Abstract 345: Novel RAS inhibitor, MCI-062, potently and selectively inhibits the growth ofKRASmutant pancreatic tumor cells by blocking GTP loading of RAS

Oncogenic mutations in RAS genes result in an intracellular elevation of active RAS and increased cellular propagation through downstream signaling pathways responsible for tumor cell growth and survival. Mutations in KRAS drive over 90% of pancreatic ductal adenocarcinomas (PDACs), presenting promising therapeutic potential for a RAS inhibitor. However, many have deemed RAS “undruggable” as a result of its relatively smooth structure and its high affinity for guanine nucleotide substrates. We have identified a novel series of indene derivatives that potently and selectively inhibits the growth of tumor cells with high levels of active RAS, while having minimal effects on tumor cells lacking constitutively active RAS, or cells derived from normal tissues. Here we report that our lead compound, MCI-062, potently and selectively inhibits the growth of KRAS mutant MIA PaCa-2 PDAC cells harboring oncogenic KRAS with an IC50 value of approximately 5 nM and greater than 300-fold selectivity over BxPC-3 PDAC cells that lack constitutively active RAS. MCI-062 also completely inhibits colony formation of a panel of PDAC cell lines with various KRAS mutations at low nanomolar concentrations. MCI-062 treatment of MIA PaCa-2 cells in basal and EGF-stimulated conditions depletes RAS-GTP levels in a dose-dependent manner. Consequently, MCI-062 treatment leads to inhibition of downstream MAPK and AKT signaling, cell cycle arrest, and induction of apoptosis in MIA PaCa-2 cells. Further investigation of the mechanism of action in cell-free systems demonstrated that this class of compounds inhibits GTP loading of RAS. MCI-062 inhibits binding of MANT-GTP to recombinant K-RAS in a dose-dependent manner. In a functional assay, MCI-062 reduces RAS-RAF-RBD binding when recombinant K-RAS is treated in a nucleotide-free state, but not when K-RAS is treated in a nucleotide-bound state. Testing in 3D spheroid models involving MIA PaCA-2 tumor cells revealed that MCI-062 potently inhibits growth of non-adherent cells. MCI-062 also has anti-tumor activity in a KRAS mutant CT26 mouse tumor xenograft model with no discernable toxicity. Western blotting of tumor lysates from mice treated with MCI-062 showed a reduction of active, GTP-bound RAS when compared to tumor lysates from control mice. These results provide in vitro and in vivo evidence that MCI-062 inhibits RAS-driven tumor cell growth by blocking GTP loading of RAS, supporting further evaluation of this novel class of RAS inhibitors for the treatment of pancreatic cancer, as well as other RAS-driven cancers. Funding provided by NCI grants R01CA131378, R01CA148817, R01CA197147, and R01CA155638. Citation Format: Tyler E. Mattox, Xi Chen, Jacob Valiyaveettil, Yulia Maxuitenko, Bing Zhu, Antonio Ward, Veronica Ramirez-Alcantara, Kristy Berry, Michael Boyd, Adam Keeton, Gary A. Piazza. Novel RAS inhibitor, MCI-062, potently and selectively inhibits the growth of KRAS mutant pancreatic tumor cells by blocking GTP loading of RAS [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 345.