Bromodomain Drug Discovery - the Past, the Present, and the Future

Cancer plasticity in therapy resistance: Mechanisms and novel strategies

Therapy resistance poses a significant obstacle to effective cancer treatment. Recent insights into cell plasticity as a new paradigm for understanding resistance to treatment: as cancer progresses, cancer cells experience phenotypic and molecular alterations, corporately known as cell plasticity. These alterations are caused by microenvironment factors, stochastic genetic and epigenetic changes, and/or selective pressure engendered by treatment, resulting in tumor heterogeneity and therapy resistance. Increasing evidence suggests that cancer cells display remarkable intrinsic plasticity and reversibly adapt to dynamic microenvironment conditions. Dynamic interactions between cell states and with the surrounding microenvironment form a flexible tumor ecosystem, which is able to quickly adapt to external pressure, especially treatment. Here, this review delineates the formation of cancer cell plasticity (CCP) as well as its manipulation of cancer escape from treatment. Furthermore, the intrinsic and extrinsic mechanisms driving CCP that promote the development of therapy resistance is summarized. Novel treatment strategies, e.g., inhibiting or reversing CCP is also proposed. Moreover, the review discusses the multiple lines of ongoing clinical trials globally aimed at ameliorating therapy resistance. Such advances provide directions for the development of new treatment modalities and combination therapies against CCP in the context of therapy resistance.

Cancer cell plasticity: from cellular, molecular, and genetic mechanisms to tumor heterogeneity and drug resistance

Cancer is a complex disease displaying a variety of cell states and phenotypes. This diversity, known as cancer cell plasticity, confers cancer cells the ability to change in response to their environment, leading to increased tumor diversity and drug resistance. This review explores the intricate landscape of cancer cell plasticity, offering a deep dive into the cellular, molecular, and genetic mechanisms that underlie this phenomenon. Cancer cell plasticity is intertwined with processes such as epithelial-mesenchymal transition and the acquisition of stem cell-like features. These processes are pivotal in the development and progression of tumors, contributing to the multifaceted nature of cancer and the challenges associated with its treatment. Despite significant advancements in targeted therapies, cancer cell adaptability and subsequent therapy-induced resistance remain persistent obstacles in achieving consistent, successful cancer treatment outcomes. Our review delves into the array of mechanisms cancer cells exploit to maintain plasticity, including epigenetic modifications, alterations in signaling pathways, and environmental interactions. We discuss strategies to counteract cancer cell plasticity, such as targeting specific cellular pathways and employing combination therapies. These strategies promise to enhance the efficacy of cancer treatments and mitigate therapy resistance. In conclusion, this review offers a holistic, detailed exploration of cancer cell plasticity, aiming to bolster the understanding and approach toward tackling the challenges posed by tumor heterogeneity and drug resistance. As articulated in this review, the delineation of cellular, molecular, and genetic mechanisms underlying tumor heterogeneity and drug resistance seeks to contribute substantially to the progress in cancer therapeutics and the advancement of precision medicine, ultimately enhancing the prospects for effective cancer treatment and patient outcomes.

Combination Therapy with a TLR7 Agonist and a BRD4 Inhibitor Suppresses Tumor Growth via Enhanced Immunomodulation

JQ-1 is a typical BRD4 inhibitor with the ability to directly fight tumor cells and evoke antitumor immunity via reducing the expression of PD-L1. However, problems arise with the development of JQ-1 in clinical trials, such as marked lymphoid and hematopoietic toxicity, leading to the investigation of combination therapy. SZU-101 is a TLR7 agonist designed and synthesized by our group with potent immunostimulatory activity. Therefore, we hypothesized that combination therapy of SZU-101 and JQ-1 would target innate immunity and adaptive immunity simultaneously, to achieve a better antitumor efficacy than monotherapy. In this study, the repressive effects of the combination administration on tumor growth and metastasis were demonstrated in both murine breast cancer and melanoma models. In 4T1 tumor-bearing mice, i.t. treatment with SZU-101 in combination with i.p. treatment with JQ-1 suppressed the growth of tumors at both injected and uninjected sites. Combination therapy increased M1/M2 ratio in TAMs, decreased PD-L1 expression and promoted the recruitment of activated CD8+ T cells in the TME. In summary, the improved therapeutic efficacy of the novel combination therapy appears to be feasible for the treatment of a diversity of cancers.

CAFs Homologous Biomimetic Liposome Bearing BET Inhibitor and Pirfenidone Synergistically Promoting Antitumor Efficacy in Pancreatic Ductal Adenocarcinoma

BRD4 is a member of the BET protein family involved in chromatin remodeling and transcriptional regulation. Several BET inhibitors (BETi) have entered clinical trials, demonstrating potential in inducing cancer cell apoptosis and tumor regression. However, resistance to BETi is common in solid tumors. In pancreatic cancer, it is found that cancer-associated fibroblasts (CAFs) in the tumor microenvironment reduce the BET inhibitor JQ1 sensitivity by inducing BRD4 expression. Moreover, CAFs play a crucial role in the formation of a dense stromal barrier. Therefore, targeting CAFs in the tumor microenvironment of pancreatic cancer not only enhances cancer cells sensitivity to JQ1 but also increases drug perfusion and improves oxygen supply, thus reducing glycolysis and limiting energy supply. To address this challenge, a homologous targeting mechanism utilizing activated fibroblast membrane-coated liposomes is proposed for specific drug precise target to CAFs-rich pancreatic cancer. Additionally, TAT peptides enable liposomes penetration, delivering PFD for targeted anti-fibrotic therapy, reducing extracellular matrix generation and glycolysis, and enhancing JQ1 delivery and sensitivity. In conclusion, the findings indicate the tremendous potential of this CAFs-targeting liposomal delivery system in pancreatic cancer.

Hypoxia-cleavable and specific targeted nanomedicine delivers epigenetic drugs for enhanced treatment of breast cancer and bone metastasis

Breast cancer bone metastasis has become a common cancer type that still lacks an effective treatment method. Although epigenetic drugs have demonstrated promise in cancer therapy, their nontargeted accumulation and drug resistance remain nonnegligible limiting factors. Herein, we first found that icaritin had a strong synergistic effect with an epigenetic drug (JQ1) in the suppression of breast cancer, which could help to relieve drug resistance to JQ1. To improve tumor-targeted efficacy, we developed a hypoxia-cleavable, RGD peptide-modified poly(D,L-lactide-co-glycolide) (PLGA) nanoparticle (termed ARNP) for the targeted delivery of JQ1 and icaritin. The decoration of long cleavable PEG chains can shield RGD peptides during blood circulation and reduce cellular uptake at nonspecific sites. ARNP actively targets breast cancer cells via an RGD-αvβ3 integrin interaction after PEG chain cleavage by responding to hypoxic tumor microenvironment. In vitro and in vivo assays revealed that ARNP exhibited good biodistribution and effectively suppressed primary tumor and bone metastasis. Meanwhile, ARNP could alleviate bone erosion to a certain extent. Furthermore, ARNP significantly inhibited pulmonary metastasis secondary to bone metastasis. The present study suggests that ARNP has great promise in the treatment of breast cancer and bone metastasis due to its simple and practical potential.

Molecular Structure, Spectral Analysis, Molecular Docking and Physicochemical Studies of 3-Bromo-2-hydroxypyridine Monomer and Dimer as Bromodomain Inhibitors

In this paper, both methods (DFT and HF) were used in a theoretical investigation of 3-bromo-2-Hydroxypyridine (3-Br-2HyP) molecules where the molecular structures of the title compound have been optimized. Molecular electrostatic potential (MEP) was computed using the B3LYP/6-311++G(d,p) level of theory. The time-dependent density functional theory (TD-DFT) approach was used to simulate the HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital) on the one hand to achieve the frontier orbital gap and on the other hand to calculate the UV–visible spectrum of the compound in gas phase and for different solvents. In addition, electronic localization function and Fukui functions were carried out. Intermolecular interactions were discussed by the topological AIM (atoms in molecules) approach. The thermodynamic functions have been reported with the help of spectroscopic data using statistical methods revealing the correlations between these functions and temperature. To describe the non-covalent interactions, the reduced density gradient (RDG) analysis is performed. To study the biological activity of the compound of the molecule, molecular docking studies were executed on the active sites of BRD2 inhibitors and to explore the hydrogen bond interaction, minimum binding energies with targeted receptors such as PDB ID: 5IBN, 3U5K, 6CD5 were calculated.

Potent bromodomain and extraterminal domain inhibitor JAB-8263 suppresses MYC expression and exerts anti-tumor activity in colorectal cancer models

BACKGROUND

The overexpression of the MYC gene plays an important role in the occurrence, development and evolution of colorectal cancer (CRC). Bromodomain and extraterminal domain (BET) inhibitors can decrease the function BET by recognizing acetylated lysine residues, thereby downregulating the expression of MYC.

AIM

To investigate the inhibitory effect and mechanism of a BET inhibitor on CRC cells.

METHODS

The effect of the BET inhibitor JAB-8263 on the proliferation of various CRC cell lines was studied by CellTiter-Glo method and colony formation assay. The effect of JAB-8263 on the cell cycle and apoptosis of CRC cells was studied by propidium iodide staining and Annexin V/propidium iodide flow assay, respectively. The effect of JAB-8263 on the expression of c-MYC, p21 and p16 in CRC cells was detected by western blotting assay. The anti-tumor effect of JAB-8263 on CRC cells in vivo and evaluation of the safety of the compound was predicted by constructing a CRC cell animal tumor model.

RESULTS

JAB-8263 dose-dependently suppressed CRC cell proliferation and colony formation in vitro. The MYC signaling pathway was dose-dependently inhibited by JAB-8263 in human CRC cell lines. JAB-8263 dose-dependently induced cell cycle arrest and apoptosis in the MC38 cell line. SW837 xenograft model was treated with JAB-8263 (0.3 mg/kg for 29 d), and the average tumor volume was significantly decreased compared to the vehicle control group (P < 0.001). The MC38 syngeneic murine model was treated with JAB-8263 (0.2 mg/kg for 29 d), and the average tumor volume was significantly decreased compared to the vehicle control group (P = 0.003).

CONCLUSION

BET could be a potential effective drug target for suppressing CRC growth, and the BET inhibitor JAB-8263 can effectively suppress c-MYC expression and exert anti-tumor activity in CRC models.

The Saccharomyces cerevisiae Yta7 ATPase hexamer contains a unique bromodomain tier that functions in nucleosome disassembly

The Saccharomyces cerevisiae Yta7 is a chromatin remodeler harboring a histone-interacting bromodomain (BRD) and two AAA+ modules. It is not well understood how Yta7 recognizes the histone H3 tail to promote nucleosome disassembly for DNA replication or RNA transcription. By cryo-EM analysis, here we show that Yta7 assembles a three-tiered hexamer with a top BRD tier, a middle AAA1 tier, and a bottom AAA2 tier. Unexpectedly, the Yta7 BRD stabilizes a four-stranded β-helix, termed BRD-interacting motif (BIM), of the largely disordered N-terminal region. The BIM motif is unique to the baker's yeast, and we show both BRD and BIM contribute to nucleosome recognition. We found that Yta7 binds both acetylated and nonacetylated H3 peptides but with a higher affinity for the unmodified peptide. This property is consistent with the absence of key residues of canonical BRDs involved in acetylated peptide recognition and the role of Yta7 in general nucleosome remodeling. Interestingly, the BRD tier exists in a spiral and a flat-ring form on top of the Yta7 AAA+ hexamer. The spiral is likely in a nucleosome-searching mode because the bottom BRD blocks the entry to the AAA+ chamber. The flat ring may be in a nucleosome disassembly state because the entry is unblocked and the H3 peptide has entered the AAA+ chamber and is stabilized by the AAA1 pore loops 1 and 2. Indeed, we show that the BRD tier is a flat ring when bound to the nucleosome. Overall, our study sheds light on the nucleosome disassembly by Yta7.

Design, synthesis, and biological evaluation of BRD4 degraders

Epigenetic proteins are one of the important targets in the current research fields of cancer therapy. A family of bromodomain-containing (BRD) and extra terminal domain (BET) proteins act as epigenetic readers to regulate the expression of key oncogenes and anti-apoptotic proteins. Recently, although BET degraders based on PROTAC technology have achieved significant antitumor effects, the lack of selectivity for BET protein degradation has not been fully addressed. Herein, a series of small molecule BRD4 PROTACs were designed and synthesized. Most of the degraders were effective in inhibiting MM.1S and MV-4-11 cell lines, especially in MV-4-11. Among them, degrader 8b could induce the degradation of BRD4 and exhibited a time- and concentration-dependent depletion manner and there was a significant depletion of BRD4, laying a foundation for effectively treating leukemia and multiple myeloma. Moreover, 8b could also effectively prevent the activation of MRC5 cells by inducing the degradation of BRD4 protein, which preliminarily proves that the BRD4 degrader based on the PROTAC concept has great potential for the treatment of pulmonary fibrosis. Taken together, these findings laid a foundation for BRD4 degraders as an effective strategy for treating related diseases.

Comprehensive analysis of the prognosis and immune infiltrates for the BET protein family reveals the significance of BRD4 in glioblastoma multiforme

Background: Glioblastoma multiforme (GBM) is the most common and invasive primary central nervous system tumor. The prognosis after surgery, radiation and chemotherapy is very poor. Bromodomain (BRD) proteins have been identified in oncogenic rearrangements, and play a key role in the development of multiple cancers. However, the relationship between BET proteins and prognosis of GBM are still worth exploring, and the distinct functions of BET proteins and tumor immunology in GBM have not been fully elucidated. Therefore, it is particularly important to develop effective biomarkers to predict the prognosis of GBM patients. Methods: Metascape, David, Kaplan-Meier Plotter, Oncomine, GEPIA, TCGA, TIMER, and LinkedOmics databases were used to assess the expression and prognosis for BET proteins in GBM. ROC analysis of risk model was established to identify the correlation between BET genes and overall survival in GBM patients. TIMER and GEPIA databases were used to comprehensively investigate the correlation between BET genes and tumor immune infiltration cells. Moreover, the image of immunohistochemistry staining of BET proteins in normal tissue and tumor tissue were retrived from the HPA database. In addition, differential analysis and pathway enrichment analysis of BRD4 gene expression profile were also carried out. Finally, immune-fluorescence and Western blot were used to clarify the expression of BRD4 in GBM cells. Results: Bioinformatics analysis showed that the expression levels of BET genes in GBM may play an important role in oncogenesis. Specifically, bioinformatic and immunohistochemistry analysis showed that BRD4 protein was more highly expressed in tumor tissues than that in normal tissues. The high expression of BRD4 was associated with poor prognosis in GBM. The expression of BET genes were closely related to the immune checkpoint in GBM. The correlation effect of BRD4 was significantly higher than other BET genes, which represented negative correlation with immune checkpoint. The expression of BRD4 was positively associated with tumor purity, and negatively associated with immune infiltration abundance of macrophage, neutrophil and CD8⁺ T-cell, respectively. Cox analysis showed that the model had good survival prediction and prognosis discrimination ability. In addition, the expression levels of BRD4 protein was significantly higher in U-251 MG cells than that in normal cells, which was consistent with the results of bioinformatics data. Conclusion: This study implied that BRD4 could be hopeful prognostic biomarker in GBM. The increased expression of BRD4 may act as a molecular marker to identify GBM patients with high-risk subgroups. BRD4 may be a valuable prognostic biomarker, and a potential target of precision therapy against GBM.

PROTACs for BRDs proteins in cancer therapy: a review

BRDs proteins that recognise chromatin acetylation regulate gene expression, are epigenetic readers and master transcription coactivators. BRDs proteins are now emerging as targets for new therapeutic development. Blocking the function of any of BRDs proteins can be a control agent for diseases, such as cancer. Traditional drugs like enzyme inhibitors and protein–protein inhibitors have many limitations. The therapeutic efficacy of them remains to be proven. Recently, Proteolysis-Targeting Chimaeras (PROTACs) have become an advanced tool in therapeutic intervention as they remove disease-causing proteins. Extremely potent and efficacious small-molecule PROTACs of the BRDs proteins, based on available, potent, and selective BRDs inhibitors, have been reported. This review presents a comprehensive overview of the development of PROTACs for BRDs proteins regulation in cancer, and the chances and challenges associated with this area are also highlighted.

A positron emission tomography imaging probe selectively targeting the BD1 bromodomain and extra-terminal domain

The two tandem bromodomains of BET (bromodomain and extra-terminal domain) proteins (BD1 and BD2) may play distinct and critical roles in neurological diseases. To better understand the underlying mechanisms of the BD1 bromodomain and facilitate brain permeable domain-selective inhibitor development, we describe here the development of the first BET BD1 positron emission tomography (PET) radioligand [¹¹C]1a. Compound 1a was tested to possess potent binding affinities and good selectivity (>20-fold over BD2) for BD1 bromodomains of BRD2 (K_d = 25 nM), BRD3 (K_d = 24 nM), and BRD4 (K_d = 19 nM). Physicochemical characterization of 1a indicated the brain permeability and specific binding. [¹¹C]1a was radiosynthesized in a good radiochemical yield (RCY: 25-30%) and molar activity (258 GBq μmol^-1). The PET imaging studies of [¹¹C]1a in mice showed moderate brain uptake (with peak SUV = 0.7) and binding specificity. Furthermore, [¹¹C]1a demonstrated translational potential in the non-human primate (NHP) PET imaging study, which sets the stage for clinical translation.

The prognostic significance of bromodomain protein 4 expression in solid tumor patients: A meta-analysis

BACKGROUND

Cancer is a leading cause of death worldwide. At present, several inhibitors of bromodomain protein 4 have shown promising anti-tumor responses in clinical trials. Numerous studies have reported the value of bromodomain protein 4 expression in predicting the prognosis of patients with cancers, but their conclusions remain controversial. Therefore, we conducted a meta-analysis to explore the association between bromodomain protein 4 and patient prognosis with the aim to provide new directions for the development of strategies for targeted cancer therapy.

METHODS

The meta-analysis was registered in the International Prospective Register of Systematic Reviews (https://www.crd.york.ac.uk/prospero/; Registration No. CRD42020184948) and followed the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) statement. PubMed Central, PubMed, Cochrane Library and Embase were thoroughly searched to identify eligible studies published through March 31, 2021. Odds ratios with 95% confidence intervals were calculated to demonstrate the relationship between bromodomain protein 4 expression and clinicopathological features. We computed pooled estimated hazard ratios with 95% confidence intervals using Stata 12.0 software to clarify the relationship between bromodomain protein 4 expression and overall survival of various cancers. A quality assessment of the eligible articles was performed based on the Newcastle-Ottawa scale.

RESULTS

A total of 974 patients from 10 studies were enrolled in the meta-analysis. Our results revealed that compared to low bromodomain protein 4 expression, high bromodomain protein 4 expression in cancer tissues was significantly associated with lymph node metastasis (Odds ratio = 3.59, 95% confidence interval: 2.62-4.91), distant metastasis (Odds ratio = 4.22, 95% confidence interval: 2.40-7.45), advanced TNM stage (III+IV vs. I+II: Odds ratio = 3.23, 95% confidence interval: 1.29-8.08), and poorly differentiated tumors (Odds ratio = 1.87, 95% confidence interval: 1.33-2.63). In addition, an elevated expression of bromodomain protein 4 tended to shorten survival time (Hazard ratio = 2.23, 95% confidence interval: 1.62-3.07). The subgroup analysis results showed that bromodomain protein 4 upregulation was related to poor prognosis in patients with digestive system cancers (Hazard ratio = 2.54, 95% confidence interval: 1.85-3.50).

CONCLUSION

This meta-analysis indicated that bromodomain protein 4 may serve as a promising prognostic biomarker for cancers and a direct effective cancer treatment target.

Targeting Bromodomain-Selective Inhibitors of BET Proteins in Drug Discovery and Development

Blocking the interactions between bromodomain and extraterminal (BET) proteins and acetylated lysines of histones by small molecules has important implications for the treatment of cancers and other diseases. Many pan-BET inhibitors have shown satisfactory results in clinical trials, but their potential for poor tolerability and toxicity persist. However, recently reported studies illustrate that some BET bromodomain (BET-BD1 or BET-BD2)-selective inhibitors have advantage over pan-inhibitors, including reduced toxicity concerns. Furthermore, some selective BET inhibitors have similar or even better therapeutic efficacy in inflammatory diseases or cancers. Therefore, the development of selective BET inhibitors has become a hot spot for medicinal chemists. Here, we summarize the known selective BET-BD1 and BET-BD2 inhibitors and review the methods for enhancing the selectivity and potency of these inhibitors based on their different modes of interactions with BET-BD1 or BET-BD2. Finally, we discuss prospective strategies that selectively target the bromodomains of BET proteins.

Epigenomic and enhancer dysregulation in uterine leiomyomas

BACKGROUND

Uterine leiomyomas, also known as uterine fibroids or myomas, are the most common benign gynecological tumors and are found in women of reproductive and postmenopausal age. There is an exceptionally high prevalence of this tumor in women by the age of 50 years. Black women are particularly affected, with an increased incidence, earlier age of onset, larger and faster growing fibroids and greater severity of symptoms as compared to White women. Although advances in identifying genetic and environmental factors to delineate these fibroids have already been made, only recently has the role of epigenomics in the pathogenesis of this disease been considered.

OBJECTIVE AND RATIONALE

Over recent years, studies have identified multiple epigenomic aberrations that may contribute to leiomyoma development and growth. This review will focus on the most recent discoveries in three categories of epigenomic changes found in uterine fibroids, namely aberrant DNA methylation, histone tail modifications and histone variant exchange, and their translation into altered target gene architecture and transcriptional outcome. The findings demonstrating how the altered 3D shape of the enhancer can regulate gene expression from millions of base pairs away will be discussed. Additionally, translational implications of these discoveries and potential roadblocks in leiomyoma treatment will be addressed.

SEARCH METHODS

A comprehensive PubMed search was performed to identify published articles containing keywords relevant to the focus of the review, such as: uterine leiomyoma, uterine fibroids, epigenetic alterations, epigenomics, stem cells, chromatin modifications, extracellular matrix [ECM] organization, DNA methylation, enhancer, histone post-translational modifications and dysregulated gene expression. Articles until September 2021 were explored and evaluated to identify relevant updates in the field. Most of the articles focused on in the discussion were published between 2015 and 2021, although some key discoveries made before 2015 were included for background information and foundational purposes. We apologize to the authors whose work was not included because of space restrictions or inadvertent omission.

OUTCOMES

Chemical alterations to the DNA structure and of nucleosomal histones, without changing the underlying DNA sequence, have now been implicated in the phenotypic manifestation of uterine leiomyomas. Genome-wide DNA methylation analysis has revealed subsets of either suppressed or overexpressed genes accompanied by aberrant promoter methylation. Furthermore, differential promoter access resulting from altered 3D chromatin structure and histone modifications plays a role in regulating transcription of key genes thought to be involved in leiomyoma etiology. The dysregulated genes function in tumor suppression, apoptosis, angiogenesis, ECM formation, a variety of cancer-related signaling pathways and stem cell differentiation. Aberrant DNA methylation or histone modification is also observed in altering enhancer architecture, which leads to changes in enhancer-promoter contact strength, producing novel explanations for the overexpression of high mobility group AT-hook 2 and gene dysregulation found in mediator complex subunit 12 mutant fibroids. While many molecular mechanisms and epigenomic features have been investigated, the basis for the racial disparity observed among those in the Black population remains unclear.

WIDER IMPLICATIONS

A comprehensive understanding of the exact pathogenesis of uterine leiomyoma is lacking and requires attention as it can provide clues for prevention and viable non-surgical treatment. These findings will widen our knowledge of the role epigenomics plays in the mechanisms related to uterine leiomyoma development and highlight novel approaches for the prevention and identification of epigenome targets for long-term non-invasive treatment options of this significantly common disease.

Recent Developments in Targeting Bromodomain and Extra Terminal Domain Proteins for Cancer Therapeutics

Abstract:

Bromodomain and extra-terminal domain (BET) proteins are a well-studied family of proteins associated with a variety of diseases including malignancy and chronic inflammation. Currently, numerous pan BET inhibitors have exhibited potent efficacy in several in vivo preclinical models and entered clinical trials, but have largely stalled due to their adverse events. Therefore, the development of new selective inhibitors and PROTACs (Proteolysis Targeting Chimeras) targeting BET is urgently needed. In the present review, we summarize the BET protein structure, the recent development of BET inhibitors, focusing mainly on BRD4-selective inhibitors and PROTAC degraders.

Evaluation of JQ1 Combined With Docetaxel for the Treatment of Prostate Cancer Cells in 2D- and 3D-Culture Systems

Introduction: Prostate cancer (PCa) is dependent on coupled androgen-androgen receptor (AR) signaling for growth and progression. Significant efforts have been made in this research field, as hormonal therapies have greatly improved the survival of patients with metastatic PCa (mPCa). The drug treatment agent JQ1, which potently abrogates bromodomain 4 (BRD4) localization to the AR target loci and therefore significantly impairs AR-mediated gene transcription, is a potent therapeutic option for patients with advanced PCa. In this study, we aimed to investigate the inhibitory effect of JQ1 combined with docetaxel on PCa cells in vitro for the first time. Furthermore, the 3D spheroid culture system was modeled to more accurately simulate the response of PCa cells to drugs.

Methods: We established and measured 3D LNCaP spheroids in vitro in order to evaluate the susceptibility of 2D- and 3D-cultured LNCaP cells exposed to the same anti-cancer drug.

Results: We demonstrated that JQ1 was an effective drug for promoting cell inhibition after docetaxel treatment in 2D- and 3D- cultured LNCaP cells. Inhibition of 3D cultured formation in the combined treatment group was significantly higher than that in docetaxel or JQ1 alone. Under the same conditions of drug solubility, the drug resistance of 3D spheroids was significantly higher than that of 2D cells. Moreover, dmax and lg volume were suitable parameters for LNCaP cells/spheroid size displaying and evaluating cell viability.

Conclusion: 3D cultured spheroids of PCa are an effective tool for studying PCa drug trials. JQ1 combined with docetaxel may be an effective treatment for advanced PCa. This combination therapy strategy deserves further evaluation in clinical trials.

Progress in the development of domain selective inhibitors of the bromo and extra terminal domain family (BET) proteins

Dysfunction of the bromo and extra terminal domain (BET) family proteins is associated with many human diseases, therefore the BET family proteins have been considered as promising targets for drug development. Numerous small molecular compounds targeting the N-terminal two tandem bromodomains BD1 and BD2 of the BET family proteins have been reported, and a number of them have been advanced into clinical trials. Most of the BET inhibitors entered clinical trials are pan-BET inhibitors which show poor selectivity among BET members and bind to the BD1 and BD2 of the BET family proteins with comparable binding affinities. In order to elucidate the distinct functions of BD1s and BD2s, many BD1 and BD2 selective BET inhibitors have also been developed. In this review, we summarized the recent progress in the development of BD1 and BD2 selective BET inhibitors, and provided the perspectives for future studies of BET inhibitors.

Protein degradation technology: a strategic paradigm shift in drug discovery

Targeting pathogenic proteins with small-molecule inhibitors (SMIs) has become a widely used strategy for treating malignant tumors. However, most intracellular proteins have been proven to be undruggable due to a lack of active sites, leading to a significant challenge in the design and development of SMIs. In recent years, the proteolysis-targeting chimeric technology and related emerging degradation technologies have provided additional approaches for targeting these undruggable proteins. These degradation technologies show a tendency of superiority over SMIs, including the rapid and continuous target consumption as well as the stronger pharmacological effects, being a hot topic in current research. This review mainly focuses on summarizing the development of protein degradation technologies in recent years. Their advantages, potential applications, and limitations are also discussed. We hope this review would shed light on the design, discovery, and clinical application of drugs associated with these degradation technologies.

Structural variation of protein-ligand complexes of the first bromodomain of BRD4

The bromodomain-containing protein 4 (BRD4), a member of the bromodomain and extra-terminal domain (BET) family, plays a key role in several diseases, especially cancers. With increased interest in BRD4 as a therapeutic target, many X-ray crystal structures of the protein in complex with small molecule inhibitors are publicly available over the recent decade. In this study, we use this structural information to investigate the conformations of the first bromodomain (BD1) of BRD4. Structural alignment of 297 BRD4-BD1 complexes shows a high level of similarity between the structures of BRD4-BD1, regardless of the bound ligand. We employ WONKA, a tool for detailed analyses of protein binding sites, to compare the active site of over 100 of these crystal structures. The positions of key binding site residues show a high level of conformational similarity, with the exception of Trp81. A focused analysis on the highly conserved water network in the binding site of BRD4-BD1 is performed to identify the positions of these water molecules across the crystal structures. The importance of the water network is illustrated using molecular docking and absolute free energy perturbation simulations. 82% of the ligand poses were better predicted when including water molecules as part of the receptor. Our analysis provides guidance for the design of new BRD4-BD1 inhibitors and the selection of the best structure of BRD4-BD1 to use in structure-based drug design, an important approach for faster and more cost-efficient lead discovery.

Fms-like tyrosine kinase 3-internal tandem duplications epigenetically activates checkpoint kinase 1 in acute myeloid leukemia cells

It is not clear how Fms-like tyrosine kinase 3-internal tandem duplications (FLT3-ITD) regulates checkpoint kinase 1 (CHK1) in acute myeloid leukemia (AML). In this study, we investigated the regulatory effect of FLT3-ITD on CHK1. Our results showed that CHK1 was highly expressed in FLT3-ITD positive AML. The overall survival rate and disease-free survival rate of AML patients with high CHK1 level were lower than those of patients with low CHK1 level. Mechanistically, FLT3-ITD recruited p300 to the CHK1 promoter and subsequently acetylated H3K27, thereby enhancing the transcription of CHK1. Interfering with the expression of CHK1 significantly inhibited the cell proliferation and induced cell apoptosis in FLT3-ITD positive MV4-11 cells. In addition, CHK1 knockdown promoted the sensitivity of MV4-11 cells to the epigenetic inhibitors JQ1 and C646. This study discovers a new therapeutic target for FLT3-ITD + AML and provided evidence for the combination of epigenetic inhibitors for AML treatment.

Synthesis and Characterization of a Positron Emission Tomography Imaging Probe Selectively Targeting the Second Bromodomain of Bromodomain Protein BRD4

Two tandem bromodomains (BD1 and BD2) of bromodomain and extraterminal domain (BET) family proteins have shown distinct roles in mediating gene transcription and expression. Inhibitors that interact with a specific bromodomain may contribute to a specific therapeutic potential with fewer side effects. However, little is known about this disease-related target. Positron emission tomography (PET) imaging could allow us to achieve in-depth knowledge of the BD2 bromodomain. Herein we describe the radiosynthesis and evaluation of [¹¹C]1 as a BRD4 BD2 bromodomain PET imaging radioligand. Our preliminary PET imaging results in rodents demonstrated that [¹¹C]1 had suitable biodistribution in peripheral organs and tissues. Further blocking studies indicated that [¹¹C]1 had good binding specificity toward the BD2 bromodomain. This study may pave the way for the development of a PET radioligand specifically targeting BD1/2 bromodomains as well as for the biological mechanism investigation of BD1/2 bromodomains.

MYC in T-cell acute lymphoblastic leukemia: functional implications and targeted strategies

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological cancer that frequently occurs in children and adolescents, which results from the transformation of immature T-cell progenitors. Aberrant cell growth and proliferation of T-ALL lymphoblasts are sustained by activation of strong oncogenic drivers. Mounting evidence highlights the critical role of the NOTCH1-MYC highway toward the initiation and progression of T-ALL. MYC has been emphasized as a primary NOTCH1 transcriptional target impinging in leukemia-initiating cell activity particularly responsible for disease onset and relapse. These findings lay a foundation of T-ALL as an ideal disease model for studying MYC-mediated cancer. The biology of MYC deregulation in T-ALL supports innovative strategies for therapeutic targeting of MYC. To summarize the relevant literature and data in recent years, we here provide a comprehensive overview of the functional importance of MYC in T-ALL development, and the molecular mechanisms underlying MYC deregulation in T-ALL. Finally, we illustrate the innovative MYC-targeted approaches that have been evaluated in pre-clinical models and shown significant efficacy. Given the complexity of T-ALL molecular pathogenesis, we propose that a combination of anti-MYC strategies with conventional chemotherapies or other targeted/immunotherapies may provide the most durable response, especially for those patients with relapsed and refractory T-ALL.

BET inhibitor suppresses migration of human hepatocellular carcinoma by inhibiting SMARCA4

Hepatocellular carcinoma (HCC) is one of the most prevalent and poorly responsive cancers worldwide. Bromodomain and extraterminal (BET) inhibitors, such as JQ1 and OTX-015, inhibit BET protein binding to acetylated residues in histones. However, the physiological mechanisms and regulatory processes of BET inhibition in HCC remain unclear. To explore BET inhibitors’ potential role in the molecular mechanisms underlying their anticancer effects in HCC, we analyzed BET inhibitor-treated HCC cells’ gene expression profiles with RNA-seq and bioinformatics analysis. BET inhibitor treatment significantly downregulated genes related to bromodomain-containing proteins 4 (BRD4), such as ACSL5, SLC38A5, and ICAM2. Importantly, some cell migration-related genes, including AOC3, CCR6, SSTR5, and SCL7A11, were significantly downregulated. Additionally, bioinformatics analysis using Ingenuity Knowledge Base Ingenuity Pathway Analysis (IPA) revealed that SMARCA4 regulated migration response molecules. Furthermore, knockdown of SMARCA4 gene expression by siRNA treatment significantly reduced cell migration and the expression of migration-related genes. In summary, our results indicated that BET inhibitor treatment in HCC cell lines reduces cell migration through the downregulation of SMARCA4.

PROTACs: Promising Approaches for Epigenetic Strategies to Overcome Drug Resistance

Epigenetic modulation of gene expression is essential for tissue-specific development and maintenance in mammalian cells. Disruption of epigenetic processes, and the subsequent alteration of gene functions, can result in inappropriate activation or inhibition of various cellular signaling pathways, leading to cancer. Recent advancements in the understanding of the role of epigenetics in cancer initiation and progression have uncovered functions for DNA methylation, histone modifications, nucleosome positioning, and non-coding RNAs. Epigenetic therapies have shown some promise for hematological malignancies, and a wide range of epigenetic-based drugs are undergoing clinical trials. However, in a dynamic survival strategy, cancer cells exploit their heterogeneous population which frequently results in the rapid acquisition of therapy resistance. Here, we describe novel approaches in drug discovery targeting the epigenome, highlighting recent advances the selective degradation of target proteins using Proteolysis Targeting Chimera (PROTAC) to address drug resistance.

Selective Targeting of Epigenetic Readers and Histone Deacetylases in Autoimmune and Inflammatory Diseases: Recent Advances and Future Perspectives

Histone deacetylases (HDACs) and bromodomain-containing proteins (BCPs) play a key role in chromatin remodeling. Based on their ability to regulate inducible gene expression in the context of inflammation and cancer, HDACs and BCPs have been the focus of drug discovery efforts, and numerous small-molecule inhibitors have been developed. However, dose-limiting toxicities of the first generation of inhibitors, which typically target multiple HDACs or BCPs, have limited translation to the clinic. Over the last decade, an increasing effort has been dedicated to designing class-, isoform-, or domain-specific HDAC or BCP inhibitors, as well as developing strategies for cell-specific targeted drug delivery. Selective inhibition of the epigenetic modulators is helping to elucidate the functions of individual epigenetic proteins and has the potential to yield better and safer therapeutic strategies. In accordance with this idea, several in vitro and in vivo studies have reported the ability of more selective HDAC/BCP inhibitors to recapitulate the beneficial effects of pan-inhibitors with less unwanted adverse events. In this review, we summarize the most recent advances with these strategies, discussing advantages and limitations of these approaches as well as some therapeutic perspectives, focusing on autoimmune and inflammatory diseases.

Major advances in targeted protein degradation: PROTACs, LYTACs, and MADTACs

Of late, targeted protein degradation (TPD) has surfaced as a novel and innovative chemical tool and therapeutic modality. By co-opting protein degradation pathways, TPD facilitates complete removal of the protein molecules from within or outside the cell. While the pioneering Proteolysis-Targeting Chimera (PROTAC) technology and molecular glues hijack the ubiquitin-proteasome system, newer modalities co-opt autophagy or the endo-lysosomal pathway. Using this mechanism, TPD is posited to largely expand the druggable space far beyond small-molecule inhibitors. In this review, we discuss the major advances in TPD, highlight our current understanding, and explore outstanding questions in the field.

FOSL1 promotes metastasis of head and neck squamous cell carcinoma through super-enhancer-driven transcription program

Previously, we discovered that FOSL1 facilitates the metastasis of head and neck squamous cell carcinoma (HNSCC) cancer stem cells in a spontaneous mouse model. However, the molecular mechanisms remained unclear. Here, we demonstrated that FOSL1 serves as the dominant activating protein 1 (AP1) family member and is significantly upregulated in HNSCC tumor tissues and correlated with metastasis of HNSCC. Mechanistically, FOSL1 exerts its function in promoting tumorigenicity and metastasis predominantly via selective association with Mediators to establish super-enhancers (SEs) at a cohort of cancer stemness and pro-metastatic genes, such as SNAI2 and FOSL1 itself. Depletion of FOSL1 led to disruption of SEs and expression inhibition of these key oncogenes, which resulted in the suppression of tumor initiation and metastasis. We also revealed that the abundance of FOSL1 is positively associated with the abundance of SNAI2 in HNSCC and the high expression levels of FOSL1 and SNAI2 are associated with short overall disease-free survival. Finally, the administration of the FOSL1 inhibitor SR11302 significantly suppressed tumor growth and lymph node metastasis of HNSCC in a patient-derived xenograft model. These findings indicate that FOSL1 is a master regulator that promotes the metastasis of HNSCC through a SE-driven transcription program that may represent an attractive target for therapeutic interventions.

Synergistic Therapy for Cervical Cancer by Codelivery of Cisplatin and JQ1 Inhibiting Plk1-Mutant Trp53 Axis

JQ1, a specific inhibitor of bromodomain-containing protein 4 (BRD4), could have great potential in the treatment of cervical cancer. However, its clinical application is limited by its short plasma half-life and limited antitumor efficacy. In this work, cisplatin (CDDP) was first utilized as the stabilizer and cooperator in the nanosystem (mPEG₁₁₃-b-P(Glu₁₀-co-Phe₁₀)-CDDP/JQ1, called PGP-CDDP/JQ1) to break through the efficiency limitation of JQ1. The PGP-CDDP/JQ1 had a combination index (CI) of 0.21, exerting a strong cytotoxic synergistic effect. In vivo experiments revealed that PGP-CDDP/JQ1 had a significantly higher tumor inhibition effect (tumor inhibition rate: 85% vs 14%) and plasma stability of JQ1 (area under the curve (AUC_0-∞): 335.97 vs 16.88 μg × h/mL) than free JQ1. The mechanism underling the synergism of JQ1 with CDDP in PGP-CDDP/JQ1 was uncovered to be inhibiting Plk1-mutant Trp53 axis. Thus, this study provides an optional method for improving the clinical application of JQ1 in cervical cancer.

Insights into interaction mechanism of inhibitors E3T, E3H and E3B with CREB binding protein by using molecular dynamics simulations and MM-GBSA calculations

CREB binding protein (CBP) and its paralog E1A binding protein (p300) are related to the development of inflammatory diseases, cancers and other diseases, and have been potential targets for the treatment of human diseases. In this work, interaction mechanism of three small molecules E3T, E3H, and E3B with CBP was investigated by employing molecular dynamics (MD) simulations, principal component analysis (PCA), and molecular mechanics/generalized born surface area (MM-GBSA) method. The results indicate that inhibitor bindings cause the changes of movement modes and structural flexibility of CBP, and van der Waals interactions mostly drive associations of inhibitors with CBP. In the meantime, the results based on inhibitor-residue interactions not only show that eight residues of CBP can strongly interact with E3T, E3H and E3B but also verify that the CH-CH, CH-π, and π-π interactions are responsible for vital contributions in associations of E3T, E3H and E3B with CBP. In addition, the H-O radial distribution functions (RDFs) were computed to assess the stability of hydrogen bonding interactions between inhibitors and CBP, and the obtained information identifies several key hydrogen bonds playing key roles in bindings of E3T, E3H and E3B to CBP. Potential new inhibitors have been proposed.

BET-Family Bromodomains Can Recognize Diacetylated Sequences from Transcription Factors Using a Conserved Mechanism

Almost all eukaryotic proteins receive diverse post-translational modifications (PTMs) that modulate protein activity. Many histone PTMs are well characterized, heavily influence gene regulation, and are often predictors of distinct transcriptional programs. Although our understanding of the histone PTM network has matured, much is yet to be understood about the roles of transcription factor (TF) PTMs, which might well represent a similarly complex and dynamic network of functional regulation. Members of the bromodomain and extra-terminal domain (BET) family of proteins recognize acetyllysine residues and relay the signals encoded by these modifications. Here, we have investigated the acetylation dependence of several functionally relevant BET-TF interactions in vitro using surface plasmon resonance, nuclear magnetic resonance, and X-ray crystallography. We show that motifs known to be acetylated in TFs E2F1 and MyoD1 can interact with all bromodomains of BRD2, BRD3, and BRD4. The interactions are dependent on diacetylation of the motifs and show a preference for the first BET bromodomain. Structural mapping of the interactions confirms a conserved mode of binding for the two TFs to the acetyllysine binding pocket of the BET bromodomains, mimicking that of other already established functionally important histone- and TF-BET interactions. We also examined a motif from the TF RelA that is known to be acetylated but were unable to observe any interaction, regardless of the acetylation state of the sequence. Our findings overall advance our understanding of BET-TF interactions and suggest a physical link between the important diacetylated motifs found in E2F1 and MyoD1 and the BET-family proteins.

JMJD6 Is a Druggable Oxygenase That Regulates AR-V7 Expression in Prostate Cancer

Endocrine resistance (EnR) in advanced prostate cancer is fatal. EnR can be mediated by androgen receptor (AR) splice variants, with AR splice variant 7 (AR-V7) arguably the most clinically important variant. In this study, we determined proteins key to generating AR-V7, validated our findings using clinical samples, and studied splicing regulatory mechanisms in prostate cancer models. Triangulation studies identified JMJD6 as a key regulator of AR-V7, as evidenced by its upregulation with in vitro EnR, its downregulation alongside AR-V7 by bromodomain inhibition, and its identification as a top hit of a targeted siRNA screen of spliceosome-related genes. JMJD6 protein levels increased (P < 0.001) with castration resistance and were associated with higher AR-V7 levels and shorter survival (P = 0.048). JMJD6 knockdown reduced prostate cancer cell growth, AR-V7 levels, and recruitment of U2AF65 to AR pre-mRNA. Mutagenesis studies suggested that JMJD6 activity is key to the generation of AR-V7, with the catalytic machinery residing within a druggable pocket. Taken together, these data highlight the relationship between JMJD6 and AR-V7 in advanced prostate cancer and support further evaluation of JMJD6 as a therapeutic target in this disease. SIGNIFICANCE: This study identifies JMJD6 as being critical for the generation of AR-V7 in prostate cancer, where it may serve as a tractable target for therapeutic intervention.

Update and Potential Opportunities in CBP [Cyclic Adenosine Monophosphate (cAMP) Response Element-Binding Protein (CREB)-Binding Protein] Research Using Computational Techniques

CBP [cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB)-binding protein] is one of the most researched proteins for its therapeutic function. Several studies have identified its vast functions and interactions with other transcription factors to initiate cellular signals of survival. In cancer and other diseases such as Alzheimer's, Rubinstein-taybi syndrome, and inflammatory diseases, CBP has been implicated and hence an attractive target in drug design and development. In this review, we explore the various computational techniques that have been used in CBP research, furthermore we identified computational gaps that could be explored to facilitate the development of highly therapeutic CBP inhibitors.

Bromodomain-containing-protein-4 and cyclin-dependent-kinase-9 inhibitors interact synergistically in vitro and combined treatment reduces post-traumatic osteoarthritis severity in mice

OBJECTIVE

Joint injury rapidly induces expression of primary response genes (PRGs), which activate a cascade of secondary genes that destroy joint tissues and initiate post-traumatic osteoarthritis (PTOA). Bromodomain-containing-protein-4 (Brd4) and cyclin-dependent-kinase-9 (CDK9) cooperatively control the rate-limiting step of PRG transactivation, including pro-inflammatory genes. This study investigated whether Brd4 and CDK9 inhibitors suppress inflammation and prevent PTOA development in vitro and in a mouse PTOA model.

METHODS

The effects of Brd4 and CDK9 inhibitors (JQ1 and Flavopiridol) on PRG and associated secondary damage were rigorously tested in different settings. Short-term effects of inflammatory stimuli (IL-1β, IL-6, TNF) on human chondrocyte PRG expression were assessed by RT-PCR and microarray after 5-h. We quantified glycosaminoglycan release from IL-1β-treated bovine cartilage explants after 3-6 days, and osteoarthritic changes in mice after ACL-rupture using RT-PCR (2-24hrs), in vivo imaging of MMP activity (24hrs), AFM-nanoindentation (3-7days), and histology (3days-4wks).

RESULTS

Flavopiridol and JQ1 inhibitors act synergistically, and a combination of both almost completely prevented the activation of most IL-1β-induced PRGs in vitro by microarray analysis, and prevented IL-1β-induced glycosaminoglycan release from cartilage explants. Mice given the drug combination showed reduced IL-1β and IL-6 expression, less in vivo MMP activity, and lower synovitis (1.5 vs 4.9) and OARSI scores (2.8 vs 6.0) than untreated mice with ACL-rupture.

CONCLUSIONS

JQ1 and Flavopiridol work synergistically to reduce injury response after joint trauma, suggesting that targeting Brd4 and/or CDK9 could be a viable strategy for PTOA prevention and treatment of early OA.

Targeting Epigenetic 'Readers' with Natural Compounds for Cancer Interception

Natural compounds from diverse sources, including botanicals and commonly consumed foods and beverages, exert beneficial health effects via mechanisms that impact the epigenome and gene expression during disease pathogenesis. By targeting the so-called epigenetic 'readers', 'writers', and 'erasers', dietary phytochemicals can reverse abnormal epigenome signatures in cancer cells and preneoplastic stages. Thus, such agents provide avenues for cancer interception via prevention or treatment/therapeutic strategies. To date, much of the focus on dietary agents has been directed towards writers (e.g., histone acetyltransferases) and erasers (e.g., histone deacetylases), with less attention given to epigenetic readers (e.g., BRD proteins). The drug JQ1 was developed as a prototype epigenetic reader inhibitor, selectively targeting members of the bromodomain and extraterminal domain (BET) family, such as BRD4. Clinical trials with JQ1 as a single agent, or in combination with standard of care therapy, revealed antitumor efficacy but not without toxicity or resistance. In pursuit of second-generation epigenetic reader inhibitors, attention has shifted to natural sources, including dietary agents that might be repurposed as 'JQ1-like' bioactives. This review summarizes the current status of nascent research activity focused on natural compounds as inhibitors of BET and other epigenetic 'reader' proteins, with a perspective on future directions and opportunities.

Discovery of BAZ1A bromodomain inhibitors with the aid of virtual screening and activity evaluation

BAZ1A is a bromodomain-containing protein, and has been recognized as a potential target for multiple diseases, particularly cancer. However, there is no BAZ1A inhibitor reported so far. In this study, we used a consensus docking/scoring strategy to screen for BAZ1A bromodomain inhibitors from commercial chemical libraries and an in-house chemical database. The retrieved hit compounds were evaluated experimentally and four compounds were found to be active against BAZ1A bromodomain. To the most active compounds, similarity and substructure searches were used to find more BAZ1A bromodomain inhibitors. Among all the obtained active compounds, Cpd-2 is the most potent one, which showed a K_D value of 0.52 μM. The interaction model of Cpd-2 with BAZ1A bromodomain was revealed by molecular docking. In a cellular assay, Cpd-2 displayed good anti-viability activity against cancer cell lines expressing a high level of BAZ1A. Overall, we discovered a number of BAZ1A bromodomain inhibitors for the first time, which can be a good starting point for subsequent drug discovery targeting BAZ1A bromodomain.

The bromodomains of BET family proteins can recognize diacetylated histone H2A.Z

Chemical modifications of histone tails influence genome accessibility and the transcriptional state of eukaryotic cells. Lysine acetylation is one of the most common modifications and acetyllysine-binding bromodomains (BDs) provide a means for acetyllysine marks to be translated into meaningful cellular responses. Here, we have investigated the mechanism underlying the reported association between the Bromodomain and Extra Terminal (BET) family of BD proteins and the essential histone variant H2A.Z. We use NMR spectroscopy to demonstrate a physical interaction between the N-terminal tail of H2A.Z and the BDs of BRD2, BRD3, and BRD4, and show that the interaction is dependent on lysine acetylation in H2A.Z. The BDs preferentially engage a diacetylated H2A.Z-K4acK7ac motif that is reminiscent of sequences found in other biologically important BET BD target proteins, including histones and transcription factors. A H2A.Z-K7acK11ac motif can also bind BET BDs-with a preference for the second BD of each protein. Chemical shift perturbation mapping of the interactions, together with an X-ray crystal structure of BRD2-BD1 bound to H2A.Z-K4acK7ac, shows that H2A.Z binds the canonical AcK binding pocket of the BDs. This mechanism mirrors the conserved binding mode that is unique to the BET BDs, in which two acetylation marks are read simultaneously by a single BD. Our findings provide structural corroboration of biochemical and cell biological data that link H2A.Z and BET-family proteins, suggesting that the function of H2A.Z is enacted through interactions with these chromatin readers.

Protein Interaction Domains and Post-Translational Modifications: Structural Features and Drug Discovery Applications

Background:

Many pathways regarding healthy cells and/or linked to diseases onset and progression depend on large assemblies including multi-protein complexes. Protein-protein interactions may occur through a vast array of modules known as protein interaction domains (PIDs).

Objective:

This review concerns with PIDs recognizing post-translationally modified peptide sequences and intends to provide the scientific community with state of art knowledge on their 3D structures, binding topologies and potential applications in the drug discovery field.

Method:

Several databases, such as the Pfam (Protein family), the SMART (Simple Modular Architecture Research Tool) and the PDB (Protein Data Bank), were searched to look for different domain families and gain structural information on protein complexes in which particular PIDs are involved. Recent literature on PIDs and related drug discovery campaigns was retrieved through Pubmed and analyzed.

Results and Conclusion:

PIDs are rather versatile as concerning their binding preferences. Many of them recognize specifically only determined amino acid stretches with post-translational modifications, a few others are able to interact with several post-translationally modified sequences or with unmodified ones. Many PIDs can be linked to different diseases including cancer. The tremendous amount of available structural data led to the structure-based design of several molecules targeting protein-protein interactions mediated by PIDs, including peptides, peptidomimetics and small compounds. More studies are needed to fully role out, among different families, PIDs that can be considered reliable therapeutic targets, however, attacking PIDs rather than catalytic domains of a particular protein may represent a route to obtain selective inhibitors.

Cyclic peptides can engage a single binding pocket through highly divergent modes

Large DNA-encoded libraries of cyclic peptides are emerging as powerful sources of molecules to tackle challenging drug targets. The structural and functional diversity contained within these libraries is, however, little explored. Here we demonstrate that one such library contains members that use unexpectedly diverse mechanisms to recognize the same surface on the same target proteins with high affinity and specificity. This range of binding modes is much larger than observed in natural ligands of the same proteins, demonstrating the power and versatility of the technology. Our data also reveal opportunities for the development of more sophisticated approaches to achieving specificity when trying to selectively target one member of a family of closely related proteins.

Cyclic peptide library screening technologies show immense promise for identifying drug leads and chemical probes for challenging targets. However, the structural and functional diversity encoded within such libraries is largely undefined. We have systematically profiled the affinity, selectivity, and structural features of library-derived cyclic peptides selected to recognize three closely related targets: the acetyllysine-binding bromodomain proteins BRD2, -3, and -4. We report affinities as low as 100 pM and specificities of up to 10⁶-fold. Crystal structures of 13 peptide–bromodomain complexes reveal remarkable diversity in both structure and binding mode, including both α-helical and β-sheet structures as well as bivalent binding modes. The peptides can also exhibit a high degree of structural preorganization. Our data demonstrate the enormous potential within these libraries to provide diverse binding modes against a single target, which underpins their capacity to yield highly potent and selective ligands.

A chemical conjugation of JQ-1 and a TLR7 agonist induces tumoricidal effects in a murine model of melanoma via enhanced immunomodulation

In recent years, inhibitors of the BET bromodomain proteins, such as BRD4 inhibitors, have demonstrated robust antitumor activity. JQ-1, a representative small molecular BRD4 inhibitor, is also effective to block PD-1/PD-L1 signaling by significantly decreasing the PD-L1 expression on tumor cells. However, toxicity of BRD4 inhibitors on lymphoid and hematopoietic tissues limits their clinical usage. In this research, we designed and studied an immunogenic BRD4 inhibitor, SZU-119, by coupling JQ-1 with a TLR7 agonist, SZU-101. In vitro, SZU-119 stimulated the production of cytokines in mouse BMDCs and spleen lymphocytes, and inhibited the expression of PD-L1 in mouse B16 tumor cells. In vivo, SZU-119 suppressed the B16 tumor growth at both injected and uninjected sites, and prolonged the survival time of mice. SZU-119 elevated the number of total CD8⁺ and IFN-γ⁺ CD8⁺ T cells in spleens, with greater CTL cytotoxicity to B16 tumor cells. It was also observed that the infiltration of CD8⁺ T cells was increased in tumors at both local and distant sites, and the PD-L1 expression was decreased in tumor cells at the primary site. In conclusion, we have demonstrated that SZU-119 activated the innate immune cells, kept efficacy of PD-L1 blockade and abrogated immune toxicity, showing more potent antitumor effects than the simple mixture of SZU-101 and JQ-1 in a mouse melanoma model. Our work provides new insights for the development of anti-melanoma drugs that concurrently target innate and adaptive immunity.

Inhibitors of bromodomain and extra-terminal proteins for treating multiple human diseases

Clinical development of bromodomain and extra‐terminal (BET) protein inhibitors differs from the traditional course of drug development. These drugs are simultaneously being evaluated for treating a wide spectrum of human diseases due to their novel mechanism of action. BET proteins are epigenetic “readers,” which play a primary role in transcription. Here, we briefly describe the BET family of proteins, of which BRD4 has been studied most extensively. We discuss BRD4 activity at latent enhancers as an example of BET protein function. We examine BRD4 redistribution and enhancer reprogramming in embryonic development, cancer, cardiovascular, autoimmune, and metabolic diseases, presenting hallmark studies that highlight BET proteins as attractive targets for therapeutic intervention. We review the currently available approaches to targeting BET proteins, methods of selectively targeting individual bromodomains, and review studies that compare the effects of selective BET inhibition to those of pan‐BET inhibition. Lastly, we examine the current clinical landscape of BET inhibitor development.

Development of a Novel Positron Emission Tomography (PET) Radiotracer Targeting Bromodomain and Extra-Terminal Domain (BET) Family Proteins

Bromodomain and extra-terminal domain (BET) family proteins have become a hot research area because of their close relationship with a variety of human diseases. The non-invasive imaging technique, such as positron emission tomography (PET), provides a powerful tool to visualize and quantify the BET family proteins that accelerating the investigation of this domain. Herein, we describe the development of a promising PET probe, [¹¹C]1, specifically targeting BET family proteins based on the potent BET inhibitor CF53. [¹¹C]1 was successfully radio-synthesized with good yield and high purity after the optimization of radiolabeling conditions. The in vivo bio-activities evaluation of [¹¹C]1 was performed using PET imaging in rodents. The results demonstrated that [¹¹C]1 has favorable uptake in peripheral organs and moderate uptake in the brain. Further blocking studies indicated the high binding specificity and selectivity for BET proteins of this probe. Our findings suggest that [¹¹C]1 is a promising BET PET probe for BET proteins as well as epigenetic imaging.