Uveal melanoma (UM) is the most common cancer of the eye in adults.,Many UM patients develop metastases for which no curative treatment has been identified.,Novel therapeutic approaches are therefore urgently needed.,UM is characterized by mutations in the genes GNAQ and GNA11 which activate the PKC pathway, leading to the use of PKC inhibitors as a rational strategy to treat UM tumors.,Encouraging clinical activity has been noted in UM patients treated with PKC inhibitors.,However, it is likely that curative treatment regimens will require a combination of targeted therapeutic agents.,Employing a large panel of UM patient-derived xenograft models (PDXs), several PKC inhibitor-based combinations were tested in vivo using the PKC inhibitor AEB071.,The most promising approaches were further investigated in vitro using our unique panel of UM cell lines.,When combined with AEB071, the two agents CGM097 (p53-MDM2 inhibitor) and RAD001 (mTORC1 inhibitor) demonstrated greater activity than single agents, with tumor regression observed in several UM PDXs.,Follow-up studies in UM cell lines on these two drug associations confirmed their combination activity and ability to induce cell death.,While no effective treatment currently exists for metastatic uveal melanoma, we have discovered using our unique panel of preclinical models that combinations between PKC/mTOR inhibitors and PKC/p53-MDM2 inhibitors are two novel and very effective therapeutic approaches for this disease.,Together, our study reveals that combining PKC and p53-MDM2 or mTORC1 inhibitors may provide significant clinical benefit for UM patients.
Uveal melanomas possess activation of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT/mammalian Target of Rapamycin (mTOR) pathways.,MAPK activation occurs via somatic mutations in the heterotrimeric G protein subunits GNAQ and GNA11 for over 70% of tumors and less frequently via V600E BRAF mutations.,In this report, we describe the impact of dual pathway inhibition upon uveal melanoma cell lines with the MEK inhibitor selumetinib (AZD6244/ARRY-142886) and the ATP-competitive mTOR kinase inhibitor AZD8055.,While synergistic reductions in cell viability were observed with AZD8055/selumetinib in both BRAF and GNAQ mutant cell lines, apoptosis was preferentially induced in BRAF mutant cells only.,In vitro apoptosis assay results were predictive of in vivo drug efficacy as tumor regressions were observed only in a BRAF mutant xenograft model, but not GNAQ mutant model.,We went on to discover that GNAQ promotes relative resistance to AZD8055/selumetinib-induced apoptosis in GNAQ mutant cells.,For BRAF mutant cells, both AKT and 4E-BP1 phosphorylation were modulated by the combination; however, decreasing AKT phosphorylation alone was not sufficient and decreasing 4E-BP1 phosphorylation was not required for apoptosis.,Instead, cooperative mTOR complex 2 (mTORC2) and MEK inhibition resulting in downregulation of the pro-survival protein MCL-1 was found to be critical for combination-induced apoptosis.,These results suggest that the clinical efficacy of combined MEK and mTOR kinase inhibition will be determined by tumor genotype, and that BRAF mutant malignancies will be particularly susceptible to this strategy.