IN-VITRO SENSITIVITY OF HUMAN-MELANOMA CELLS TO CHEMOTHERAPEUTIC-AGENTS AND INTERFERONS

The purpose of our study was to evaluate systematically the anti-proliferative effects of eight chemotherapeutic drugs as well as of four recombinant interferons (IFNs) (alpha-2a, alpha-2b, beta, gamma). All drugs and IFNs were tested separately and in combination at several concentrations on four human melanoma cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5,-diphenyltetrazolium (MTT) test. In all cases, drug inhibitory concentrations of chemotherapeutic agents required to kill 25% of melanoma cells (IC25) in vitro were in the range of the maximal achievable plasma peak level in vivo. Sensitivity to the anti-proliferative action of bleomycin, DTIC, doxorubicin, cisplatin and carboplatin was similar for all melanoma cell lines, whereas cell lines exposed to 5-fluorouracil (5-FU), vindesine and fotemustine differed up to 26-fold in their sensitivity. Studies with IFN showed that IFN-beta and IFN-gamma proved to be more anti-proliferative than IFN-alpha in a dose-dependent fashion in all cell lines. However, the ability of IFNs to improve cytotoxicity of chemotherapeutic agents was limited. Pre-incubation of melanoma cells with IFN as well as exposure to IFN after incubation with the drugs showed mainly additive effects (231/256). These results confirm the high chemoresistance of human melanoma cells, independently of the drug chosen. Combinations of chemotherapeutic agents with IFN will provide additional therapeutic benefit, but are unlikely to change the overall high chemoresistance of human melanoma cells.