Application of oligo-(14-amino-3,6,9,12-tetraoxatetradecanoic acid) lipid conjugates as steric barrier molecules in liposomal formulations

Lipid conjugates of oligo-(14-amino-3,6,9,12-tetraoxatetradecanoic acid) (A TTAn) were synthesized as monodisperse analogues of poly(ethylene glycol) ( PEG) derivatives used in liposomal drug delivery systems. The new lipids we re shown to be at least equivalent to MePEGA-2000-DSPE in assays designed t o evaluate the effectiveness of polymers as steric barrier molecules in lip osomes. Liposomes containing 1-5% of ATTA8-DSPE (octamer) showed comparable long circulation behavior relative to PEG-2000-DSPE analogues. Surprisingl y, the shorter ATTA4-DSPE (tetramer) appeared to be quite effective in redu cing clearance. Liver enzyme levels and systemic single dose tolerability o f ATTA8-DSPE liposomes were comparable to controls, suggesting that the new materials are nontoxic. Prolonged exposure of ATTA8-DSPE liposomes to sple nocytes in vitro showed no evidence of mitogenicity relative to controls or MePEGA-2000-DSPE liposomes. ATTA8-DSPE was as effective as MePEGC-2000-DSP E in preventing complement activation by cationic liposome systems. Repeat dosage in vivo regimes in ICR mice using DSPC/cholesterol liposomes, with a nd without 5% ATTA8-DSPE and MePEGC-2000-DSPE, showed no evidence of enhanc ed clearance on successive doses. Splenocytes recovered after repeat doses showed no significant evidence of mitogenicity on restimulation with liposo mes. Cellular differentiation and activation marker levels in splenocytes r ecovered after the fourth in vivo administration were at normal levels. The se results suggest that ATTAn oligomers do not induce an immune response in isolation. It was demonstrated that ATTA8-DSPE could be used to replace PE G-lipids in the formulation of doxorubicin, plasmid DNA and oligonucleotide s using a variety of formulation techniques. The study demonstrates that AT TAn oligomers can be safely and effectively used in place of poly(ethylene glycol) as well-defined biomaterials in liposomal applications where reprod ucible behavior is critical.