Anti-leukemic effect of MAR-3.6.2, a novel RAN inhibitor, on AML-LSCs by targeting RAN.

The small GTPase RAN plays a role in the biogenesis of mature miR-126, which is supplied by the bone marrow arterioles to leukemic stem cells (LSCs). MiR-126 supports the homeostasis of LSCs that initiate and maintain acute myeloid leukemia (AML). While therapeutic targeting of RAN has been difficult due to its structural features, through molecular dynamics simulations and docking studies, we have identified MAR-3.6.2 as a novel allosteric inhibitor that binds in a cryptic pocket in the C-terminal domain of RAN. We showed that MAR-3.6.2 disrupted RAN interaction with its guanine nucleotide exchange factor RCC1 and prevented the nuclear switch of RAN-GDP to RAN-GTP. This in turn led to RAN nuclear retention and reduced the RAN/XPO5-mediated export of pre-miR-126, thereby limiting mature miR-126 biogenesis in endothelial cells and their exogenous supply of mature miR-126 to LSCs. In a MllPTD/WT/Flt3ITD/ITD AML murine model, MAR-3.6.2 reduced leukemia burden, prolonged survival, and decreased LSC frequency in secondary transplants. These findings highlight MAR-3.6.2 and future, potential derivates as a promising small molecule-based approach to eradicate AML LSCs via inhibition of RAN/XPO5 trafficking and block of miR-126 biogenesis.