Hijacking the E3 Ubiquitin Ligase Cereblon to Efficiently Target BRD4

Abstract

Summary BRD4, a bromodomain and extraterminal domain (BET) family member, is an attractive target in multiple pathological settings, particularly cancer. While BRD4 inhibitors have shown some promise in MYC-driven malignancies such as Burkitt’s Lymphoma (BL), we show that BRD4 inhibitors lead to robust BRD4 protein accumulation, which may account for their limited suppression of MYC expression, modest anti-proliferative activity and lack of apoptotic induction. To address these limitations, we designed ARV-825, a heterobifunctional PROTAC (Proteolysis Targeting Chimera) that recruits BRD4 to the E3 ubiquitin ligase cereblon leading to fast, efficient, and prolonged degradation of BRD4 in all BL cell lines tested. Consequently, ARV-825 more effectively suppresses c-MYC levels and downstream signaling than small molecule BRD4 inhibitors resulting in more effective cell proliferation inhibition and apoptosis induction in BL. Our findings provide strong evidence that cereblon-based PROTACs provide a better and more efficient strategy in targeting BRD4 than traditional small molecule inhibitors.

Degradation of the BAF Complex Factor BRD9 by Heterobifunctional Ligands

“…In our prior research, we directed the degradation of BET family proteins by appending CRBN ligands to JQ1, resulting in rapid and potent degradation of BRD2, BRD3 and BRD4. These findings have been well validated, suggesting a broader utility of this strategy [20][21][22] .…”

“…In our prior research, we directed the degradation of BET family proteins by appending CRBN ligands to JQ1, resulting in rapid and potent degradation of BRD2, BRD3 and BRD4. These findings have been well validated, suggesting a broader utility of this strategy [20][21][22] .Toward the elaboration of BRD9-directed degraders, we initially evaluated putative pharmacophores from reported bromodomain probes LP99 and I-BRD9, and subsequently expanded our study to a third probe, BI7273, reported during the course of this research (Figure 1 A). [12,14,15] To explore the potential of bifunctional derivatives to induce BRD9 degradation, we initially selected as our starting point a close chemical analog of I-BRD9 described by GlaxoSmithKline (GSK-39).…”

BET Bromodomain as a Target of Epigenetic Therapy

“…dBET1 and ARV-825 consist of BET inhibitors, (+)-JQ1 and OTX-015, respectively, coupled via a spacer moiety to a ligand of E3 ubiquitin ligase. [52][53][54][55] dBET1 induced selective CUL4-RBX1-DDB1-cereblon (CRBN)-dependent degradation of BET family proteins, including BRD2, BRD3 and BRD4, in vitro and in vivo, and it delayed leukemia progression in mice. 54) ARV-825 induced BRD4 degradation via a CRBN-mediated and proteasome-dependent mechanism, leading to persistent suppression of c-MYC and its downstream signaling.…”

“…54) ARV-825 induced BRD4 degradation via a CRBN-mediated and proteasome-dependent mechanism, leading to persistent suppression of c-MYC and its downstream signaling. 55) ARV-825 inhibited cell proliferation and induced apoptosis in Burkitt's lymphoma (BL), which is MYC-driven malignancy. 55) Both dBET1 and ARV-825 were more effective against cancer cells than JQ1 or OTX-015 alone.…”

“…55) ARV-825 inhibited cell proliferation and induced apoptosis in Burkitt's lymphoma (BL), which is MYC-driven malignancy. 55) Both dBET1 and ARV-825 were more effective against cancer cells than JQ1 or OTX-015 alone. Degradation of BET family proteins by MZ1, which utilizes a different E3 ligase system, has also been reported.…”