Role of BET Inhibitors in Triple Negative Breast Cancers

Polymeric nanomaterials-based theranostic platforms for triple-negative breast cancer (TNBC) treatment

Breast cancer, the second leading global cause of death, affects 2.1 million women annually, with an alarming 15 percent mortality rate. Among its diverse forms, Triple-negative breast cancer (TNBC) emerges as the deadliest, characterized by the absence of hormone receptors. This article underscores the urgent need for innovative treatment approaches in tackling TNBC, emphasizing the transformative potential of polymeric nanomaterials (PNMs). Evolved through nanotechnology, PNMs offer versatile biomedical applications, particularly in addressing the intricate challenges of TNBC. The synthesis methods of PNMs, explored within the tumor microenvironment using cellular models, showcase their dynamic nature in cancer treatment. The article anticipates the future of TNBC therapeutics through the optimization of PNMs-based strategies, integrating them into photothermal (PT), photodynamic (PT), and hyperthermia therapy (HTT), drug delivery, and active tumor targeting strategies. Advancements in synthetic methods, coupled with a nuanced understanding of the tumor microenvironment, hold promise for personalized interventions. Comparative investigations of therapeutic models and a thorough exploration of polymeric nanoplatforms toxicological perspectives become imperative for ensuring efficacy and safety. We have explored the interdisciplinary collaboration between nanotechnology, oncology, and molecular biology as pivotal in translating PNMs innovations into tangible benefits for TNBC patients.

Epigenetic modulations in triple-negative breast cancer: Therapeutic implications for tumor microenvironment

Triple-negative breast cancer (TNBC) is an aggressive subtype lacking estrogen receptors, progesterone receptors and lacks HER2 overexpression. This absence of critical molecular targets poses significant challenges for conventional therapies. Immunotherapy, remarkably immune checkpoint blockade, offers promise for TNBC treatment, but its efficacy remains limited. Epigenetic dysregulation, including altered DNA methylation, histone modifications, and imbalances in regulators such as BET proteins, plays a crucial role in TNBC development and resistance to treatment. Hypermethylation of tumor suppressor gene promoters and the imbalance of histone methyltransferases such as EZH2 and histone deacetylases (HDACs) profoundly influence tumor cell proliferation, survival, and metastasis. In addition, epigenetic alterations critically shape the tumor microenvironment (TME), including immune cell composition, cytokine signaling, and immune checkpoint expression, ultimately contributing to immune evasion. Targeting these epigenetic mechanisms with specific inhibitors such as EZH2 and HDAC inhibitors in combination with immunotherapy represents a compelling strategy to remodel the TME, potentially overcoming immune evasion and enhancing therapeutic outcomes in TNBC. This review aims to comprehensively elucidate the current understanding of epigenetic modulation in TNBC, its influence on the TME, and the potential of combining epigenetic therapies with immunotherapy to overcome the challenges posed by this aggressive breast cancer subtype.

Epigenetic modulation of antitumor immunity and immunotherapy response in breast cancer: biological mechanisms and clinical implications

Breast cancer (BC) is the most common non-skin cancer and the second leading cause of cancer death in American women. The initiation and progression of BC can proceed through the accumulation of genetic and epigenetic changes that allow transformed cells to escape the normal cell cycle checkpoint control. Unlike nucleotide mutations, epigenetic changes such as DNA methylation, histone posttranslational modifications (PTMs), nucleosome remodeling and non-coding RNAs are generally reversible and therefore potentially responsive to pharmacological intervention. Epigenetic dysregulations are critical mechanisms for impaired antitumor immunity, evasion of immune surveillance, and resistance to immunotherapy. Compared to highly immunogenic tumor types, such as melanoma or lung cancer, breast cancer has been viewed as an immunologically quiescent tumor which displays a relatively low population of tumor-infiltrating lymphocytes (TIL), low tumor mutational burden (TMB) and modest response rates to immune checkpoint inhibitors (ICI). Emerging evidence suggests that agents targeting aberrant epigenetic modifiers may augment host antitumor immunity in BC via several interrelated mechanisms such as enhancing tumor antigen presentation, activation of cytotoxic T cells, inhibition of immunosuppressive cells, boosting response to ICI, and induction of immunogenic cell death (ICD). These discoveries have established a highly promising basis for using combinatorial approaches of epigenetic drugs with immunotherapy as an innovative paradigm to improve outcomes of BC patients. In this review, we summarize the current understanding of how epigenetic processes regulate immune cell function and antitumor immunogenicity in the context of the breast tumor microenvironment. Moreover, we discuss the therapeutic potential and latest clinical trials of the combination of immune checkpoint blockers with epigenetic agents in breast cancer.

Targeting the epigenetic reader "BET" as a therapeutic strategy for cancer

Bromodomain and extraterminal (BET) proteins have the ability to bind to acetylated lysine residues present in both histones and non-histone proteins. This binding is facilitated by the presence of tandem bromodomains. The regulatory role of BET proteins extends to chromatin dynamics, cellular processes, and disease progression. The BET family comprises of BRD 2, 3, 4 and BRDT. The BET proteins are a class of epigenetic readers that regulate the transcriptional activity of a multitude of genes that are involved in the pathogenesis of cancer. Thus, targeting BET proteins has been identified as a potentially efficacious approach for the treatment of cancer. BET inhibitors (BETis) are known to interfere with the binding of BET proteins to acetylated lysine residues of chromatin, thereby leading to the suppression of transcription of several genes, including oncogenic transcription factors. Here in this review, we focus on role of Bromodomain and extra C-terminal (BET) proteins in cancer progression. Furthermore, numerous small-molecule inhibitors with pan-BET activity have been documented, with certain compounds currently undergoing clinical assessment. However, it is apparent that the clinical effectiveness of the present BET inhibitors is restricted, prompting the exploration of novel technologies to enhance their clinical outcomes and mitigate undesired adverse effects. Thus, strategies like development of selective BET-BD1, & BD2 inhibitors, dual and acting BET are also presented in this review and attempts to cover the chemistry needed for proper establishment of designed molecules into BRD have been made. Moreover, the review attempts to summarize the details of research till date and proposes a space for future development of BET inhibitor with diminished side effects. It can be concluded that discovery of isoform selective BET inhibitors can be a way forward in order to develop BET inhibitors with negligible side effects.

Selectivity Mechanism of Pyrrolopyridone Analogues Targeting Bromodomain 2 of Bromodomain-Containing Protein 4 from Molecular Dynamics Simulations

Bromodomain and extra-terminal domain (BET) proteins play an important role in epigenetic regulation and are linked to several diseases; therefore, they are interesting targets. BET has two bromodomains: bromodomain 1 (BD1) and BD2. Selective targeting of BD1 or BD2 may produce different activities and greater effects than pan-BD inhibitors. However, the selective mechanism of the specific core must be studied at the atomic level. This study determined the effectiveness of pyrrolopyridone analogues to selectively inhibit BD2 using a pan-BD inhibitor (ABBV-075) and a selective-BD2 inhibitor (ABBV-744). Molecular dynamics simulations and calculations of binding free energies were used to systematically study the selectivity of BD2 inhibition by the pyrrolopyridone analogues. Overall, the pyrrolopyridone analogue inhibitors targeting BD2 interacted mainly with the following amino acid pairs between bromodomain-containing protein 4 (BRD4)-BD1 and BRD4-BD2 complexes: I146/V439, N140/N433, D144/H437, P82/P375, V87/V380, D88/D381, and Y139/Y432. The pyrrolopyridone analogues targeting BRD4-BD2 were divided into five regions based on selectivity mechanism. These results suggest that the R3 and R5 regions of pyrrolopyridone analogues can be modified to improve the selectivity between BRD4-BD1 and BRD4-BD2. The selectivity of BD2 inhibition by pyrrolopyridone analogues can be used to design novel BD2 inhibitors based on a pyrrolopyridone core.

Hypoxia: syndicating triple negative breast cancer against various therapeutic regimens

Triple-negative breast cancer (TNBC) is one of the deadliest subtypes of breast cancer (BC) for its high aggressiveness, heterogeneity, and hypoxic nature. Based on biological and clinical observations the TNBC related mortality is very high worldwide. Emerging studies have clearly demonstrated that hypoxia regulates the critical metabolic, developmental, and survival pathways in TNBC, which include glycolysis and angiogenesis. Alterations to these pathways accelerate the cancer stem cells (CSCs) enrichment and immune escape, which further lead to tumor invasion, migration, and metastasis. Beside this, hypoxia also manipulates the epigenetic plasticity and DNA damage response (DDR) to syndicate TNBC survival and its progression. Hypoxia fundamentally creates the low oxygen condition responsible for the alteration in Hypoxia-Inducible Factor-1alpha (HIF-1α) signaling within the tumor microenvironment, allowing tumors to survive and making them resistant to various therapies. Therefore, there is an urgent need for society to establish target-based therapies that overcome the resistance and limitations of the current treatment plan for TNBC. In this review article, we have thoroughly discussed the plausible significance of HIF-1α as a target in various therapeutic regimens such as chemotherapy, radiotherapy, immunotherapy, anti-angiogenic therapy, adjuvant therapy photodynamic therapy, adoptive cell therapy, combination therapies, antibody drug conjugates and cancer vaccines. Further, we also reviewed here the intrinsic mechanism and existing issues in targeting HIF-1α while improvising the current therapeutic strategies. This review highlights and discusses the future perspectives and the major alternatives to overcome TNBC resistance by targeting hypoxia-induced signaling.

The Robust Tumoricidal Effects of Combined BET/HDAC Inhibition in Cutaneous T-Cell Lymphoma Can Be Reproduced by ΔNp73 Depletion

Combined BET inhibitor/histone deacetylase inhibitor treatment induces marked apoptosis of cutaneous T-cell lymphoma (CTCL) with minimal normal T-cell toxicity. At 96 hours when apoptosis was extensive, a majority of CTCL lines showed ≥2-fold suppression of T-cell survival factors (e.g., AKT1, BCL2 antiapoptotic factors, BIRC5, CD40, CD70, GADD45A, PRKCA, TNFRSF1B, ΔNp73) and ≥2-fold upregulation of proapoptotic factors and tumor suppressors (e.g., ATM, BAK, BIM, multiple caspases, FHIT, HIC1, MGMT, NOD1) (P < 0.05). The largest alterations were in TP73 isoform expression, resulting in increased TAp73/ΔNp73 ratios in CTCL lines and leukemic Sézary cells. Targeted ΔNp73 inhibition by small interfering RNA knockdown resulted in robust CTCL apoptosis comparable with that induced by BET inhibitor/histone deacetylase inhibitor with minimal normal T-cell toxicity. Chromatin immunoprecipitation analysis showed that BET inhibitor/histone deacetylase inhibitor treatment reduced RNA polymerase II binding to ΔNp73, MYC, and AKT1 while increasing its binding to TAp73. CTCL skin lesions expressed both TAp73 and ΔNp73 isoforms in situ. In aggregate, these findings implicate TAp73/ΔNp73 balance as a major factor governing CTCL survival, show that the expression of p73 isoforms can be altered by molecular biological and pharmaceutical means, show that p73 isoforms are expressed across the entire CTCL clinical spectrum, and identify the p73 pathway as a potential target for therapeutics.

Epigenetic alterations in canine mammary cancer

In dogs, mammary cancer is the most common tumor type, especially in unspayed females. As in humans, this type of cancer has spontaneous development and is influenced by several risk factors, such as age and hormonal exposure in addition to genetic and epigenetic factors. Epigenetic mechanisms are responsible for gene expression modulation without alterations in the DNA sequence and include but are not limited to DNA methylation, histone modifications, and noncoding RNAs. Epigenetic patterns are known to influence a variety of biological mechanisms, such as cellular differentiation and development, and dysregulations of those patterns may result in several diseases, such as cancer. In this respect, this review summarizes the main findings concerning epigenetic alterations in canine mammary cancer, their relationship with the carcinogenic process, and their use as diagnostic and prognostic markers.

The binding mechanism of NHWD-870 to bromodomain-containing protein 4 based on molecular dynamics simulations and free energy calculation

Bromodomain and extra-terminal (BET) proteins (BRD2, BRD3, BRD4, and BRDT) are epigenetic readers with tandem bromodomains.

A Novel Circular RNA circPTCD3 Promotes Breast Cancer Progression Through Sponging miR-198

Introduction

Circular RNAs (circRNAs), a new type of non-coding RNA, have been demonstrated to play critical roles in the progression of various of malignant cancers. However, the function of circRNAs in breast cancer is not clearly understood.

Methods

qPCR was used to evaluate the gene expression. Function studies including MTT, transwell, wound healing and colony formation assay were performed to evaluate the function of circPTCD3 in breast cancer. Luciferase and RNA pull-down assays were used to verify the interaction between circPTCD3 and miR-198. The xenograft model was established to evaluate the function of circPTCD3 in vivo.

Results

In the present study, we identified a novel circRNA termed as circPTCD3 which was indicated to be significantly up-regulated in breast cancer tissues and cell lines. The results revealed that ectopic expression of circPTCD3 promoted the cell proliferation, migration and colony formation ability of breast cancer cells. Constantly, silencing of circPTCD3 inhibited those of breast cancer cells. Furthermore, we identified that circPTCD3 was able to target miR-198 in breast cancer cell. miR-198 has the function of inhibiting proliferation and migration of breast cancer cells which can be reversed by circPTCD3.

Conclusion

Taken together, our findings for the first time identified a novel circRNA (circPTCD3) and revealed its oncogenic role in breast cancer. Mechanically, we reported that circPTCD3 served as a competing endogenous RNA (ceRNA) to sponge miR-198. These findings provide insights into breast cancer progression and also potential new targets for diagnosis or treatment of breast cancer.

Discovery of Potent and Selective CDK9 Degraders for Targeting Transcription Regulation in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is highly aggressive with very limited treatment options due to the lack of efficient targeted therapies and thus still remains clinically challenging. Targeting transcription-associated cyclin-dependent kinases to remodel transcriptional regulation shows great promise in cancer therapy. Herein, we report the synthesis, optimization, and evaluation of new series of heterobifunctional molecules as highly selective and efficacious CDK9 degraders, enabling potent inhibition of TNBC cell growth and rapidly targeted degradation of CDK9. Moreover, the most potent CDK9 degrader (compound 45) induces cell apoptosis in vitro and inhibits tumor growth in the MDA-MB-231 TNBC model. Furthermore, the RNA-seq, immunohistochemistry assays demonstrate that the CDK9 degrader downregulates the downstream targets, such as MYC, at the transcriptional level, resulting apoptosis in TNBC cells. Our work establishes that 45 is a highly potent and efficacious CDK9 degrader for targeting transcription regulation, which represents an effective strategy and great potential as a new targeted therapy for TNBC.

Brd4 Regulates the Homeostasis of CD8+ T-Lymphocytes and Their Proliferation in Response to Antigen Stimulation

CD8+ T cells are major components of adaptive immunity and confer robust protective cellular immunity, which requires adequate T-cell numbers, targeted migration, and efficient T-cell proliferation. Altered CD8+ T-cell homeostasis and impaired proliferation result in dysfunctional immune response to infection or tumorigenesis. However, intrinsic factors controlling CD8+ T-cell homeostasis and immunity remain largely elusive. Here, we demonstrate the prominent role of Brd4 on CD8+ T cell homeostasis and immune response. By upregulating Myc and GLUT1 expression, Brd4 facilitates glucose uptake and energy production in mitochondria, subsequently supporting naïve CD8+ T-cell survival. Besides, Brd4 promotes the trafficking of naïve CD8+ T cells partially through maintaining the expression of homing receptors (CD62L and LFA-1). Furthermore, Brd4 is required for CD8+ T cell response to antigen stimulation, as Brd4 deficiency leads to a severe defect in clonal expansion and terminal differentiation by decreasing glycolysis. Importantly, as JQ1, a pan-BRD inhibitor, severely dampens CD8+ T-cell immune response, its usage as an anti-tumor agent or latency-reversing agent for human immunodeficiency virus type I (HIV-1) should be more cautious. Collectively, our study identifies a previously-unexpected role of Brd4 in the metabolic regulation of CD8+ T cell-mediated immune surveillance and also provides a potential immunomodulation target.

Bromodomain protein BRD4 directs and sustains CD8 T cell differentiation during infection

In response to infection, pathogen-specific CD8 T cells differentiate into functionally diverse effector and memory T cell populations critical for resolving disease and providing durable immunity. Through small-molecule inhibition, RNAi studies, and induced genetic deletion, we reveal an essential role for the chromatin modifier and BET family member BRD4 in supporting the differentiation and maintenance of terminally fated effector CD8 T cells during infection. BRD4 bound diverse regulatory regions critical to effector T cell differentiation and controlled transcriptional activity of terminal effector-specific super-enhancers in vivo. Consequentially, induced deletion of Brd4 or small molecule-mediated BET inhibition impaired maintenance of a terminal effector T cell phenotype. BRD4 was also required for terminal differentiation of CD8 T cells in the tumor microenvironment in murine models, which we show has implications for immunotherapies. Taken together, these data reveal an unappreciated requirement for BRD4 in coordinating activity of cis regulatory elements to control CD8 T cell fate and lineage stability.

Inhibiting BRD4 to generate BETter T cell memory

BRD4 is a bromodomain-containing protein that binds acetylated histones to regulate transcription. In this issue of JEM, Milner et al. (2021. J. Exp. Med.https://doi.org/10.1084/jem.20202512) show that BRD4 plays a critical role in the effector function of CD8 T cells responding to infection and cancer.

MZ1 co-operates with trastuzumab in HER2 positive breast cancer

BACKGROUND

Although the anti-HER2 antibody trastuzumab augments patient survival in HER2+ breast cancer, a relevant number of patients progress to this treatment. In this context, novel drug combinations are needed to increase its antitumor activity. In this work, we have evaluated the efficacy of proteolysis targeting chimera (PROTAC) compounds based on BET inhibitors (BETi) to augment the activity of trastuzumab in HER2+ breast cancer models.

METHODS

BT474 and SKBR3 HER2+ breast cancer cell lines were used. The effects of trastuzumab and the BET-PROTAC MZ1 either alone or in combination, were evaluated using MTT proliferation assays, three-dimensional invasion and adhesion cultures, flow cytometry, qPCR and Western blot. In vivo studies were carried out in a xenografted model in mice. Finally, a Clariom_S_Human transcriptomic array was applied to identify deregulated genes after treatments.

RESULTS

MZ1 induced a higher antiproliferative effect compared to the BETi JQ1. The combination of MZ1 and -trastuzumab significantly decreased cell proliferation, the formation of three-dimensional structures and cellular invasion compared to either of the drugs alone. Evaluation of apoptosis resulted in an increase of cell death following treatment with the combination, and biochemical studies displayed modifications of apoptosis and DNA damage components. In vivo administration of agents alone or combined, to tumors orthotopically xenografted in mice, resulted in a decrease of the tumor volume only after MZ1-Trastuzumab combination treatment. Results from a transcriptomic array indicated a series of newly described transcription factors including HOXB7, MEIS2, TCERG1, and DNAJC2, that were associated to poor outcome in HER2+ breast cancer subtype and downregulated by the MZ1-trastuzumab combination.

CONCLUSIONS

We describe an active novel combination that includes the BET-PROTAC MZ1 and trastuzumab, in HER2+ tumors. Further studies should be performed to confirm these findings and pave the way for their future clinical development.

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.

Epigenetics in Inflammatory Breast Cancer: Biological Features and Therapeutic Perspectives

Evidence has emerged implicating epigenetic alterations in inflammatory breast cancer (IBC) origin and progression. IBC is a rare and rapidly progressing disease, considered the most aggressive type of breast cancer (BC). At clinical presentation, IBC is characterized by diffuse erythema, skin ridging, dermal lymphatic invasion, and peau d'orange aspect. The widespread distribution of the tumor as emboli throughout the breast and intra- and intertumor heterogeneity is associated with its poor prognosis. In this review, we highlighted studies documenting the essential roles of epigenetic mechanisms in remodeling chromatin and modulating gene expression during mammary gland differentiation and the development of IBC. Compiling evidence has emerged implicating epigenetic changes as a common denominator linking the main risk factors (socioeconomic status, environmental exposure to endocrine disruptors, racial disparities, and obesity) with IBC development. DNA methylation changes and their impact on the diagnosis, prognosis, and treatment of IBC are also described. Recent studies are focusing on the use of histone deacetylase inhibitors as promising epigenetic drugs for treating IBC. All efforts must be undertaken to unravel the epigenetic marks that drive this disease and how this knowledge could impact strategies to reduce the risk of IBC development and progression.