Targeted therapy has become a cornerstone for the treatment of melanoma patients. Targeting NRAS function is particularly challenging. To date, only single MEK inhibitor treatment was able to show minimal clinical efficacy. The discovery that co-targeting of MEK and CDK4,6 has antitumor activity created excitement for patients and clinicians; however, it is largely unknown if only NRAS mutant patients might benefit from MEK/CDK4,6 blockade. In this study we investigate response patterns of NRAS, BRAF mutant and 'wild type' melanoma cells in vitro and in vivo when challenged with inhibitors of MEK, CDK4,6 and the combination of both. Data revealed, that in vitro growth response patterns of cells treated with the MEK/CDK4,6 combination correspond to in vivo efficacy of MEK/CDK4,6 co-targeting in melanoma xenograft models. Strikingly, this was consistently observed in NRAS and BRAF mutant, as well as in 'wild type' melanoma cells. Additionally, cells displaying elevated p-Rb levels after single MEK inhibition, showed more effective growth reduction with MEK/CDK4,6 co-targeting compared to single MEK inhibitor treatment in vivo. Findings indicate that combined MEK/CDK4,6 inhibition could offer an effectively therapeutic modality in a subset of BRAF and NRAS mutant, as well as 'wild type' melanoma patients.
Keywords: BRAF; CDK4; MEK; NRAS; melanoma.