Inhibition of p53 DNA binding by a small molecule protects mice from radiation toxicity.

Transcription factors are attractive therapeutic targets that are considered non-druggable because they do not have binding sites for small drug-like ligands. We established a cell-free high-throughput screening assay to search for small molecule inhibitors of DNA binding by transcription factors. A screen was performed using p53 as a target, resulting in the identification of NSC194598 that inhibits p53 sequence-specific DNA binding in vitro (IC50 = 180 nM) and in vivo. NSC194598 selectively inhibited DNA binding by p53 and homologs p63/p73, but did not affect E2F1, TCF1, and c-Myc. Treatment of cells with NSC194598 alone paradoxically led to p53 accumulation and modest increase of transcriptional output owing to disruption of the MDM2-negative feedback loop. When p53 was stabilized and activated by irradiation or chemotherapy drug treatment, NSC194598 inhibited p53 DNA binding and induction of target genes. A single dose of NSC194598 increased the survival of mice after irradiation. The results suggest DNA binding by p53 can be targeted using small molecules to reduce acute toxicity to normal tissues by radiation and chemotherapy.

Targeting the BRD4-HOXB13 Coregulated Transcriptional Networks with Bromodomain-Kinase Inhibitors to Suppress Metastatic Castration-Resistant Prostate Cancer.

Resistance to androgen receptor (AR) antagonists is a significant problem in the treatment of castration-resistant prostate cancers (CRPC). Identification of the mechanisms by which CRPCs evade androgen deprivation therapies (ADT) is critical to develop novel therapeutics. We uncovered that CRPCs rely on BRD4-HOXB13 epigenetic reprogramming for androgen-independent cell proliferation. Mechanistically, BRD4, a member of the BET bromodomain family, epigenetically promotes HOXB13 expression. Consistently, genetic disruption of HOXB13 or pharmacological suppression of its mRNA and protein expression by the novel dual-activity BET bromodomain-kinase inhibitors directly correlates with rapid induction of apoptosis, potent inhibition of tumor cell proliferation and cell migration, and suppression of CRPC growth. Integrative analysis revealed that the BRD4-HOXB13 transcriptome comprises a proliferative gene network implicated in cell-cycle progression, nucleotide metabolism, and chromatin assembly. Notably, although the core HOXB13 target genes responsive to BET inhibitors (HOTBIN10) are overexpressed in metastatic cases, in ADT-treated CRPC cell lines and patient-derived circulating tumor cells (CTC) they are insensitive to AR depletion or blockade. Among the HOTBIN10 genes, AURKB and MELK expression correlates with HOXB13 expression in CTCs of mCRPC patients who did not respond to abiraterone (ABR), suggesting that AURKB inhibitors could be used additionally against high-risk HOXB13-positive metastatic prostate cancers. Combined, our study demonstrates that BRD4-HOXB13-HOTBIN10 regulatory circuit maintains the malignant state of CRPCs and identifies a core proproliferative network driving ADT resistance that is targetable with potent dual-activity bromodomain-kinase inhibitors.

Design, Synthesis, and Characterization of a Fluorescence Polarization Pan-BET Bromodomain Probe.

Several chemical probes have been developed for use in fluorescence polarization screening assays to aid in drug discovery for the bromodomain and extra-terminal domain (BET) proteins. However, few of those have been characterized in the literature. We have designed, synthesized, and thoroughly characterized a novel fluorescence polarization pan-BET chemical probe suitable for high-throughput screening, structure-activity relationships, and hit-to-lead potency and selectivity assays to identify and characterize BET bromodomain inhibitors.

Advances of small molecule targeting of kinases.

Reversible protein phosphorylation regulates virtually all aspects of life in the cell. As a result, dysregulation of protein kinases, the enzymes responsible for transferring phosphate groups from ATP to proteins, are often the cause or consequence of many human diseases including cancer. Almost three dozen protein kinase inhibitors (PKIs) have been approved for clinical applications since 1995, the vast majority of them for the treatment of cancer. According to the NCI, there are more than 100 types of cancer. However, FDA-approved PKIs only target 14 of them. Importantly, of the more than 500 protein kinases encoded by the human genome, only 22 are targets for currently approved PKIs, suggesting that the reservoir of PKIs still has room to grow significantly. In this short review we will discuss the most recent advances, challenges, and alternatives to currently adopted strategies in this burgeoning field.

An Advanced Tool To Interrogate BRD9.

Selective inhibitors of bromodomain-containing protein 9 (BRD9) may have therapeutic potential in the treatment of human malignancies and inflammatory diseases. A selective small molecule inhibitor that is well tolerated and has proper pharmacokinetic properties is required to explore the function of BRD9 in diseases. BI-9564 (2) is a cell permeable and noncytotoxic BRD9 inhibitor provided to the scientific community to explore BRD9 biology and determine its potential as a drug target.