Sterol derivatives, liposomes comprising sterol derivatives and method of loading liposomes with active substances

Abstract

A sterol derivative with a pKa value of between 3.5 and 8, according to the general formula cation-spacer 2-Y-spacer 1-X-sterol, wherein Y and X represent linking groups, is suggested, as well as liposomes comprising such sterol derivatives.

1 . A sterol derivative according to general formula (I):
   cation-spacer 2-Y-spacer 1-X-sterol (1), wherein:   said cation is a nitrogen base selected from the group consisting of piperazines, imidazoles, morpholines, purines, pyrimidines, and pyridines;   said spacers 1 and 2 are independently linear, branched or cyclic C 1-8  alkyl, and comprise 0-2 ethylenically unsaturated bonds, wherein at least one of said spacers 1 and 2 is cyclic C 1-8  alkyl;   said linking group X is selected from the group consisting of —(C=0)-O— and —(C=0)-NH—;   said linking group Y is selected from the group consisting of —O-(0=C)—, —NH-(0=C)-1-(C=0)-O—, and —(C=0)-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 a pKa value of between about 3.5 and about 8.   
     
     
         2 . The sterol derivative according to  claim 1 , wherein at least on of said spacers 1 and 2 have hydroxyl groups. 
     
     
         3 . The sterol derivative according to  claim 1 , wherein the sterol derivative has a pKa value of between about 4 and about 7. 
     
     
         4 . A liposome comprising the sterol derivative of  claim 1 . 
     
     
         5 . The liposome of  claim 4 , wherein said liposome comprises between about 5 mole-% and about 50 mole-% of sterol derivatives. 
     
     
         6 . The liposome of  claim 5 , wherein said liposome comprises between about 5 mole-% and about 40 mole-% of sterol derivatives. 
     
     
         7 . The liposome of  claim 6 , wherein said liposome comprises between about 10 mole-% and about 30 mole-% of sterol derivatives. 
     
     
         8 . The liposome of  claim 4 , wherein the liposome comprises one or more lipids selected from the group consisting of phosphatidyl choline, phosphatidyl ethanolamine, and diacylglycerol. 
     
     
         9 . The liposome of  claim 8 , wherein said liposome is neutral or negatively charged at a pH of from about 7.0 to about 7.8. 
     
     
         10 . The liposome of  claim 4 , wherein said liposome has an average size of between about 50 and 1000 nm n. 
     
     
         11 . The liposome of  claim 10 , wherein said liposome has an average size of between about 50 and 300 nm. 
     
     
         12 . The liposome of  claim 11 , wherein said liposome has an average size of between about 60 and 130 nm. 
     
     
         13 . The liposome of  claim 4 , wherein said liposome further comprises an active substance. 
     
     
         14 . The liposome  claim 13 , 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. 
     
     
         15 . The liposome of  claim 13 , wherein at least about 80% of said active substance is situated inside the liposome. 
     
     
         16 . A method of loading the liposome of  claim 13  with an 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.   
     
     
         17 . A method of loading the liposome of  claim 13  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.   
     
     
         18 . 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 13 . 
     
     
         19 . The method of  claim 18 , wherein said administration is intravenous or peritoneal. 
     
     
         20 . A transport and release system for the transport and release of an active substance in a subject, said system comprising the liposome of  claim 13 . 
     
     
         21 . A depot formulation or circulative depot comprising the liposome of  claim 13 . 
     
     
         22 . A nanocapsule prepared from the liposome of  claim 4 . 
     
     
         23 . A vector for transfecting cells in vivo, in vitro or ex vivo, said vector comprising the liposome of  claim 4  and a nucleic acid.