The use of cholesteryl pullulan for the preparation of stable vincristine liposomes

An improved method for the synthesis of cholesteryl pullulan has been developed. This method involves 1,4-diazabicyclo(2,2,2)octane as a catalyst which greatly reduced the reaction time. The synthesized cholesteryl pullulan (CHP) was characterized using FT-IR and FT-NMR and used for coating the vincristine liposomes. Phosphatidylcholine liposomes with and without vincristine sulfate were prepared by a sonication method. The percentage of vincristine encapsulated in the liposomes was determined by solubilizing the bilayers using Triton-X 100. The liposomes were coated with two different concentrations of CHP solution (PC/CHP weight ratio of 3:0.5 [CHP-CL1] and PC/CHP weight ratio of 3:1 [CHP-CL2]). Both the CHP coated liposomes were characterized by transmission electron microscopy and turbidity measurement. Transmission electron micrograph showed the spherical shape of the CHP-CL1 and CHP-CL2 liposomes. The micrograph further showed the complete coat of CHP at the outermost surface of the CHP-CL2 liposomes. The average sizes of CHP-CL1 and CHP-CL2 liposomes are 340 and 350 nm, respectively. The turbidity measurement clearly indicated that the vincristine liposomes coated with higher concentration of CHP (CHP-CL2) are more stable than the liposomes coated with low concentration of CHP (CHP-CL1). The in vitro release of the encapsulated vincristine was carried out in phosphate buffered saline, pH 7.4. In phosphate buffered saline, the liposomes coated with higher concentration of CHP (CHP-CL2) released the drug for prolonged period of time compared to the CHP-CL1 liposomes. These experiments demonstrated that the CHP could be synthesized in a shorter reaction time and the vincristine liposomes coated with PC/CHP weight ratio of 3:1 could be the optimum concentration to achieve the more stable liposomes. These CHP coated liposomes are ideal carriers for the targeted delivery of therapeutic molecules.