The modulation of thermal properties of vinblastine by cholesterol in membrane bilayers.

It has been shown that the partitioning of vinblastine in 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) single and multiple bilayer dispersions induces partial interdigitation of the lipid alkyl chains. Similar behavior has been observed for abietic and ursodeoxycholic acids and may well be generalized for the partitioning of bulky amphoteric molecules, which tend to localize in the vicinity of the polar heads. For the present study, differential scanning calorimetry (DSC) has been employed to investigate the role of lipid molecular characteristics such as the alkyl chain length and the polarity of the head-group, as well as the impact of cholesterol upon vinblastine-induced interdigitation. It is found that vinblastine does not induce interdigitation in lipids with either shorter or longer alkyl chains than DPPC, or having head-groups of different polarity. In addition, it is shown that the presence of cholesterol in the lipid bilayer tends to modulate the phase behavior of the lipid/vinblastine bilayer system. Preliminary studies show that such properties directly affect the encapsulation efficiency and the pharmacokinetics of liposomes.