CASP9 and melanoma: Therefore, in hydroxytyrosol treated melanoma cells we report a dose-dependent induction of the intrinsic apoptotic pathway through the activation of pro-apoptotic proteins such as p53 and caspases-9 and -3, the down regulation of survival proteins such as PARP and AKT, the increased expression of γH2AX protein, as well as the inhibition of cell colony formation.