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Vassiliki Poulaki, Sue Anne Chew, Bin He, Nicholas Mitsiades; Genotype-Dependent Sensitivity Of Ocular Melanoma Cell Lines To Inhibitors Of Kinases, Including BRAF, MEK And Akt: Rationale For Personalized Therapy. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4758.
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© ARVO (1962-2015); The Authors (2016-present)
Inhibitors of BRAF and MEK kinases hold promise for treatment of cutaneous melanomas (CMs) harboring a BRAF(V600E) mutation (~50% of CMs). BRAF mutations are rare in ocular melanomas (OMs), but approximately half of OMs harbor mutations in the GNAQ gene. The impact of BRAF and MEK inhibitors on BRAF-mutant (mt) and GNAQ-mt OMs remains unknown.
Using cell viability assays and immunoblotting, we tested the impact of the BRAF inhibitor PLX4720, the MEK inhibitor AZD6244 and the Akt inhibitor MK2206 on 3 OM cell lines: OCM3 (BRAF-mt), OMM1.3 and Mel202 (both GNAQ-mt/BRAF wild-type (wt)). We also used the multikinase inhibitors dasatinib (that targets Src, other Src-family kinases, Abl, EphA2, c-KIT, PDGFR, and c-fms) and PKC412 (midostaurin, that targets protein kinase C, VEGFR2, c-KIT, PDGFR and FLT3). The BRAF-mt CM cell lines A375 and M14 served as controls.
BRAF-mt OM cells were very sensitive to both the MEK and the BRAF inhibitors (IC50s: ~0.05 microM and ~2 microM, respectively), similarly to their CM counterparts. Treatment with either one of these inhibitors decreased levels of phosphorylated ERK and increased p27 levels. GNAQ-mt/BRAF-wt OM cells were mildly sensitive to MEK inhibition, exhibiting growth arrest (IC50>3 microM, which is significantly less sensitive than BRAF-mt cells), decreased levels of phosphorylated ERK and increased p27 levels, but were completely resistant to the BRAF inhibitor PLX4720. In fact, PLX4720 paradoxically increased ERK phosphorylation and promoted cell proliferation in GNAQ-mt/BRAF-wt OM cells. The combination of the MEK inhibitor with the BRAF inhibitor had synergistic anticancer activity in the BRAF-mt OM cells, but no beneficial enhanced anticancer activity in GNAQ-mt/BRAF-wt OM cells. The Akt inhibitor MK2206 potently enhanced the anticancer activity of both the BRAF inhibitor and the MEK inhibitor against the BRAF-mt OM cells, and mildly enhanced the anticancer activity of the MEK inhibitor against the GNAQ-mt/BRAF-wt OM cells, but did not overcome the resistance of the GNAQ-mt/BRAF-wt OM cells to the BRAF inhibitor. GNAQ-mt/BRAF-wt OM cells were more sensitive to dasatinib and PKC412 than their BRAF-mt counterparts.
The response of OM cells to inhibition of BRAF, MEK and Akt and to dasatinib and PKC12 depends on their genotype. These observations support the design of clinical trials of these inhibitors for the treatment of carefully selected OM patients and provide the rationale for personalized therapy.
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