Targeting LEDGF Interactions in MLL Leukemia

Abstract 2500

Chromosomal translocations of MLL (Mixed Lineage Leukemia) gene result in aggressive acute leukemias, affecting both children and adults. Fusion of MLL to one of more than 60 partner genes results in MLL fusion oncoproteins which upregulate expression of Hox genes required for normal blood cell development, ultimately leading to development of acute leukemia. Regardless of the fusion partner, the presence of MLL translocations is associated with early relapse and poor prognosis. Survival rates are particularly low for infants and there is a pressing need for the development of targeted therapies against leukemias with MLL translocations. The oncogenic activity of MLL fusion proteins is dependent on association with LEDGF (lens epithelium-derived growth factor) and menin, both of which interact with the N-terminus of MLL retained in all MLL fusion proteins. LEDGF is a chromatin-associated protein, which interacts conjointly with MLL and menin on the chromatin of the cancer associated genes, and both interactions are required for the MLL-mediated leukemogenesis and misregulation of HOXA9 expression. Therefore, LEDGF functions as an essential oncogenic cofactor in MLL related leukemias, and may represent a valuable molecular target for therapeutic intervention with small molecules.

We have performed rigorous biophysical and biochemical studies and revealed that LEDGF is involved in simultaneous interaction with menin and with the N-terminus of MLL. Interestingly, the association of LEDGF with the menin-MLL complex has relatively low affinity which limits the application of conventional screening methods for lead identification. To develop small molecule inhibitors targeting LEDGF interactions we have employed two strategies: Fragment Based Drug Discovery (FBDD) approach and High Throughput Screening (HTS). We have identified several compounds that bind directly to LEDGF. By applying NMR spectroscopy we discovered that these compounds interact with the menin binding site on LEDGF. Then we have assessed the activity of these compounds using a broad range of cell based assays. We found that compounds targeting LEDGF specifically inhibit proliferation of the MLL leukemia cells without affecting the non-MLL leukemia cells. They also induce apoptosis and differentiation of MLL leukemia cells as assessed by increased expression of CD11b differentiation marker and substantial change in morphology of these cells. Furthermore, these compounds reduce transforming properties of MLL fusion proteins and downregulate expression of Hoxa9 and Meis1 genes confirming a highly specific mode of action. Overall, our results demonstrate that targeting of LEDGF by small molecules is feasible and may results in development of potent inhibitors of LEDGF interaction with menin and MLL fusion proteins in leukemias with MLL rearrangements. Such compounds might provide a new therapeutic approach for the treatment of MLL-rearranged leukemias.