Effect of amide linkage of PEG-lipid conjugates on the stability and cytotoxic activity of goniodiol loaded in PEGylated liposomes

Abstract

Goniodiol, isolated from Goniothalamus species, has previously shown cytotoxic activity in several human cancer cell lines. The purpose of this study was to develop a liposome system to improve the stability and cytotoxic activity of goniodiol. Polyethylene glycol (PEG) and distearoylphosphatidylethanolamine (DSPE) were conjugated with acetamide linkage to form PEG-A-DSPE, and with pentanamide linkage to form PEG-P-DSPE. Goniodiol-loaded PEGylated liposomes consisted of goniodiol, 1,2-distearoyl-sn-glycero-3-phosphocholine lipid and PEG-A-DSPE or PEG-P-DSPE. It was found that about 40% of goniodiol leaks from conventional liposomes when stored in phosphate buffer solution (PBS), but the PEGylated liposomes containing 5, 10 or 15 mole% of PEG-A-DSPE or PEG-P-DSPE (PEG-P liposome) greatly reduced this leakage. Also, both PEGylated liposomes significantly decreased the degradation of goniodiol in fetal bovine serum (FBS). Interestingly, PEG-P liposome exhibited the lowest leakage amount of goniodiol in PBS and the highest remaining amount of goniodiol in FBS. Additionally, the lowest viability of HepG2 cells was observed after treatment of PEG-P liposome. Our results demonstrate that PEG-P liposome enhances the stability and cytotoxicity of goniodiol by reducing the leakage of goniodiol from liposomes, which suggests that the linkage length between PEG and lipid of PEG-lipid conjugates is an important factor relevant to drug leakage.