Preclinical Safety Assessment of a Highly Selective and Potent Dual Small-Molecule Inhibitor of CBP/P300 in Rats and Dogs

Discovery of CZL-046 with an (S)-3-Fluoropyrrolidin-2-one Scaffold as a p300 Bromodomain Inhibitor for the Treatment of Multiple Myeloma

E1A binding protein (p300) is a promising therapeutic target for the treatment of cancer. Herein, we report the discovery of a series of novel inhibitors with an (S)-3-fluoropyrrolidin-2-one scaffold targeting p300 bromodomain. The best compound 29 (CZL-046) shows potent inhibitory activity of p300 bromodomain (IC50 = 3.3 nM) and antiproliferative activity in the multiple myeloma (MM) cell line (OPM-2 IC50 = 51.5 nM). 29 suppressed the mRNA levels of c-Myc and IRF4 and downregulated the expression of c-Myc and H3K27Ac. Compared to the lead compound 5, 29 exhibits significantly improved in vitro and in vivo metabolic properties. Oral administration of 29 with 30 mg/kg achieved a TGI value of 44% in the OPM-2 xenograft model, accompanied by good tolerability. The cocrystal structure of CREB binding protein bromodomain with 29 provides an insight into the precise binding mode. The results demonstrate that 29 is a promising p300 bromodomain inhibitor for the treatment of MM.

Discovery of a potent and selective CBP bromodomain inhibitor (Y08262) for treating acute myeloid leukemia

The bromodomain of CREB (cyclic-AMP response element binding protein) binding protein (CBP) is an epigenetic "reader" and plays a key role in transcriptional regulation. CBP bromodomain is considered to be a promising therapeutic target for acute myeloid leukemia (AML). Herein, we report the discovery of a series of 1-(indolizin-3-yl)ethan-1-one derivatives as potent, and selective CBP bromodomain inhibitors focused on improving cellular potency. One of the most promising compounds, 7e (Y08262), inhibits the CBP bromodomain at the nanomolar level (IC50 = 73.1 nM) with remarkable selectivity. In addition, the new inhibitor also displays potent inhibitory activities in AML cell lines. Collectively, this study provides a new lead compound for further validation of CBP bromodomain as a molecular target for AML drug development.

Targeting of epigenetic co-dependencies enhances anti-AML efficacy of Menin inhibitor in AML with MLL1-r or mutant NPM1

Monotherapy with Menin inhibitor (MI), e.g., SNDX-5613, induces clinical remissions in patients with relapsed/refractory AML harboring MLL1-r or mtNPM1, but most patients either fail to respond or eventually relapse. Utilizing single-cell RNA-Seq, ChiP-Seq, ATAC-Seq, RNA-Seq, RPPA, and mass cytometry (CyTOF) analyses, present pre-clinical studies elucidate gene-expression correlates of MI efficacy in AML cells harboring MLL1-r or mtNPM1. Notably, MI-mediated genome-wide, concordant, log2 fold-perturbations in ATAC-Seq and RNA-Seq peaks were observed at the loci of MLL-FP target genes, with upregulation of mRNAs associated with AML differentiation. MI treatment also reduced the number of AML cells expressing the stem/progenitor cell signature. A protein domain-focused CRISPR-Cas9 screen in MLL1-r AML cells identified targetable co-dependencies with MI treatment, including BRD4, EP300, MOZ and KDM1A. Consistent with this, in vitro co-treatment with MI and BET, MOZ, LSD1 or CBP/p300 inhibitor induced synergistic loss of viability of AML cells with MLL1-r or mtNPM1. Co-treatment with MI and BET or CBP/p300 inhibitor also exerted significantly superior in vivo efficacy in xenograft models of AML with MLL1-r. These findings highlight novel, MI-based combinations that could prevent escape of AML stem/progenitor cells following MI monotherapy, which is responsible for therapy-refractory AML relapse.

Recent Advances on Small-Molecule Bromodomain-Containing Histone Acetyltransferase Inhibitors

In recent years, substantial research has been conducted on molecular mechanisms and inhibitors targeting bromodomains (BRDs) and extra-terminal (BET) family proteins. On this basis, non-BET BRD is gradually becoming a research hot spot. BRDs are abundant in histone acetyltransferase (HAT)-associated activating transcription factors, and BRD-containing HATs have been linked to cancer, inflammation, and viral replication. Therefore, the development of BRD-containing HATs as chemical probes is useful for understanding the specific biological roles of BRDs in diseases and drug discovery. Several types of BRD-containing HATs, including CBP/P300, PCAF/GCN5, and TAF1, are discussed in this context in terms of their structures, functions, and small-molecule inhibitors. Additionally, progress in BRD inhibitors/chemical probes and proteolysis targeting chimeras in terms of drug design, biological activity, and disease application are summarized. These findings provide insights into the development of BRD inhibitors as potential drug candidates for various diseases.

Discovery of a Novel Bromodomain and Extra Terminal Domain (BET) Protein Inhibitor, I-BET282E, Suitable for Clinical Progression

The functions of the bromodomain and extra terminal (BET) family of proteins have been implicated in a wide range of diseases, particularly in the oncology and immuno-inflammatory areas, and several inhibitors are under investigation in the clinic. To mitigate the risk of attrition of these compounds due to structurally related toxicity findings, additional molecules from distinct chemical series were required. Here we describe the structure- and property-based optimization of the in vivo tool molecule I-BET151 toward I-BET282E, a molecule with properties suitable for progression into clinical studies.

Targeting the p300/CBP Axis in Lethal Prostate Cancer

Resistance to androgen receptor (AR) blockade in castration-resistant prostate cancer (CRPC) is associated with sustained AR signaling, including through alternative splicing of AR (AR-SV). Inhibitors of transcriptional coactivators that regulate AR activity, including the paralog histone acetyltransferase proteins p300 and CBP, are attractive therapeutic targets for lethal prostate cancer. Herein, we validate targeting p300/CBP as a therapeutic strategy for lethal prostate cancer and describe CCS1477, a novel small-molecule inhibitor of the p300/CBP conserved bromodomain. We show that CCS1477 inhibits cell proliferation in prostate cancer cell lines and decreases AR- and C-MYC-regulated gene expression. In AR-SV-driven models, CCS1477 has antitumor activity, regulating AR and C-MYC signaling. Early clinical studies suggest that CCS1477 modulates KLK3 blood levels and regulates CRPC biopsy biomarker expression. Overall, CCS1477 shows promise for the treatment of patients with advanced prostate cancer. SIGNIFICANCE: Treating CRPC remains challenging due to persistent AR signaling. Inhibiting transcriptional AR coactivators is an attractive therapeutic strategy. CCS1477, an inhibitor of p300/CBP, inhibits growth and AR activity in CRPC models, and can affect metastatic CRPC target expression in serial clinical biopsies.See related commentary by Rasool et al., p. 1011.This article is highlighted in the In This Issue feature, p. 995.

Current development of CBP/p300 inhibitors in the last decade

CBP/p300, functioning as histone acetyltransferases and transcriptional co-factors, represents an attractive target for various diseases, including malignant tumor. The development of small-molecule inhibitors targeting the bromodomain and HAT domains of CBP/p300 has aroused broad interests of medicinal chemist in expectation of providing new hope for anti-cancer treatment. In particular, the CBP/p300 bromodomain inhibitor CCS1477, identified by CellCentric, is currently undergone clinical evaluation for the treatment of haematological malignancies and prostate cancer. In this review, we depict the development of CBP/p300 inhibitors reported from 2010 to 2020 and particularly highlight their structure-activity relationships (SARs), binding modes, selectivity and pharmacological functions with the aim to facilitate rational design and development of CBP/p300 inhibitors.