Characterization of 7-dehydrocholesterol cytotoxic effects on melanoma cell lines

Ultraviolet radiation is the main cause of skin cancers, and melanoma is the most serious form of tumor. Surgery is standard treatment for localized melanoma, while there is no therapy for advanced-stage of melanoma and its metastasis, because of the high resistance of melanoma cells to various anticancer therapies. Human skin is an important metabolic organ in which occurs photo-induced synthesis of vitamin D3 from 7-dehydrocholesterol (7-DHC). The 7-DHC, the precursor of cholesterol biosynthesis, is highly reactive and easily modifiable to produce 7-DHCderived compounds. The intracellular levels of 7-DHC or its derivatives can have deleterious effects on cellular functionality and viability. In this study we evaluated the effect on melanoma cell lines by 7-DHC as such and for this aim much care to minimize 7-DHC modifications was used. We found that from 12 to 72 hours of treatment 82-86% of 7-DHC entered into the cells, and the levels of 7-DHC-derivative compounds were not significant. At same time ROS production was significantly increased already after 2 hours and, after 24 hours, a reduction of cell viability was observed. Indeed, after 48-72 hours a pro-apoptotic effect of 7-DHC was detected. The cytotoxic effect of 7-DHC was associated with an increase in Bax levels, decrease in Bcl-2/Bax ratio, reduction of mitochondrial membrane potential, increase in apoptosis-inducing factor levels, unchanged caspase-3 activity, and absence of cleavage of PARP-1. These findings could partially explain the mechanism through which 7-DHC exerts its cytotoxic effects. This is the first report in which the biological effects found in melanoma cells are mainly attributable to 7-DHC as such.