Abstract 4718: ABBV-075, a novel BET family bromodomain inhibitor, represents a promising therapeutic agent for a broad spectrum of cancer indications

Bromodomain-Containing Protein 4: A Druggable Target

Bromodomain-containing protein 4 (BRD4) belongs to the bromodomain and extraterminal family. BRD4 inhibitors can regulate acetylated lysine and form protein complexes that initiate transcriptional programs as an epigenetic regulator of the histone code. BRD4 was initially considered to be one of the most promising targets for combating malignant tumors. However, many recent studies have shown that BRD4 plays a crucial role in various kinds of diseases, including cancer, coronary heart disease, neurological disorder, and obesity. Currently, several BRD4 inhibitors are undergoing clinical trials. A search for new BRD4 inhibitors appears to be of great utility for developing novel drugs. In this mini-review, we highlight the inhibitors of BRD4 from natural products and synthesized sources, as well as their applications in cancer, glucolipid metabolism, inflammation, neuronal stimulation activation, human immunodeficiency virus and renal fibrosis.

Discovery of potent and selective BRD4 inhibitors capable of blocking TLR3-induced acute airway inflammation

A series of diverse small molecules have been designed and synthesized through structure-based drug design by taking advantage of fragment merging and elaboration approaches. Compounds ZL0420 (28) and ZL0454 (35) were identified as potent and selective BRD4 inhibitors with nanomolar binding affinities to bromodomains (BDs) of BRD4. Both of them can be well docked into the acetyl-lysine (KAc) binding pocket of BRD4, forming key interactions including the critical hydrogen bonds with Asn140 directly and Tyr97 indirectly via a H2O molecule. Both compounds 28 and 35 exhibited submicromolar potency of inhibiting the TLR3-dependent innate immune gene program, including ISG54, ISG56, IL-8, and Groβ genes in cultured human small airway epithelial cells (hSAECs). More importantly, they also demonstrated potent efficacy reducing airway inflammation in a mouse model with low toxicity, indicating a proof of concept that BRD4 inhibitors may offer the therapeutic potential to block the viral-induced airway inflammation.

Synthesis and biological evaluation of indazole-4,7-dione derivatives as novel BRD4 inhibitors

Bromodomain-containing protein 4 (BRD4) is known to regulate the expression of c-Myc to control the proliferation of cancer cells. Therefore, development of small-molecule inhibitors targeting the bromodomain has been widely studied. However, some clinical trials on BRD4 inhibitors have shown its drawbacks such as toxicity including the loss of organ weight. Here, we report the development of the novel and promising scaffold, 1H-indazol-4,7-dione, as a bromodomain inhibitor and synthesized derivatives for the inhibition of binding of bromodomain to acetylated histone peptide. Through this effort, we obtained 6-chloro-5-((2,6-difluorophenyl)amino)-1H-indazole-4,7-dione (5i), which showed a highly potent activity with a half-maximal inhibitory concentration (IC₅₀) of 60 nM. The in vivo xenograft assay confirmed that the 1H-indazol-4,7-dione compound reduced the tumor size significantly. These results show that the 1H-indazol-4,7-dione scaffold is highly potent against bromodomain.

Design and Optimization of Benzopiperazines as Potent Inhibitors of BET Bromodomains

A protein structure-guided drug design approach was employed to develop small molecule inhibitors of the BET family of bromodomains that were distinct from the known (+)-JQ1 scaffold class. These efforts led to the identification of a series of substituted benzopiperazines with structural features that enable interactions with many of the affinity-driving regions of the bromodomain binding site. Lipophilic efficiency was a guiding principle in improving binding affinity alongside drug-like physicochemical properties that are commensurate with oral bioavailability. Derived from this series was tool compound FT001, which displayed potent biochemical and cellular activity, translating to excellent in vivo activity in a mouse xenograft model (MV-4-11).

Drug Discovery Targeting Bromodomain-Containing Protein 4

BRD4, the most extensively studied member of the BET family, is an epigenetic regulator that localizes to DNA via binding to acetylated histones and controls the expression of therapeutically important gene regulatory networks through the recruitment of transcription factors to form mediator complexes, phosphorylating RNA polymerase II, and by its intrinsic histone acetyltransferase activity. Disrupting the protein–protein interactions between BRD4 and acetyl-lysine has been shown to effectively block cell proliferation in cancer, cytokine production in acute inflammation, and so forth. To date, significant efforts have been devoted to the development of BRD4 inhibitors, and consequently, a dozen have progressed to human clinical trials. Herein, we summarize the advances in drug discovery and development of BRD4 inhibitors by focusing on their chemotypes, in vitro and in vivo activity, selectivity, relevant mechanisms of action, and therapeutic potential. Opportunities and challenges to achieve selective and efficacious BRD4 inhibitors as a viable therapeutic strategy for human diseases are also highlighted.