Influence of cholesterol inclusion on the doxorubicin release characteristics of lysolipid-based thermosensitive liposomes

Fast hyperthermia (i.e. 39-42 °C) triggered doxorubicin release from lysolipid-containing thermosensitive liposomes (LTSL) in the tumor vasculature has been demonstrated to result in considerable enhancement of bioavailable drug levels in heated tumor tissue in preclinical tumor models. However, there is also significant leakage of doxorubicin already at 37 °C in the bloodstream, making these LTSL less efficient and increasing the risk for systemic toxicity. In conventional liposomes, cholesterol is incorporated in the bilayer to increase the stability of the liposomes. Here, we investigate the effect of cholesterol inclusion on the doxorubicin release characteristics of LTSL at 37 °C and hyperthermic temperatures. For this purpose, three LTSL formulations with 0, 5 and 10 mol% cholesterol were prepared. Inclusion of cholesterol reduced the undesired doxorubicin leakage at 37 °C in Hepes-buffered saline (HBS) as well as in fetal bovine serum (FBS). The incorporation of cholesterol in the LTSL bilayers did not influence the hyperthermia-triggered release property of the LTSL. These results were supported by DSC measurements. Therefore, in conclusion, our data indicate that cholesterol inclusion in LTSL offers a simple solution to the problem of significant leakage of doxorubicin from LTSL already at 37 °C in the bloodstream.