Design, synthesis and evaluation of EZH2-based PROTACs targeting PRC2 complex in lymphoma

EZH2 is a member of PcG and can induce the occurrence of cancer when it is highly expressed. As an EZH2 inhibitor, Tazemetostat (EPZ6438) can inhibit the methylation catalytic activity of EZH2. However, many studies have shown that inhibition of EZH2 alone does not efficiently block tumor development. Therefore, in this study, proteolytic targeting chimera technology was employed to enhance the antiproliferative potency of EPZ6438 by degrading the oncogenic activity of EZH2. Several PROTACs have been synthesized by combining EPZ6438 with four E3 ligase ligands based on VHL, CRBN, MDM2, and cIAP E3 ligase systems. In our study, compound E-3P-MDM2 is the most active PROTAC molecule. It degraded EZH2 of the SU-DHL-6 cells in a concentration and dose-dependent manner and also degraded both EED and SUZ12 protein without affecting their mRNA levels, then significantly inhibited the expression of H3K27me3. The in vitro antiproliferative activity of E-3P-MDM2 was much stronger than that of EPZ6438.

Inhibition of Ezh2 redistributes bivalent domains within transcriptional regulators associated with WNT and Hedgehog pathways in osteoblasts

Bivalent epigenomic regulatory domains containing both activating histone 3 lysine 4 (H3K4me3) and repressive lysine 27 (H3K27me3) trimethylation are associated with key developmental genes. These bivalent domains repress transcription in the absence of differentiation signals but maintain regulatory genes in a poised state to allow for timely activation. Previous studies demonstrated that enhancer of zeste homolog 2 (Ezh2), a histone 3 lysine 27 (H3K27) methyltransferase, suppresses osteogenic differentiation and that inhibition of Ezh2 enhances commitment of osteoblast progenitors in vitro and bone formation in vivo. Here, we examined the mechanistic effects of Tazemetostat (EPZ6438), an Food and Drug Administration approved Ezh2 inhibitor for epithelioid sarcoma treatment, because this drug could potentially be repurposed to stimulate osteogenesis for clinical indications. We find that Tazemetostat reduces H3K27me3 marks in bivalent domains in enhancers required for bone formation and stimulates maturation of MC3T3 preosteoblasts. Furthermore, Tazemetostat activates bivalent genes associated with the Wingless/integrated (WNT), adenylyl cyclase (cAMP), and Hedgehog (Hh) signaling pathways based on transcriptomic (RNA-seq) and epigenomic (chromatin immunoprecipitation [ChIP]-seq) data. Functional analyses using selective pathway inhibitors and silencing RNAs demonstrate that the WNT and Hh pathways modulate osteogenic differentiation after Ezh2 inhibition. Strikingly, we show that loss of the Hh-responsive transcriptional regulator Gli1, but not Gli2, synergizes with Tazemetostat to accelerate osteoblast differentiation. These studies establish epigenetic cooperativity of Ezh2, Hh-Gli1 signaling, and bivalent regulatory genes in suppressing osteogenesis. Our findings may have important translational ramifications for anabolic applications requiring bone mass accrual and/or reversal of bone loss.

Remarkable Synergy When Combining EZH2 Inhibitors with YM155 Is H3K27me3-Independent

Targeting multiple molecules in the same biological network may maximize therapeutic efficacy. In this study, we identified a 27-gene module that is highly expressed in solid tumors, encoding actionable targets including EZH2 and BIRC5. The combination of EZH2 inhibitors and a BIRC5 inhibitor, YM155, results in a remarkable synergistic effect. The action of EZH2 inhibitors in this process is independent of the histone methyltransferase activity of polycomb repressive complex 2. Our study reveals a potential therapeutic approach for treating solid tumors by simultaneously targeting EZH2 and BIRC5.