Surprisingly, although PD0332991 is a more potent inhibitor of CDK4 (IC50=0.011 μM compared to 0.35 μM for fascaplysin), the melanoma cell lines were generally less sensitive to PD0332991 than to fascaplysin with IC50 values ranging from 0.13 to 2.29 μM (Table II and Fig. 4). This evidence concerns the gene CDK4 and melanoma.