BET protein proteolysis targeting chimera (PROTAC) exerts potent lethal activity against Mantle Cell Lymphoma cells

Bromodomain extraterminal protein (BETP) inhibitors transcriptionally repress oncoproteins and NFkB target genes, which undermines the growth and survival of MCL cells. However, BETi treatment causes accumulation of BETPs, associated with reversible binding and incomplete inhibition of BRD4, which potentially compromises the activity of BETi in MCL cells. Unlike BETi, BET-PROTACs (proteolysis-targeting chimera) ARV-825 and ARV-771 (Arvinas, Inc.) recruit and utilize an E3-ubiquitin ligase to effectively degrade BETPs in MCL cells. BET-PROTACs induce more apoptosis than BETi of MCL cells, including those resistant to ibrutinib. BET-PROTAC treatment induced more perturbations in the mRNA and protein expressions than BETi, with depletion of c-Myc, CDK4, cyclin D1, and the NFkB transcriptional targets Bcl-xL, XIAP and BTK, while inducing the level of HEXIM1, NOXA and CDKN1A/p21. Treatment with ARV-771, which possesses superior pharmacological properties compared to ARV-825, inhibited the in vivo growth and induced greater survival improvement than the BETi OTX015 of immune-depleted mice engrafted with MCL cells. Co-treatment of ARV-771 with ibrutinib or the BCL2-antagonist venetoclax or CDK4/6 inhibitor palbociclib synergistically induced apoptosis of MCL cells. These studies highlight promising and superior pre-clinical activity of BET-PROTAC than BETi, requiring further in vivo evaluation of BET-PROTAC as a therapy for ibrutinib-sensitive or resistant MCL. Overall design: Twelve samples in biologic triplicates

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Sun B, Fiskus W, Qian Y, Rajapakshe K, Raina K, Coleman KG, Crew AP, Shen A, Saenz DT, Mill CP, Nowak AJ, Jain N, Zhang L, Wang M, Khoury JD, Coarfa C, Crews CM, Bhalla KN