Abstract PO-032: Targeting the KRAS dimerization interface enhances T-cell mediated anti-tumor response in vivo

Abstract

Abstract RAS is the most frequently mutated human oncogene and about 20% of all human cancers harbor mutations in one of three RAS oncogenes (K, N and H-RAS) with pancreatic cancers harboring RAS mutations in >90% of tumors. Therapeutically targeting RAS has been highly challenging and other than allele specific KRAS (G12C) inhibitors, no direct RAS inhibitor has been approved for clinical trial. However, KRAS (G12C) mutations are less abundant in some cancers like pancreatic cancer, thus there remains an unmet need for inhibitors that target the more common RAS mutants. This demand devising novel strategies to identify new approaches to inhibit RAS. Previously, we developed the H/KRAS-specific monobody called NS1 that allosterically inhibit RAS-mediated signaling by targeting the α4-α5 dimerization interface. When used as a genetically encoded intracellular reagent, NS1 inhibited the growth of H/KRAS-mutant human tumor lines both in vitro and in xenograft tumor models. However, these tumor models lack a functional immune system. Here, we evaluated the potency of targeting KRAS dimerization interface with NS1 in an immune-competent murine model of pancreatic cancer. Although human and murine KRAS differ by a single amino acid [Asp (D) to Glu (E)] at position 132 in the NS1 binding region of the allosteric lobe, NS1 bound similarly to human and murine KRAS both in vitro and in vivo. Furthermore, NS1 expression inhibited ERK-MAPK activation, proliferation and anchorage-independent growth of engineered KPC cells derived from pancreatic tumor in the KPC genetic mouse model. Finally, when these engineered KPC cells were injected orthotopically in immune-competent C57/B6 mice, we observed a dramatic decrease in tumor growth kinetics and tumor burden in NS1 expressing cohorts. Similarly, NS1 expression resulted in decreased ERK-MAPK activation and increased apoptosis. NS1 expressing tumors were characterized by increased infiltration of helper CD4+ T cells and macrophage. Thus, inhibition of mutant KRAS by NS1 results in an enhanced anti-tumor immune response in a syngeneic model for pancreatic cancer. These results establish that targeting α4-α5 dimerization interface of RAS can be a viable therapeutic option for targeting KRAS-mutant pancreatic cancer. Citation Format: Imran Khan, Julia Lefler, Catherine Marelia, Mariyam Zuberi, Eric Denbaum, Akiko Koide, Cynthia Timmers, Michael Ostrowski, Shohei Koide, John O’Bryan. Targeting the KRAS dimerization interface enhances T-cell mediated anti-tumor response in vivo [abstract]. In: Proceedings of the AACR Virtual Special Conference on Pancreatic Cancer; 2020 Sep 29-30. Philadelphia (PA): AACR; Cancer Res 2020;80(22 Suppl):Abstract nr PO-032.