Abstract A051: Recurrent <i>RRAS</i> and <i>RRAS2</i> mutations in lung cancer define actionable oncogenic drivers with therapeutic susceptibility to pan-RAS inhibition

Abstract Introduction. RRAS and RRAS2 are members of the RAS family, which includes KRAS, HRAS, NRAS and MRAS. These small GTPases share roughly 55-60% amino acid sequence identity with each other, including conserved domains. Despite similarities in structure, effector binding, and activation of similar growth promoting pathways, the role of RRAS and RRAS2 as oncogenic drivers in lung cancer remains to be defined. Moreover, there are no approved therapeutic strategies to target RRAS or RRAS2. Here, we examined the prevalence and targetability of mutant RRAS and RRAS2 in lung cancer. Methods. 8,488 non-small cell lung carcinoma (NSCLC) cases sequenced by MSK-IMPACT between 2016-2024 were queried for RRAS/RRAS2 mutations. Hotspot mutations were modeled in Ba/F3, HEK-293T, and immortalized human lung cells (HBEC) via virally transduced cDNA. Oncogenicity was assessed via IL-3 withdrawal in Ba/F3 cells and tumor formation in immunocompromised mice (NSG). Protein phosphorylation was analyzed by phospho-proteomic arrays and Western blotting. Results. RRAS Q87L or RRAS2 Q72L missense mutations, homologous to RAS Q61X mutations, were identified in 0.45% of NSCLC cases (38/8,488) and demonstrated mutual exclusivity with other canonical RTK-MAPK oncogenic drivers. RRAS/RRAS2 mutations homologous to RAS G12/G13 mutants were identified at lower frequencies. Expression of RRAS Q87L or RRAS2 Q72L but not RRAS G38C/D and RRAS2 G23C (homologous to RAS G12X ) stimulated phosphorylation of ERK1/2, p90RSK, and S6. In Ba/F3 and HBEC cells, expression of RRAS Q87L or RRAS2 Q72L caused activation of MAPK and PI3K-mTOR pathways and these cells became transformed. Inhibitors of the MAPK pathway including binimetinib (MEK1/2), SCH772984 and ulixertinib (ERK1/2), and RMC-6236 (pan-RAS) blocked the growth of RRASQ87L or RRAS2Q72L- expressing cells to a greater degree than cells expressing the wildtype counterparts. RMC-6236 inhibited phosphorylation of ERK1/2 and S6 at doses similar to those seen in studies of KRASG12X mutants. However, RMC-6236 did not block AKT phosphorylation in lung cells expressing RRASQ87L or RRAS2Q72L. RMC-6236 treatment (10-50 mg/kg once daily) inhibited growth of HBEC-RRASQ87L and HBEC-RRAS2Q72L xenograft tumors in a dose-dependent manner. Similar to in vitro results, RMC-6236-treated HBEC-RRAS2Q72L - xenograft tumors showed reduced phosphorylation of ERK1/2 and S6 but not AKT. Conclusions. RRASQ87L and RRAS2Q72L are recurrent and actionable oncogenic drivers in NSCLC. RRASQ87L and RRAS2Q72L-expressing cells demonstrated in vitro and in vivo sensitivity to currently approved and experimental therapies, including the pan-RAS inhibitor RMC-6236 (currently in clinical trials in patients with RAS mutant solid tumors). This work provides preclinical evidence for the inclusion of patients with RRAS/RRAS2-mutant tumors into future trials of RAS-targeted therapies. Lack of inhibition of the PI3K-AKT pathway with RMC-6236 suggests that combination therapies should also be explored. Citation Format: Alexander J. Pfeil, Tom Zhang, Ryan Cheng, Christopher A. Febres-Aldana, Juan Luis Gomez Marti, Rohan P. Master, Marissa S. Mattar, Marc Ladanyi, Soo-Ryum Yang, Romel Somwar. Recurrent RRAS and RRAS2 mutations in lung cancer define actionable oncogenic drivers with therapeutic susceptibility to pan-RAS inhibition [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RAS Oncogenesis and Therapeutics; 2026 Mar 5-8; Los Angeles, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(5_Suppl_1):Abstract nr A051.