CASP3 and melanoma: Addition of low concentrations of digitoxin to culture increased the frequency of activated caspase-3/7+ cells among melanoma cells derived from three patients (M481, M491 and M214), but not normal human melanocytes from two donors (hMEL2 and hMEL3) or immortalized melanocytes from another donor (hiMEL23; Supplementary Fig. 1a).