Our study demonstrates that in vitro treatment of melanoma cells with GTPs decreases the expressions of cyclins and CDKs (CDK2, CDK4 and CDK6) of G1 phase in both A375 and Hs294t cell lines suggesting that GTPs induce a marked disruption of the uncontrolled cell cycle progression, and that may be a mechanism by which GTPs inhibit the proliferation or suppress the cell viability of melanoma cells. This evidence concerns the gene CDK6 and melanoma.