BRD4 Research Articles

Dual targeting and bioresponsive nano-PROTAC induced precise and effective lung cancer therapy

Epigenetic regulation has emerged as a promising therapeutic strategy for lung cancer treatment, which can facilitate the antitumor responses by modulating epigenetic dysregulation of target proteins in lung cancer. The proteolysis-targeting chimera (PROTAC) reagent, dBET6 shows effective inhibition of bromodomain-containing protein 4 (BRD4) that exerts antitumor efficacy by degrading BRD4 via the ubiquitin-proteasome system. Nevertheless, the low tissue specificity and bioavailability impede its therapeutic effects and clinical translation on lung cancer treatment. Herein, we developed a type of dual targeting and bioresponsive nano-PROTAC (c R GD/L LC membrane/D S-P LGA/d B ET6, named RLDPB), which was constructed by using the pH and glutathione (GSH)-responsive polymer, disulfide bond-linked poly(lactic-co-glycolic acid) (PLGA-S-S-PLGA, DS-PLGA) to load the PROTAC agent dBET6, and further camouflaged with the homotypic LLC cell membranes, followed by the conjugation with cRGD ligand to the surface of the nanoparticles. Notably, RLDPB showed enhanced celluar uptake by lung cancer cells in vitro and accumulation in the tumors via the dual targeting structure including cRGD and LLC membrane. The pH/GSH responsiveness improved the release of dBET6 from the DS-PLGA-based nanoparticles within the cells. RLDPB was demonstrated to facilitate tumor regression by inducing the apoptosis of lung cancer cells with the degradation of BRD4. Thus, RLDPB can be considered a powerful tool to suppress lung cancer, which opens a new avenue to treat lung cancer by PROTAC.Graphical abstract

Augmenting Protein Degradation Capacity of PROTAC through Energy Metabolism Regulation and Targeted Drug Delivery.

The ubiquitin-proteasome system (UPS) is responsible for degrading over 70-80% of cellular proteins. Consequently, proteolysis-targeting chimeras (PROTACs) are developed to induce the ubiquitination and subsequent degradation of proteins of interest (POIs) by the UPS. To amplify the therapeutic efficacy of PROTACs, energy metabolism regulation is first harnessed to boost UPS function in tumor cells. Proteomic and ubiquitinome analyzes reveal that total ubiquitinated proteins and proteasome activity are significantly increased in 143B and MDA-MB-231 tumor cells following fasting-mimicking diet (FMD) treatment. As a result, the degradation efficiency of PROTACs targeting focal adhesion kinase (FAK-P) or bromodomain-containing protein 4 (BRD4-P) is significantly enhanced in FMD-treated 143B and MDA-MB-231 tumor cells. Then, silica-coated iron oxide nanoparticles are developed modified with tumor cell membranes for targeted delivery of PROTACs. Magnetic resonance imaging (MRI) and fluorescence imaging confirm that nanocarriers significantly improve the delivery efficiency of PROTACs in FMD-treated 143B or MDA-MB-231 tumors. In vivo studies demonstrate that the antitumor efficacy of FAK-P and BRD4-P is greatly augmented when combined with targeted delivery and FMD treatment. Overall, this study presents a strategy to enhance the efficacy of PROTACs in cancer therapy.

Effects of BET Inhibition on lung micro-environmental changes in obesity-related pulmonary Arterial Hypertension (PAH)

Abstract Background Obesity is emerging as a pivotal risk factor for pulmonary arterial hypertension (PAH) but the underlying molecular mechanisms are poorly explored. The lung microenvironment, namely the cell-cell communication among fibroblasts, immune and endothelial cells, may significantly impact on vascular structure and function thus promoting microvascular disease in this setting. Obesity-induced chromatin modifications lead to maladaptive transcriptional programs altering cell function in different organs. Apabetalone (APA), a selective inhibitor of bromodomain and extra-terminal containing protein family (BET) proteins, prevents bromodomain-containing protein 4 (BRD4) interactions with chromatin thus modulating gene expression. Purpose To determine whether a new epi-drug, namely APA, affects the lung microenvironment in obesity-related PAH. Methods Mice were fed a normal diet (ND, control) or high-fat-diet (HFD) and L-NAME for 15 weeks to induce obesity-related PAH (obPAH). Echocardiography was performed. Pathways regulating obPAH were identified by single-cell nuclei RNA sequencing in lung specimens. Primary endothelial cells (ECs) and Fibroblasts (mFs) were freshly isolated from obPAH lungs and treated with APA for 48 hours. Cells and lung samples were used for molecular biology and histology. Cellular migration was investigated by in vitro gap closure. Results Obese mice displayed PAH as shown by increased pulmonary artery (PA) pressure, PA resistance, right ventricular wall thickness and reduced PA acceleration time. Of note, chronic APA treatment prevented PAH-related features in obese mice. To determine the cell types affected by APA, we performed scRNAseq. We found that fibroblast and endothelial cells had the highest enrichment of genes whose expression significantly correlated with echo-determined PAH features. ECs and mFs from obese mice displayed an altered phenotype whereas treatment with APA rescued obesity-driven ECs and mFs dysfunction. In obPAH ECs, we found increased expression of NF-kB p65-related inflammatory genes (IL-1β, IL-6, TNF-alpha) as well as enhanced p53 signaling. Moreover, obPAH-ECs expressed high levels of hypoxia-inducible factor (HIF1-α) and NADPH-oxidase-NOX4 with subsequent increase in ROS generation. Furthermore, APA treatment protected against cellular inflammation, senescence and oxidative stress. To evaluate the effect of APA and the paracrine response of fibroblasts, we performed a scratch assay on control mFs exposed to TGF-β or conditioned media collected from obPAH-ECs with and without APA. In both experimental settings, APA affected gap closure, suggesting that the treatment influences fibroblast migration through both a direct effect and paracrine mechanisms. Conclusions APA is able to reset the lung micro-envirnment in obesity thus reducing inflammation and senescence. BET inhibitors could represent potential therapeutic approaches in this setting.

The BET inhibitor Apabetalone protects against heart failure with preserved ejection fraction by suppressing myocardial inflammation

Abstract Background Posttranslational histone modifications, play a major role in cardiac hypertrophy and dysfunction. Apabetalone (APA), a selective inhibitor of bromodomain and extraterminal containing protein family (BET) proteins, prevents bromodomain-containing protein 4 (BRD4) interactions with chromatin thus modulating transcriptional programs in different organs. Purpose We sought to investigate whether APA could be beneficial in cardiometabolic heart failure with preserved ejection fraction (cHFpEF). Methods Mice were subjected to high fat diet feeding and L-NAME treatment for 15 weeks to induce cHFpEF. Histology, mouse echocardiography (Vevo3100) and Treadmill exhaustion test were performed. Unbiased gene expression profiling by PCR array and proteomics analysis (Olink) was employed in left ventricular (LV) myocardial specimens from HFpEF mice and control animals. Cultured cardiomyocytes (CMs) treated with palmitic acid (PA) were used as an in vitro model of metabolic stress. cHFpEF mice were chronically treated with the BET inhibitor APA (150mg/kg/day) or vehicle (DMSO). In order to translate our findings to the human setting, passive stiffness of skinned CMs collected from cHFpEF patients was assessed before and after APA treatment. Results HFpEF mice displayed LV hypertrophy, diastolic dysfunction, myocardial fibrosis, lung congestion and impaired exercise tolerance as compared to controls. Interestingly, diastolic dysfunction - assessed by E/A ratio and isovolumic relaxation time (IVRT) - and lung congestion were significantly reduced in HFpEF mice treated with APA, while exercise tolerance was improved. Transcriptomic analysis in PA-treated CMs and LV mouse specimens from cHFpEF mice showed a profound deregulation of genes controlling inflammation, namely IL-6, TNF-alpha, and IL-1beta. ChIP assays showed BRD4 occupancy on the promoter of several inflammatory genes, including IL6. Treatment with APA suppressed most of inflammatory genes, with a pronounced effect on IL6 expression. Moreover, APA reduced circulating levels of several inflammatory chemokines. The beneficial effects of APA were explained by modulation of IL-6/CaMKII/STAT3 pathway both in cHFpEF hearts and PA-treated CMs. In skinned CMs from cHFpEF patients, both APA and IL6 blockade were able to attenuate passive stiffness. Conclusions Our findings set the stage for preclinical studies and exploratory clinical trials testing APA in patients with cHFpEF.

In Silico Design, Chemical Synthesis, Biophysical and in Vitro Evaluation for the Identification of 1-Ethyl-1H-Pyrazolo[3,4-b]Pyridine-Based BRD9 Binders.

In this work, we report the identification of novel bromodomain-containing protein 9 (BRD9) binders through a virtual screening based on our developed 3D structure-based pharmacophore model. The in silico workflow here described led to the identification of a promising initial hit (1) featuring the 1-ethyl-1H-pyrazolo[3,4-b]pyridine motif which represented an unexplored chemotype for the development of a new class of BRD9 ligands. The encouraging biophysical results achieved for compound 1 prompted us to explore further tailored structural modification around the C-4 and C-6 positions of the central core. Hence, the design and synthesis of a set of 19 derivatives (2-20) were performed to extensively investigate the chemical space of BRD9 binding site. Among them, four compounds (5, 11, 12, and 19) stood out in biophysical assays as new valuable BRD9 ligands featuring IC50 values in the low-micromolar range. Noteworthy, a promising antiproliferative activity was detected in vitro for compound 5 on HeLa and A375 cancer cell line. The successful combination and application of in silico tools, chemical synthesis, and biological assays allowed to identify novel BRD9 binders and to expand the arsenal of promising chemical entities amenable to the recognition of this important epigenetic target.

Methylarginine targeting chimeras for lysosomal degradation of intracellular proteins.

A paradigm shift in drug development is the discovery of small molecules that harness the ubiquitin-proteasomal pathway to eliminate pathogenic proteins. Here we provide a modality for targeted protein degradation in lysosomes. We exploit an endogenous lysosomal pathway whereby protein arginine methyltransferases (PRMTs) initiate substrate degradation via arginine methylation. We developed a heterobifunctional small molecule, methylarginine targeting chimera (MrTAC), that recruits PRMT1 to a target protein for induced degradation in lysosomes. MrTAC compounds degraded substrates across cell lines, timescales and doses. MrTAC degradation required target protein methylation for subsequent lysosomal delivery via microautophagy. A library of MrTAC molecules exemplified the generality of MrTAC to degrade known targets and neo-substrates-glycogen synthase kinase 3β, MYC, bromodomain-containing protein 4 and histone deacetylase 6. MrTAC selectively degraded target proteins and drove biological loss-of-function phenotypes in survival, transcription and proliferation. Collectively, MrTAC demonstrates the utility of endogenous lysosomal proteolysis in the generation of a new class of small molecule degraders.

Genome-wide analysis of Triticum aestivum bromodomain gene family and expression analysis under salt stress.

This study identified 82 wheat BRD genes, revealing both conserved evolutionary and functional characteristics across plant species and novel features specific to wheat. GTE8-12 cluster TaBRDs were found as positive response to salt stress. Bromodomain-containing proteins (BRDs) are crucial in histone acetylation "reading" and chromatin remodeling in eukaryotes. Despite some of their members showing importance in various biological processes in plants, our understanding of the BRD family in wheat (Triticum aestivum) remains limited. This study comprehensively analyzes the T. aestivum BRD (TaBRD) family. We identified 82 TaBRD genes in wheat genome encoding hydrophobic proteins with a conserved pocket structure. Phylogenetic analysis classified these genes into 16 distinct clusters, with conserved protein motifs and gene structures within clusters but diverse patterns across clusters. Gene duplication analysis revealed that whole-genome or segmental duplication events were the primary expansion mechanism for the TaBRD family, with purifying selection acting on these genes. Subcellular localization and Gene Ontology (GO) analyses indicated that TaBRD proteins are predominantly nuclear-localized and involved in transcription regulation and RNA metabolism. Promoter analysis and interaction network prediction suggested diverse regulatory mechanisms for TaBRDs. Notably, TaBRDs from the GTE8-12 cluster were enriched with cis-elements responsive to abscisic acid (ABA), methyl jasmonate (MeJA), and light, implying their involvement in physiological functions and abiotic stress responses. Expression analysis confirmed tissue-specific patterns and responsiveness to salinity stress. This comprehensive study enhances our understanding of the BRD family in higher plants and provides a foundation for developing salt-tolerant wheat varieties.

Targeted nanoliposomes of oncogenic protein degraders: Significant inhibition of tumor in lung-cancer bearing mice

With 60 % of non-small cell lung cancer (NSCLC) expressing epidermal growth factor receptor (EGFR), it has been explored as an important therapeutic target for lung tumors. However, even the well-established EGFR inhibitors tend to promptly develop resistance over time. Moreover, strategies that could impede resistance development and be advantageous for both EGFR-Tyrosine kinase inhibitor (TKI)-sensitive and mutant NSCLC patients are constrained. Based on the critical relationship between EGFR, c-MYC, and Kirsten rat sarcoma virus (K-Ras), simultaneous degradation of EGFR and Bromodomain-containing protein 4 (BRD4) using “Proteolysis Targeting Chimeras (PROTACs)” could be a promising approach. PROTACs are emerging class of oncoprotein degraders but very challanging to deliver in vivo. Compared to individual IC50s, strong synergism was observed at 1:1 ratio of BPRO and EPRO in NSCLC cell lines with diverse mutation. Significant inhibition of cell growth with higher cellular apoptosis was observed in 2D and 3D-based cell assays in nanomolar concentrations. EGFR activation assay revealed 47.60 % EGFR non-expressing cells confirming EGFR-degrading potential of EPRO. A lung cancer specific nanoliposomal formulation of EGFR and BRD4-degrading PROTACs (EPRO and BPRO) was prepared and characetrized. Successful encapsulation of the two highly lipophilic molecules was achieved in EGFR-targeting nanoliposomal carriers (T-BEPRO) using a modified hydration technique. T-BEPRO revealed a particle size of 109.22 ± 0.266 nm with enhanced cellular uptake and activity. Remarkably, parenterally delivered T-BEPRO in tumor-bearing mice showed a substantially higher % tumor growth inhibition (TGI) of 77.6 % with long-lasting tumor inhibitory potential as opposed to individual drugs.

Enhancing therapeutic efficacy in homologous recombination-proficient pancreatic cancer via the combination of PARP1-PROTAC and a BRD4 inhibitor

Currently, poly (ADP-ribose) polymerase inhibitors (PARPi) have been approved by the U.S. Food and Drug Administration for BRCA-mutated pancreatic cancer therapy. However, limited indications hinder their further application. Bromodomain-containing protein 4 (BRD4) repression can block the homologous recombination (HR) repair pathway and has the potential to enhance the response to PARPi in HR-proficient pancreatic cancer therapy. In addition, proteolysis targeting chimeras (PROTACs) can hijack E3 ligase within the cell to ubiquitinate degradation-targeted proteins effectively and quickly, thus enhancing the therapeutic effect on tumors. In the present study, the LB23 compound (with the ability to induce PARP1 degradation) was employed in combination with the BRD4 inhibitor, JQ1, and their synergistic effect in HR-proficient pancreatic cancer was confirmed via various methods. Moreover, compared with the JQ1 and PARPi olaparib combination, it was revealed that PARP1-PROTAC and JQ1 had more notable synergistic effects. Further research into the synergistic mechanism demonstrated that combination therapy enhanced DNA damage and suppressed DNA repair by inducing cell cycle arrest and cell apoptosis. The present study therefore provides the experimental data for this type of combination therapy, which is expected to be an innovative approach for the treatment of HR-proficient pancreatic cancer.

1,3,4-oxadiazoles as inhibitors of the atypical member of the BET family bromodomain factor 3 from Trypanosoma cruzi (TcBDF3).

Chagas disease, caused by the protozoan parasite Trypanosoma cruzi, affects millions globally, with increasing urban cases outside of Latin America. Treatment is based on two compounds, namely, benznidazole (BZ) and nifurtimox, but chronic cases pose several challenges. Targeting lysine acetylation, particularly bromodomain-containing proteins, shows promise as a novel antiparasitic target. Our research focuses on TcBDF3, a cytoplasmic protein, which is crucial for parasite differentiation that recognizes acetylated alpha-tubulin. In our previous study, A1B4 was identified as a high-affinity binder of TcBDF3, showing significant trypanocidal activity with low host toxicity in vitro. In this report, the binding of TcBDF3 to A1B4 was validated using differential scanning fluorescence, fluorescence polarization, and molecular modeling, confirming its specific interaction. Additionally, two new 1,3,4-oxadiazoles derived from A1B4 were identified, which exhibited improved trypanocide activity and cytotoxicity profiles. Furthermore, TcBDF3 was classified for the first time as an atypical divergent member of the bromodomain extraterminal family found in protists and plants. These results make TcBDF3 a unique target due to its localization and known functions not shared with higher eukaryotes, which holds promise for Chagas disease treatment.

Combining Data-Driven and Structure-Based Approaches in Designing Dual PARP1-BRD4 Inhibitors for Breast Cancer Treatment.

Poly(ADP-ribose) polymerase 1 (PARP1) inhibitors have revolutionized the treatment of many cancers with DNA-repairing deficiencies via synthetic lethality. Advocated by the polypharmacology concept, recent evidence discovered that a significantly synergistic effect in increasing the death of cancer cells was observed by simultaneously perturbating the enzymatic activities of bromodomain-containing protein 4 (BRD4) and PARP1. Here, we developed a novel cheminformatics approach combined with a structure-based method aiming to facilitate the design of dual PARP1-BRD4 inhibitors. Instead of linking pharmacophores, the developed approach first identified merged pharmacophores (a pool of amide-containing ring systems), from which phenanthridin-6(5H)-one was further prioritized. Based on this starting point, several small molecules were rationally designed, among which HF4 exhibited low micromolar inhibitory activity against BRD4 and PARP1, particularly exhibiting strong inhibition of BRD4 BD1 with an IC50 value of 204 nM. Furthermore, it demonstrated potent antiproliferative effects against breast cancer gene-deficient and proficient breast cancer cell lines by arresting cell cycle progression and impeding DNA damage repair. Collectively, our systematic efforts to design lead-like molecules have the potential to open doors for the exploration of dual PARP1-BRD4 inhibitors as a promising avenue for breast cancer treatment. Furthermore, the developed approach can be extended to systematically design inhibitors targeting PARP1 and other related targets.

Resistance of estrogen receptor function to BET bromodomain inhibition is mediated by transcriptional coactivator cooperativity.

The bromodomain and extraterminal domain (BET) family of proteins are critical chromatin readers that bind to acetylated histones through their bromodomains to activate transcription. Here, we reveal that bromodomain inhibition fails to repress oncogenic targets of estrogen receptor because of an intrinsic transcriptional mechanism. While bromodomains are necessary for the transcription of many genes, bromodomain-containing protein 4 (BRD4) binds to estrogen receptor binding sites and activates transcription of critical oncogenes such as MYC, independently of its bromodomains. BRD4 associates with the Mediator complex and disruption of Mediator reduces BRD4's enhancer occupancy. Profiling changes of the post-initiation RNA polymerase II (Pol II)-associated factors revealed that BET proteins regulate interactions between Pol II and elongation factors SPT5, SPT6 and the polymerase-associated factor 1 complex, which associate with BET proteins independently of their bromodomains and mediate their transcription elongation effect. Our findings highlight the importance of bromodomain-independent functions and interactions of BET proteins in the development of future therapeutic strategies.

TRIM28 promotes tumor growth and metastasis in breast cancer by targeting the BRD7 protein for ubiquitination and degradation.

Bromodomain-containing protein 7 (BRD7) is downregulated and functions as a tumor suppressor in many types of cancers including breast cancer, and the dysregulation of BRD7 expression is closely related to the development and progression of breast cancer. Whereas little attention has been focused on the regulation of BRD7 protein levels in breast cancer, which needs to be further elucidated. The protein stability of BRD7 in breast cancer cells and BRD7 protein level in breast cancer tissues was examined by Western Blotting. The potential E3 ubiquitin ligase proteins that interact with the BRD7 was screened by coimmunoprecipitation combined with mass spectrometry analysis in MDA-MB-231 cells. We proved the interaction between BRD7 and tripartite motif containing 28 (TRIM28) through Co-Immunoprecipitation (Co-IP) and immunofluorescence assays. Co-IP and ubiquitination assay were used to explore the specific binding domain between BRD7 and TRIM28 and the ubiquitination site of BRD7. The effects of TRIM28 on the BRD7 protein stability and ubiquitination level was investigated by qPCR, Western Blot and Co-IP assay. CCK-8 and clone formation assays were carried out to assess the effect of TRIM28 on proliferation ability of breast cancer ells. Transwell assay and wound healing assay were used to investigate the effect of TRIM28 on breast cancer cell invasion and migration. Flow cytometry was used to detect the effect of TRIM28 on cell cycle and apoptosis of breast cancer cells. In addition, we confirmed effect of TRIM28 on tumor growth and metastasis by xenograft and metastatic mouse models. We designed some recovery assays to explore the role of recovery BRD7 in TRIM28-mediated promotion of malignant progression of breast cancer in vivo and in vitro. Finally, the clinical significance of TRIM28 and BRD7 was proved by immunohistochemistry. In this study, we demonstrated that BRD7 was an unstable protein and might be regulated by ubiquitination in breast cancer; furthermore, we found that the Coiled-Coil region of TRIM28 could directly bind to N-terminal of BRD7, and TRIM28 mediates BRD7 ubiquitination and degradation dependent on K21 by acting as a potential E3 ubiquitin ligase. Moreover, TRIM28 promoted cell proliferation, migration, invasion, xenograft tumor growth and metastasis, thus playing an oncogenic role in breast cancer. Furthermore, the restoration of BRD7 expression in breast cancer significantly reversed the promotional effects of TRIM28 on malignant progression both in vitro and in vivo. In addition, TRIM28 was highly expressed in the biopsy tissues of breast cancer, and its expression was negatively correlated with BRD7 expression and positively correlated with TNM stage and poor prognosis of BC patients. Our findings provide a novel mechanism by which TRIM28 significantly facilitates BRD7 ubiquitination and degradation, thus promoting breast cancer malignant progression. Targeting the TRIM28/BRD7 axis might be a novel potential strategy for the clinical diagnosis and treatment of breast cancer.

Inhibition of Renin Expression Is Regulated by an Epigenetic Switch From an Active to a Poised State.

Renin-expressing cells are myoendocrine cells crucial for the maintenance of homeostasis. Renin is regulated by cAMP, p300 (histone acetyltransferase p300)/CBP (CREB-binding protein), and Brd4 (bromodomain-containing protein 4) proteins and associated pathways. However, the specific regulatory changes that occur following inhibition of these pathways are not clear. We treated As4.1 cells (tumoral cells derived from mouse juxtaglomerular cells that constitutively express renin) with 3 inhibitors that target different factors required for renin transcription: H-89-dihydrochloride, PKA (protein kinase A) inhibitor; JQ1, Brd4 bromodomain inhibitor; and A-485, p300/CBP inhibitor. We performed assay for transposase-accessible chromatin with sequencing (ATAC-seq), single-cell RNA sequencing, cleavage under targets and tagmentation (CUT&Tag), and chromatin immunoprecipitation sequencing for H3K27ac (acetylation of lysine 27 of the histone H3 protein) and p300 binding on biological replicates of treated and control As4.1 cells. In response to each inhibitor, Ren1 expression was significantly reduced and reversible upon washout. Chromatin accessibility at the Ren1 locus did not markedly change but was globally reduced at distal elements. Inhibition of PKA led to significant reductions in H3K27ac and p300 binding specifically within the Ren1 super-enhancer region. Further, we identified enriched TF (transcription factor) motifs shared across each inhibitory treatment. Finally, we identified a set of 9 genes with putative roles across each of the 3 renin regulatory pathways and observed that each displayed differentially accessible chromatin, gene expression, H3K27ac, and p300 binding at their respective loci. Inhibition of renin expression in cells that constitutively synthesize and release renin is regulated by an epigenetic switch from an active to poised state associated with decreased cell-cell communication and an epithelial-mesenchymal transition. This work highlights and helps define the factors necessary for renin cells to alternate between myoendocrine and contractile phenotypes.

Novel inhibitors of bromodomain and extra-terminal domain trigger cell death in breast cancer cell lines

Small molecule inhibitors targeting the bromodomain and extra-terminal domain (BET) family proteins have emerged as a promising class of anti-cancer drugs. Nevertheless, the clinical advancement of these agents has been significantly hampered by challenges related to their potency, oral bioavailability, or toxicity. In this study, virtual screening approaches were employed to discover novel inhibitors of the bromodomain-containing protein 4 (BRD4) by analyzing their comparable chemical structural features to established BRD4 inhibitors. Several of these compounds exhibited inhibitory effects on BRD4 activity ranging from 60 % to 70 % at 100 µM concentrations, while one compound also exhibited an 84 % inhibition of Sirtuin 2 (SIRT2) activity. Furthermore, a subset of structurally diverse compounds from the BRD4 inhibitors was selected to investigate their anti-cancer properties in both 2D and 3D cell cultures. These compounds exhibited varying effects on cell numbers depending on the specific cell line, and some of them induced cell cycle arrest in the G0/G1 phase in breast cancer (MDA-MB-231) cells. Moreover, all the compounds studied reduced the sizes of spheroids, and the most potent compound exhibited a 90 % decrease in growth at a concentration of 10 µM in T47D cells. These compounds hold potential as epigenetic regulators for future studies.

RUNX1 expression is regulated by a super-enhancer and is a therapeutic target in adult T-cell leukemia/lymphoma

Super-enhancers (SEs) play an important role in regulating tumor-specific gene expression. JQ1, a Bromodomain-containing protein 4 (BRD4) inhibitor, exerts antitumor effects by disrupting SE-mediated regulation of gene expression. We investigated the anti-adult T-cell leukemia/lymphoma (ATL) effects of JQ1. JQ1 induced apoptosis and inhibited ATL cell proliferation. JQ1 suppressed RUNX1expression through the disruption of SE-mediated gene regulation. In the previous reports, it was shown that IC50s of AI-10-104 and Ro5-3335, RUNX1 inhibitors were 1-10 µM for lymphoblastic leukemia cell lines carrying RUNX1 mutations. In the present study, we demonstrated that IC50s of AI-10-104 and Ro5-3335 were also 1-10 µM or lower for ATL cell lines. Simultaneously, AI-10-104 suppressed MYC proto-oncogene (c-MYC) expression. RUNX1 is a potential therapeutic target for ATL that promotes c-MYC expression. We showed that RUNX1 expression is regulated via SEs in ATL and that RUNX1 may be a novel therapeutic target for ATL.

Targeted BET inhibition with OPN-51107 synergizes with venetoclax in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) remains incurable and its ability to acquire resistance to front-line therapeutics has proved challenging. Bromodomain and extra-terminal proteins, particularly bromodomain-containing protein 4 (BRD4), are integral to gene expression in CLL and offer a promising therapeutic target. In this study, we examined the activity of the BRD4 inhibitor OPN-51107 alone and in combination with the BCL-2 inhibitor, venetoclax, in CLL cell lines and patient-derived CLL samples. We demonstrate that OPN-51107 induces anti-tumor activity in both CLL cell lines and patient-derived samples, including relapsed/refractory (R/R) samples and those with high-risk features (i.e. ATM and/or TP53 deletions). Importantly, the combination of OPN-51107 and venetoclax exhibited synergistic cytotoxicity in ibrutinib-resistant CLL cells and patient-derived CLL samples regardless of R/R or deletion status. This study establishes the preclinical efficacy of using OPN-51107 and venetoclax in combination in therapy-resistant and/or high-risk CLL, lending support for its further development as a combination therapy.

Identification of Novel Bromodomain-Containing Protein 4 (BRD4) Binders through 3D Pharmacophore-Based Repositioning Screening Campaign.

A 3D structure-based pharmacophore model built for bromodomain-containing protein 4 (BRD4) is reported here, specifically developed for investigating and identifying the key structural features of the (+)-JQ1 known inhibitor within the BRD4 binding site. Using this pharmacophore model, 273 synthesized and purchased compounds previously considered for other targets but yielding poor results were screened in a drug repositioning campaign. Subsequently, only six compounds showed potential as BRD4 binders and were subjected to further biophysical and biochemical assays. Compounds 2, 5, and 6 showed high affinity for BRD4, with IC50 values of 0.60 ± 0.25 µM, 3.46 ± 1.22 µM, and 4.66 ± 0.52 µM, respectively. Additionally, these compounds were tested against two other bromodomains, BRD3 and BRD9, and two of them showed high selectivity for BRD4. The reported 3D structure-based pharmacophore model proves to be a straightforward and useful tool for selecting novel BRD4 ligands.

Controlled bioorthogonal activation of Bromodomain-containing protein 4 degrader by co-delivery of PROTAC and Pd-catalyst for tumor-specific therapy

The precise and safe treatment of bioorthogonal prodrug system is hindered by separate administration of prodrug and its activator, which often results in poor therapeutic effects and severe side effects. To address above issues, we herein construct a single bioorthogonal-activated co-delivery system for simultaneous PROTAC prodrug (proPROTAC) delivery and controlled, site-specific activation for tumor-specific treatment. In this co-delivery system (termed AuPLs), prodrug (proPROTAC) and water-soluble Pd-catalyst are first encapsulated by gold nanocubes (AuNCs), which are further coated with a layer of phase-change material (lauric acid/stearic acid, LA/SA). Below 39 °C, the solid state of LA/SA prevents the activation of Pd-mediated bioorthogonal reaction due to the solidification of Pd-catalyst and proPROTAC. Nevertheless, once over 42 °C, the phase change of LA/SA into liquid state, enabled by the photothermal effect of AuNCs, triggers the simultaneous release of proPROTAC and Pd-catalyst and initiates the in situ bioorthogonal reaction for proPROTAC activation. In the tumor-bearing mouse models, the systemic administration of AuPLs results in the accumulation in tumor region, where the photothermal effect activates and controls the tumor-specific bioorthogonal reaction to degrade BRD4 protein, leading to anti-tumor effects with minimized side effects. Overall, the co-delivery proPROTAC and Pd-catalyst and controlled activation by photothermal effects provide a precise way for biorthogonal-based anticancer prodrugs.

BRD4 absence inactivates endoplasmic reticulum stress to retard dehydroepiandrosterone-triggered ovarian granular cell apoptosis in polycystic ovary syndrome via GRP78

Polycystic ovary syndrome (PCOS) is a hormonal disorder and significantly affects reproductive and metabolic function. Bromodomain-containing protein 4 (BRD4) is reported to promote ovarian fibrosis in PCOS. The present work was conducted to investigate the detailed role of BRD4 and the corresponding functional mechanism in PCOS. Functional experiments including CCK-8 method, EDU staining and TUNEL staining were used to detect the key cellular processes. Western blot examined the expression of BRD4, apoptosis- and endoplasmic reticulum stress (ERS)-associated proteins. HDOCK server predicted the binding of BRD4 with Glucose-Regulated Protein 78 (GRP78), which was validated by Co-IP assay. BRD4 expression was increased and ERS was activated in dehydroepiandrosterone (DHEA)-induced KGN cells. Inhibition of BRD4 improved the viability whereas it inhibited the apoptosis and ERS of KGN cells induced by DHEA. In addition, BRD4 bound to GRP78. GRP78 elevation or ERS activator tunicamycin (TM) partly abolished the impacts of BRD4 silencing on the ERS, proliferation and apoptosis in DHEA-treated KGN cells. Anyway, knockdown of BRD4 may reduce DHEA-induced ovarian granular cell damage in PCOS via inactivating GRP78-mediated ERS.