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Development of a liposomal formulation of a cytotoxic labdane type diterpene and in vitro evaluation

Over the last years liposomes have been proved adequate drug carriers. Labdane type diterpenes have been reported to exhibit a variety of biological activities [Demetzos, C. and Dimas, K. Studies in Natural Products Chemistry, Elsevier Science Vol 25, 2001, 235]. Labd-7,13-dien-15-ol (1) and labd-7,13-dien-15-ylacetate (2) were isolated from plants of the genus Cistus. The overall goals of this study were: first, to incorporate 1 into EPC/DPPG liposomes, and characterize the final liposomal formulation; second to study its cytotoxic/cytostatic activity against different human cancer cell lines; and third to evaluate and compare the thermal effects of 1 and 2 on phospholipid bilayers using DSC. The incorporation efficiency of 1, stability (4C) and release studies into RPMI-1640 medium at 37C were evaluated. Stable SUV’s incorporated 1 were formed (65.7 ± 7.4 nm). Drug to lipid molar ratio was found to be 0.500 ± 0.072 and the incorporation efficiency was 90.8 ± 4.1%. No significant release into RPMI-1640 medium was observed. The liposomal formulation of 1 exhibited cytotoxic/cytostatic activity against the five cancer cell lines tested. The thermal changes induced by the presence of 1 and 2 are summarized as abolition of pre-transition and reduction of the main phase transition and enthalpy change of the gel to liquid-crystalline phase transition of DPPC bilayers.