Importance of the liposomal cationic lipid content and type in tumor vascular targeting: Physicochemical characterization and in vitro studies using human primary and transformed endothelial cells

Using cationic liposomes to deliver cytotoxic molecules to the tumor microvasculature is currently being developed for the treatment of cancer and other angiogenesis-related diseases. To improve on their beneficial properties, the authors have examined whether the particular cationic lipid type and lipid content employed are important factors influencing cellular interactions and formulation effects. The authors prepared different PEG (polyethylene glycol)-modified cationic liposomes (PCLs) with varying percent cationic lipid content and lipid type, and evaluated liposome size, surface charge (zeta) potential, and cellular properties in vitro. The cell lines used were human umbilical vein (HUVEC), lung microvascular (HMVEC-L and HPVE-26), coronary microvascular (HMVEC-C), dermal microvascular (HMVEC-D), and immortalized dermal microvascular (HMEC-1) endothelial cells. In vitro experiments consisted of cellular uptake and cytotoxicity studies, florescence-activated cell sorting (FACS) analysis, fluorescence, and transmission electron microscopic analysis. Liposome size and zeta potential analysis of five different PCLs revealed significant differences in their physicochemical properties. Some cationic lipids formed relatively toxic liposomes compared to others. The efficiency of loading chemotherapeutic drugs (doxorubicin hydrochloride, etoposide), affinity of PCLs for endothelial cells, and formulation effects varied according to cationic lipid content and the lipid type. Cellular uptake was observed in lung, dermal, and coronary endothelial cells. Heparan sulfate proteoglycans were found present on HMEC-1 cells, which may have enabled PCL uptake. In conclusion, physicochemical properties of cationic liposomes and their ability to interact with endothelial cells are important factors to consider during the early stages of formulation development for the treatment of cancer and other angiogenesis-dependent diseases.