Effects of MTA on human melanoma cell viability (A) A375, Hs294T, HT144 and MeWo human melanoma cells were treated with different doses of MTA for 24, 48 and 72 h and cell viability was assessed by mean of the XTT viability assay. MTA significantly reduced cell viability in all melanoma cell lines and in Calu-3 while there was no significant effect on H1299 (a human NSCLC lacking p53 expression). Presented values are mean of at least 2 independent experiments. The IC50 values for MTA in A375, Hs294T, HT144 and MeWo human melanoma cells were 0.27, 0.41, 0.32 and 0.99 μM, respectively and 10 μM for the Calu-3 NSCLC line. Data represent mean ± SD of six determinations in three separate experiments for each cell line. (B) Effect of MTA on mouse embryonic fibroblast (MEF). Cells were exposed to the indicated MTA doses for 24, 48 and 72 h (only results of 72 h are shown). There was no significant cytotoxic effect on MEF cell line. Data represent mean ± SD of six determinations in two separate experiments. (C) Effect of MTA on the colony-forming ability of human melanoma cells and NSCLC cells. Cells were exposed to 0.84 μM MTA for 24 h followed by incubation in MTA-free culture medium for 10 days before performance of crystal violet staining and counting of colonies. MTA significantly reduced colony-forming ability in human melanoma cells and in Calu-3 cells, but not in the H1299 cell line, corroborating results obtained in the viability assay. *p < 0.05 (Student t-test). (D) Colony-forming ability: details of A375 cell line formed colonies growing in MTA-free medium (control) and in MTA-containing medium. This micrographs show that not only the amount of colonies buy also the morphology of formed colonies changed which are composed for significantly less number of cells.