A novel pan-selective bromodomain inhibitor for epigenetic drug design.

For a long time, the development of bromodomain (BD) inhibitors (BDi) was almost exclusively related to the BET family. More recently, BDi for BDs outside the BET family have also been developed. Here we present a novel pan-BDi with micromolar affinities to various BDs, and nanomolar affinities to representatives of BD families I, II (Bromodomain and Extra-Terminal Domain (BET) family), III, and IV. The inhibitor shows a broad activity profile with nanomolar growth inhibition (GI50) values on various cancer cell lines. Subsequently, we were able to control the selectivity of the inhibitor by simple modifications and turned it into a highly selective BRD9 inhibitor.

4-Acyl Pyrrole Capped HDAC Inhibitors: A New Scaffold for Hybrid Inhibitors of BET Proteins and Histone Deacetylases as Antileukemia Drug Leads.

Multitarget drugs are an emerging alternative to combination therapies. In three iterative cycles of design, synthesis, and biological evaluation, we developed a novel type of potent hybrid inhibitors of bromodomain, and extra-terminal (BET) proteins and histone deacetylases (HDACs) based on the BET inhibitor XD14 and well-established HDAC inhibitors. The most promising new hybrids, 49 and 61, displayed submicromolar inhibitory activity against HDAC1-3 and 6, and BRD4(1), and possess potent antileukemia activity. 49 induced apoptosis more effectively than the combination of ricolinostat and birabresib (1:1). The most balanced dual inhibitor, 61, induced significantly more apoptosis than the related control compounds 62 (no BRD4(1) affinity) and 63 (no HDAC inhibition) as well as the 1:1 combination of both. Additionally, 61 was well tolerated in an in vivo zebrafish toxicity model. Overall, our data suggest an advantage of dual HDAC/BET inhibitors over the combination of two single targeted compounds.

4-Acyl Pyrroles as Dual BET-BRD7/9 Bromodomain Inhibitors Address BETi Insensitive Human Cancer Cell Lines.

Various malignant human diseases show disturbed signaling pathways due to increased activity of proteins within the epigenetic machinery. Recently, various novel inhibitors for epigenetic regulation have been introduced which promise a great therapeutic benefit. Inhibitors for the bromo- and extra-terminal domain (BET) family were of particular interest after inhibitors had shown a strong antiproliferative effect. More recently, the focus has increasingly shifted to bromodomains (BDs) outside the BET family. Based on previously developed inhibitors, we have optimized a small series of 4-acyl pyrroles, which we further analyzed by ITC, X-ray crystallography, selectivity studies, the NCI60 cell-panel, and GI50 determinations for several cancer cell lines. The inhibitors address both, BET and BRD7/9 BDs, with very high affinity and show a strong antiproliferative effect on various cancer cell lines that could not be observed for BD family selective inhibitors. Furthermore, a synergistic effect on breast cancer (MCF-7) and melanoma (SK-MEL-5) was proven.