Abstract 3885: A secondary Gαq mutation confers resistance to Gαq inhibitors in uveal melanoma

Abstract

Abstract Uveal melanoma (UM) is a rare subtype of melanoma that originates from melanocytes of the choroidal plexus, ciliary body and iris. Despite successful treatment of the primary by radiation or surgery, 50% of UM patients develop metastases, mostly in the liver, as an invariably lethal complication. Over 90% of UM harbor activating mutations in the closely related GNAQ or GNA11 genes, mainly at codons Q209, compromising the GTPase activity. Mutant GNAQ and GNA11 can be successfully targeted by the cyclic depsipeptide YM-254890. To anticipate mechanisms of resistance that might arise under treatment with this novel class of Gαq inhibitors, we generated UM cell lines resistant to YM-254890 using an in-vitro cell culture system. Upon chronic growth suppression of a GNA11Q209L mutant UM cell line, we established 12 YM-254890 resistance clones. We identified a secondary GNA11F75Y mutation in one clone and GNA11Y192H mutations in the other 11 clones. The secondary mutations were present in cis with the original GNA11 Q209L mutations. To validate the functional role of these secondary mutations in conveying resistance, we engineered two double mutants, GNA11Q209L/F75Y and GNA11Q209L/Y192H, and introduced them into 293FT cells respectively and confirmed that both F75Y and Y192H convey resistance to YM-254890 treatment. The proliferation of YM-254890-resistant cell lines was still dependent on GNA11 and downstream PKC/MAPK signaling. Combined inhibition of PKC and MEK synergistically reduced cell viability in YM-254890 resistant UM cells. Analysis of the crystal structure of YM-2548890 in complex with GNAQ predicts both F75Y and Y192H mutations directly affect the binding of YM-254890 to Gαq. Our data suggest that direct targeting mutant GNAQ/11 is promising but will select for secondary mutations within GNAQ/11 that will result in resistance. Combinatorial targeting of other components in the Gαq signaling pathway will increase clinical efficacy. Citation Format: Jiafang Ma, Meng Wang, Aashish Manglik, Boris C. Bastian, Xu Chen. A secondary Gαq mutation confers resistance to Gαq inhibitors in uveal melanoma. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3885.