Pan-RAS Inhibitor RMC-7977 Overcomes Oncogenic RAS Signaling and Exerts Antileukemic Effects in CMML/AML Cells

Chronic myelomonocytic leukemia (CMML) is a clonal hematopoietic stem cell disorder characterized by overlapping features of both myelodysplastic syndrome (MDS) and myeloproliferative neoplasms (MPN). Patients with CMML have dismal outcomes with a median survival of 20-30 months, and this is partly due to their poor responses to the standard-of-care treatment with hypomethylating agents. Thus, new treatments are urgently needed for CMML patients.

RAS mutations are detected in roughly 50% of CMML patients and in even higher frequency among patients who progress to acute myeloid leukemia (AML). These mutations contribute to an overall poor prognosis and are also among the most commonly acquired resistance mutations in AML patients receiving treatment with targeted therapies including BCL2, FLT3, and IDH1/2 inhibitors. As directly targeting RAS has historically been challenging, the current strategy to overcome RAS in CMML and AML is to target downstream effectors such as MEK, ERK, PI3K and MTOR, but these therapies are hindered with short-lived clinical response, emergence of resistance and high on-target toxicity. However, recent breakthroughs in the direct pharmacologic inhibition of RAS have renewed enthusiasm for targeting RAS-mutant tumors. FDA-approved KRAS^G12C inhibitors sotorasib and adagrasib demonstrate significant clinical response for non-small cell lung cancer patients harboring KRAS G12C mutation, and early data suggests that pan-RAS inhibitors are safe and effective in PDAC and NSCLC. To date, there has been little exploration of the potential efficacy and safety of RAS inhibitors in the context of myeloid malignancies. We hypothesize that the RAS^multi(ON) inhibitor RMC-7977, a highly selective inhibitor of the active GTP-bound forms of KRAS, HRAS and NRAS, will be effective against RAS-mutated CMML/AML cell lines arising from chronic myeloid neoplasms including CMML.

We first characterized the effect of RMC-7977 in a variety of AML cell lines with mutated RAS (NB4 -KRAS^A18D, NOMO-1 -KRAS^G13D, THP-1 -NRAS^G12D, TF-1 -NRAS^Q61P, MDS92 -NRAS^G12A, MDS-L -NRAS^G12A, SKM1 -KRAS^K117N) and wild-type RAS that is activated by alternative mutations (Kasumi-1 -KIT^N882K, MOLM13 -FLT3/ITD, SET2 -JAK2^V617F,). MTT studies reveal that RMC-7977 treatment suppressed proliferation in the low nanomolar range in both RAS-mutated and wild type models, with most cell lines having an IC50 of less than 10 nM. The AML cell lines arising from MDS/CMML (SKML, MDS92, and MDS-L) were very sensitive to the RAS inhibitor, with IC50s of less than 3 nM. These cell lines also exhibited increased apoptosis when treated with low nanomolar concentrations of RMC-7977, with MDS92 having over 14-fold increased cell death when treated with 1 nM RMC-7977 compared to DMSO control. Cell signaling experiments with immunoblot analysis revealed that low doses of RMC-7977 treatment significantly decreased phosphorylation of MEK and ERK, as well as suppressed ERK transcriptional output. Significant induction of apoptosis was induced in RAS mutated AML blasts from patients with relapsed/refractory disease by treatment with 1 and 5 nM RCM-7977.

Since RMC-7977 displays potent effects on proliferation and apoptosis with low nanomolar doses, we evaluated its effects on the hematopoiesis of healthy bone marrow cells. CD34+ cells were sorted from healthy bone marrow donors, treated with RMC-7977, and assessed differentiation and apoptosis. RMC-7977 showed no effect on the survival and differentiation of healthy hematopoietic stem and progenitor cells, strengthening its potential as an effective therapy in CMML and AML with low toxicity. Experiments evaluating the effects of RMC-7977 in cell line xenografts and additional patients' primary samples are ongoing and will be presented.

Collectively, we have demonstrated that the pan-RAS inhibitor RCM-7977 is highly effective against RAS mutated CMML/AML cell lines arising from chronic myeloid neoplasms including CMML while sparing healthy hematopoietic stem and progenitor cells. This work provides the rationale to continue evaluating RAS inhibitors as a targeted therapy in RAS-mutated myeloid malignancies, which is a significant unmet need in the treatment of these conditions.

Stahl:BMS: Membership on an entity's Board of Directors or advisory committees; Kymera: Membership on an entity's Board of Directors or advisory committees; Sierra Oncolgy: Membership on an entity's Board of Directors or advisory committees; GSK: Membership on an entity's Board of Directors or advisory committees; Rigel: Membership on an entity's Board of Directors or advisory committees; Sobi: Membership on an entity's Board of Directors or advisory committees; Syndax: Membership on an entity's Board of Directors or advisory committees. Levis:Abbvie: Consultancy; Astellas: Consultancy; Bristol Myers Squibb: Consultancy; Daiichi Sankyo: Consultancy; Novartis: Consultancy; Takeda: Consultancy. Ambinder:Astellas: Honoraria. Misale:Boehringer Ingelheim: Research Funding; Daiichi Sankyo: Research Funding; Bionseek: Membership on an entity's Board of Directors or advisory committees.