Abstract 526: RMC-9805, a first-in-class, mutant-selective, covalent and oral KRASG12D(ON) inhibitor that induces apoptosis and drives tumor regression in preclinical models of KRASG12D cancers

KRASG12D is the most frequent KRAS mutation in human cancers, with the highest prevalence in pancreatic ductal adenocarcinoma (PDAC), colorectal cancer (CRC) and non-small cell lung cancer (NSCLC). RMC-9805 is a first-in-class, oral, mutant-selective covalent inhibitor of the GTP-bound and active RAS(ON) form of KRASG12D. The formation of a stable, high affinity tri-complex between RMC-9805, KRASG12D and cyclophilin A results in the suppression of signaling downstream of KRASG12D(ON) by disrupting its interactions with downstream effectors such as RAF kinases. RMC-9805 treatment caused selective and persistent modification of KRASG12D leading to deep and durable suppression of RAS pathway activity, inhibition of cell proliferation, and apoptosis induction in KRASG12D human cancer cell lines in vitro and tumor models in vivo. In a mouse clinical trial with KRASG12D xenograft tumor models, RMC-9805 administered orally as a single agent was well tolerated and induced objective responses in 7 of 9 PDAC PDX and CDX models and 6 of 9 NSCLC PDX models, as assessed by mRECIST. In the few models that exhibited sub-optimal responses to RMC-9805 monotherapy, combination treatment with various RAS Companion Inhibitors improved depth and/or duration of anti-tumor response. In contrast to RASMUTANT NSCLC and PDAC, CRC tumors are less dependent on RAS driver mutations. For example, a more heterogeneous response to KRASG12C inhibitors has been reported in CRC than in NSCLC patients, suggesting combinations will be desired to achieve significant clinical benefit in CRC. Likewise, RMC-9805 monotherapy is less active in CRC models at doses that were highly active in KRASG12D NSCLC and PDAC models. However, combinations of RMC-9805 with vertical or parallel pathway RAS Companion Inhibitors such as SHP2, mTORC1 or RASMULTI(ON) inhibitors, achieved objective response rates up to 60% and delayed the onset of resistance in tumor models in vivo. RMC-9805 also synergized with anti-PD1 therapy in KRASG12D tumors in immune-competent animal models by shaping a favorable tumor immune microenvironment through cytokine modulation. In addition, RMC-9805 engaged the adaptive immune system by increasing presentation and recognition of tumor antigens, promoting a diversification of the TCR repertoire, and inducing immunological memory. Overall, RMC-9805 monotherapy elicited tumor regressions in most preclinical PDAC and NSCLC cancer models harboring KRASG12D. Furthermore, RMC-9805 combination therapies drove regressions in CRC models relatively less responsive to monotherapy. Supported by these findings, RMC-9805 is currently in IND-enabling development to permit clinical evaluation of single agent and combination strategies in patients with KRASG12D tumors. Citation Format: Lingyan Jiang, Marie Menard, Caroline Weller, Zhican Wang, Les Burnett, Ida Aronchik, Shelby Steele, Mike Flagella, Ruiping Zhao, James W W. Evans, Shook Chin, Kang-Jye Chou, Yunming Mu, Michael Longhi, Laura McDowell, John E. Knox, Adrian Gill, Jacqueline A. Smith, Mallika Singh, Elsa Quintana, Jingjing Jiang. RMC-9805, a first-in-class, mutant-selective, covalent and oral KRASG12D(ON) inhibitor that induces apoptosis and drives tumor regression in preclinical models of KRASG12D cancers [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 526.