Abstract B004: Pre-treatment with azacytidine sensitizes <i>RAS</i> mutated secondary AML to the pan-RAS inhibitor RMC-7977

Abstract Patients with acute myeloid leukemia (AML) arising from antecedent myeloid neoplasms (secondary AML, sAML) continue to have poorer outcomes than those with de novo AML, characterized by a high incidence of refractory disease and relapse after initial response. Most patients with sAML are treated with combinations of hypomethylating agents, such as azacytidine, together with venetoclax, a BCL-2 inhibitor. However, RAS mutations, present in approximately 20–30% of these patients, confer resistance to venetoclax and are associated with shorter overall survival. Although RAS oncogenes were long considered “undruggable,” KRAS mutant–specific inhibitors have recently shown promise in clinical trials for solid tumors. Notably, treatment with the RAS-MULTI(ON) inhibitor RMC-7977 has been reported to sensitize AML cells to FLT3 and BCL-2 inhibition. In this study, we found that pretreatment with azacitidine enhances the sensitivity of RAS-mutated sAML cells to RMC-7977. Analysis of the BEAT AML 2.0 dataset revealed that mutations affecting RAS signaling, particularly in KRAS, NRAS, and PTPN11, rank among the top alterations associated with resistance to azacytidine treatment in AML samples. These findings suggest that combining azacytidine with RAS inhibition may represent a promising therapeutic strategy for RAS-mutated AML. To evaluate this, we compared three treatment approaches in SKM1 cells: concurrent administration of azacytidine and RMC-7977, sequential treatment with azacytidine followed by RMC-7977, and the reverse sequence. Only pretreatment with azacytidine followed by RMC-7977 produced synergistic effects in reducing cell viability. RAS signaling pathway analysis revealed that treatment with azacytidine increased ERK phosphorylation and DUPS6 levels in SKM1 cells, potentially sensitizing to subsequent RAS inhibition with RMC-7977. This sequential regimen also produced synergistic effects on inducing apoptosis in the MDS/sAML cell lines MDS92, MDS-L, and SKM1. Consistently, treatment of primary RAS-mutated sAML samples with azacytidine followed by RMC-7977 significantly reduced clonogenic growth compared with either agent alone, without impairing the clonogenicity of healthy hematopoietic cells. Finally, pretreatment of SKM1 xenografts with azacytidine (5 mg/kg for 5 days) markedly improved RMC-7977-mediated control of leukemic burden in vivo. In conclusion, we found that azacytidine treatment sensitizes RAS-mutated sAML cells to RAS inhibition by RMC-7977 in both in vitro and in vivo models. Ongoing studies aim to elucidate the underlying molecular mechanisms, including the potential role of methylation changes in modulating oncogenic signaling dependencies. Together, these findings provide a strong rationale for continued evaluation of RAS inhibitors as part of combination treatment strategies for RAS-mutated AML. Citation Format: Tessa Seale, Xinghan Zheng, Yuju An, Brandy Perkins, Erotokritos Georgantzinos, Theodora Chatzilygeroudi, Bogdan Paun, Maximillian Stahl, Mark J. Levis, Styliani Karanika, Alexander J. Ambinder, Theodoros Karantanos, Sandra Misale. Pre-treatment with azacytidine sensitizes RAS mutated secondary AML to the pan-RAS inhibitor RMC-7977 [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 B004.