Dual inhibition of topoisomerases enhances apoptosis in melanoma cells.

The cytotoxicity of topoisomerase I inhibiting camptothecin, topoisomerase II inhibiting etoposide and their combination were investigated in wild type p53 Bowes and mutant p53 SK-MEL-28 melanoma cell lines during 24h. A combination of camptothecin and etoposide (1 microg/ml + 10 microg/ml) proved to be efficient in both types of cell lines, although mutant p53 cells exhibited a higher resistance. Further studies proved that in Bowes cells, a combination of drugs induced p53-dependent mitochondrial apoptosis characterized by activation of caspases-8 and -2, -9 and -3 with some concurrent involvement of oxidative stress. In SK-MEL-28 cells, apoptosis was found to be mediated via increased oxidative stress, activation of stress kinases such as p38 and SAPK/JNK and mitochondrial dysfunction without significant involvement of p53 and its transactivated target genes. These results demonstrate efficiency of dual inhibition of topoisomerases in melanoma cells with functional as well as mutant p53 and point out at possible further investigation of this modality in preclinical and clinical oncology.