Combining Menin and MEK Inhibition to Target Poor Prognostic KMT2A-Rearranged RAS Pathway-Mutant Acute Leukemia

Approximately 10% of all acute leukemias harbor a chromosomal translocation involving the Mixed Lineage Leukemia 1 ( MLL1/ KMT2A) gene locus with over 90 fusion partners. These fusions are especially prevalent in pediatric acute leukemias. The resulting KMT2A fusion proteins (KMT2A-r) drive leukemogenic gene expression through an interaction with a chromatin complex that includes the scaffold protein menin, giving rise to aggressive acute myeloid leukemia (AML) or acute lymphoblastic leukemia (ALL).

In infant ALL, frequently characterized by KMT2A-r, the presence of RAS pathway mutations has been associated with a poor prognosis. The prognostic impact of RAS pathway mutations in pediatric KMT2A-r AML is less established. We thus analyzed data from 1605 pediatric patients with AML treated on the Children's Oncology Group (COG) AAML0531 and AAML1031 studies, with 336 of these having KMT2A-r. 51% (170/336) of these patients had mutations in NRAS, KRAS or PTPN11. The combination of KMT2A-r with RAS pathway mutations was associated with worse EFS and OS, HR=1.71 (p<0.001) for EFS and OS multivariable models.

Given the prevalence of RAS pathway mutations co-occurring with KMTA-r, and the high-risk leukemia associated with this mutational profile, we sought to identify efficacious targeted drug combinations for this subset of childhood leukemia. Early clinical trial data for the menin inhibitor revumenib (SNDX-5613) demonstrated efficacy in KMT2A-r leukemias. Responding patients, however, typically develop progressive disease with a subset having mutations in MEN1 the gene encoding menin. Effective combination treatments for full efficacy of this targeted therapy are needed. We evaluated the combination of RAS/MAPK targeting using the MEK1/2 inhibitor selumetinib with VTP-50469, a close analog of revumenib, in pediatric leukemias harboring both KMT2A-r and RAS mutations. Treatment of AML and ALL cell lines and cells from an AML patient-derived xenograft (PDX) model in vitro with this drug combination resulted in a synergistic decrease in viability, a G0/G1 cell cycle arrest, and an increase in apoptosis. The combination also resulted in decreased AML colony formation.

We next explored potential mechanisms by which the combination treatment had a synergistic anti-leukemic effect. Both selumetinib and VTP-50469 treatment individually reduced phosphorylated ERK levels, but the combination had the most complete inhibitory effect. The combination treatment also resulted in loss of stem-like gene expression signatures, an increase in myeloid differentiation programs, and most strikingly, downregulation of targets of MYC signaling. Both MYC transcript and protein levels were reduced by each drug alone and even more effectively with the combination.

Next, we evaluated the in vivo efficacy of this drug combination in three orthotopic pediatric AML and ALL pediatric PDX models harboring different KMT2A-r and RAS mutations (AML: KMT2A- AF10 with KRAS, KMT2A- PICALM with NRAS, ALL: MLL- AF4 with NRAS). NSG mice engrafted with PDX models via tail vein injection were assigned to four treatment groups: vehicle, chow containing revumenib (0.03%), selumetinib (50 mg/kg/day, 5 days a week), or the combination. After treatment for 18-28 days leukemia burden in bone marrow, spleen and peripheral blood was markedly decreased with the combination compared to the single drug-treated cohorts in 2 models with RAS mutations. In one of the AML models, single agent treatment with revumenib or selumetinib was highly efficacious at eradicating disease at the measured time point. We also found a striking decrease in levels of MYC, P-ERK and MEIS1 by western immunoblotting, highlighting on-target activity of the drugs and supporting our in vitro data for a role for MYC in the synergistic effect observed with the combination.

In conclusion, new clinical data from a large cohort of COG patients demonstrates that KMT2A-r and co-occurring RAS pathway mutations portend a distinctively worse outcome for children with AML. The findings in our preclinical study suggest a promising, readily translatable targeted treatment for this patient population. Mechanistically, enhanced downregulation of both MYC signaling and the RAS/MAPK pathway with the combinatorial therapy is likely a strong contributor to the observed efficacy.