Amphoteric sterols and the use thereof
An amphoteric compound based on a sterol skeleton, the 3-position of the sterol ring system being substituted by one or more amphoteric groups having an isoelectric point of between about 4 and 9, together with liposomes containing such compounds and their uses.
1. A sterol derivative according to formula (1):
Amphoteric substance -Y- spacer -X- sterol (1),
wherein:
said amphoteric substance comprises a first portion having a cationic charge with a pKa value between about 4 and about 8.5 and a second portion of anionic charge with a pKa value between about 3 and about 7;
said first portion of said amphoteric substance is selected from the group consisting of piperazines, imidazoles, morpholines, purines, and pyrimidines;
said second portion of said amphoteric substance comprises a carboxyl group;
said spacer is a linear or branched C 1-8 alkyl comprising 0-2 ethylenically unsaturated bonds;
said linking group X is selected from the group consisting of —(C═O)—O—, —(C═O)—NH— and —NH—(C═O)—O—;
said linking group Y is selected from the group consisting of —O—(C═O), —NH—(C═O), —(C═O)—O— and —(C═O)—NH—;
said sterol is selected from the group consisting of cholesterol, sitosterol, campesterol, desmosterol, fucosterol, 22-ketosterol, 20-hydroxysterol, stigmasterol, 22-hydroxycholesterol, 25 -hydroxycholesterol, lanosterol, 7-dehydrocholesterol, dihydrocholesterol, 19-hydroxycholesterol, 5α-cholest-7-en-3β-ol, 7-hydroxycholesterol, epicholesterol, ergosterol, and dehydroergosterol; and
said sterol derivative has an isoelectric point between about 4.5 and about 8.5.
2. The sterol derivative according to claim 1 wherein said amphoteric substance comprises 1-3 portions of cationic charge and 1-3 portions of anionic charge.
3. The sterol derivative according to claim 1 wherein said sterol derivative has an isoelectric point between about 5 and about 7.
4. The sterol derivative according to claim 1 wherein said amphoteric substance comprises a peptide of 1-10 amino acids, wherein said peptide comprises as a charge carrier one or more amino acids selected from the group consisting of histidine, arginine, lysine, glutamic acid, and aspartic acid.
5. The sterol derivative according to claim 4 wherein the sum of glutamic acid and aspartic acid amino acids of said peptide is greater than the sum of arginine, lysine, and histidine amino acids of said peptide.
6. The sterol derivative according to claim 4 wherein said peptide comprises solely histidine as cationic amino acid, and wherein the sum of glutamic acid amino acids and aspartic acid amino acids is greater than or equal to the number of histidine amino acids.
7. A liposome comprising the sterol derivative of claim 1 .
8. The liposome according to claim 7 wherein said liposome comprises less than about 50 mole- % of sterol derivative.
9. The liposome according to claim 8 wherein said liposome comprises between about 2 mole- % and about 50 mole- % of sterol derivative.
10. The liposome according to claim 9 wherein said liposome comprises between about 10 mole- % and about 40 mole- % of sterol derivative.
11. The liposome according to claim 7 , wherein the liposome comprises one or more lipids selected from the group consisting of phosphatidyl choline, phosphatidyl ethanolamine, diacylglycerol, tetraether lipid, and PEG lipid.
12. The liposome according to claim 7 wherein said liposome has an average size of between about 50 and about 1000 nm.
13. The liposome according to claim 12 wherein said liposome has an average size of between about 50 and about 300 nm.
14. The liposome according to claim 13 wherein said liposome has an average size of between about 60 and about 130 nm.
15. The liposome according to claim 7 wherein said liposome further comprises an active substance.
16. The liposome according to claim 15 wherein said active substance is selected from the group consisting of a protein, a peptide, a DNA, an RNA, an antisense nucleotide, a decoy nucleotide, and a mixture thereof.
17. The liposome according to claim 15 wherein at least about 80% of said active substance is entrapped inside the liposome.
18. A method of loading the liposome according to claim 15 with said active substance, said method comprising:
encapsulating said active substance in said liposome at a binding pH value; and
removing unbound active substances at a second pH value.
19. A method of loading the liposome according to claim 8 with an active substance, said method comprising:
permeabilizing said liposome by treatment at a pH value sufficient to enable loading of said active substance, and
sealing said liposome.
20. A method for the transport and release of an active substance in a subject, said method comprising administering to said subject the liposome of claim 15 .
21. The method of claim 20 , wherein said administration is intravenous or peritoneal.
22. A depot formulation or circulative depot comprising the liposome of claim 7 .
23. A nanocapsule prepared from the liposome of claim 7 .
24. A vector for transfecting cells in vivo, in vitro or at vivo, said vector comprising the liposome of claim 7 and a nucleic acid.