Cytosolic delivery of macromolecules: I. Synthesis and characterization of pH-sensitive acyloxyalkylimidazoles.
A series of 1-(acyloxyalkyl)imidazoles (AAI) were synthesized by nucleophilic substitution of chloroalkyl esters of fatty acids with imidazole. The former was prepared from fatty acid chloride and an aldehyde. When incorporated into liposomes, these lipids show an apparent pK(a) value ranging from 5.12 for 1-(palmitoyloxymethyl)imidazole (PMI) to 5.29 for 1-[(alpha-myristoyloxy)ethyl]imidazole (alpha-MEI) as determined by a fluorescence assay. When the imidazole moiety was protonated, the lipids were surface-active, as demonstrated by hemolytic activity towards red blood cells. As expected, AAI were hydrolyzed in serum as well as in cell homogenate. They were significantly less toxic than biochemically stable N-dodecylimidazole (NDI) towards Chinese hamster ovary (CHO) and RAW 264.7 (RAW) cells as determined by MTT assay. When fed to RAW cells, fluorescein-labeled oligonucleotides encapsulated in liposomes containing 20 mol% 1-(stearoyloxymethyl)imidazole (SMI) resulted in punctate as well as partially diffuse fluorescence. In a functional assay involving down-regulation of luciferase in CV-1 cells, neutral liposomes containing imidazole lipids showed suboptimal delivery of antisense phosphorothioate oligomers. Taken together, the results suggest that AAI are of potential use in developing nontoxic, pH-sensitive liposomes. However, these liposomal formulations need to be optimized to achieve higher concentrations of pH-sensitive detergents within the endosome to facilitate efficient cytosolic release of liposome-entrapped contents.
Chen
Feng-Jing
FJ
Lipocine Inc, Salt Lake City, UT 84103, USA.
Asokan
Aravind
A
Cho
Moo J
MJ
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D006224:Cricetinae; D003600:Cytosol / Q000737:chemistry / Q000378:metabolism*; D004337:Drug Carriers; D004355:Drug Stability; D011992:Endosomes / Q000378:metabolism; D005227:Fatty Acids / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles / Q000138:chemical synthesis*; D008081:Liposomes / Q000737:chemistry* / Q000378:metabolism; D046911:Macromolecular Substances; D015394:Molecular Structure; D013501:Surface-Active Agents
D004337:Drug Carriers; D005227:Fatty Acids; D007093:Imidazoles; D008081:Liposomes; D046911:Macromolecular Substances; D013501:Surface-Active Agents