Targeting Genetic Aberrations in Uveal Melanoma

Abstract

Purpose: : Metastatic uveal melanoma has a six month median overall survival and no effective treatment. Recent studies have identified somatic activating GNAQ mutations in uveal melanoma. Although multiple studies have failed to identify BRAF mutations in uveal melanoma, recent studies employing more sensitive techniques show the presence of BRAF mutations in a subset of uveal melanoma tissues. The purpose of this study was to test uveal melanoma cell lines for the presence of these and other activating point mutations, and to test the effectiveness of inhibiting their aberrant protein products and signaling pathways.

Methods: : We tested eleven uveal melanoma cell lines using a mass spectroscopy-based approach to identify point mutations known to exist in other types of melanoma or in high frequency in other cancers. Cells were treated with small molecule inhibitors targeting the aberrant proteins or their downstream signaling molecules. A cell viability assay was used to determine the efficacy of treatment. Western blot analysis was performed to characterize the alterations in signaling components that resulted from treatment.

Results: : GNAQ or BRAF mutations were identified in eight of eleven cell lines. All cell lines lacked point mutations in AKT1-3, FGFR3, FLT3, KIT, MEK, NRAS, MET, RET at commonly mutated residues. Using a MEK inhibitor (AZD6244) we demonstrated that the viability of GNAQ or BRAF mutant cells is markedly reduced by 40-60% with 100 nM (0-10 uM) of AZD6244. Only one of three cell lines with wild-type GNAQ and BRAF was sensitive to AZD6244 treatment. Only cell lines with a BRAF mutation showed a decrease in cell viability to the BRAF mutant specific inhibitor PLX4720. Western blot analysis demonstrated the differential downstream signaling effects in the MAPK pathway to these drug treatments in different cell lines.

Conclusions: : The majority of uveal melanoma cell lines in this study harbor either BRAF or GNAQ mutations. MEK inhibition with AZD6244 caused significant reduction in cell viability in BRAF and GNAQ mutant cells. These results suggest that MEK inhibition may be an effective therapeutic strategy in patients with uveal melanoma who have BRAF or GNAQ mutations.

Keywords: melanoma • signal transduction: pharmacology/physiology • mutations