WIN site inhibition disrupts a subset of WDR5 function.

WDR5 nucleates the assembly of histone-modifying complexes and acts outside this context in a range of chromatin-centric processes. WDR5 is also a prominent target for pharmacological inhibition in cancer. Small-molecule degraders of WDR5 have been described, but most drug discovery efforts center on blocking the WIN site of WDR5, an arginine binding cavity that engages MLL/SET enzymes that deposit histone H3 lysine 4 methylation (H3K4me). Therapeutic application of WIN site inhibitors is complicated by the disparate functions of WDR5, but is generally guided by two assumptions-that WIN site inhibitors disable all functions of WDR5, and that changes in H3K4me drive the transcriptional response of cancer cells to WIN site blockade. Here, we test these assumptions by comparing the impact of WIN site inhibition versus WDR5 degradation on H3K4me and transcriptional processes. We show that WIN site inhibition disables only a specific subset of WDR5 activity, and that H3K4me changes induced by WDR5 depletion do not explain accompanying transcriptional responses. These data recast WIN site inhibitors as selective loss-of-function agents, contradict H3K4me as a relevant mechanism of action for WDR5 inhibitors, and indicate distinct clinical applications of WIN site inhibitors and WDR5 degraders.

Core pathway proteins and the molecular basis of planar polarity in the zebrafish gastrula.

The planar polarization of cells and subcellular structures is critical for embryonic development. Coordination of this polarity can provide cells a sense of direction in relation to the anterior-posterior and dorsal-ventral body axes. Fly epithelia use a core pathway comprised of transmembrane (Van Gogh/Strabismus, Frizzled, and Flamingo/Starry night) and cytoplasmic (Prickle or Spiny-legs, Dishevelled, and Diego) proteins to communicate directional information between cells and thereby promote the uniform orientation of structures such as hairs. In the zebrafish gastrula, planar polarity underlies complex cellular processes, including directed migration and intercalation, that are required to shape the embryo body. Like other vertebrates, the zebrafish genome encodes homologs of each core protein, and it is well-established that polarized gastrula cell behaviors are regulated by some of them. However, it is unknown whether a conserved six-member core protein pathway regulates planar polarity during zebrafish gastrulation. Here, we review our current understanding of core protein function as it relates to two specific examples of planar polarity, the dorsal convergence of lateral gastrula cells and the mediolateral intercalation of midline cells. We consider the hallmarks of fly planar polarity and discuss data regarding asymmetric protein localization and function, and the intercellular communication of polarity information.

Discovery of WD Repeat-Containing Protein 5 (WDR5)-MYC Inhibitors Using Fragment-Based Methods and Structure-Based Design.

The frequent deregulation of MYC and its elevated expression via multiple mechanisms drives cells to a tumorigenic state. Indeed, MYC is overexpressed in up to ∼50% of human cancers and is considered a highly validated anticancer target. Recently, we discovered that WD repeat-containing protein 5 (WDR5) binds to MYC and is a critical cofactor required for the recruitment of MYC to its target genes and reported the first small molecule inhibitors of the WDR5-MYC interaction using structure-based design. These compounds display high binding affinity, but have poor physicochemical properties and are hence not suitable for in vivo studies. Herein, we conducted an NMR-based fragment screening to identify additional chemical matter and, using a structure-based approach, we merged a fragment hit with the previously reported sulfonamide series. Compounds in this series can disrupt the WDR5-MYC interaction in cells, and as a consequence, we observed a reduction of MYC localization to chromatin.

Interaction of the oncoprotein transcription factor MYC with its chromatin cofactor WDR5 is essential for tumor maintenance.

The oncoprotein transcription factor MYC is overexpressed in the majority of cancers. Key to its oncogenic activity is the ability of MYC to regulate gene expression patterns that drive and maintain the malignant state. MYC is also considered a validated anticancer target, but efforts to pharmacologically inhibit MYC have failed. The dependence of MYC on cofactors creates opportunities for therapeutic intervention, but for any cofactor this requires structural understanding of how the cofactor interacts with MYC, knowledge of the role it plays in MYC function, and demonstration that disrupting the cofactor interaction will cause existing cancers to regress. One cofactor for which structural information is available is WDR5, which interacts with MYC to facilitate its recruitment to chromatin. To explore whether disruption of the MYC-WDR5 interaction could potentially become a viable anticancer strategy, we developed a Burkitt's lymphoma system that allows replacement of wild-type MYC for mutants that are defective for WDR5 binding or all known nuclear MYC functions. Using this system, we show that WDR5 recruits MYC to chromatin to control the expression of genes linked to biomass accumulation. We further show that disrupting the MYC-WDR5 interaction within the context of an existing cancer promotes rapid and comprehensive tumor regression in vivo. These observations connect WDR5 to a core tumorigenic function of MYC and establish that, if a therapeutic window can be established, MYC-WDR5 inhibitors could be developed as anticancer agents.