Receptor(SSTR4)-selective somatostatin analogs

• US 7,238,775 B2
• Filed: 01/24/2005
• Issued: 07/03/2007
• Est. Priority Date: 07/24/2002
• Status: Expired due to Fees

• Current Assignee: Salk Institute for Biological Studies
• Original Assignee: Salk Institute for Biological Studies
• Inventors: Riek, Roland, Reubi, Jean Claude, Rivier, Jean E. F., Erchegyi, Judit
• Primary Examiner(s): Tsang; Cecilia J.
• Assistant Examiner(s): HEARD, THOMAS SWEENEY
• Application Number:
  US11/041,676
• Publication Number:
  US 20050245438A1
• Time in Patent Office: 890 Days
• Field of Search: None
• US Class Current: 530/311
• CPC Class Codes: A61K 38/00 Medicinal preparations containing peptides peptides containing beta-lactam rings A61K31/00; cyclic dipeptides not having in their molecule any other peptide link than those which form their ring, e.g. piperazine-2,5-diones, A61K31/00; ergot alkaloids of the cyclic peptide type A61K31/48; containing macromolecular compounds having statistically distributed amino acid units A61K31/74; medicinal preparations containing antigens or antibodies A61K39/00; medicinal preparations characterised by the non-active ingredients, e.g. peptides as drug carriers, A61K47/00
• CPC Class Codes: C07K 14/655 Somatostatins

Abstract

Analogs of SRIF which are selective for SSTR4 in contrast to the other cloned SRIF receptors are useful in determining tissue and cellular expression of the receptor SSTR4 and its biological role in regulating tumor growth. SRIF analog peptides, such as des-AA^{1,2,4,5,12,13}[Ala⁷]-SRIF; des-AA^{1,2,4,5,12,13}[Aph⁷]-SRIF, des-AA^{1,2,4,5,12,13}[Aph⁷]Cbm-SRIF; des-AA^{1,2,4,5,12,13}[Tyr²,Ala⁷]-Cbm-SRIF, and des-AA^{1,2,4,5,12,13}[Tyr⁷,C^βMe-L-2Nal⁸]-SRIF, and counterparts incorporating D-Cys³ and/or D-Trp⁸ and/or Ala¹¹, bind with high affinity to the cloned human receptor SSTR4 and activate the receptor, but they do not bind with significant affinity to human SSTR1, SSTR2, SSTR3 or SSTR5. By incorporating an iodinated tyrosine in position-2 in these SSTR4-selective SRIF analogs, a labeled compound useful in drug-screening methods is provided. Alternatively, for use in therapy, cytotoxins or highly radioactive elements can be N-terminally coupled or complexed thereto.

Claims

1. A cyclic somatostatin(SRIF) analog peptide which selectively binds the SRIF receptor SSTR4 in contrast to its affinity for SSTR1, SSTR2, SSTR3 and SSTR5, which peptide comprises the amino acid sequence (cyclo)Xaa₁-Xaa₂-Xaa₃-Xaa₄-Xaa₅-Phe-Xaa₇-Xaa₈-Lys-Thr-Xaa₁₁-Xaa₁₂-Xaa₁₃-Cys (SEQ ID NO:

2) wherein

Xaa₁ is des-Xaa, D-Ala, Ala, L-Hor, Cbm, an acyl group having up to 20 carbon atoms or alkyl(C₁ to C₆);

Xaa₂ is Tyr, D-Tyr, Gly or des-Xaa;

Xaa₃ is Cys or D-Cys;

Xaa₄ is des-Xaa;

Xaa₅ is des-Xaa;

Xaa₇ is an amino acid selected from the group consisting of Ala, Aph, Amp, Iamp, and Val;

Xaa₈ is an amino acid selected from the group consisting of (A)Trp, (A)D-Trp, and 2Nal, wherein A is H, Cl, F, Br, Me, NO₃, OMe or formyl;

Xaa₁₁ is Ala, Gly, Val, Phe or Tyr;

Xaa₁₂ is des-Xaa; and

Xaa₁₃ is des-Xaa.

2. The peptide according to claim 1 wherein Xaa₁ and Xaa₂, are des-Xaa.

3. The peptide according to claim 1 wherein

Xaa₁ is Cbm;

Xaa₂ is des-Xaa;

Xaa₇ is Aph;

Xaa₈ is Trp; and

Xaa₁₁ is Phe.

4. The peptide according to claim 1 comprising the amino acid sequence:

(cyclo)Xaa₁-Tyr-Xaa₃-Xaa₄-Xaa₅-Phe-Xaa₇-Xaa₈-Lys-Thr-Xaa₁₁-Xaa₁₂-Xaa₁₃-Cys (SEQ ID NO;

2), where

Xaa₁ is Acyl, Cbm or des-Xaa;

Xaa₃ is Cys or D-Cys;

Xaa₇ is Ala, Aph, Amp or Iamp;

Xaa₈ is Trp, D-Trp or 2Nal;

Xaa₁₁ is Ala, Phe or Tyr; and

Xaa₄, Xaa₅, Xaa₁₂ and Xaa₁₃ are des-Xaa.

5. A cyclic somatostatin(SRIF) analog peptide having specific affinity for the SRIF receptor SSTR4 in contrast to its affinity for SSTR1, SSTR2, SSTR3 and SSTR5, which peptide has an amino acid sequence (cyclo)Xaa₁-Xaa₂-Xaa₃-Xaa₄-Xaa₅-Phe-Xaa₇-Xaa₈-Lys-Thr-Xaa₁₁-Xaa₁₂-Xaa₁₃-Cys (SEQ ID NO:

2), where

Xaa₁ is Ac, Cbm or des-Xaa;

Xaa₂ is Tyr, D-Tyr or des-Xaa;

Xaa₃ is Cys or D-Cys;

Xaa₇ is Ala, Aph, Amp or Iamp;

Xaa₈ is Trp, D-Trp or 2Nal,

Xaa₁₁ is Phe or Tyr; and

Xaa₄, Xaa₅, Xaa₁₂ and Xaa₁₃ are des-Xaa.

12. The peptide according to claim 5 wherein Xaa₇ is Ala, Aph or Amp.

13. The peptide according to claim 12 wherein Xaa₇ is Ala and Xaa₁₁ is Ala.

6. A cyclic somatostatin(SRIF) analog peptide having specific affinity for the SRIF receptor SSTR4 in contrast to its affinity for SSTR1, SSTR2, SSTR3 and SSTR5, which peptide has an amino acid sequence (cyclo)Xaa₁-Tyr-Xaa₃-Xaa₄-Xaa₅-Phe-Xaa₇-Xaa₈-Lys-Thr-Xaa₁₁-Xaa₁₂-Xaa₁₃-Cys (SEQ ID NO:

2), where

Xaa₁ is Ac, Cbm or des-Xaa;

Xaa₃is Cys;

Xaa₇ is Ala, Aph or Amp;

Xaa₈ is Trp, D-Trp or 2Nal

Xaa₁₁ is Phe or Tyr; and

Xaa₄, Xaa₅, Xaa₁₂ and Xaa₁₃ are des-Xaa.

7. The peptide according to claim 6 wherein Xaa₇ is Ala and Xaa₈ is Trp or 2Nal.

10. The peptide according to claim 6 wherein Xaa₇ is Aph.

11. The peptide according to claim 6 wherein Xaa₇ is Amp.

17. A pharmaceutical composition comprising a mixture of the peptide according to claim 6 and at least one pharmaceutically acceptable carrier.

20. A method for screening for ligands that bind with high affinity to SSTR4, which method comprises

carrying out a competitive binding assay with (1) SSTR4, (2) the peptide according to claim 6 which is labeled and (3) a candidate ligand, and

determining the ability of the said candidate ligand to displace said labeled peptide.

8. A peptide comprising the amino acid sequence:

Tyr-Cys-Phe-Ala-Trp-Lys-Thr-Phe-Cys (SEQ ID NO;

8).

9. The peptide according to claim 8 wherein Tyr is radioactively iodinated.

14. The peptide according to claim 8 wherein there is also present at the N-terminus a complexing agent or a conjugating agent.

15. The peptide according to claim 8 wherein a complexing agent is present at the N-terminus which is capable of joining to a radioactive nuclide.

16. The peptide according to claim 8 wherein a conjugating agent is present at the N-terminus which is capable of linking to a cytotoxin.

18. A method for destroying SSTR4-containing cells, which method comprises administering an amount of the peptide to the cell according to claim 14 which includes a radioactive nuclide or a cytotoxin, which amount is effective to destroy such cells.

19. A method of detecting, in the body of a human being, tumors having SSTR4 and their metastases in tissues, which in healthy condition and in non-neoplastic conditions of chronic inflammation do not contain substantial quantities of SSTR4, which method comprises

(i) administering to said human, in a quantity sufficient for external imaging, a composition comprising a peptide according to claim 8, said peptide being labeled with (a) a radioactive metal isotope or (b) a paramagnetic metal atom or (c) a radioactive halogen isotope, and thereupon

(ii) subjecting said human to external imaging, by radioactive scanning or by magnetic resonance imaging, to determine the targeted sites in the body thereof in relation to the background activity, in order to allow detection and localization of said tumors in the body.