Distinct Pathways Affected by Menin versus MLL1/MLL2 in MLL-rearranged Acute Myeloid Leukemia.

Disrupting protein-protein interaction for molecularly targeted cancer therapeutics can be a challenging but promising strategy. Compounds that disrupt the interaction between Menin, a chromatin-binding protein, and oncogenic MLL fusion proteins (FPs) have shown significant promise in pre-clinical models of leukemia and show a high degree of selectivity for leukemia versus normal hematopoietic cells. Biochemical and structural studies demonstrate that, in addition to disrupting Menin-MLL-FP interaction, such compounds also inhibit Menin-MLL1, Menin-MLL2, and other Menin interacting proteins. Here we address the degree to which disruption of Menin-MLL-FP interactions or Menin-MLL1/MLL2 interactions contribute to the anti-leukemia effect of Menin inhibition. We show that Men1 deletion in MLL-AF9-transformed leukemia cells produces distinct cellular and molecular consequences as compared to Mll1;Mll2 co-deletion, and that compounds disrupting Menin-MLL-N terminal interactions largely phenocopy Menin loss. Moreover, we show that Mll1;Mll2-deficient leukemia cells exhibit enhanced sensitivity to Menin-interaction inhibitors consistent with each regulating complementary genetic pathways. These data illustrate the heightened dependency of MLL-FPs on Menin, as compared to wild-type MLL1/MLL2 for regulation of downstream target genes, and argue that the predominant action of Menin inhibitory compounds is through direct inhibition of MLL-FPs without significant contribution from MLL1/MLL2 inhibition.