Purpose: Cationic liposomes preferentially target tumor vessels compared to vessels in normal tissues; the interaction of cationic liposomes with tumor vessels is heterogeneous. To target tumor vessels more uniformly we seek to combine the electrostatic properties of cationic liposomes with the strength of an external magnetic field (EMF). For this reason we characterize MAG-C (magnetite) cationic liposomes, study their interactions with tumor cell models. We evaluate the growth inhibitory properties of chemotherapeutic agents and drugs encapsulated in MAG-C cationic liposomes against melanoma (B16-F10 & HTB-72) and endothelial (HMVE-D) cells. We also determine tissue distribution profile of particular formulations in (melanoma) tumor bearing mice. Methods: Chemotherapeutic agents used in this study were Vinblastine, Etoposide and Dacarbazine. Particle size and zeta potential were analyzed by 90PlusBI-MAS/ Zeta Pals. DPH polarization was used to evaluate effect of MAG-C on bilayer phase transition temperature (Tc). Cell association studies were carried out using FLX800 microplate reader. SRB assay was conducted to measure cell viability. DIC and fluorescence microscopy was used to evaluate intercellular uptake of liposomes. For biodistribution studies, percent recovery of 111In labeled MAG-C cationic liposomes was determined by Beckman Gamma Counter. Results: The size of cationic liposomes for MAG-C and unincorporated variety was 142 ± 27.40 nm and 105 ± 26.64 nm respectively. Zeta potential for MAG-C cationic liposomes (43.79 ± 10.93 mv) was lower than liposomes without MAG-C (43.79 ± 10.93 mv). The inclusion of PEG did not alter liposome size, but reduced zeta potential. The Tc of MAG-C cationic liposomes (41.2°C) was lower than unincorporated liposomes (51°C). MAG-C cationic liposomes were taken up avidly by melanoma and human dermal endothelial cells; PEG significantly reduced all cellular interactions. Addition of FeCl3 exerted no additional effect on size & zeta potential but significantly reduced the interactions of MAG-C cationic liposomes with HMVE-D. Fluorescence microscopy showed perinuclear localization of magnetic cationic liposomes with all cell lines. Higher cell growth inhibition was observed when B16-F10 was treated with drugs loaded in MAG-C cationic liposomes compared to free drugs, but similar cell growth inhibition was observed for HMVE-D. In vitro cytotoxicity studies: Vinblastine > Etoposide > Dacarbazine. The inclusion of PEG (5 mole%) in MAG-C cationic liposomes did not improve (B16-F10) tumor specific uptake, but significantly reduced accumulation in liver, lung and spleen. Conclusions: The results suggest that MAG-C cationic liposomes may be used to target drugs to solid tumors, while preserving cytotoxic drug effects, and minimizing accumulation in healthy tissues. Subsequent in vivo investigations with EMF are warranted.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]