Menin-MLL inhibitors enhance JUND activity in MLLr leukemic cells contributing to tumorigenesis and therapy resistance

MLL-rearranged (MLLr) acute myeloid leukemia (AML) and acute lymphoid leukemia (ALL) involve reciprocal translocations of the KMT2A (MLL1) gene with various translocation partner genes, which yields oncogenic chimeric MLL1 fusion proteins (MLL-FPs). Menin, the protein product of the MEN1 gene, is essential for the leukemogenic activity of MLL-FPs. Revumenib is a small-molecule inhibitor that selectively disrupts the menin-MLL interaction, and it is now in clinical use for treatment of MLLr and NPM1-mutated (NPM1c) acute leukemia. Notably, menin also interacts with the JUND member of the AP-1 transcription factor family through a conserved protein sequence in the MLL1/2 binding pocket of menin. Despite this structural similarity, the impact of menin-MLL inhibitors on JUND function has remained unexplored. Here, we investigated the influence of menin-MLL inhibitors on JUND activity. Quantitative mass spectrometry analysis of MLLr leukemic cells demonstrated that menin-MLL inhibitors also disrupt menin-JUND interactions. Furthermore, CRISPR-mediated inactivation of JUND or pharmacological inhibition using JNK inhibitors synergistically enhanced the anti-leukemic effects of menin-MLL inhibitors leading to reduced cell proliferation, cell cycle arrest and apoptosis. RNA sequencing and chromatin binding assays revealed that menin-MLL inhibitor treatment increased JUND chromatin occupancy leading to upregulation of target genes and contributing to resistance against menin-MLL inhibitors. Immunocompromised mice engrafted with JUND-deficient leukemia cells exhibited reduced tumor burden compared to control mice engrafted with wild type leukemic cells. These findings reveal a role for JUND in MLLr AML and suggest that targeting JUND transcription factor activity enhances the efficacy of menin-MLL inhibitors towards MLLr leukemic cells.