Abstract 1343: Preclinical evaluation of a PKC and MET inhibitor combination in metastatic uveal melanoma

Background: Uveal melanoma (UM) is a common intraocular tumor that primarily metastasizes to the liver. Patients with metastatic uveal melanoma (MUM) have a poor prognosis with a median overall survival of 10 months. The liver microenvironment has high levels of HGF, and high MET receptor expression in UM is associated with metastatic progression. HGF induces cell proliferation and survival through MAPK and PI3Ksignaling and may elicit resistance to MEK inhibitors in MUM patients. IDE196is a potent and selective PKC inhibitor currently in clinical trials for MUM(NCT03947385). In order to identify combination partners for IDE196, we hypothesized that the rich growth factor microenvironment in the liver may prevent MUM tumor cells from responding to IDE196 and that a combination of IDE196 with a MET inhibitor may synergistically inhibit tumor cell proliferation. Methods: Combinations were assessed in 92.1 and MEL-202 (primary) and also in MM28(metastatic). Cells were treated for 3-5 days with increasing doses of IDE196 (0-10uM) in combination with either increasing doses of HGF (0-100ng/ml), or with increasing doses of crizotinib (0-10uM) in the presence of HGF, to form a matrix of doses. Cell viability was assessed using cell-titer glo. To assess PD modulation, cells were treated for 2hrs with IDE196, HGF or crizotinib alone or in combination and relevant phospho MAPK and PI3K effectors were assessed by western blotting. Results: Addition of HGF alone significantly antagonized IDE196 activity at doses ≥1.23ng/ml. In 92.1 cells, HGF modestly antagonized IDE196, which could be attributed to a lower expression level of MET receptor in this cell line. Crizotinib synergized strongly with IDE196 at clinically relevant doses (80nM) in MEL202 and MM28 in contrast to the 92.1 where mild or no synergy was observed. PD analysis showed that in the absence of HGF, IDE196 dose-dependently inhibited pERK, pMARCKS and pPKC-delta in all three cell lines. Addition of HGF dose-dependently induced pMET, pERK levels, pAkt and pPRAS40 levels in all cell lines which was not inhibited by IDE196. Addition of crizotinib alone or in combination with IDE196 strongly inhibited the activation of these pathways in these cell lines. Our results demonstrate that high HGF signaling, as observed in the liver, may activate MAPK and PI3K signaling to antagonizeIDE196 activity and that this antagonism may be overcome by combining IDE196 with a MET inhibitor. Independently, a retrospective analysis of human clinical samples from a Phase 1IDE196 monotherapy trial (NCT02601378) identified cMET expression/activation as a prognostic biomarker. IDEAYA plans to evaluate the combination of IDE196 and crizotinib in a Phase 1/2clinical trial. Citation Format: Marie-Claire Wagle, Nandini Ravindran, Divya Pankajakshan, Mark Lackner, Zineb Mounir. Preclinical evaluation of a PKC and MET inhibitor combination in metastatic uveal melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1343.