Toppling the HAT to Treat Lethal Prostate Cancer

Targeting dependency on a paralog pair of CBP/p300 against de-repression of KREMEN2 in SMARCB1-deficient cancers

SMARCB1, a subunit of the SWI/SNF chromatin remodeling complex, is the causative gene of rhabdoid tumors and epithelioid sarcomas. Here, we identify a paralog pair of CBP and p300 as a synthetic lethal target in SMARCB1-deficient cancers by using a dual siRNA screening method based on the "simultaneous inhibition of a paralog pair" concept. Treatment with CBP/p300 dual inhibitors suppresses growth of cell lines and tumor xenografts derived from SMARCB1-deficient cells but not from SMARCB1-proficient cells. SMARCB1-containing SWI/SNF complexes localize with H3K27me3 and its methyltransferase EZH2 at the promotor region of the KREMEN2 locus, resulting in transcriptional downregulation of KREMEN2. By contrast, SMARCB1 deficiency leads to localization of H3K27ac, and recruitment of its acetyltransferases CBP and p300, at the KREMEN2 locus, resulting in transcriptional upregulation of KREMEN2, which cooperates with the SMARCA1 chromatin remodeling complex. Simultaneous inhibition of CBP/p300 leads to transcriptional downregulation of KREMEN2, followed by apoptosis induction via monomerization of KREMEN1 due to a failure to interact with KREMEN2, which suppresses anti-apoptotic signaling pathways. Taken together, our findings indicate that simultaneous inhibitors of CBP/p300 could be promising therapeutic agents for SMARCB1-deficient cancers.

Design, synthesis and biological evaluation of new RNF126-based p300/CBP degraders

Histone acetyltransferase CREB-binding protein (CBP) and its homologous protein p300 are key transcriptional activators that can activate oncogene transcription, which present promising targets for cancer therapy. Here, we designed and synthesized a series of p300/CBP targeted low molecular weight PROTACs by assembling the covalent ligand of RNF126 E3 ubiquitin ligase and the bromodomain ligand of the p300/CBP. The optimal molecule A8 could effectively degrade p300 and CBP through the ubiquitin-proteasome system in time- and concentration-dependent manners, with half-maximal degradation (DC50) concentrations of 208.35/454.35 nM and 82.24/79.45 nM for p300/CBP in MV4-11 and Molm13 cell lines after 72 h of treatment. And the degradation of p300/CBP by A8 is dependent on the ubiquitin-proteasome pathway and its simultaneous interactions with the target proteins and RNF126. A8 exhibits good antiproliferative activity in a series of p300/CBP-dependent cancer cells. It could transcriptionally inhibit the expression of c-Myc, induce cell cycle arrest in the G0/G1 phase and apoptosis in MV4-11 cells. This study thus provided us a new chemotype for the development of drug-like PROTACs targeting p300/CBP, which is expected to be applied in cancer therapy.

Characteristics of anticancer activity of CBP/p300 inhibitors - Features of their classes, intracellular targets and future perspectives of their application in cancer treatment

Due to the contribution of highly homologous acetyltransferases CBP and p300 to transcription elevation of oncogenes and other cancer promoting factors, these enzymes emerge as possible epigenetic targets of anticancer therapy. Extensive efforts in search for small molecule inhibitors led to development of compounds targeting histone acetyltransferase catalytic domain or chromatin-interacting bromodomain of CBP/p300, as well as dual BET and CBP/p300 inhibitors. The promising anticancer efficacy in in vitro and mice models led CCS1477 and NEO2734 to clinical trials. However, none of the described inhibitors is perfectly specific to CBP/p300 since they share similarity of a key functional domains with other enzymes, which are critically associated with cancer progression and their antagonists demonstrate remarkable clinical efficacy in cancer therapy. Therefore, we revise the possible and clinically relevant off-targets of CBP/p300 inhibitors that can be blocked simultaneously with CBP/p300 thereby improving the anticancer potential of CBP/p300 inhibitors and pharmacokinetic predicting data such as absorption, distribution, metabolism, excretion (ADME) and toxicity.

Discovery of CBPD-409 as a Highly Potent, Selective, and Orally Efficacious CBP/p300 PROTAC Degrader for the Treatment of Advanced Prostate Cancer

CBP/p300 are critical transcriptional coactivators of the androgen receptor (AR) and are promising cancer therapeutic targets. Herein, we report the discovery of highly potent, selective, and orally bioavailable CBP/p300 degraders using the PROTAC technology with CBPD-409 being the most promising compound. CBPD-409 induces robust CBP/p300 degradation with DC50 0.2-0.4 nM and displays strong antiproliferative effects with IC50 1.2-2.0 nM in the VCaP, LNCaP, and 22Rv1 AR+ prostate cancer cell lines. It has a favorable pharmacokinetic profile and achieves 50% of oral bioavailability in mice. A single oral administration of CBPD-409 at 1 mg/kg achieves >95% depletion of CBP/p300 proteins in the VCaP tumor tissue. CBPD-409 exhibits strong tumor growth inhibition and is much more potent and efficacious than two CBP/p300 inhibitors CCS1477 and GNE-049 and the AR antagonist Enzalutamide. CBPD-409 is a promising CBP/p300 degrader for further extensive evaluations for the treatment of advanced prostate cancer and other types of human cancers.

Protein lysine acetyltransferase CBP/p300: A promising target for small molecules in cancer treatment

CBP and p300 are homologous proteins exhibiting remarkable structural and functional similarity. Both proteins function as acetyltransferase and coactivator, underscoring their significant roles in cellular processes. The function of histone acetyltransferases is to facilitate the release of DNA from nucleosomes and act as transcriptional co-activators to promote gene transcription. Transcription factors recruit CBP/p300 by co-condensation and induce transcriptional bursting. Disruption of CBP or p300 functions is associated with different diseases, especially cancer, which can result from either loss of function or gain of function. CBP and p300 are multidomain proteins containing HAT (histone acetyltransferase) and BRD (bromodomain) domains, which perform acetyltransferase activity and maintenance of HAT signaling, respectively. Inhibitors targeting HAT and BRD have been explored for decades, and some BRD inhibitors have been evaluated in clinical trials for treating hematologic malignancies or advanced solid tumors. Here, we review the development and application of CBP/p300 inhibitors. Several inhibitors have been evaluated in vivo, exhibiting notable potency but limited selectivity. Exploring these inhibitors emphasizes the promise of targeting CBP and p300 with small molecules in cancer therapy.