reduces the expression of LDLR and/or LRP. Such approaches include oligonucleotide-based therapies such as RNA interference, antisense, ribozymes, and aptamers. Exemplary inhibitory nucleic acids to LDLR and LRP are described below.
LDLR shRNA: Sigma NM_000527
LRP1 shRNA: Sigma NM_002332
i. siRNA Molecules
RNA interference (RNAi) is a process whereby double-stranded RNA (dsRNA, also referred to herein as siRNAs or ds siRNAs, for double-stranded small interfering RNAs) induces the sequence-specific degradation of homologous mRNA in animals and plant cells (Hutvagner and Zamore, Curr Opin Genet Dev 12:225-232, 2002; Sharp, Genes Dev 15:485-490, 2001). In mammalian cells, RNAi can be triggered by 21-nucleotide (nt) duplexes of small interfering RNA (siRNA) (Chiu et al., Mol Cell 10:549-561, 2002; Elbashir et al., Nature 411:494-498, 2001), or by micro-RNAs (miRNA), functional small-hairpin RNA (shRNA), or other dsRNAs which are expressed in vivo using DNA templates with RNA polymerase III promoters (Zeng et al., Mol Cell 9:1327-1333, 2002; Paddison et al., Genes Dev 16:948-958, 2002; Lee et al., Nature Biotechnol 20:500-505, 2002; Paul et al., Nature Biotechnol 20:505-508, 2002; Tuschl, Nature Biotechnol 20:440-448, 2002; Yu et al., Proc Natl Acad Sci USA 99:6047-6052, 2002; McManus et al., RNA 8:842-850, 2002; Sui et al., Proc Natl Acad Sci USA 99:5515-5520, 2002).
The nucleic acid molecules or constructs can include dsRNA molecules comprising 16-30, e.g., 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30 nucleotides in each strand, wherein one of the strands is substantially identical, e.g., at least 80% (or more, e.g., 85%, 90%, 92%, 95%, or 100%) identical, e.g., having 3, 2, 1, or 0 mismatched nucleotide(s), to a target region in the mRNA, and the other strand is complementary to the first strand. The dsRNA molecules can be chemically synthesized, or can transcribed in vitro from a DNA template, or in vivo from, e.g., shRNA. The dsRNA molecules can be designed using any method known in the art; a number of algorithms are known, and are commercially available. Gene walk methods can be used to optimize the inhibitory activity of the siRNA.
The nucleic acid compositions can include both siRNA and modified siRNA derivatives, e.g., siRNAs modified to alter a property such as the pharmacokinetics of the composition, for example, to increase half-life in the body, as well as engineered RNAi precursors.
siRNAs can be delivered into cells by methods known in the art, e.g., cationic liposome transfection and electroporation. siRNA duplexes can be expressed within cells from engineered RNAi precursors, e.g., recombinant DNA constructs using mammalian Pol III promoter systems (e.g., H1 or U6/snRNA promoter systems (Tuschl 2002, supra) capable of expressing functional double-stranded siRNAs; (Bagella et al., J Cell Physiol 177:206-213, 1998; Lee et al., 2002, supra; Miyagishi et al., 2002, supra; Paul et al., 2002, supra; Yu et al., 2002, supra; Sui et al., 2002, supra). Transcriptional termination by RNA Pol III occurs at runs of four consecutive T residues in the DNA template, providing a mechanism to end the siRNA transcript at a specific sequence. The siRNA is complementary to the sequence of the target gene in 5′-3′ and 3′-5′ orientations, and the two strands of the siRNA can be expressed in the same construct or in separate constructs. Hairpin siRNAs, driven by H1 or U6 snRNA promoter and expressed in cells, can inhibit target gene expression (Bagella et al., 1998, supra; Lee et al., 2002, supra; Miyagishi et al., 2002, supra; Paul et al., 2002, supra; Yu et al., 2002, supra; Sui et al., 2002, supra). Constructs containing siRNA sequence under the control of T7 promoter also make functional siRNAs when cotransfected into the cells with a vector expression T7 RNA polymerase (Jacque, 2002, supra).
ii. Antisense Nucleic Acids
An “antisense” nucleic acid can include a nucleotide sequence that is complementary to a “sense” nucleic acid encoding a protein, e.g., complementary to the coding strand of a double-stranded cDNA molecule or complementary to a LDLR or LRP mRNA sequence. The antisense nucleic acid can be complementary to an entire coding strand of a target sequence, or to only a portion thereof. In another embodiment, the antisense nucleic acid molecule is antisense to a “noncoding region” of the coding strand of a nucleotide sequence (e.g., the 5′ and 3′ untranslated regions).
An antisense nucleic acid can be designed such that it is complementary to the entire coding region of a target mRNA, but can also be an oligonucleotide that is antisense to only a portion of the coding or noncoding region of the target mRNA. For example, the antisense oligonucleotide can be complementary to the region surrounding the translation start site of the target mRNA, e.g., between the −10 and +10 regions of the target gene nucleotide sequence of interest. An antisense oligonucleotide can be, for example, about 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, or more nucleotides in length.
An antisense nucleic acid can be constructed using chemical synthesis and enzymatic ligation reactions using procedures known in the art. For example, an antisense nucleic acid (e.g., an antisense oligonucleotide) can be chemically synthesized using naturally occurring nucleotides or variously modified nucleotides designed to increase the biological stability of the molecules or to increase the physical stability of the duplex formed between the antisense and sense nucleic acids, e.g., phosphorothioate derivatives and acridine substituted nucleotides can be used. The antisense nucleic acid also can be produced biologically using an expression vector into which a nucleic acid has been subcloned in an antisense orientation (i.e., RNA transcribed from the inserted nucleic acid will be of an antisense orientation to a target nucleic acid of interest, described further in the following subsection).
Based upon the sequences disclosed herein, one of skill in the art can easily choose and synthesize any of a number of appropriate antisense molecules for use in accordance with the present invention. For example, a “gene walk” comprising a series of oligonucleotides of 15-30 nucleotides spanning the length of a target nucleic acid can be prepared, followed by testing for inhibition of target gene expression. Optionally, gaps of 5-10 nucleotides can be left between the oligonucleotides to reduce the number of oligonucleotides synthesized and tested.
In some embodiments, the antisense nucleic acid molecule is an α-anomeric nucleic acid molecule. An α-anomeric nucleic acid molecule forms specific double-stranded hybrids with complementary RNA in which, contrary to the usual β-units, the strands run parallel to each other (Gaultier et al., Nucleic Acids Res 15:6625-6641, 1987). The antisense nucleic acid molecule can also comprise a 2′-o-methylribonucleotide (Inoue et al., Nucleic Acids Res 15:6131-6148, 1987) or a chimeric RNA-DNA analogue (Inoue et al., FEBS Lett 215:327-330, 1987).
In some embodiments, the antisense nucleic acid is a morpholino oligonucleotide (see, e.g., Heasman, Dev Biol 243:209-14, 2002; Iversen, Curr Opin Mol Ther 3:235-8, 2001; Summerton, Biochim Biophys Acta 1489:141-58, 1999).
Target gene expression can be inhibited by targeting nucleotide sequences complementary to a regulatory region (e.g., promoters and/or enhancers) to form triple helical structures that prevent transcription of the Spt5 gene in target cells. See generally, Helene, Anticancer Drug Des 6:569-84, 1991; Helene, Ann NY Acad Sci 660:27-36, 1992; and Maher, Bioassays 14:807-15, 1992. The potential sequences that can be targeted for triple helix formation can be increased by creating a so called “switchback” nucleic acid molecule. Switchback molecules are synthesized in an alternating 5′-3′, 3′-5′ manner, such that they base pair with first one strand of a duplex and then the other, eliminating the necessity for a sizeable stretch of either purines or pyrimidines to be present on one strand of a duplex.
Ribozymes are a type of RNA that can be engineered to enzymatically cleave and inactivate other RNA targets in a specific, sequence-dependent fashion. By cleaving the target RNA, ribozymes inhibit translation, thus preventing the expression of the target gene. Ribozymes can be chemically synthesized in the laboratory and structurally modified to increase their stability and catalytic activity using methods known in the art. Alternatively, ribozyme genes can be introduced into cells through gene-delivery mechanisms known in the art. A ribozyme having specificity for a target nucleic acid can include one or more sequences complementary to a nucleotide sequence of a cDNA described herein, and a sequence having known catalytic sequence responsible for mRNA cleavage (see U.S. Pat. No. 5,093,246 or Haselhoff and Gerlach, Nature 334:585-591, 1988). For example, a derivative of a Tetrahymena L-19 IVS RNA can be constructed in which the nucleotide sequence of the active site is complementary to the nucleotide sequence to be cleaved in a target mRNA. See, e.g., Cech et al., U.S. Pat. Nos. 4,987,071 and 5,116,742. Alternatively, a target mRNA can be used to select a catalytic RNA having a specific ribonuclease activity from a pool of RNA molecules. See, e.g., Bartel and Szostak, Science 261:1411-1418, 1993.
Aptamers are short oligonucleotide sequences which can specifically bind specific proteins. It has been demonstrated that different aptameric sequences can bind specifically to different proteins, for example, the sequence GGNNGG where N=guanosine (G), cytosine (C), adenosine (A) or thymidine (T) binds specifically to thrombin (Bock et al., Nature 355:564-566, 1992; and U.S. Pat. No. 5,582,981, Toole et al., 1996). Methods for selection and preparation of such RNA aptamers are known in the art (see, e.g., Famulok, Curr Opin Struct Biol 9:324, 1999; Herman and Patel, J Sci 287:820-825, 2000; Kelly et al., J Mol Biol 256:417, 1996; and Feigon et al., Chem Biol 3:611, 1996).
Administration of Inhibitory Nucleic Acid Molecules
The inhibitory nucleic acid molecules described herein can be administered to a subject (e.g., by direct injection at a tissue site), or generated in situ such that they hybridize with or bind to cellular mRNA and/or genomic DNA encoding a target protein to thereby inhibit expression of the protein, e.g., by inhibiting transcription and/or translation. Alternatively, inhibitory nucleic acid molecules can be modified to target selected cells and then administered systemically. For systemic administration, inhibitory nucleic acid molecules can be modified such that they specifically bind to receptors or antigens expressed on a selected cell surface, e.g., by linking the inhibitory nucleic acid molecules to peptides or antibodies that bind to cell surface receptors or antigens. The inhibitory nucleic acid molecules can also be delivered to cells using the vectors described herein. To achieve sufficient intracellular concentrations of the inhibitory nucleic acid molecules, vector constructs in which the inhibitory nucleic acid molecule is placed under the control of a strong promoter can be used.
A “therapeutically effective amount” is an amount sufficient to effect beneficial or desired results. For example, a therapeutically effective amount is one that achieves the desired therapeutic effect. This amount can be the same or different from a prophylactically effective amount, which is an amount necessary to reduce or inhibit a HBV infection. An effective amount can be administered in one or more administrations, applications, or dosages. A therapeutically effective amount of a composition depends on the composition selected. The compositions can be administered from one or more times per day to one or more times per week, including once every other day. The skilled artisan will appreciate that certain factors may influence the dosage and timing required to effectively treat a subject, including but not limited to the severity of the disease or disorder, previous treatments, the general health and/or age of the subject, and other diseases present. Moreover, treatment of a subject with a therapeutically effective amount of the compositions described herein can include a single treatment or a series of treatments.
Methods for Identifying Compounds Capable of Treating a HBV Infection
The invention provides methods for screening test compounds for an ability to treat a HBV infection or reduce a risk of a HBV infection. A “test compound” as described herein is any compound that can be screened using the methods described herein. For example, a test compound can be, e.g., a small organic or inorganic molecule (M.W. less than 1,000 Da). Alternatively or in addition, the test compound can be a polypeptide (e.g., a polypeptide having a random or predetermined amino acid sequence or a naturally-occurring or synthetic polypeptide) or a nucleic acid, such as a DNA or RNA molecule. A test compound can be naturally occurring (e.g., an herb or a natural product), or synthetic, or can include both natural and synthetic components. A test compound can have a formula weight of less than about 10,000 grams per mole, less than 5,000 grams per mole, less than 1,000 grams per mole, or less than about 500 grams per mole. The test compound can be, for example, any organic or inorganic compound (e.g., heteroorganic or organometallic compound), an amino acid, amino acid analog, polypeptide, peptidomimetic (e.g., peptoid), oligopeptide (e.g., from about 5 to about 25 amino acids in length, preferably from about 10 to 20 or 12 to 18 amino acids in length, preferably 12, 15, or 18 amino acids in length), nucleotide, nucleotide analog, polynucleotide, polynucleotide analog, ribonucleic acid, deoxyribonucleic acid, antisense oligonucleotide, ribozyme, saccharide, lipid (e.g., a sphingolipid), and/or a fatty acid, or any combination thereof.
The terms “antagonist” or “inhibitor” of HBV refer to compounds that, e.g., bind to HBV and/or LDLR, LRP, and/or FXa (e.g., a component of a HBV receptor complex) and/or partially or totally block or inhibit HBV interaction with LDLR, LRP, and/or FXa (e.g., a component of a HBV receptor complex) as measured in known assays. Inhibitors include, e.g., antibodies directed against LDLR, LRP, or FXa, modified versions of LDLR or LRP, naturally occurring and synthetic ligands, antagonists, agonists, antibodies, small chemical molecules, and the like. Assays for detecting inhibitors or antagonists are described in more detail below.
Libraries of Test Compounds
In certain embodiments, screens of the present invention utilize libraries of test compounds. A “library” is a collection of compounds (e.g., as a mixture or as physically separated individual compounds) synthesized from various combinations of one or more starting components. At least some of the compounds must differ from at least some of the other compounds in the library. A library can include, e.g., 5, 10, 50, 100, 1000, or even 10,000, 50,000, or 100,000, or more different compounds (i.e., not simply multiple copies of the same compounds, although some compounds in the library may be duplicated or represented more than once). Each of the different compounds will be present in an amount such that its presence can be determined by some means, e.g., can be isolated, analyzed, and/or detected with a receptor or suitable probe. The actual quantity of each different compound needed so that its presence can be determined will vary due to the actual procedures used and may change as the technologies for isolation, detection, and analysis advance. When the compounds are present in a mixture in substantially equimolar amounts, for example, an amount of 100 picomoles of each compound can often be detected. Libraries can include both libraries of individual compounds (e.g., present substantially as a single type of compound-per-well, made via parallel synthesis or the pool and split pool method) and mixtures containing substantially equimolar amounts of each desired compound (i.e., wherein no single compound dominates). Either library format can allow identification of an active compound discovered in an assay.
Test compounds can be screened individually or in parallel. An example of parallel screening is a high throughput drug screen of large libraries of chemicals. Such libraries of candidate compounds can be generated or purchased, e.g., from Chembridge Corp., San Diego, Calif. Alternatively, prior experimentation and anecdotal evidence can suggest a class or category of compounds of enhanced potential. A library can be designed and synthesized to cover such a class of chemicals.
The synthesis of combinatorial libraries is well known in the art and has been reviewed (see, e.g., E. M. Gordon et al., J. Med. Chem. (1994) 37:1385-1401; DeWitt, S. H.; Czarnik, A. W. Acc. Chem. Res. (1996) 29:114; Armstrong, R. W.; Combs, A. P.; Tempest, P. A.; Brown, S. D.; Keating, T. A. Acc. Chem. Res. (1996) 29:123; Ellman, J. A. Acc. Chem. Res. (1996) 29:132; Gordon, E. M.; Gallop, M. A.; Patel, D. V. Acc. Chem. Res. (1996) 29:144; Lowe, G. Chem. Soc. Rev. (1995) 309, Blondelle et al. Trends Anal. Chem. (1995) 14:83; Chen et al. J. Am. Chem. Soc. (1994) 116:2661; U.S. Pat. Nos. 5,359,115, 5,362,899, and 5,288,514; PCT Publication Nos. WO92/10092, WO93/09668, WO91/07087, WO93/20242, and WO94/08051).
Libraries of compounds can be prepared according to a variety of methods, some of which are known in the art. For example, a “split-pool” strategy can be implemented in the following way: beads of a functionalized polymeric support are placed in a plurality of reaction vessels; a variety of polymeric supports suitable for solid-phase peptide synthesis are known, and some are commercially available (for examples, see, e.g., M. Bodansky, “Principles of Peptide Synthesis,” 2nd edition, Springer-Verlag, Berlin (1993)). To each aliquot of beads is added a solution of a different activated amino acid, and the reactions are allowed to proceed to yield a plurality of immobilized amino acids, one in each reaction vessel. The aliquots of derivatized beads are then washed, “pooled” (i.e., recombined), and the pool of beads is again divided, with each aliquot being placed in a separate reaction vessel. Another activated amino acid is then added to each aliquot of beads. The cycle of synthesis is repeated until a desired peptide length is obtained. The amino acid residues added at each synthesis cycle can be randomly selected; alternatively, amino acids can be selected to provide a “biased” library, e.g., a library in which certain portions of the inhibitor are selected non-randomly, e.g., to provide an inhibitor having known structural similarity or homology to a known peptide capable of interacting with an antibody, e.g., the an anti-idiotypic antibody antigen binding site. It will be appreciated that a wide variety of peptidic, peptidomimetic, or non-peptidic compounds can be readily generated in this way.
The “split-pool” strategy can result in a library of peptides, e.g., modulators, which can be used to prepare a library of test compounds of the invention. In another illustrative synthesis, a “diversomer library” is created by the method of Hobbs DeWitt et al. (Proc. Natl. Acad. Sci. U.S.A. 90:6909 (1993)). Other synthesis methods, including the “tea-bag” technique of Houghten (see, e.g., Houghten et al., Nature 354:84-86 (1991)) can also be used to synthesize libraries of compounds according to the subject invention.
Libraries of compounds can be screened to determine whether any members of the library have a desired activity, and, if so, to identify the active species. Methods of screening combinatorial libraries have been described (see, e.g., Gordon et al., J. Med. Chem., supra). Soluble compound libraries can be screened by affinity chromatography with an appropriate receptor to isolate ligands for the receptor, followed by identification of the isolated ligands by conventional techniques (e.g., mass spectrometry, NMR, and the like). Immobilized compounds can be screened by contacting the compounds with a soluble receptor; preferably, the soluble receptor is conjugated to a label (e.g., fluorophores, colorimetric enzymes, radioisotopes, luminescent compounds, and the like) that can be detected to indicate ligand binding. Alternatively, immobilized compounds can be selectively released and allowed to diffuse through a membrane to interact with a receptor. Exemplary assays useful for screening libraries of test compounds are described above.
The invention provides methods for identifying compounds capable of treating a HBV infection or reducing a risk of a HBV infection. Although applicants do not intend to be bound by any particular theory as to the biological mechanism involved, such compounds are thought to modulate specifically HBV interaction with a component of the HBV receptor complex (e.g., by inhibiting or reducing binding of HBV to LDLR, LRP, and/or FXa).
In one aspect, the invention includes methods for screening test compounds to identify a compound that modulates (i.e., increases or decreases) HBsAg secretion from a cell, e.g., a hepatocyte. For example, a cell, e.g., a hepatocyte, expressing a polypeptide comprising an amino acid sequence that has at least 90% identity to SEQ ID NO:2 or 4 can be contacted with a HBV in the presence of a test compound. A level of HBsAg secretion can be determined by any art-recognized method. Exemplary assays for determining a level of HBsAg secretion are described in the Examples section, below. The level of HBsAg secretion in the presence of the test compound can be compared with the level of HBsAg secretion in the absence of the test compound, and if there is a reduced level of HBsAg secretion in the presence of the test compound than in its absence, the test compound is a candidate anti-HBV agent.
In certain aspects of the present invention, screening for such compounds is accomplished by (i) identifying from a group of test compounds those that bind to LDLR or LRP and/or modulate (i.e., increase or decrease) an interaction between LDLR and/or LRP and HBV; and, optionally, (ii) further testing such compounds for their ability to treat HBV in vitro or in vivo. Test compounds that decrease an interaction between LDLR and/or LRP with HBV are referred to herein as “candidate anti-HBV agents.” Candidate anti-HBV agents further tested and found to be capable of treating or reducing a risk of a HBV infection are considered “anti-HBV agents.” In the screening methods of the present invention, candidate anti-HBV agents can be, but do not necessarily have to be, tested to determine whether they are anti-HBV agents. Assays of the present invention may be carried out in biological samples, whole cell preparations, and/or ex vivo cell-free systems.
In one aspect, the invention includes methods for screening test compounds to identify compounds that bind to LDLR and/or LRP, e.g., a polypeptide comprising an amino acid sequence that has at least about 90%, e.g., at least about 92%, 95%, 96%, 97%, 98%, 99%, or 100% identity to SEQ ID NO:2 or 4. Binding of a test compound to LDLR and/or LRP can be detected, for example, in vitro, by reversibly or irreversibly immobilizing the test compound(s) or LDLR and/or LRP on a substrate, e.g., the surface of a well of a 96-well polystyrene microtiter plate. Methods for immobilizing polypeptides and other small molecules are well known in the art. For example, microtiter plates can be coated with LDLR and/or LRP by adding the polypeptide in a solution (typically, at a concentration of 0.05 to 1 mg/ml in a volume of 1-100 μl) to each well, and incubating the plates at room temperature to 37° C. for a given amount of time, e.g., for 0.1 to 36 hours. Polypeptides not bound to the plate can be removed by shaking excess solution from the plate, and then washing the plate (once or repeatedly) with water or a buffer. Typically, the polypeptide is in water or a buffer. The plate can then be washed with a buffer that lacks the bound polypeptide. To block the free protein-binding sites on the plates, plates can be blocked with a protein that is unrelated to the bound polypeptide. For example, 300 μl of bovine serum albumin (BSA) at a concentration of 2 mg/ml in Tris-HCl can be used. Suitable substrates include those substrates that contain a defined cross-linking chemistry (e.g., plastic substrates, such as polystyrene, styrene, or polypropylene substrates from Corning Costar Corp. (Cambridge, Mass.), for example). If desired, a particle, e.g., beaded agarose or beaded sepharose, can be used as the substrate. Test compounds can then be added to the coated plate and allowed to bind to LDLR and/or LRP (e.g., at 37° C. for 0.5 to 12 hours). The plate can then be rinsed as described above. Skilled practitioners will appreciate that many variations of this method are possible. For example, the method can include coating a substrate with a test compound and adding LDLR and/or LRP to the substrate-bound compound.
Binding of LDLR and/or LRP to a test compound can be detected by any of a variety of art-known methods. For example, an antibody that specifically binds to LDLR and/or LRP (i.e., an anti-LDLR antibody or an anti-LRP antibody) can be used in an immunoassay. Antibodies useful in the methods and treatments described herein can be raised using art known methods or obtained from commercial sources. The antibody can be labeled (e.g., fluorescently or with a radioisotope) and detected directly (see, e.g., West and McMahon, J. Cell Biol. 74:264, 1977). Alternatively, a second antibody can be used for detection (e.g., a labeled antibody that binds to the Fc portion of the anti-LDLR or anti-LRP antibody). In an alternative detection method, LDLR and/or LRP is labeled (e.g., with a radioisotope, fluorophore, chromophore, or the like), and the label is detected. In still another method, LDLR and/or LRP is produced as a fusion protein with a protein that can be detected optically, e.g., green fluorescent protein (which can be detected under a light source, e.g., a blue light (e.g., a 488 nm light) source or UV light source). In an alternative method, the polypeptide is produced as a fusion protein with an enzyme having a detectable enzymatic activity, such as horseradish peroxidase, alkaline phosphatase, β-galactosidase, or glucose oxidase. Genes encoding all of these enzymes have been cloned and are available for use by skilled practitioners. If desired, the fusion protein can include an antigen or epitope that can be detected and measured with a polyclonal or monoclonal antibody using conventional methods. Suitable antigens include enzymes (e.g., horse radish peroxidase, alkaline phosphatase, and β-galactosidase) and non-enzymatic polypeptides (e.g., serum proteins, such as BSA and globulins, and milk proteins, such as caseins).
In various methods for identifying polypeptides (e.g., test polypeptides) that bind to LDLR and/or LRP, conventional two-hybrid assays of protein/protein interactions can be used (see e.g., Chien et al., Proc. Natl. Acad. Sci. USA, 88:9578, 1991; Fields et al., U.S. Pat. No. 5,283,173; Fields and Song, Nature, 340:245, 1989; Le Douarin et al., Nucleic Acids Research, 23:876, 1995; Vidal et al., Proc. Natl. Acad. Sci. USA, 93:10315-10320, 1996; and White, Proc. Natl. Acad. Sci. USA, 93:10001-10003, 1996). Generally, two-hybrid methods involve reconstitution of two separable domains of a transcription factor. One fusion protein includes LDLR or LRP fused to either a transactivator domain or DNA binding domain of a transcription factor (e.g., of Gal4). The other fusion protein contains a test polypeptide or a binding partner for the polypeptide included in the first fusion protein, fused to either the DNA binding domain or a transactivator domain of a transcription factor. Binding of LDLR or LRP to the test polypeptide or binding partner reconstitutes the transcription factor. Reconstitution of the transcription factor can be detected by detecting expression of a gene (i.e., a reporter gene) that is operably linked to a DNA sequence that is bound by the DNA binding domain of the transcription factor. Kits for practicing various two-hybrid methods are commercially available (e.g., from Clontech; Palo Alto, Calif.).
In still another aspect, the invention provides methods of identifying test compounds that modulate (e.g., increase or decrease) expression of LDLR or LRP. The method includes contacting a LDLR and/or LRP nucleic acid with a test compound and then measuring expression of the encoded LDLR and/or LRP polypeptide. Since the LDLR and LRP nucleic acids described herein have been identified, they can be cloned into various host cells (e.g., mammalian cells, insect cells, bacteria or fungi) for carrying out such assays in whole cells.
In certain embodiments, an isolated nucleic acid molecule encoding LDLR or LRP is used to identify a compound that modulates (e.g., increases or decreases) the expression of LDLR or LRP in vivo (e.g., in a LDLR- or LRP-producing cell). In such embodiments, cells that express LDLR or LRP are cultured, exposed to a test compound (or a mixture of test compounds), and the level of LDLR and/or LRP expression is compared with the level of LDLR and/or LRP expression or activity in cells that are otherwise identical, but have not been exposed to the test compound(s). Standard quantitative assays of gene expression can be used.
Expression of LDLR and LRP can be measured using art-known methods, for example, by Northern blot, PCR analysis, or RNAse protection analyses using a nucleic acid molecule of the invention as a probe. Other examples include enzyme-linked immunosorbent assay (ELISA), radioimmunoassay (RIA) and fluorescent activated cell sorting (FACS). The level of expression in the presence of the test molecule, compared with the level of expression in its absence, will indicate whether or not the test compound modulates the expression of LDLR or LRP.
In certain embodiments, the methods include identifying candidate compounds that interfere with steps in LDLR or LRP translational accuracy, such as maintaining a proper reading frame during translation and terminating translation at a stop codon. This method involves constructing cells in which a detectable reporter polypeptide can only be produced if the normal process of staying in one reading frame or of terminating translation at a stop codon has been disrupted. This method further involves contacting the cell with a test compound to examine whether it increases or decreases the production of the reporter polypeptide.
In other embodiments, the cell system is a cell-free extract and the method involves measuring transcription or translation in vitro. Conditions are selected so that transcription or translation of the reporter is increased or decreased by the addition of a transcription modifier or a translation modifier to the cell extract.
One method for identifying candidate compounds relies upon a transcription-responsive gene product. This method involves constructing a cell in which the production of a reporter molecule changes (i.e., increases or decreases) under conditions in which cell transcription of LDLR and/or LRP nucleic acid changes (i.e., increases or decreases). Specifically, the reporter molecule is encoded by a nucleic acid transcriptionally linked to a sequence constructed and arranged to cause a relative change in the production of the reporter molecule when transcription of LDLR or LRP nucleic acid changes. A gene sequence encoding the reporter may, for example, be fused to part or all of the gene encoding the transcription-responsive gene product and/or to part or all of the genetic elements that control the production of the gene product. Alternatively, the transcription-responsive gene product may stimulate transcription of the gene encoding the reporter, either directly or indirectly. The method further involves contacting the cell with a test compound, and determining whether the test compound increases or decreases the production of the reporter molecule in the cell.
Alternatively, the method for identifying candidate compounds can rely upon a translation-responsive gene product. This method involves constructing a cell in which cell translation of LDLR or LRP changes (i.e., increases or decreases). Specifically, the reporter molecule is encoded by a nucleic acid translationally linked to a sequence constructed and arranged to cause a relative increase or decrease in the production of the reporter molecule when transcription of LDLR or LRP nucleic acid changes. A gene sequence encoding the reporter may, for example, be fused to part or all of the gene encoding the translation-responsive gene product and/or to part or all of the genetic elements that control the production of the gene product. Alternatively, the translation-responsive gene product may stimulate translation of the gene encoding the reporter, either directly or indirectly. The method further involves contacting the cell with a test compound, and determining whether the test compound increases or decreases the production of the first reporter molecule in the cell.
For these and any method described herein, a wide variety of reporters may be used, with typical reporters providing conveniently detectable signals (e.g., by spectroscopy). By way of example, a reporter gene may encode an enzyme that catalyzes a reaction that alters light absorption properties.
Examples of reporter molecules include but are not limited to β-galactosidase, invertase, green fluorescent protein, luciferase, chloramphenicol acetyltransferase, beta-glucuronidase, exo-glucanase, glucoamylase and radiolabeled reporters. For example, the production of the reporter molecule can be measured by the enzymatic activity of the reporter gene product, such as β-galactosidase.
Any of the methods described herein can be used for high throughput screening of numerous test compounds to identify candidate anti-HBV agents. By high-throughput screening is meant that the method can be used to screen a large number of candidate compounds relatively easily and quickly.
Having identified a test compound as a candidate anti-HBV agent, the compound can be further tested in vivo or in vitro using techniques known in the art to confirm whether it is an anti-HBV agent, i.e., to determine whether it can modulate HBsAg levels in vitro (e.g., using isolated cells or cell-free systems) or in vivo (e.g., using an animal, e.g., rodent, model system) if desired.
In vitro testing of a candidate compound can be accomplished by means known to those in the art, such as assays involving the use of cells, e.g., primary human hepatocytes. Exemplary assays for monitoring HBV infection as well as useful cells that can be used in such assays are described in the Examples section, below.
Alternatively or in addition, in vivo testing of candidate compounds can be performed by means known to those in the art. For example, the candidate compound(s) can be administered to a mammal, such as a rodent (e.g., mouse) or rabbit. Such animal model systems are art-accepted for testing potential pharmaceutical agents to determine their therapeutic efficacy in patients, e.g., human patients. Animals that are particularly useful for in vivo testing are immunodeficient animals (e.g., mice) with a human liver.
In a typical in vivo assay, an animal (e.g., a wild type or transgenic mouse) is administered, by any route deemed appropriate (e.g., by injection), a dose of a candidate compound. Conventional methods and criteria can then be used to monitor animals for the desired activity. If needed, the results obtained in the presence of the candidate compound can be compared with results in control animals that are not treated with the test compound.
Once a compound (or agent) of interest has been identified, standard principles of medicinal chemistry can be used to produce derivatives of the compound for further rounds of testing. Derivatives can be screened for improved pharmacological properties, for example, efficacy, pharmaco-kinetics, stability, solubility, and clearance. The moieties responsible for a compound'"'"'s activity in the assays described above can be delineated by examination of structure-activity relationships (SAR) as is commonly practiced in the art. A person of ordinary skill in pharmaceutical chemistry could modify moieties on a candidate compound or agent and measure the effects of the modification on the efficacy of the compound or agent to thereby produce derivatives with increased potency. For an example, see Nagarajan et al. (1988) J. Antibiot. 41: 1430-8. Furthermore, if the biochemical target of the compound (or agent) is known or determined, the structure of the target and the compound can inform the design and optimization of derivatives. Molecular modeling software is commercially available (e.g., Molecular Simulations, Inc.) for this purpose.
Also described herein are pharmaceutical compositions, which include, e.g., LDLR, LRP, or RAP, e.g., where the LDLR, LRP, or RAP comprises a polypeptide that has at least 90, 92, 95, 96, 97, 98, or 99% identity to the amino acid sequence of SEQ ID NO:2, 4, or 6, respectively. The pharmaceutical compositions can include a combination of two or more of a LDLR, LRP, and RAP. Further, the pharmaceutical compositions can include a FXa inhibitor, a pegylated interferon, a nucleoside or nucleotide analogue, and/or a HBV vaccine.
The compounds and agents, e.g., small molecules, nucleic acids, polypeptides, and antibodies (all of which can be referred to herein as “active compounds”), can be incorporated into pharmaceutical compositions. Such compositions typically include the active compound and a pharmaceutically acceptable carrier. A “pharmaceutically acceptable carrier” can include solvents, dispersion media, coatings, antibacterial and antifungal agents, isotonic and absorption delaying agents, and the like, compatible with pharmaceutical administration. Supplementary active compounds can also be incorporated into the compositions. The pharmaceutical compositions can be included in a container, pack, or dispenser together with instructions for administration.
A pharmaceutical composition is formulated to be compatible with its intended route of administration. Examples of routes of administration include parenteral, e.g., intravenous, intradermal, subcutaneous, oral (e.g., inhalation), transdermal (topical), transmucosal, and rectal administration. Solutions or suspensions used for parenteral, intradermal, or subcutaneous application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. pH can be adjusted with acids or bases, such as hydrochloric acid or sodium hydroxide. The parenteral preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.
Pharmaceutical compositions suitable for injectable use include sterile aqueous solutions (where water soluble) or dispersions and sterile powders for the extemporaneous preparation of sterile injectable solutions or dispersion. For intravenous administration, suitable carriers include physiological saline, bacteriostatic water, Cremophor EL™ (BASF, Parsippany, N.J.) or phosphate buffered saline (PBS). In all cases, the composition must be sterile and should be fluid to the extent that easy syringability exists. It should be stable under the conditions of manufacture and storage and must be preserved against the contaminating action of microorganisms such as bacteria and fungi. The carrier can be a solvent or dispersion medium containing, for example, water, ethanol, a polyol (for example, glycerol, propylene glycol, and liquid polyethylene glycol, and the like), or a suitable mixture thereof. The proper fluidity can be maintained, for example, by the use of a coating such as lecithin, by the maintenance of the required particle size in the case of dispersion and by the use of surfactants. Prevention of the action of microorganisms can be achieved by various antibacterial and antifungal agents, for example, parabens, chlorobutanol, phenol, ascorbic acid, thimerosal, and the like. In many cases, it will be preferable to include isotonic agents, for example, sugars, polyalcohols such as mannitol, sorbitol, sodium chloride in the composition. Prolonged absorption of the injectable compositions can be achieved by including an agent that delays absorption, e.g., aluminum monostearate or gelatin, in the composition.
Sterile injectable solutions can be prepared by incorporating the active compound in the required amount in an appropriate solvent with one or a combination of ingredients enumerated above, as required, followed by filtered sterilization. Typically, dispersions are prepared by incorporating the active compound into a sterile vehicle which contains a basic dispersion medium and the required other ingredients from those enumerated above. In the case of sterile powders for the preparation of sterile injectable solutions, the preferred methods of preparation are vacuum drying and freeze-drying which yields a powder of the active ingredient plus any additional desired ingredient from a previously sterile-filtered solution thereof.
Injectable compositions may contain various carriers such as vegetable oils, dimethylacetamide, dimethylformamide, ethyl lactate, ethyl carbonate, isopropyl myristate, ethanol, and polyols (glycerol, propylene glycol, liquid polyethylene glycol, and the like). For intravenous injections, the compounds may be administered by the drip method, whereby a pharmaceutical composition containing the active compound(s) and a physiologically acceptable excipient is infused. Physiologically acceptable excipients may include, for example, 5% dextrose, 0.9% saline, Ringer'"'"'s solution, or other suitable excipients. For intramuscular preparations, a sterile composition of a suitable soluble salt form of the compound can be dissolved and administered in a pharmaceutical excipient such as Water-for-Injection, 0.9% saline, or 5% glucose solution, or depot forms of the compounds (e.g., decanoate, palmitate, undecylenic, enanthate) can be dissolved in sesame oil.
Oral compositions typically include an inert diluent or an edible carrier. For the purpose of oral therapeutic administration, the active compound can be incorporated with excipients and used in the form of tablets, troches, or capsules, e.g., gelatin capsules. Oral compositions can also be prepared using a fluid carrier for use as a mouthwash. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition. The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring. Alternatively, the pharmaceutical composition can be formulated as a chewing gum, lollipop, or the like.
Liquid compositions for oral administration prepared in water or other aqueous vehicles can include solutions, emulsions, syrups, and elixirs containing, together with the active compound(s), wetting agents, sweeteners, coloring agents, and flavoring agents. Various liquid and powder compositions can be prepared by conventional methods for inhalation into the lungs of the patient to be treated.
For administration by inhalation, the compounds are delivered in the form of an aerosol spray from pressured container or dispenser that contains a suitable propellant, e.g., a gas such as carbon dioxide, or a nebulizer.
Systemic administration can also be by transmucosal or transdermal means. For transmucosal or transdermal administration, penetrants appropriate to the barrier to be permeated are used in the formulation. Such penetrants are known in the art, and include, for example, for transmucosal administration, detergents, bile salts, and fusidic acid derivatives. Transmucosal administration can be accomplished through the use of nasal sprays or suppositories. For transdermal administration, the active compounds are formulated into ointments, salves, gels, or creams as known in the art.
The compounds can also be prepared in the form of suppositories (e.g., with conventional suppository bases such as cocoa butter and other glycerides) or retention enemas for rectal delivery.
In one embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters, and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation and Nova Pharmaceuticals, Inc. Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) can also be used as pharmaceutically acceptable carriers. These can be prepared according to methods known to those skilled in the art, for example, as described in U.S. Pat. No. 4,522,811.
It is advantageous to formulate oral or parenteral compositions in dosage unit form for ease of administration and uniformity of dosage. Dosage unit form as used herein refers to physically discrete units suited as unitary dosages for the subject to be treated; each unit containing a predetermined quantity of active compound calculated to produce the desired therapeutic effect in association with the required pharmaceutical carrier.
In all of the methods described herein, appropriate dosages of LDLR, LRP, and RAP can readily be determined by those of ordinary skill in the art of medicine, e.g., by monitoring the patient for signs of disease amelioration or inhibition, and increasing or decreasing the dosage and/or frequency of treatment as desired. Toxicity and therapeutic efficacy of such compounds can be determined by standard pharmaceutical procedures in cell cultures or experimental animals, e.g., for determining the LD50 (the dose lethal to 50% of the population) and the ED50 (the dose therapeutically effective in 50% of the population). The dose ratio between toxic and therapeutic effects is the therapeutic index and it can be expressed as the ratio LD50/ED50. Compounds which exhibit high therapeutic indices are preferred. While compounds that exhibit toxic side effects may be used, care should be taken to design a delivery system that targets such compounds to the site of affected tissue, e.g., bone or cartilage, in order to minimize potential damage to uninfected cells and, thereby, reduce side effects.
The data obtained from cell culture assays and animal studies can be used in formulating a range of dosage for use in humans. The dosage of such compounds lies preferably within a range of circulating concentrations that include the ED50 with little or no toxicity. The dosage may vary within this range depending upon the dosage form employed and the route of administration utilized. For any compound used in the method of the invention, the therapeutically effective dose can be estimated initially from cell culture assays. A dose may be formulated in animal models to achieve a circulating plasma concentration range that includes the IC50 (i.e., the concentration of the test compound which achieves a half-maximal inhibition of symptoms) as determined in cell culture. Such information can be used to more accurately determine useful doses in humans. Levels in plasma may be measured, for example, by high performance liquid chromatography.
For the compounds described herein, an effective amount, e.g., of a protein or polypeptide (i.e., an effective dosage), ranges from about 0.001 to 30 mg/kg body weight, e.g., about 0.01 to 25 mg/kg body weight, e.g., about 0.1 to 20 mg/kg body weight. The protein or polypeptide can be administered one time per day, twice per day, one time per week, twice per week, for between about 1 to 52 weeks per year, e.g., between 2 to 50 weeks, about 6 to 40 weeks, or for about 4, 5, or 6 weeks. The skilled artisan will appreciate that certain factors influence the dosage and timing required to effectively treat a patient, including but not limited to the type of patient to be treated, the severity of the disease or disorder, previous treatments, the general health and/or age of the patient, and other diseases present. Moreover, treatment of a patient with a therapeutically effective amount of a protein, polypeptide, antibody, nucleic acid, or other compound can include a single treatment or, preferably, can include a series of treatments.
For antibodies, a useful dosage is 5 mg/kg of body weight (typically 3 mg/kg to 20 mg/kg). Typically, partially human antibodies and fully human antibodies have a longer half-life within the human body than other antibodies. Accordingly, lower dosages and less frequent administration are possible. Modifications such as lipidation can be used to stabilize antibodies or other therapeutic proteins and to enhance uptake and tissue penetration. A method for lipidation of antibodies is described by Cruikshank et al. (J. Acquir. Immune Defic. Syndr. Hum. Retrovirol. 14:193, 1997). Alternatively, an antibody or a fragment thereof may be joined to a protein transduction domain, e.g., an HIV Tat-1 activator domain or the homeodomain of Antennapedia transcription factor (for review, see Heng and Cao, Medical Hypotheses 64:1105-8, 2005). Fusion proteins thus generated have been found to transduce into the cells of tissues in a mouse model system (Schwarze et al., Science 285:1569-1572, 1999).
If the compound is a small molecule, exemplary doses include milligram or microgram amounts of the small molecule per kilogram of subject or sample weight (e.g., about 1 microgram per kilogram to about 500 milligrams per kilogram, about 100 micrograms per kilogram to about 5 milligrams per kilogram, or about 1 microgram per kilogram to about 50 micrograms per kilogram. It is furthermore understood that appropriate doses of a small molecule depend upon the potency of the small molecule with respect to the expression or activity to be modulated. When one or more of these small molecules is to be administered to an animal (e.g., a human) to modulate expression or activity of a polypeptide or nucleic acid of the invention, a physician, veterinarian, or researcher may, for example, prescribe a relatively low dose at first, subsequently increasing the dose until an appropriate response is obtained. In addition, it is understood that the specific dose level for any particular animal subject will depend upon a variety of factors including the activity of the specific compound employed, the age, body weight, general health, gender, and diet of the subject, the time of administration, the route of administration, the rate of excretion, any drug combination, and the degree of expression or activity to be modulated.
The invention is further described in the following examples, which do not limit the scope of the invention described in the claims.
Differentiated HepaRG cells (4×104), which are susceptible to HBV infection (Gripon et al., Proc Natl Acad Sci USA 99:15655-60, 2002), were incubated overnight with HBV inoculum in the presence or absence of increasing concentrations of RAP or GST-RAP, and washed extensively to remove unbound HBV virions and HBsAg. Medium was changed every 2-3 days. HBsAg level in culture supernatant was measured 10 days later (at this point there was no more residual HBsAg from the inoculum, and signals detected reflect newly synthesized and secreted proteins). The level of HBsAg secreted into the culture supernatant was determined by an ELISA assay using a commercially available kit (e.g., Novus Biologicals, NEO BioLab, Cusabio Biotech Co., Ltd.). Briefly, culture medium was added to wells containing capture antibody (anti-HBsAg), followed by incubation at 37° C. for 30 min. After washing with provided washing buffer, conjugate (anti-HBsAg conjugated with HRP) was added followed by incubation at 37° C. for 30 min. After washing, signals were revealed by addition of HRP substrate and optical density measured at 450 nm. A dose-dependent reduction of HBsAg secretion to culture supernatant was observed (
HepaRG is a human liver progenitor cell line. It is undifferentiated during its growth phase. Treatment of confluent HepaRG cells with 2% DMSO for two weeks induces its differentiation into islands of hepatocytes surrounded by bile duct cells (Parent et al., Gastroenterology 126:1147-56, 2004). LRP was immunoprecipitated from cell lysate using a monoclonal antibody against its heavy chain, followed by Western blot analysis with an antibody against its light chain. Only a fraction of hepatocytes, but not bile duct cells, in differentiated HepaRG cells are susceptible to HBV infection. LRP expression was greatly enhanced in differentiated HepaRG cells relative to undifferentiated counterparts (
Hepatocytes are polarized. LRP is distributed at the basolateral side rather than apical side of hepatocytes (Marzolo et al., Traffic 4:273-88, 2003) consistent with HBV infection from the bloodstream. It was recently reported that HBV preferentially infects hepatocytes near the edge of hepatocyte islands (Schulze et al., Hepatology 55:373-83, 2012). Pseudomonas exotoxin, which uses LRP as its receptor (Kounnas et al., J Biol Chem 267:12420-3, 1992), selectively killed cells in the periphery of hepatocyte islands of HepaRG cells when used at a low dose (
To specifically test the role of LRP in mediating HBV infection, LRP expression was knocked down by shRNA. Proliferating HepaRG cells cultured in a 12-well plate were infected overnight with lentivirus carrying LRP shRNA or control shRNA. LRP shRNA was obtained from Santa Cruz Biotechnology, sc-40101-V, with lentiviral particles containing three to five expression constructs that each encode target-specific 19 to 25 nucleotides (plus hairpin) shRNA designed to knockdown gene expression. Control shRNA was obtained from Santa Cruz Biotechnology, sc-108080. Stably transduced cells were selected by puromycin (5 μg/ml). Cells were then differentiated for two weeks and infected with purified HBV particles. Measurement of HBsAg level at day 12 post-infection revealed about 50% reduction in infectivity with LRP shRNA when compared to cells transduced with control shRNA (
Besides testing the effect of LRP on HBV infectivity, LRP'"'"'s impact on HBsAg and virion secretion was also evaluated. This experiment was performed on Huh7 cells, a human hepatoma cell line. Although Huh7 cells are resistant to HBV infection, the cells support viral gene expression, genome replication, as well as release of HBsAg and virions if transfected with full-length HBV DNA constructs. Huh7 cells were transfected with full-length HBV construct K85, together with vector DNA, LRP, or LDLR cDNA. Secreted HBsAg was measured at day 4 and 7 post-transfection, respectively. The amount of HBsAg secreted was markedly increased if the full-length HBV construct was co-transfected with LRP cDNA or LDLR cDNA instead of vector DNA (
FXa could cleave envelope proteins on both HBV (
A seven amino acid antistasin-related peptide, a direct FXa inhibitor (Tuszynski et al., J Biol Chem 262:9718-23, 1987; Nutt et al., J Biol Chem 263:10162-7, 1988), efficiently blocked HBV infection of HepaRG cells in a dose-dependent manner (
It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.