Preparation, optimization, and characterization of topotecan loaded PEGylated liposomes using factorial design

This study reports the development of liposomal system for a potent antitumor drug, topotecan. To achieve this goal conventional and PEGylated liposomes were prepared according to a factorial design by hydration method followed by extrusion. Parameters such as type of lipid, percentage of cholesterol, percentage of phosphatidylglycerols, percentage of polyethylene glycol (PEG)-lipids, and drug to lipid molar ratio were considered as important factors for the optimizing the entrapment and retention of topotecan inside the liposomes. The size and zeta-potential of the PEGylated and conventional liposomes were measured by particle size analyzer and zeta-potentiometer, respectively. The stability and release characteristics of PEGylated liposome loaded topotecan were compared with conventional liposomes and free topotecan. The optimized PEGylated [distearoyl phosphatidylcholine (DSPC)/cholesterol/ distearoyl phosphatidylglycerol (DSPG)/ distearoyl phosphatidylethanolamine-PEG(2000) (DSPE-PEG(2000)); 7:7:3:1.28] and related conventional [DSPC/cholesterol/DSPG; 7:7:3] liposomes showed a narrow size distribution with a polydipersity index of 0.15 and 0.10, an average diameter of 103.0 +/- 13.1 and 95.2 +/- 11.10 nm, and with drug loading of 11.44 and 6.21%, respectively. Zeta-potential was -10 +/- 2.3 and -22 +/- 2.8 mV for PEGylated and conventional liposomes, respectively. The results of stability evaluation showed that the lactone ring of topotecan was notably preserved upon liposome encapsulation. PEGylated liposomes containing topotecan showed a significant decrease (P < 0.001) in release rate in comparison with conventional leptosomes. These results indicate the suitability of PEGylated liposomes in controlling topotecan release. The prepared liposomes (especially PEGylated liposomes) as those described here may be clinically useful to stabilize and deliver topotecan for the treatment of cancer.