Applications of liposomes on anti-cancer agents

Abstract

Toxicity is a major limitation in clinical use of most anticancer drugs. Liposomes, especially targeted long-circulating liposomes, provide the possibility of delivering drugs specifically to targeted cancer tissues, thus increasing anticancer activity and minimizing toxicity. 2-4'-Amino-3'-methylphenylbenzothiazole (AMPB), a potent anticancer drug, is inappropriate for traditional oral or parenteral formulations because of its severe dose-limiting hepatotoxicity. Several PEG-coated liposomal formulations were developed by using different drug/lipid ratios. Particle size and encapsulation efficiency of each formulation were investigated; the most stable liposomal formulation was selected for animal testing. The formulation with AMPB/egg phosphatidyl choline/cholesterol/1, 2-distearoyl-sn-glycero-3-phosphoethanolamine-N-polyethylene glycol 2000, PEG2000-DSPE in a 1/5/5/1 molar ratio is the best formulation. This formulation contains 2 mg/ml AMPB with encapsulation efficiency above 95%, average particle size 120-150 nm. Daunorubicin is a well known anti cancer agent. To minimize its cardiotoxicity, targeted folate-PEG-liposomes were developed in this study. The pH-gradient loading method was used to increase the drug loading efficiency. Above 97% loading efficiency was reached by creating a 3 to 4 unit pH difference across the liposome membrane. The final folate-PEG-liposomml formulation contained 2.5 mg/ml daunorubicin HCI, with average particle size of 110∼120 nm, pH of ∼7.4, and a drug/lipid ratio 1/20 (w/w). The solvent, chloroform, commonly used for liposome preparation, is harmful to humans. Therefore, halothane, a commonly used inhalation anesthetic, was used in this study in place of chloroform to prepare liposomes. AMPB and several other proprietary anticancer agents were formulated in liposomes by using halothane and chloroform. No obvious differences in physicochemical properties were observed between halothane and chloroform mediated liposomes.