EFFECTS OF INCUBATION WITH LIPOSOMES AT DIFFERENT TEMPERATURES ON CULTURED MELANOMA-CELLS (M14)

A melanoma cell line (M14) was used in order to investigate the effect of hyperthermia on the mechanisms of interaction between liposomes an d cultured cells. The treatment was performed by adding different conc entrations of multilamellar liposomes (L-alpha-dipalmitoylphosphatidyl choline, stearylamine and cholesterol in the ratio 7:2:1) to cell cult ures which were then incubated at 37.0 or 41.5-degrees-C for 2 h. The damage induced by liposome treatment in normothermia or hyperthermia w as evaluated by determining cell survival and by electron microscopy. When different concentrations of liposomes were used, a dose-dependent impairment of cell survival was observed. An enhancement of the cytot oxic effect was observed when the treatment was performed at 41.5-degr ees-C. This effect went on even after 24 h from the end of the treatme nt, but the difference between cells treated in normothermia and hyper thermia was remarkably reduced. The mechanism of the liposome-plasma m embrane interaction has been investigated by electron microscopy. Our observations demonstrated that the outer bilayer of the multilamellar liposomes was capable of fusing with the plasma membrane, inducing cha nges in its fluidity and molecular organization. Following this proces s the inner liposomal bilayers entered the cell. These effects seemed to be favoured when the treatment was performed under mild hyperthermi c conditions, accounting for the synergic cytotoxic action displayed b y the liposome-hyperthermia association.