MIPP has similar effects on cell morphology and viability in temozolomide-resistant (U251-TR) and parental (U251) glioblastoma cells. A) Cells were treated with the indicated concentrations of TMZ for 48 h. Colonies were counted as described in Materials and Methods and the results were expressed as the percentage of the mean value for parallel control plates for the same cell lines without drug. Each point is the mean from three plates (± SD). B) Phase-contrast images were obtained after treatment of cells for 48 h with 10 μM MIPP or an equivalent volume of DMSO (control). C) MTT assays were performed after treatment for 48 h with the indicated concentrations of MIPP or an equivalent volume of DMSO. The quadruplicate MTT values for the MIPP-treated wells were expressed as percent of the mean for the parallel DMSO-treated wells. Relative IC50 values were calculated from nonlinear regression analysis of sigmoidal dose response curves plotted with GraphPad Prizm 4.0 (La Jolla, CA). D) U251-TR cells were treated with 10 μM MIPP or an equivalent volume of DMSO (control) for 2 days and colony forming assays were performed. The results shown are the mean (± SD) of triplicate dishes, with representative dishes shown at the right. The decrease in the number of colonies for the MIPP-treated cells (*) was significant at p < 0.001.