Liposomes as contrast agents for ultrasonic imaging and methods for preparing the same

• US 5,123,414 A
• Filed: 08/26/1991
• Issued: 06/23/1992
• Est. Priority Date: 12/22/1989
• Status: Expired due to Term

• Current Assignee: Lantheus Medical Imaging, Inc. (Lantheus Holdings, Inc.)
• Original Assignee: Evan C. Unger
• Inventors: Unger, Evan C.
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): AKERS, SCOTT
• Application Number:
  US07/750,877
• Time in Patent Office: 302 Days
• Field of Search: 128/662.02, 128/654, 128/660.01, 424/4, 424/43, 424/44, 424/450, 436/829, 264/4.1, 264/4.3, 264/4.6
• US Class Current: 600/431
• CPC Class Codes: A61K 41/0028 Disruption, e.g. by heat or ultrasounds, sonophysical or sonochemical activation, e.g. thermosensitive or heat-sensitive liposomes, disruption of calculi with a medicinal preparation and ultrasounds
• CPC Class Codes: A61K 41/0052 Thermotherapy; Hyperthermia; Magnetic induction; Induction heating therapy
• CPC Class Codes: A61K 47/6925 the form being a microcapsule, nanocapsule, microbubble or nanobubble
• CPC Class Codes: A61K 49/223 Microbubbles, hollow microspheres, free gas bubbles, gas microspheres
• CPC Class Codes: A61K 49/227 Liposomes, lipoprotein vesicles, e.g. LDL or HDL lipoproteins, micelles, e.g. phospholipidic or polymeric
• CPC Class Codes: A61K 9/127 Liposomes
• CPC Class Codes: A61K 9/1277 Processes for preparing; Proliposomes
• CPC Class Codes: A61K 9/1278 Post-loading, e.g. by ion or pH gradient

Abstract

Liposomes suitable as ultrasound contrast agents which contain media of various types including gases, gaseous precursors activated by pH, temperature or pressure, as well as other solid or liquid contrast enhancing agents, are described. Methods of using the same as ultrasound contrast agents are also disclosed. The present invention also comprises novel methods for synthesizing liposomes having encapsulated therein gases.

Claims

1. A method of synthesizing a liposome having encapsulated therein a gas and employing said liposome in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in a vessel,

(b) pressurizing said vessel with a cooled gas, thereby dissolving a first portion of said gas into said liquid media, so that a portion of said dissolved gas enters said liposomes,

(c) rapidly depressurizing said vessel by releasing a second portion of said gas from said vessel, thereby causing said dissolved gas having entered said liposomes to form bubbles within said liposomes,

(d) administering said liposomes to a patient, and

(e) scanning said patient with a medical imaging device to obtain enhanced visible images of an internal region of said patient.

2. A method of synthesizing a liposome having encapsulated therein a gas and employing said liposome in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in a vessel,

(b) pressurizing said vessel with a gas,

(c) bubbling said gas through said liquid media, thereby dissolving a portion of said gas in said liquid media, so that a portion of said dissolved gas enters said liposomes,

(d) depressurizing said vessel, thereby causing said dissolved gas having entered said liposomes to form bubbles within said liposomes,

(e) administering said liposomes to a patient, and

(f) scanning said patient with a medical imaging device to obtain enhanced visible images of an internal region of said patient.

3. A method for synthesizing a liposome having encapsulated therein a gas and employing said liposome in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in

(b) pressurizing said vessel with a gas,

(c) cavitating said liquid media,

(d) cooling said liquid media during said cavitation,

(e) depressurizing said vessel, thereby resulting in a liposome having encapsulated therein a gas,

(f) administering said liposomes to a patient, and

(g) scanning said patient with a medical imaging device to obtain enhanced visible images of an internal region of said patient.

4. A method of synthesizing a liposome having encapsulated therein a gas, said liposome being particularly useful in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in

(b) pressurizing said vessel with a cooled gas, thereby dissolving a first portion of said gas into said liquid media, so that a portion of said dissolved gas enters said liposomes, and

(c) rapidly depressurizing said vessel by releasing a second portion of said gas from said vessel, thereby causing said dissolved gas having entered said liposomes to form bubbles within said liposomes.

5. The method according to claim 4 wherein said gas is selected from the group consisting of nitrogen, oxygen, carbon dioxide, xenon, argon, neon and helium.

6. The method according to claim 4 wherein said liquid media is a phosphate buffered saline solution.

7. The method according to claim 4 wherein said liposomes are comprised of egg phosphatidylcholine.

8. The method according to claim 4 wherein the step of pressurizing said vessel comprises the step of pressurizing said vessel to a pressure between about 50 and about 120 psi.

9. The method according to claim 4 wherein the temperature of said cooled gas prior to said pressurization of said vessel is between about 1°

to about 4°

C.

10. A method of synthesizing a liposome having encapsulated therein a gas, said liposome being particularly useful in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in a vessel,

(b) pressurizing said vessel with a gas,

(c) bubbling said gas through said liquid media, thereby dissolving a portion of said gas in said liquid media, so that a portion of said dissolved gas enters said liposomes, and

(d) depressurizing said vessel, thereby causing said dissolved gas having entered said liposomes to form bubbles within said liposomes.

11. The method according to claim 10 wherein the step of depressurizing said vessel further comprises the step of rapidly releasing a portion of said liquid media from said vessel.

12. The method according to claim 11 wherein:

(a) said vessel is approximately cylindrically shaped, said vessel having an inlet port, and outlet port, and a bottom, a tube disposed in said vessel, said tube having first and second ends, said first end of said tube disposed in said bottom of said vessel, said second end of said tube in flow communication with said inlet port, and

(b) the step of pressurizing said vessel and bubbling said gas comprises the steps of introducing said gas into said inlet port under pressure and allowing said gas to flow through said tube, said gas discharging from said tube at said first end of said tube.

13. The method according to claim 12 wherein the step of depressurizing said vessel is performed in less than about 5 seconds.

14. The method according to claim 12 wherein:

(a) said second end of said tube is in flow communication with said outlet port, and

(b) the step of depressurizing said vessel comprises the step of allowing said pressurizing gas to force said liquid to flow through said tube and out said outlet port.

15. The method according to claim 12 wherein said bottom of said vessel curves convexly inward, said first end of said tube being closest to the most inward point on said convex bottom.

16. The method according to claim 10 wherein said gas is selected from a group consisting of nitrogen, oxygen, carbon dioxide, xenon, argon, neon and helium.

17. The method according to claim 10 wherein the step of pressurizing said vessel comprises the step of pressurizing said vessel to a pressure in approximately the 50-120 psi range.

18. The method according to claim 10 wherein said liquid media is a phosphate buffered saline solution.

19. The method according to claim 10 wherein said liposomes are comprised of egg phosphatidylcholine.

20. A method for synthesizing a liposome having encapsulated therein a gas, said liposome being particularly useful in medical imaging, comprising the steps of:

(a) placing a liquid media containing liposomes in

(b) pressurizing said vessel with a gas,

(c) cavitating said liquid media,

(d) cooling said liquid media during said cavitation, and

(e) depressurizing said vessel, thereby resulting in a liposome having encapsulated therein a gas.

21. The method according to claim 20 wherein the step of cavitating said liquid media comprises the step of generating high frequency sound waves in said liquid media.

22. The method according to claim 21 wherein the step of generating high frequency sound waves comprises the step of generating waves at a frequency of about 20 kHz and an amplitude about in the range of about 30-120 μ

m.

23. The method according to claim 21 wherein the step of generating high frequency sound waves in said liquid media comprises the step of sonicating said liquid media.

24. The method according to claim 22 wherein the step of pressurizing said vessel comprises the step of pressurizing said vessel to a pressure in the range of about 50 to about 120 psi using carbon dioxide cooled to about 1°

to about 4°

C. range.

25. The method according to claim 23 wherein the step of cooling said liquid media comprises the step of circulating a cooling fluid over the exterior of said vessel.

26. The method according to claim 24 wherein the step of cooling said liquid media comprises the step of maintaining the temperature of said liquid media in a range of about 1°

C. to about 4°

C.

27. The method according to claim 24 wherein said liposomes comprise cholesterol mixed with egg phosphatidylcholine.

28. The method according to claim 24 wherein said liposomes comprise cholesterol mixed with saturated phospholipids.