Discovery of First-in-class WDR5 PROTACs as a Novel Therapeutic Strategy for MLL-rearranged Leukemias

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PROJECT SUMMARY Rearrangements of the mixed-lineage leukemia (MLL) gene account for approximately 10% of all human leukemias. Such rearrangements are more common in pediatric leukemias. Up to 80% of infant acute lymphoblastic leukemias (ALL) and 35-50% of infant acute myeloid leukemias (AML) are characterized by MLL rearrangements. MLL-rearranged (MLL-r) leukemia patients have particularly poor response to standard treatments and a dismal prognosis. To date, no effective targeted therapies have been approved for treating these deadly cancers. WD40 repeat domain protein 5 (WDR5) is an essential subunit of the MLL1 histone methyltransferase complex (MLL1 complex) and is crucial for MLL1 complex-mediated regulations of gene transcription. WDR5 also interacts with non-MLL partners such as c-MYC. Importantly, interactions between WDR5 and its various binding partners are essential for sustaining oncogenesis, and genetic depletion of WDR5 suppresses the proliferation of MLL-r leukemias. Therefore, WDR5 is a promising drug target for MLL-r leukemias. However, while small-molecule inhibitors that effectively block the protein-protein interactions (PPI) between WDR5 and its binding partners have been developed, these WDR5 PPI inhibitors are largely ineffective in killing MLL-r leukemia cells and lack in vivo efficacy, as opposed to the cell killing effect of WDR5 genetic knockout or knockdown. We hypothesize that pharmacological degradation of WDR5 by small-molecule degraders as a novel therapeutic strategy will be effective and superior to pharmacological inhibition of WDR5 by PPI inhibitors for the treatment of MLL-r leukemias. To test this hypothesis, we propose to discover first-in- class WDR5 small-molecule degraders using the proteolysis targeting chimera (PROTAC) technology and evaluate them in MLL-r leukemia cellular and mouse models. We have generated very promising preliminary results, suggesting that the proposed research is feasible. The WDR5 PROTAC degraders generated in this project will not only help us test our innovative therapeutic hypothesis, but can also be developed further into a drug candidate for advancing to clinical trials with MLL-r leukemia patients. These WDR5 PROTACs are also valuable chemical probes for assessing the therapeutic potential of WDR5 degradation in other cancers.