MS436

MS436 is a potent and selective small-molecule inhibitor of BRD4 with Ki values of ＜0.085μM and 0.34μM, respectively for BrD1 and BrD2 [1].

BRD4 plays a role in gene transcription and is a drug target for cancer and inflammation. It has two bromodomains. MS436 is a diazobenzene compound, it is designed from the SAR studies to have higher selectivity. In vitro fluorescent anisotropy assay shows MS436 has about 10-fold higher affinity of BrD1 over BrD2. MS436 binds to BRD4 through a set of water-mediated interaction and this is the molecular basis for the binding affinity. MS436 also has activity to CBP BrD. In RAW264.7 cells, MS436 can block NF-κB-directed NO production and block the expression of proinflammatory cytokine interleukin (IL)-6 induced by LPS [1].

References:
[1] Zhang G, Plotnikov AN, Rusinova E, Shen T, Morohashi K, Joshua J, Zeng L, Mujtaba S, Ohlmeyer M, Zhou MM. Structure-guided design of potent diazobenzene inhibitors for the BET bromodomains. J Med Chem. 2013 Nov 27;56(22):9251-64.

Structure-guided design of potent diazobenzene inhibitors for the BET bromodomains.[Pubmed:24144283]

J Med Chem. 2013 Nov 27;56(22):9251-64.

BRD4, characterized by two acetyl-lysine binding bromodomains and an extra-terminal (ET) domain, is a key chromatin organizer that directs gene activation in chromatin through transcription factor recruitment, enhancer assembly, and pause release of the RNA polymerase II complex for transcription elongation. BRD4 has been recently validated as a new epigenetic drug target for cancer and inflammation. Our current knowledge of the functional differences of the two bromodomains of BRD4, however, is limited and is hindered by the lack of selective inhibitors. Here, we report our structure-guided development of diazobenzene-based small-molecule inhibitors for the BRD4 bromodomains that have over 90% sequence identity at the acetyl-lysine binding site. Our lead compound, MS436, through a set of water-mediated interactions, exhibits low nanomolar affinity (estimated Ki of 30-50 nM), with preference for the first bromodomain over the second. We demonstrated that MS436 effectively inhibits BRD4 activity in NF-kappaB-directed production of nitric oxide and proinflammatory cytokine interleukin-6 in murine macrophages. MS436 represents a new class of bromodomain inhibitors and will facilitate further investigation of the biological functions of the two bromodomains of BRD4 in gene expression.

BRD4 sustains melanoma proliferation and represents a new target for epigenetic therapy.[Pubmed:23950209]

Cancer Res. 2013 Oct 15;73(20):6264-76.

Metastatic melanoma remains a mostly incurable disease. Although newly approved targeted therapies are efficacious in a subset of patients, resistance and relapse rapidly ensue. Alternative therapeutic strategies to manipulate epigenetic regulators and disrupt the transcriptional program that maintains tumor cell identity are emerging. Bromodomain and extraterminal domain (BET) proteins are epigenome readers known to exert key roles at the interface between chromatin remodeling and transcriptional regulation. Here, we report that BRD4, a BET family member, is significantly upregulated in primary and metastatic melanoma tissues compared with melanocytes and nevi. Treatment with BET inhibitors impaired melanoma cell proliferation in vitro and tumor growth and metastatic behavior in vivo, effects that were mostly recapitulated by individual silencing of BRD4. RNA sequencing of BET inhibitor-treated cells followed by Gene Ontology analysis showed a striking impact on transcriptional programs controlling cell growth, proliferation, cell-cycle regulation, and differentiation. In particular, we found that, rapidly after BET displacement, key cell-cycle genes (SKP2, ERK1, and c-MYC) were downregulated concomitantly with the accumulation of cyclin-dependent kinase (CDK) inhibitors (p21 and p27), followed by cell-cycle arrest. Importantly, BET inhibitor efficacy was not influenced by BRAF or NRAS mutational status, opening the possibility of using these small-molecule compounds to treat patients for whom no effective targeted therapy exists. Collectively, our study reveals a critical role for BRD4 in melanoma tumor maintenance and renders it a legitimate and novel target for epigenetic therapy directed against the core transcriptional program of melanoma.

MS436 is a new class of bromodomain inhibitor, exhibits potent affinity of an estimated Ki=30-50 nM for the BRD4 BrD1 and a 10-fold selectivity over the BrD2.

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