Restoration of tamoxifen sensitivity in estrogen receptor-negative breast cancer cells: tamoxifen-bound reactivated ER recruits distinctive corepressor complexes

Drug response-based precision therapeutic selection for tamoxifen-resistant triple-positive breast cancer

Breast cancer adaptability to the drug environment reduces the chemotherapeutic response and facilitates acquired drug resistance. Cancer-specific therapeutics can be more effective against advanced-stage cancer than standard chemotherapeutics. To extend the paradigm of cancer-specific therapeutics, clinically relevant acquired tamoxifen-resistant MCF-7 proteome was deconstructed to identify possible druggable targets (N = 150). Twenty-eight drug inhibitors were used against identified druggable targets to suppress non-resistant (NC) and resistant cells (RC). First, selected drugs were screened using growth-inhibitory response against NC and RC. Seven drugs were shortlisted for their time-dependent (10-12 days) cytotoxic effect and further narrowed to three effective drugs (e.g., cisplatin, doxorubicin, and hydroxychloroquine). The growth-suppressive effectiveness of selected drugs was validated in the complex spheroid model (progressive and regressive). In the progressive model, doxorubicin (RC: 83.64 %, NC: 54.81 %), followed by cisplatin (RC: 76.66 %, NC: 68.94 %) and hydroxychloroquine (RC: 68.70 %, NC: 61.78 %) showed a significant growth-suppressive effect. However, in fully grown regressive spheroid, after 4th drug treatment, cisplatin significantly suppressed RC (84.79 %) and NC (40.21 %), while doxorubicin and hydroxychloroquine significantly suppressed only RC (76.09 and 76.34 %). Our in-depth investigation effectively integrated the expression data with the cancer-specific therapeutic investigation. Furthermore, our three-step sequential drug-screening approach unbiasedly identified cisplatin, doxorubicin, and hydroxychloroquine as an efficacious drug to target heterogeneous cancer cell populations. SIGNIFICANCE STATEMENT: Hormonal-positive BC grows slowly, and hormonal-inhibitors effectively suppress the oncogenesis. However, development of drug-resistance not only reduces the drug-response but also increases the chance of BC aggressiveness. Further, alternative chemotherapeutics are widely used to control advanced-stage BC. In contrast, we hypothesized that, compared to standard chemotherapeutics, cancer-specific drugs can be more effective against resistant-cancer. Although cancer-specific treatment identification is an uphill battle, our work shows proteome data can be used for drug selection. We identified multiple druggable targets and, using ex-vivo methods narrowed multiple drugs to disease-condition-specific therapeutics. We consider that our investigation successfully interconnected the expression data with the functional disease-specific therapeutic investigation and selected drugs can be used for effective resistant treatment with higher therapeutic response.

The vitamin D analog EB1089 sensitizes triple-negative breast cancer cells to the antiproliferative effects of antiestrogens

PURPOSE

Patients bearing estrogen receptor (ER)α-negative breast cancer tumors confront poor prognosis and are typically unresponsive to hormone therapy. Previous studies have shown that calcitriol, the active vitamin D metabolite, can induce ERα expression in ERα-negative cells. EB1089, a calcitriol analog with reduced calcemic effects, exhibits greater potency than calcitriol in inhibiting cancer cell growth. However, the impact of EB1089 on ERα expression in triple-negative breast cancer (TNBC) cells remains unexplored. This study aims to investigate whether EB1089 could induce functional ERα expression in TNBC cell lines, potentially enabling the antiproliferative effects of antiestrogens.

MATERIALS AND METHODS

TNBC cell lines HCC1806 and HCC1937 were treated with EB1089, and ERα expression was analyzed using real-time PCR and Western blots. The transcriptional activity of induced ERα was evaluated through a luciferase reporter assay. The antiproliferative effects of tamoxifen and fulvestrant antiestrogens were assessed using the sulforhodamine B assay in the EB1089-treated cells.

RESULTS

Our findings indicated that EB1089 significantly induced ERα mRNA and protein expression in TNBC cells. Moreover, EB1089-induced ERα exhibited transcriptional activity and effectively restored the inhibitory effects of antiestrogens, thereby suppressing cell proliferation in TNBC cells.

CONCLUSION

EB1089 induced the expression of functional ERα in TNBC cells, restoring the antiproliferative effects of antiestrogens. These results highlight the potential of using EB1089 as a promising strategy for re-establishment of the antiproliferative effect of antiestrogens as a possible management for TNBC. This research lays the foundation for potential advancements in TNBC treatment, offering new avenues for targeted and effective interventions.

Hdac3 deficiency limits periosteal reaction associated with Western diet feeding in female mice

Diet-induced obesity is associated with enhanced systemic inflammation that limits bone regeneration. HDAC inhibitors are currently being explored as anti-inflammatory agents. Prior reports show that myeloid progenitor-directed Hdac3 ablation enhances intramembranous bone healing in female mice. In this study, we determined if Hdac3 ablation increased intramembranous bone regeneration in mice fed a high-fat/high-sugar (HFD) diet. Micro-CT analyses demonstrated that HFD-feeding enhanced the formation of periosteal reaction tissue of control littermates, reflective of suboptimal bone healing. We confirmed enhanced bone volume within the defect of Hdac3-ablated females and showed that Hdac3 ablation reduced the amount of periosteal reaction tissue following HFD feeding. Osteoblasts cultured in a conditioned medium derived from Hdac3-ablated cells exhibited a four-fold increase in mineralization and enhanced osteogenic gene expression. We found that Hdac3 ablation elevated the secretion of several chemokines, including CCL2. We then confirmed that Hdac3 deficiency increased the expression of Ccl2. Lastly, we show that the proportion of CCL2-positve cells within bone defects was significantly higher in Hdac3-deficient mice and was further enhanced by HFD. Overall, our studies demonstrate that Hdac3 deletion enhances intramembranous bone healing in a setting of diet-induced obesity, possibly through increased production of CCL2 by macrophages within the defect.

Selective Estrogen Receptor Modulators' (SERMs) Influence on TET3 Expression in Breast Cancer Cell Lines with Distinct Biological Subtypes

Tamoxifen, a selective estrogen receptor modulator (SERM), exhibits dual agonist or antagonist effects contingent upon its binding to either G-protein-coupled estrogen receptor (GPER) or estrogen nuclear receptor (ESR). Estrogen signaling plays a pivotal role in initiating epigenetic alterations and regulating estrogen-responsive genes in breast cancer. Employing three distinct breast cancer cell lines-MCF-7 (ESR+; GPER+), MDA-MB-231 (ESR-; GPER-), and SkBr3 (ESR-; GPER+)-this study subjected them to treatment with two tamoxifen derivatives: 4-hydroxytamoxifen (4-HT) and endoxifen (Endox). Through 2D high-performance liquid chromatography with tandem mass spectrometry detection (HPLC-MS/MS), varying levels of 5-methylcytosine (5-mC) were found, with MCF-7 displaying the highest levels. Furthermore, TET3 mRNA expression levels varied among the cell lines, with MCF-7 exhibiting the lowest expression. Notably, treatment with 4-HT induced significant changes in TET3 expression across all cell lines, with the most pronounced increase seen in MCF-7 and the least in MDA-MB-231. These findings underscore the influence of tamoxifen derivatives on DNA methylation patterns, particularly through modulating TET3 expression, which appears to be contingent on the presence of estrogen receptors. This study highlights the potential of targeting epigenetic modifications for personalized anti-cancer therapy, offering a novel avenue to improve treatment outcomes.

Estradiol induces bone osteolysis in triple-negative breast cancer via its membrane-associated receptor ERα36

Triple-negative breast cancer (TNBC) is thought to be an estradiol-independent, hormone therapy-resistant cancer because of lack of estrogen receptor alpha 66 (ERα66). We identified a membrane-bound splice variant, ERα36, in TNBC cells that responds to estrogen (E2) and may contribute to bone osteolysis. We demonstrated that the MDA-MB-231 TNBC cell line, which expresses ERα36 similarly to MCF7 cells, is responsive to E2, forming osteolytic tumors in vivo. MDA-MB-231 cells activate osteoclasts in a paracrine manner. Conditioned media (CM) from MDA-MB-231 cells treated with bovine serum albumin-bound E2 (E2-BSA) increased activation of human osteoclast precursor cells; this was blocked by addition of anti-ERα36 antibody to the MDA-MB-231 cultures. Osteoclast activation and bone resorption genes were elevated in RAW 264.7 murine macrophages following treatment with E2-BSA-stimulated MDA-MB-231 CM. E2 and E2-BSA increased phospholipase C (PLC) and protein kinase C (PKC) activity in MDA-MB-231 cells. To examine the role of ERα36 signaling in bone osteolysis in TNBC, we used our bone-cancer interface mouse model in female athymic homozygous Foxn1nu mice. Mice with MDA-MB-231 tumors and treated with tamoxifen (TAM), E2, or TAM/E2 exhibited increased osteolysis, cortical bone breakdown, pathologic fracture, and tumor volume; the combined E2/TAM group also had reduced bone volume. These results suggest that E2 increased osteolytic lesions in TNBC through a membrane-mediated PLC/PKC pathway involving ERα36, which was enhanced by TAM, demonstrating the role of ERα36 and its membrane-associated signaling pathway in bone tumors. This work suggests that ERα36 may be a potential therapeutic target in patients with TNBC.

Progress in the Understanding of Estrogen Receptor Alpha Signaling in Triple-Negative Breast Cancer: Reactivation of Silenced ER-α and Signaling through ER-α36

Triple-negative breast cancer (TNBC) is an aggressive tumor that accounts for approximately 15% of total breast cancer cases. It is characterized by poor prognosis and high rate of recurrence compared to other types of breast cancer. TNBC has a limited range of treatment options that include chemotherapy, surgery, and radiation due to the absence of estrogen receptor alpha (ER-α) rendering hormonal therapy ineffective. However, possible targets for improving the clinical outcomes in TNBC exist, such as targeting estrogen signaling through membranous ER-α36 and reactivating silenced ER-α. It has been shown that epigenetic drugs such as DNA methyltransferase and histone deacetylase inhibitors can restore the expression of ER-α. This reactivation of ER-α, presents a potential strategy to re-sensitize TNBC to hormonal therapy. Also, this review provides up-to-date information related to the direct involvement of miRNA in regulating the translation of ER-α mRNA. Specific epi-miRNAs can regulate ER-α expression indirectly by post-transcriptional targeting of mRNAs of enzymes that are involved in DNA methylation and histone deacetylation. Furthermore, ER-α36, an alternative splice variant of ER-α66, is highly expressed in ER-negative breast tumors and activates MAPK/ERK pathway, promoting cell proliferation, escaping apoptosis, and enhancing metastasis. In the future, these recent advances may be helpful for researchers working in the field to obtain novel treatment options for TNBC, utilizing epigenetic drugs and epi-miRNAs that regulate ER-α expression. Also, there is some evidence to suggest that drugs that decrease the expression of ER-α36 may be effective in treating TNBC.

Glucocorticoid induced loss of oestrogen receptor alpha gene methylation and restoration of sensitivity to fulvestrant in triple negative breast cancer

The response to psychological stress can differ depending on the type and duration of the stressor. Acute stress can facilitate a "fight or flight response" and aid survival, whereas chronic long-term stress with the persistent release of stress hormones such as cortisol has been shown to be detrimental to health. We are now beginning to understand how this stress hormone response impacts important processes such as DNA repair and cell proliferation processes in breast cancer. However, it is not known what epigenetic changes stress hormones induce in breast cancer. Epigenetic mechanisms include modification of DNA and histones within chromatin that may be involved in governing the transcriptional processes in cancer cells in response to changes by endogenous stress hormones. The contribution of endogenous acute or long-term exposure of glucocorticoid stress hormones, and exogenous glucocorticoids to methylation patterns in breast cancer tissues with different aetiologies remains to be evaluated. In vitro and in vivo models were developed to investigate the epigenetic modifications and their contribution to breast cancer progression and aetiology. A panel of triple negative breast cancer cell lines were treated with the glucocorticoid, cortisol which resulted in epigenetic alteration characterised by loss of methylation on promoter regions of tumour suppressor genes including ESR1, and loss of methylation on LINE-1 repetitive element used as a surrogate marker for global methylation. This was verified in vivo in MDA-MB-231 xenografts; the model verified the loss of methylation on ESR1 promoter, and subsequent increase in ESR1 expression in primary tumours in mice subjected to restraint stress. Our study highlights that DNA methylation landscape in breast cancer can be altered in response to stress and glucocorticoid treatment.

MOF negatively regulates estrogen receptor α signaling via CUL4B-mediated protein degradation in breast cancer

Estrogen receptor α (ERα) is the dominant tumorigenesis driver in breast cancer (BC), and ERα-positive BC (ERα+ BC) accounts for more than two-thirds of BC cases. MOF (males absent on the first) is a highly conserved histone acetyltransferase that acetylates lysine 16 of histone H4 (H4K16) and several non-histone proteins. Unbalanced expression of MOF has been identified, and high MOF expression predicted a favorable prognosis in BC. However, the association of MOF with ERα and the regulatory mechanisms of MOF in ERα signaling remain elusive. Our study revealed that the expression of MOF is negatively correlated with that of ERα in BC. In ERα+ BC cells, MOF overexpression downregulated the protein abundance of ERα in both cytoplasm and nucleus, thus attenuating ERα-mediated transactivation as well as cellular proliferation and in vivo tumorigenicity of BC cells. MOF promoted ERα protein degradation through CUL4B-mediated ubiquitin–proteasome pathway and induced HSP90 hyperacetylation that led to the loss of chaperone protection of HSP90 to ERα. We also revealed that suppression of MOF restored ERα expression and increased the sensitivity of ERα-negative BC cells to tamoxifen treatment. These results provide a new insight into the tumor-suppressive role of MOF in BC via negatively regulating ERα action, suggesting that MOF might be a potential therapeutic target for BC.

Triple negative breast cancer (TNBC): Non-genetic tumor heterogeneity and immune microenvironment: Emerging treatment options

Triple-negative breast cancer (TNBC) is an aggressive subtype characterized by extensive intra-tumoral heterogeneity, and frequently develops resistance to therapies. Tumor heterogeneity and lack of biomarkers are thought to be some of the most difficult challenges driving therapeutic resistance and relapse. This review will summarize current therapy for TNBC, studies in treatment resistance and relapse, including data from recent single cell sequencing. We will discuss changes in both the transcriptome and epigenome of TNBC, and we will review mechanisms regulating the immune microenvironment. Lastly, we will provide new perspective in patient stratification, and treatment options targeting transcriptome dysregulation and the immune microenvironment of TNBC patients.

A high-throughput drug screen reveals means to differentiate triple-negative breast cancer

Plasticity delineates cancer subtypes with more or less favourable outcomes. In breast cancer, the subtype triple-negative lacks expression of major differentiation markers, e.g., estrogen receptor α (ERα), and its high cellular plasticity results in greater aggressiveness and poorer prognosis than other subtypes. Whether plasticity itself represents a potential vulnerability of cancer cells is not clear. However, we show here that cancer cell plasticity can be exploited to differentiate triple-negative breast cancer (TNBC). Using a high-throughput imaging-based reporter drug screen with 9 501 compounds, we have identified three polo-like kinase 1 (PLK1) inhibitors as major inducers of ERα protein expression and downstream activity in TNBC cells. PLK1 inhibition upregulates a cell differentiation program characterized by increased DNA damage, mitotic arrest, and ultimately cell death. Furthermore, cells surviving PLK1 inhibition have decreased tumorigenic potential, and targeting PLK1 in already established tumours reduces tumour growth both in cell line- and patient-derived xenograft models. In addition, the upregulation of genes upon PLK1 inhibition correlates with their expression in normal breast tissue and with better overall survival in breast cancer patients. Our results indicate that differentiation therapy based on PLK1 inhibition is a potential alternative strategy to treat TNBC.

Chemotherapy and Physical Therapeutics Modulate Antigens on Cancer Cells

Cancer cells possess specific properties, such as multidrug resistance or unlimited proliferation potential, due to the presence of specific proteins on their cell membranes. The release of proliferation-related proteins from the membrane can evoke a loss of adaptive ability in cancer cells and thus enhance the effects of anticancer therapy. The upregulation of cancer-specific membrane antigens results in a better outcome of immunotherapy. Moreover, cytotoxic T-cells may also become more effective when stimulated ex-vivo toward the anticancer response. Therefore, the modulation of membrane proteins may serve as an interesting attempt in anticancer therapy. The presence of membrane antigens relies on various physical factors such as temperature, exposure to radiation, or drugs. Therefore, changing the tumor microenvironment conditions may lead to cancer cells becoming sensitized to subsequent therapy. This paper focuses on the therapeutic approaches modulating membrane antigens and enzymes in anticancer therapy. It aims to analyze the possible methods for modulating the antigens, such as pharmacological treatment, electric field treatment, photodynamic reaction, treatment with magnetic field or X-ray radiation. Besides, an overview of the effects of chemotherapy and immunotherapy on the immunophenotype of cancer cells is presented. Finally, the authors review the clinical trials that involved the modulation of cell immunophenotype in anticancer therapy.

Rewiring of the Endocrine Network in Triple-Negative Breast Cancer

The immunohistochemical definition of estrogen/progesterone receptors dictates endocrine feasibility in the treatment course of breast cancer. Characterized by the deficiency of estrogen receptor α, ERα-negative breast cancers are dissociated from any endocrine regimens in the routine clinical setting, triple-negative breast cancer in particular. However, the stereotype was challenged by triple-negative breast cancers’ retained sensitivity and vulnerability to endocrine agents. The interplay of hormone action and the carcinogenic signaling program previously underscored was gradually recognized along with the increasing investigation. In parallel, the overlooked endocrine-responsiveness in ERα-negative breast cancers attracted attention and supplied fresh insight into the therapeutic strategy in an ERα-independent manner. This review elaborates on the genomic and non-genomic steroid hormone actions and endocrine-related signals in triple-negative breast cancers attached to the hormone insensitivity label. We also shed light on the non-canonical mechanism detected in common hormone agents to showcase their pleiotropic effects.

Nuclear Receptor Coregulators in Hormone-Dependent Cancers

Nuclear receptors (NRs) function collectively as a transcriptional signaling network that mediates gene regulatory actions to either maintain cellular homeostasis in response to hormonal, dietary and other environmental factors, or act as orphan receptors with no known ligand. NR complexes are large and interact with multiple protein partners, collectively termed coregulators. Coregulators are essential for regulating NR activity and can dictate whether a target gene is activated or repressed by a variety of mechanisms including the regulation of chromatin accessibility. Altered expression of coregulators contributes to a variety of hormone-dependent cancers including breast and prostate cancers. Therefore, understanding the mechanisms by which coregulators interact with and modulate the activity of NRs provides opportunities to develop better prognostic and diagnostic approaches, as well as novel therapeutic targets. This review aims to gather and summarize recent studies, techniques and bioinformatics methods used to identify distorted NR coregulator interactions that contribute as cancer drivers in hormone-dependent cancers.

Epigenetic Factors as Etiological Agents, Diagnostic Markers, and Therapeutic Targets for Luminal Breast Cancer

Luminal breast cancer, an etiologically heterogeneous disease, is characterized by high steroid hormone receptor activity and aberrant gene expression profiles. Endocrine therapy and chemotherapy are promising therapeutic approaches to mitigate breast cancer proliferation and recurrence. However, the treatment of therapy-resistant breast cancer is a major challenge. Recent studies on breast cancer etiology have revealed the critical roles of epigenetic factors in luminal breast cancer tumorigenesis and drug resistance. Tumorigenic epigenetic factor-induced aberrant chromatin dynamics dysregulate the onset of gene expression and consequently promote tumorigenesis and metastasis. Epigenetic dysregulation, a type of somatic mutation, is a high-risk factor for breast cancer progression and therapy resistance. Therefore, epigenetic modulators alone or in combination with other therapies are potential therapeutic agents for breast cancer. Several clinical trials have analyzed the therapeutic efficacy of potential epi-drugs for breast cancer and reported beneficial clinical outcomes, including inhibition of tumor cell adhesion and invasiveness and mitigation of endocrine therapy resistance. This review focuses on recent findings on the mechanisms of epigenetic factors in the progression of luminal breast cancer. Additionally, recent findings on the potential of epigenetic factors as diagnostic biomarkers and therapeutic targets for breast cancer are discussed.

Discovering the Triad between Nav1.5, Breast Cancer, and the Immune System: A Fundamental Review and Future Perspectives

Nav1.5 is one of the nine voltage-gated sodium channel-alpha subunit (VGSC-α) family members. The Nav1.5 channel typically carries an inward sodium ion current that depolarises the membrane potential during the upstroke of the cardiac action potential. The neonatal isoform of Nav1.5, nNav1.5, is produced via VGSC-α alternative splicing. nNav1.5 is known to potentiate breast cancer metastasis. Despite their well-known biological functions, the immunological perspectives of these channels are poorly explored. The current review has attempted to summarise the triad between Nav1.5 (nNav1.5), breast cancer, and the immune system. To date, there is no such review available that encompasses these three components as most reviews focus on the molecular and pharmacological prospects of Nav1.5. This review is divided into three major subsections: (1) the review highlights the roles of Nav1.5 and nNav1.5 in potentiating the progression of breast cancer, (2) focuses on the general connection between breast cancer and the immune system, and finally (3) the review emphasises the involvements of Nav1.5 and nNav1.5 in the functionality of the immune system and the immunogenicity. Compared to the other subsections, section three is pretty unexploited; it would be interesting to study this subsection as it completes the triad.

Development of novel tetrahydroisoquinoline-hydroxamate conjugates as potent dual SERDs/HDAC inhibitors for the treatment of breast cancer

Concomitant inhibition of estrogen receptor alpha (ERα) and histone deacetylase (HDAC) signaling has been proven effective in endocrine-resistant ER+ breast cancers. Herein, a series of tetrahydroisoquinoline (THIQ)-hydroxamate conjugates were rationally designed and synthesized as dual SERDs/HDAC inhibitors by incorporating the hydroxamate, a known HDAC pharmacophore, into a privileged THIQ scaffold of selective ERα degraders (SERDs). Some of these THIQ-hydroxamate conjugates displayed remarkable HDAC6 inhibition and improved antiproliferative activity against MCF-7 cells. Particularly, the most potent HDAC inhibitor 19k also exhibits potent ERα binding affinity, good ERα degradation efficacy and the best antiproliferative activity. Besides, 19k displayed superior antitumor efficacy than the drug combination (Fulvestrant + SAHA) through promoting ERα degradation and histone acetylation in an MCF-7 xenograft model, without causing observable toxicity. Collectively, this study validates the therapeutic potential of a dual-acting compound with potent ERα degradation efficacy and HDAC6 inhibition in breast cancer.

Targeting Histone Modifications in Breast Cancer: A Precise Weapon on the Way

Histone modifications (HMs) contribute to maintaining genomic stability, transcription, DNA repair, and modulating chromatin in cancer cells. Furthermore, HMs are dynamic and reversible processes that involve interactions between numerous enzymes and molecular components. Aberrant HMs are strongly associated with tumorigenesis and progression of breast cancer (BC), although the specific mechanisms are not completely understood. Moreover, there is no comprehensive overview of abnormal HMs in BC, and BC therapies that target HMs are still in their infancy. Therefore, this review summarizes the existing evidence regarding HMs that are involved in BC and the potential mechanisms that are related to aberrant HMs. Moreover, this review examines the currently available agents and approved drugs that have been tested in pre-clinical and clinical studies to evaluate their effects on HMs. Finally, this review covers the barriers to the clinical application of therapies that target HMs, and possible strategies that could help overcome these barriers and accelerate the use of these therapies to cure patients.

The epigenetics of breast cancer - Opportunities for diagnostics, risk stratification and therapy

The stage and molecular pathology-dependent prognosis of breast cancer, the limited treatment options for triple-negative carcinomas, as well as the development of resistance to therapies illustrate the need for improved early diagnosis and the development of new therapeutic approaches. Increasing data suggests that some answers to these challenges could be found in the area of epigenetics. In this study, we focus on the current research of the epigenetics of breast cancer, especially on the potential of epigenetics for clinical application in diagnostics, risk stratification and therapy. The differential DNA methylation status of specific gene regions has been used in the past to differentiate breast cancer cells from normal tissue. New technologies as detection of circulating nucleic acids including microRNAs to early detect breast cancer are emerging. Pattern of DNA methylation and expression of histone-modifying enzymes have been successfully used for risk stratification. However, all these epigenetic biomarkers should be validated in larger clinical studies. Recent preclinical and clinical studies show a therapeutic benefit of epigenetically active drugs for breast cancer entities that are still difficult to treat (triple negative, UICC stage IV). Remarkably, epigenetic therapies combined with chemotherapies or hormone-based therapies represent the most promising strategy. At the current stage, the integration of epigenetic substances into established breast cancer therapy protocols seems to hold the greatest potential for a clinical application of epigenetic research.

BET inhibition increases βIII-tubulin expression and sensitizes metastatic breast cancer in the brain to vinorelbine

Metastases from primary breast cancer result in poor survival. βIII-tubulin (TUBB3) has been established as a therapeutic target for breast cancer metastases specifically to the brain. In this study, we conducted a systematic analysis to determine the regulation of TUBB3 expression in breast cancer metastases to the brain and strategically target these metastases using vinorelbine (VRB), a drug approved by the U.S. Food and Drug Administration (FDA). We found that human epidermal growth factor receptor 2 (HER2) signaling regulates TUBB3 expression in both trastuzumab-sensitive and trastuzumab-resistant neoplastic cells. We further discovered that bromodomain and extra-terminal domain (BET) inhibition increases TUBB3 expression, rendering neoplastic cells more susceptible to apoptosis by VRB. Orthotopic xenograft assays using two different breast cancer cell models revealed a reduction in tumor volume with BET inhibition and VRB treatment. In addition, in vivo studies using a model of multiple brain metastasis (BM) showed improved survival with the combination of radiation + BET inhibitor (iBET-762) + VRB (75% long-term survivors, P < 0.05). Using in silico analysis and BET inhibition, we found that the transcription factor myeloid zinc finger-1 (MZF-1) protein binds to the TUBB3 promoter. BET inhibition decreases MZF-1 expression and subsequently increases TUBB3 expression. Overexpression of MZF-1 decreases TUBB3 expression and reduces BM in vivo, whereas its knockdown increases TUBB3 expression in breast cancer cells. In summary, this study demonstrates a regulatory mechanism of TUBB3 and provides support for an application of BET inhibition to sensitize breast cancer metastases to VRB-mediated therapy.

Identification of epigenetic regulators in the estrogen signaling pathway via siRNA screening

Breast cancer is the most prevalent malignant disease among women across the globe. Notably, estrogen signaling plays a vital role in the progression of estrogen receptor-positive breast cancer. Therefore, targeting epigenetic regulators is a promising therapy for cancer. To identify epigenetic regulators, we conducted a siRNA screening targeting 140 epigenetic genes by which 32 positive and 15 negative regulators of estrogen signaling were obtained. The protein-protein interaction network of the candidate genes was constructed and the topological parameters of the network were calculated. As a result, the top 10 genes with higher MCC (Maximal Clique Centrality) scores were considered as hub genes. Notably, the hub genes all belong to polycomb group genes. The transcription levels of the above genes were compared between breast cancer and normal tissues using the UALCAN database. Then, the survival analysis of the hub genes was conducted using the Kaplan-Meier Plotter online database. Lastly, the effect of hub genes on MCF-7 cell proliferation and ER target gene expression were investigated. These results indicate that PcG genes regulate estrogen signaling and breast cancer development.

Targeting Histone Modifications in Bone and Lung Metastatic Cancers

PURPOSE OF REVIEW

Breast cancer frequently metastasizes to the bone and lung, but the ability to treat metastatic tumor cells remains a pressing clinical challenge. Histone deacetylases (HDACs) and histone acetyltransferases (HATs) have emerged as promising targets since these enzymes are aberrantly expressed in numerous cancers and regulate the expression of genes that drive tumorigenesis and metastasis. This review focuses on the abnormal expression of histone-modifying enzymes in cancers that have a high tropism for the bone and lung and explores the clinical use of histone deacetylase inhibitors for the treatment and prevention of metastasis to these sites.

RECENT FINDINGS

Preclinical studies have demonstrated that the role for HDACs is highly dependent on tumor type and stage of disease progression. HDAC inhibitors can induce apoptosis, senescence, cell differentiation, and tumor dormancy genes and inhibit angiogenesis, making these promising therapeutics for the treatment of metastatic disease. HDAC inhibitors are already FDA approved for hematologic malignancies and are in clinical trials with standard-of-care chemotherapies and targeted agents for several solid tumors, including cases of metastatic disease. However, these drugs can negatively impact bone homeostasis. Although HDAC inhibitors are not currently administered for the treatment of bone and lung metastatic disease, preclinical studies have shown that these drugs can reduce distant metastasis by targeting molecular factors and signaling pathways that drive tumor cell dissemination to these sites. Thus, HDAC inhibitors in combination with bone protective therapies may be beneficial in the treatment of bone metastatic cancers.

Tamoxifen overcomes the trastuzumab-resistance of SK-BR-3 tumorspheres by targeting crosstalk between cytoplasmic estrogen receptor α and the EGFR/HER2 signaling pathway

Since trastuzumab-resistance remains a major obstacle to the successful treatment of HER2-positive breast cancer, a detailed understanding of the mechanisms responsible is required to direct future pharmacotherapeutic strategies. Recently, several studies have indicated that the quiescent natures of cancer stem cells contribute to treatment resistance and tumor recurrence. Thus, in this study, we investigated the mechanism underlying trastuzumab resistance in a quiescent cell population using tumorsphere cultures and explored better therapeutic strategies to overcome trastuzumab resistance in HER2-positive breast cancer patients. We observed that most cells in SK-BR-3 tumorspheres were quiescent, showing the accumulation of cells at the G0/G1 phase as compared to cells in monolayer culture. Furthermore, SK-BR-3 tumorspheres exhibited enhanced EGFR/HER2 signaling, which was incompletely inhibited by trastuzumab, and subsequently led to trastuzumab-resistance. Interestingly, cytoplasmic estrogen receptor α (ERα) expression was markedly elevated in tumorspheres and was associated with enhanced EGFR/HER2 signaling. Accordingly, inhibition of ERα with tamoxifen selectively targeted tumorspheres rather than cells in monolayer culture and overcame trastuzumab resistance in tumorspheres. Taken together, our findings indicate that crosstalk between cytoplasmic ERα and the HER2/EGFR signaling pathway can be considered a novel therapeutic target for quiescent cell populations within HER2-positive breast cancer and that simultaneous inhibition of ER and the EGFR/HER2 pathway may prevent trastuzumab resistance. We hope that these results provide a basis for the use of combinations of tamoxifen and trastuzumab in HER2-positive breast cancer patients.

Therapeutic Strategies for Metastatic Triple-Negative Breast Cancers: From Negative to Positive

Metastatic triple-negative breast cancer (TNBC) is a distinct and immensely complex form of breast cancer. Among all subtypes of breast cancers, TNBC has a comparatively high rate of relapse, a high rate of distant metastasis, and poor overall survival after standard chemotherapy. Chemotherapy regimens are an essential component of the management of this estrogen receptor-negative, progesterone receptor-negative, and epidermal growth factor receptor2 negative subtype of breast cancers. Chemotherapy is critical for preventing the recurrence of the disease and for achieving long-term survival. Currently, a couple of agents are approved for the management of this disease, including chemotherapy like eribulin, targeted therapy like PARP inhibitor, as well as an antibody-drug conjugate (ADC) to target TROP2. Like many other metastatic cancers, immune checkpoint inhibitors (ICIs) have also been approved for TNBC patients with PD-L1 positive tumors and high tumor mutational burden. In this review article, we discuss these newly approved and promising novel agents that may change the therapeutic landscape for advanced/metastatic TNBC patients.

Epigenetic modulators combination with chemotherapy in breast cancer cells

Despite the concerning adverse effects on tumour development, epigenetic drugs are very promising in cancer treatment. The aim of this study was to compare the differential effects of standard chemotherapy regimens (FEC: 5-fluorouracil plus epirubicine plus cyclophosphamide) in combination with epigenetic modulators (decitabine, valproic acid): (a) on gene methylation levels of selected tumour biomarkers (LINE-1, uPA, PAI-1, DAPK); (b) their expression status (uPA and PAI-1); (c) differentiation status (5meC and H3K27me3). Furthermore, cell survival as well as changes concerning the invasion capacity were monitored in cell culture models of breast cancer (MCF-7, MDA-MB-231). A significant overall decrease of cell survival was observed in the FEC-containing combination therapies for both cell lines. Methylation results showed a general tendency towards increased demethylation of the uPA and PAI-1 gene promoters for the MCF-7 cells, as well as the proapoptotic DAPK gene in the treatment regimens for both cell lines. The uPA and PAI-1 antigen levels were mainly increased in the supernatant of FEC-only treated MDA-MB-231 cells. DAC-only treatment induced an increase of secreted uPA protein in MCF-7 cell culture, while most of the VPA-containing regimens also induced uPA and PAI-1 expression in MCF-7 cell fractions. Epigenetically active substances can also induce a re-differentiation in tumour cells, as shown by 5meC, H3K27me3 applying ICC. SIGNIFICANCE OF THE STUDY: Epigenetic modulators especially in the highly undifferentiated and highly malignant MDA-MB-231 tumour cells significantly reduced tumour malignancy thus; further clinical studies applying specific combination therapies with epigenetic modulators may be warranted.

Triple‑negative breast cancer therapy: Current and future perspectives (Review)

Triple-negative breast cancer (TNBC) accounts for 10-15% of all breast cancer cases. TNBCs lack estrogen and progesterone receptors and express low levels of HER2, and therefore do not respond to hormonal or anti-HER2 therapies. TNBC is a particularly aggressive form of breast cancer that generally displays poorer prognosis compared to other breast cancer subtypes. TNBC is chemotherapy sensitive, and this treatment remains the standard of care despite its limited benefit. Recent advances with novel agents have been made for specific subgroups with PD-L1⁺ tumors or germline Brca-mutated tumors. However, only a fraction of these patients responds to immune checkpoint or PARP inhibitors and even those who do respond often develop resistance and relapse. Various new agents and combination strategies have been explored to further understand molecular and immunological aspects of TNBC. In this review, we discuss clinical trials in the management of TNBC as well as perspectives for potential future treatments.

Comprehensive review for anticancer hybridized multitargeting HDAC inhibitors

Despite the encouraging clinical progress of chemotherapeutic agents in cancer treatment, innovation and development of new effective anticancer candidates still represents a challenging endeavor. With 15 million death every year in 2030 according to the estimates, cancer has increased rising of an alarm as a real crisis for public health and health systems worldwide. Therefore, scientist began to introduce innovative solutions to control the cancer global health problem. One of the promising strategies in this issue is the multitarget or smart hybrids having two or more pharmacophores targeting cancer. These rationalized hybrid molecules have gained great interests in cancer treatment as they are capable to simultaneously inhibit more than cancer pathway or target without drug-drug interactions and with less side effects. A prime important example of these hybrids, the HDAC hybrid inhibitors or referred as multitargeting HDAC inhibitors. The ability of HDAC inhibitors to synergistically improve the efficacy of other anti-cancer drugs and moreover, the ease of HDAC inhibitors cap group modification prompt many medicinal chemists to innovate and develop new generation of HDAC hybrid inhibitors. Notably, and during this short period, there are four HDAC inhibitor hybrids have entered different phases of clinical trials for treatment of different types of blood and solid tumors, namely; CUDC-101, CUDC-907, Tinostamustine, and Domatinostat. This review shed light on the most recent hybrids of HDACIs with one or more other cancer target pharmacophore. The designed multitarget hybrids include topoisomerase inhibitors, kinase inhibitors, nitric oxide releasers, antiandrogens, FLT3 and JAC-2 inhibitors, PDE5-inhibitors, NAMPT-inhibitors, Protease inhibitors, BRD4-inhibitors and other targets. This review may help researchers in development and discovery of new horizons in cancer treatment.

Intrinsic and Extrinsic Factors Governing the Transcriptional Regulation of ESR1

Transcriptional regulation of ESR1, the gene that encodes for estrogen receptor α (ER), is critical for regulating the downstream effects of the estrogen signaling pathway in breast cancer such as cell growth. ESR1 is a large and complex gene that is regulated by multiple regulatory elements, which has complicated our understanding of how ESR1 expression is controlled in the context of breast cancer. Early studies characterized the genomic structure of ESR1 with subsequent studies focused on identifying intrinsic (chromatin environment, transcription factors, signaling pathways) and extrinsic (tumor microenvironment, secreted factors) mechanisms that impact ESR1 gene expression. Currently, the introduction of genomic sequencing platforms and additional genome-wide technologies has provided additional insight on how chromatin structures may coordinate with these intrinsic and extrinsic mechanisms to regulate ESR1 expression. Understanding these interactions will allow us to have a clearer understanding of how ESR1 expression is regulated and eventually provide clues on how to influence its regulation with potential treatments. In this review, we highlight key studies concerning the genomic structure of ESR1, mechanisms that affect the dynamics of ESR1 expression, and considerations towards affecting ESR1 expression and hormone responsiveness in breast cancer.

HDAC3-ERα Selectively Regulates TNF-α-Induced Apoptotic Cell Death in MCF-7 Human Breast Cancer Cells via the p53 Signaling Pathway

Tumor necrosis factor-α (TNF-α) plays a significant role in inflammation and cancer-related apoptosis. We identified a TNF-α-mediated epigenetic mechanism of apoptotic cell death regulation in estrogen receptor-α (ERα)-positive human breast cancer cells. To assess the apoptotic effect of TNF-α, annexin V/ propidium iodide (PI) double staining, cell viability assays, and Western blotting were performed. To elucidate this mechanism, histone deacetylase (HDAC) activity assay and immunoprecipitation (IP) were conducted; the mechanism was subsequently confirmed through chromatin IP (ChIP) assays. Finally, we assessed HDAC3-ERα-mediated apoptotic cell death after TNF-α treatment in ERα-positive human breast cancer (MCF-7) cells via the transcriptional activation of p53 target genes using luciferase assay and quantitative reverse transcription PCR. The TNF-α-induced selective apoptosis in MCF-7 cells was negatively regulated by the HDAC3-ERα complex in a caspase-7-dependent manner. HDAC3 possessed a p53-binding element, thus suppressing the transcriptional activity of its target genes. In contrast, MCF-7 cell treatment with TNF-α led to dissociation of the HDAC3-ERα complex and substitution of the occupancy on the promoter by the p53-p300 complex, thus accelerating p53 target gene expression. In this process, p53 stabilization was accompanied by its acetylation. This study showed that p53-mediated apoptosis in ERα-positive human breast cancer cells was negatively regulated by HDAC3-ERα in a caspase-7-dependent manner. Therefore, these proteins have potential application in therapeutic strategies.

Shikonin and 4-hydroxytamoxifen synergistically inhibit the proliferation of breast cancer cells through activating apoptosis signaling pathway in vitro and in vivo

Background

Tamoxifen (TAM) is a cell type-specific anti-estrogen and is applied to improve the survival of patients with estrogen receptor positive (ER +) breast cancer. However, long-term TAM use can induce serious drug resistance, leading to breast cancer recurrence and death in patients. Further, it is almost useless among patients with estrogen receptor negative (ER −) breast cancer. Shikonin (SK) is a natural product broadly explored in cancer therapy. Some studies have demonstrated the combined treatment of SK and clinical anticancer drugs including TAM on various tumors. However, the combined effect of SK and 4-hydroxytamoxifen (4-OHT) on ER- breast cancer is not known. The current study aimed to assess the combination effects of SK and 4-OHT on human breast cancer cells, MCF-7 (ER +) and MDA-MB-435S (ER −), in vitro and in vivo and to investigate the underlying mechanisms.

Methods

CCK-8 assays and flow cytometry were conducted to determine the cell viability and apoptotic profiles of human breast cancer cell lines (MCF-7 and MDA-MB-435S) treated with SK, 4-OHT, and the combination. ROS and JC-1 assays were used to determine ROS level and mitochondrial membrane potential. Western blot analysis was performed to investigate proteins that are associated with apoptosis. Haematoxylin & Eosin (HE) staining was used to detect the tumor and kidney morphology of mice. TUNEL and immunohistochemical staining were performed to detect Ki67 expression level and cell apoptotic profile in tumor tissues.

Results

SK and 4-OHT synergistically inhibited MCF-7 and MDA-MB-435S cell proliferation and promoted apoptosis by reducing mitochondrial membrane potential and increasing the intracellular ROS level. The combination of SK and 4-OHT activated the mitochondrial-dependent apoptosis and the death receptor pathways, significantly regulating the PI3K/AKT/Caspase 9 signaling pathway. Compared with SK and 4-OHT alone, the combination of SK and 4-OHT could better inhibit tumor growth in mice.

Conclusion

The combination of SK and 4-OHT shows highly efficient anticancer effects on breast cancer therapy. SK may be a promising candidate as an adjuvant to 4-OHT for breast cancer treatments, especially for ER- breast cancer.

Mechanisms of resistance to estrogen receptor modulators in ER+/HER2- advanced breast cancer

Endocrine therapy represents a mainstay adjuvant treatment of estrogen receptor-positive (ER+) breast cancer in clinical practice with an overall survival (OS) benefit. However, the emergence of resistance is inevitable over time and is present in one-third of the ER+ breast tumors. Several mechanisms of endocrine resistance in ER+/HER2- advanced breast cancers, through ERα itself, receptor tyrosine signaling, or cell cycle pathway, have been identified to be pivotal in endocrine therapy. The epigenetic alterations also contribute to ensuring tumor cells' escape from endocrine therapies. The strategy of combined hormone therapy with targeted pharmaceutical compounds has shown an improvement of progression-free survival or OS in clinical practice, including three different classes of drugs: CDK4/6 inhibitors, selective inhibitor of PI3Kα and mTOR inhibitors. Many therapeutic targets of cell cycle pathway and cell signaling and their combination strategies have recently entered clinical trials. This review focuses on Cyclin D-CDK4/6-RB axis, PI3K pathway and HDACs. Additionally, genomic evolution is complex in tumors exposed to hormonal therapy. We highlight the genomic alterations present in ESR1 and PIK3CA genes to elucidate adaptive mechanisms of endocrine resistance, and discuss how these mutations may inform novel combinations to improve clinical outcomes in the future.

CDK2-mediated site-specific phosphorylation of EZH2 drives and maintains triple-negative breast cancer

Triple-negative breast cancer (TNBC), which lacks estrogen receptor α (ERα), progesterone receptor, and human epidermal growth factor receptor 2 (HER2) expression, is closely related to basal-like breast cancer. Previously, we and others report that cyclin E/cyclin-dependent kinase 2 (CDK2) phosphorylates enhancer of zeste homolog 2 (EZH2) at T416 (pT416-EZH2). Here, we show that transgenic expression of phospho-mimicking EZH2 mutant EZH2^T416D in mammary glands leads to tumors with TNBC phenotype. Coexpression of EZH2^T416D in mammary epithelia of HER2/Neu transgenic mice reprograms HER2-driven luminal tumors into basal-like tumors. Pharmacological inhibition of CDK2 or EZH2 allows re-expression of ERα and converts TNBC to luminal ERα-positive, rendering TNBC cells targetable by tamoxifen. Furthermore, the combination of either CDK2 or EZH2 inhibitor with tamoxifen effectively suppresses tumor growth and markedly improves the survival of the mice bearing TNBC tumors, suggesting that the mechanism-based combination therapy may be an alternative approach to treat TNBC.

EZH2 phosphorylation by CDK2 promotes progression of triple-negative breast cancer (TNBC). Here, the authors show that this signaling axis downregulates ERα, and thus combinatorial blockade of CDK2 and EZH2 sensitizes TNBC cells to tamoxifen.

Effect of 17β-estradiol on estrogen receptor negative breast cancer cells in an osteolytic mouse model

17β-Estradiol (E2) promotes metastasis of triple negative breast cancer cells to bone. Recent studies show many triple negative breast cancer cell lines lacking the 66 kDa estrogen receptor (ER) alpha (ERα66) or its splice variant ERα46, express another splice variant, ERα36 associated with membrane-mediated rapid actions of the hormone. qPCR and western blot confirmed that MCF7 cells possessed ERα splice variants ERα66, ERα46 and ERα36, while ER-negative breast cancer cells MDA-MB-231 possessed only ERα36. MDA-MB-231 breast cancer cells were implanted into medullary canals of ovariectomized female athymic nude mice femurs (N = 8 mice/treatment). To examine the effect of E2 on osteolysis, mice were treated with 0.72 mg E2 or placebo via 60 day release osmotic pumps implanted subcutaneously. Legs were examined by Faxitron through the course of the study, and by microCT and histology after 8 weeks. Greater occurrence of osteolysis and pathologic fracture was observed in E2-treated animals compared to placebo, and microCT demonstrated less bone volume remaining in MDA-MB-231 treated legs compared to contralateral control legs, as well as E2-treated animals compared to placebo. E2-treated animals had significantly greater tumor volume compared to placebo. Large nests of anaplastic tumor cells with eroded cortical margin were observed in E2-treated animals compared to placebo. MDA MB 231 breast cancer cells positive for ERα36 but negative for ERα46/66 had enhanced osteolysis, pathologic fractures, and tumor volume in an in vivo osteolytic mouse model when treated with 17β-estradiol compared to placebo, demonstrating a role for ERα36 in bone tumor progression.

Epigenetics in Metastatic Breast Cancer: Its Regulation and Implications in Diagnosis, Prognosis and Therapeutics

Despite advances in the treatment regimen, the high incidence rate of breast cancer (BC) deaths is mostly caused by metastasis. Recently, the aberrant epigenetic modifications, which involve DNA methylation, histone modifications and microRNA (miRNA) regulations become attractive targets to treat metastatic breast cancer (MBC). In this review, the epigenetic alterations of DNA methylation, histone modifications and miRNA regulations in regulating MBC are discussed. The preclinical and clinical trials of epigenetic drugs such as the inhibitor of DNA methyltransferase (DNMTi) and the inhibitor of histone deacetylase (HDACi), as a single or combined regimen with other epigenetic drug or standard chemotherapy drug to treat MBCs are discussed. The combined regimen of epigenetic drugs or with standard chemotherapy drugs enhance the therapeutic effect against MBC. Evidences that epigenetic changes could have implications in diagnosis, prognosis and therapeutics for MBC are also presented. Several genes have been identified as potential epigenetic biomarkers for diagnosis and prognosis, as well as therapeutic targets for MBC. Endeavors in clinical trials of epigenetic drugs against MBC should be continued although limited success has been achieved. Future discovery of epigenetic drugs from natural resources would be an attractive natural treatment regimen for MBC. Further research is warranted in translating research into clinical practice with the ultimate goal of treating MBC by epigenetic therapy in the near future.

Switchable genome editing via genetic code expansion

Multiple applications of genome editing by CRISPR-Cas9 necessitate stringent regulation and Cas9 variants have accordingly been generated whose activity responds to small ligands, temperature or light. However, these approaches are often impracticable, for example in clinical therapeutic genome editing in situ or gene drives in which environmentally-compatible control is paramount. With this in mind, we have developed heritable Cas9-mediated mammalian genome editing that is acutely controlled by the cheap lysine derivative, Lys(Boc) (BOC). Genetic code expansion permitted non-physiological BOC incorporation such that Cas9 (Cas9BOC) was expressed in a full-length, active form in cultured somatic cells only after BOC exposure. Stringently BOC-dependent, heritable editing of transgenic and native genomic loci occurred when Cas9BOC was expressed at the onset of mouse embryonic development from cRNA or Cas9BOC transgenic females. The tightly controlled Cas9 editing system reported here promises to have broad applications and is a first step towards purposed, spatiotemporal gene drive regulation over large geographical ranges.

BQ323636.1, a Novel Splice Variant to NCOR2, as a Predictor for Tamoxifen-Resistant Breast Cancer

Purpose: Adjuvant tamoxifen treatment revolutionized the management of estrogen receptor (ER)-positive breast cancers to prevent cancer recurrence; however, drug resistance compromises its clinical efficacy. The mechanisms underlying tamoxifen resistance are not fully understood, and no robust biomarker is available to reliably predict those who will be resistant. Here, we study BQ323636.1, a novel splice variant of the NCOR2 gene, and evaluate its efficacy in predicting tamoxifen resistance in patients with breast cancer.Experimental Design: A monoclonal anti-BQ323636.1 antibody that specifically recognizes the unique epitope of this splice variant was generated for in vitro mechanistic studies and for in vivo analysis by immunohistochemistry on tissue microarrays of two independent cohorts of 358 patients with more than 10 years clinical follow-up data, who had ER-positive primary breast cancer and received adjuvant tamoxifen treatment. An orthotopic mouse model was also used.Results: Overexpression of BQ323636.1 conferred resistance to tamoxifen in both in vitro and in an orthotopic mouse model. Mechanistically, coimmunoprecipitation showed BQ323636.1 could bind to NCOR2 and inhibit the formation of corepressor complex for the suppression of ER signaling. Nuclear BQ3232636.1 overexpression in patients samples was significantly associated with tamoxifen resistance (P = 1.79 × 10^-6, sensitivity 52.9%, specificity 72.0%). In tamoxifen-treated patients, nuclear BQ323636.1 overexpression was significantly correlated with cancer metastasis and disease relapse. Nuclear BQ323636.1 was also significantly associated with poorer overall survival (P = 1.13 × 10^-4) and disease-specific survival (P = 4.02 × 10^-5).Conclusions: These findings demonstrate that BQ323636.1 can be a reliable biomarker to predict tamoxifen resistance in patients with ER-positive breast cancer. Clin Cancer Res; 24(15); 3681-91. ©2018 AACRSee related commentary by Jordan, p. 3480.

Exploratory clinical study of chidamide, an oral subtype-selective histone deacetylase inhibitor, in combination with exemestane in hormone receptor-positive advanced breast cancer

Objective

The recurrence or progression under endocrine therapy in hormone receptor-positive (HR+) advanced breast cancer (ABC) remained a critical clinical challenge. Chidamide is an oral subtype-selective histone deacetylase (HDAC) inhibitor with multiple functions in tumor growth inhibition and microenvironment modulation via epigenetic reprogramming. The purpose of this study was to evaluate the safety, pharmacokinetics (PK), and preliminary efficacy of chidamide in combination with exemestane in HR+ ABC patients.

Methods

Eligible patients were postmenopausal women with HR+ ABC recurrent or progressed to at least one endocrine therapy. Blood samples were obtained in the run-in period and the first day of combination treatment for PK analysis. In combination treatment, patients were given exemestane 25 mg daily and chidamide 30 mg twice a week (BIW) until progression of disease or intolerable toxicities. A treatment cycle was defined as 4 weeks. Safety, PK parameters, and preliminary efficacy were evaluated.

Results

A total of 20 patients were enrolled between July and December, 2015. The median number of treatments cycle was 5.2 (20.8 weeks) with 2 patients still on treatment at the data cut-off date of October, 2017. The treatment-related adverse events (AE) ≥ grade 3 in more than 2 patients were neutropenia (35%), thrombocytopenia (30%), and leucopenia (20%). The plasma exposure of exemestane was consistent in the presence or absence of chidamide. A slight increase in chidamide exposure was noted in the presence of exemestane, probably due to the inter- and intra-patient variations. The best response in 16 evaluable patients was assessed by Response Evaluation Criteria in Solid Tumors (RECIST), including 4 patients with partial response, 10 patients with stable disease. The median progression-free survival (PFS) was 7.6 months.

Conclusions

The combination of chidamide with exemestane was generally well tolerated with promising preliminary efficacy in HR+ ABC patients. The overall results from this study encourage further pivotal trial in this patient population.

Protein-Protein Interaction Modulators for Epigenetic Therapies

Targeting protein-protein interactions (PPIs) is becoming an attractive approach for drug discovery. This is particularly true for difficult or emerging targets, such as epitargets that may be elusive to drugs that fall into the traditional chemical space. The chemical nature of the PPIs makes attractive the use of peptides or peptidomimetics to selectively modulate such interactions. Despite the fact peptide-based drug discovery has been challenging, the use of peptides as leads compounds for drug discovery is still a valid strategy. This chapter discusses the current status of PPIs in epigenetic drug discovery. A special emphasis is made on peptides and peptide-like compounds as potential drug candidates.

Single CpG site methylation controls estrogen receptor gene transcription and correlates with hormone therapy resistance

Hormone therapy is the most effective treatment for patients with estrogen receptor α-positive breast cancers. However, although resistance occurs during treatment in some cases and often reflects changed estrogen receptor α status, the relationship between changes in estrogen receptor α expression and resistance to therapy are poorly understood. In this study, we identified a mechanism for altered estrogen receptor α expression during disease progression and acquired hormone therapy resistance in aromatase inhibitor-resistant breast cancer cell lines. Subsequently, we investigated promoter switching and DNA methylation status of the estrogen receptor α promoter, and found marked changes of methylation at a single CpG site (CpG4) in resistant cells. In addition, luciferase reporter assays showed reduced transcriptional activity from this methylated CpG site. This CpG region was also completely conserved among species, suggesting that it acts as a methylation-sensitive Ets-2 transcription factor binding site, as confirmed using chromatin immunoprecipitation assays. In estrogen receptor α-positive tumors, CpG4 methylation levels were inversely correlated with estrogen receptor α expression status, suggesting that single CpG site plays an important role in the regulation of estrogen receptor α transcription.

Activation of tumor suppressor LKB1 by honokiol abrogates cancer stem-like phenotype in breast cancer via inhibition of oncogenic Stat3

Tumor suppressor and upstream master kinase Liver kinase B1 (LKB1) plays a significant role in suppressing cancer growth and metastatic progression. We show that low-LKB1 expression significantly correlates with poor survival outcome in breast cancer. In line with this observation, loss-of-LKB1 rendered breast cancer cells highly migratory and invasive, attaining cancer stem cell-like phenotype. Accordingly, LKB1-null breast cancer cells exhibited an increased ability to form mammospheres and elevated expression of pluripotency-factors (Oct4, Nanog and Sox2), properties also observed in spontaneous tumors in Lkb1^-/- mice. Conversely, LKB1-overexpression in LKB1-null cells abrogated invasion, migration and mammosphere-formation. Honokiol (HNK), a bioactive molecule from Magnolia grandiflora increased LKB1 expression, inhibited individual cell-motility and abrogated the stem-like phenotype of breast cancer cells by reducing the formation of mammosphere, expression of pluripotency-factors and aldehyde dehydrogenase activity. LKB1, and its substrate, AMP-dependent protein kinase (AMPK) are important for HNK-mediated inhibition of pluripotency factors since LKB1-silencing and AMPK-inhibition abrogated, while LKB1-overexpression and AMPK-activation potentiated HNK's effects. Mechanistic studies showed that HNK inhibited Stat3-phosphorylation/activation in an LKB1-dependent manner, preventing its recruitment to canonical binding-sites in the promoters of Nanog, Oct4 and Sox2. Thus, inhibition of the coactivation-function of Stat3 resulted in suppression of expression of pluripotency factors. Further, we showed that HNK inhibited breast tumorigenesis in mice in an LKB1-dependent manner. Molecular analyses of HNK-treated xenografts corroborated our in vitro mechanistic findings. Collectively, these results present the first in vitro and in vivo evidence to support crosstalk between LKB1, Stat3 and pluripotency factors in breast cancer and effective anticancer modulation of this axis with HNK treatment.

The zinc-finger transcriptional factor Slug transcriptionally downregulates ERα by recruiting lysine-specific demethylase 1 in human breast cancer

Estrogen receptor α (ERα) is related with epithelial-mesenchymal transition, invasion and metastasis, and serves as an important therapeutic predictor and prognostic factor in breast cancer patients. The triple negative breast cancer (TNBC) is characterized by loss of hormone receptors and human epidermal growth factor receptor 2 (Her2), and lacks effective targeted therapy with poor prognosis. Unfortunately, the molecular mechanisms of ERα deficiency, which becomes hormone independent and results in resistance to endocrine therapy, remain to be elucidated in breast cancer. In this study, we observed an inverse correlation between Slug, a zinc-finger transcriptional repressor, and ERα expression in both human breast cancer tissues and cell lines. In ERα-negative breast cancer patients, high Slug messenger RNA expression showed obviously shorter relapse-free survival. We found that Slug binds to the E-box located in the promoter of estrogen receptor 1 gene (ESR1) to suppress its expression. More specifically, Slug recruits lysine-specific demethylase 1 (LSD1) to the E-box and thereby inhibits ERα expression by demethylating H3K4me2, which is evidenced by the interaction between Slug and LSD1. Moreover, the amount of H3K4me2 binding to the E-box was significantly increased after LSD1 knockdown in MDA-MB-231 cells. Functionally, the ability to proliferate, invade and metastasize was significantly suppressed after knockdown of either Slug or LSD1 alone, or both simultaneously. Taken together, these results suggest that Slug transcriptionally inhibits ERα expression by recruiting LSD1 to the ESR1 promoter in breast cancers. Thus, targeted inhibition of Slug and LSD1 may restore ERα and lead to resensitization to hormone therapy, providing a novel therapeutic strategy for ERα-negative breast cancer patients, especially for TNBC.

肿瘤表观遗传学治疗研究进展

表观遗传学沉默几乎是人类恶性肿瘤的普遍特征, 其影响涉及从肿瘤起始到进展的所有关键信号通路, 靶向表观遗传学异常具有巨大潜力. 近年来, 表观遗传学治疗药物DNA甲基转移酶抑制剂与组蛋白去乙酰化酶抑制剂单独或与其他治疗相结合, 在一些血源性肿瘤及实体瘤中获得了突出的疗效, 正在实现从实验室到临床的快速转化. 本文就表观遗传学治疗药物单独及与其他治疗相结合在肿瘤基础与临床研究中的相关进展作一综述, 以便发现并确定进一步的研究方向, 加速其向肿瘤临床的转化.

Entinostat: a promising treatment option for patients with advanced breast cancer

Entinostat is a synthetic benzamide derivative histone deacetylase (HDAC) inhibitor, which potently and selectively inhibits class I and IV HDAC enzymes. This action promotes histone hyperacetylation and transcriptional activation of specific genes, with subsequent inhibition of cell proliferation, terminal differentiation and apoptosis. This oral HDAC inhibitor has been evaluated in Phase I and II trials in patients with advanced malignancies, and is in general well tolerated. Entinostat does not currently have regulatory approval for clinical use; however promising preclinical and clinical data exist in hormone-resistant breast cancer. An ECOG-ACRIN Phase III registration study is ongoing in advanced breast cancer (E2112, NCT02115282) and aims to confirm the overall survival advantage observed with the combination of exemestane and entinostat/placebo in the Phase II setting (ENCORE301 trial). This article provides an overview of the chemistry, pharmacokinetics/pharmacodynamics and available clinical data for entinostat with a focus on advanced breast cancer.

Benzyl Isothiocyanate potentiates p53 signaling and antitumor effects against breast cancer through activation of p53-LKB1 and p73-LKB1 axes

Functional reactivation of p53 pathway, although arduous, can potentially provide a broad-based strategy for cancer therapy owing to frequent p53 inactivation in human cancer. Using a phosphoprotein-screening array, we found that Benzyl Isothiocynate, (BITC) increases p53 phosphorylation in breast cancer cells and reveal an important role of ERK and PRAS40/MDM2 in BITC-mediated p53 activation. We show that BITC rescues and activates p53-signaling network and inhibits growth of p53-mutant cells. Mechanistically, BITC induces p73 expression in p53-mutant cells, disrupts the interaction of p73 and mutant-p53, thereby releasing p73 from sequestration and allowing it to be transcriptionally active. Furthermore, BITC-induced p53 and p73 axes converge on tumor-suppressor LKB1 which is transcriptionally upregulated by p53 and p73 in p53-wild-type and p53-mutant cells respectively; and in a feed-forward mechanism, LKB1 tethers with p53 and p73 to get recruited to p53-responsive promoters. Analyses of BITC-treated xenografts using LKB1-null cells corroborate in vitro mechanistic findings and establish LKB1 as the key node whereby BITC potentiates as well as rescues p53-pathway in p53-wild-type as well as p53-mutant cells. These data provide first in vitro and in vivo evidence of the integral role of previously unrecognized crosstalk between BITC, p53/LKB1 and p73/LKB1 axes in breast tumor growth-inhibition.

Combination Epigenetic Therapy in Advanced Breast Cancer with 5-Azacitidine and Entinostat: A Phase II National Cancer Institute/Stand Up to Cancer Study

Purpose: In breast cancer models, combination epigenetic therapy with a DNA methyltransferase inhibitor and a histone deacetylase inhibitor led to reexpression of genes encoding important therapeutic targets, including the estrogen receptor (ER). We conducted a multicenter phase II study of 5-azacitidine and entinostat in women with advanced hormone-resistant or triple-negative breast cancer (TNBC).Experimental Design: Patients received 5-azacitidine 40 mg/m² (days 1-5, 8-10) and entinostat 7 mg (days 3, 10) on a 28-day cycle. Continuation of epigenetic therapy was offered with the addition of endocrine therapy at the time of progression [optional continuation (OC) phase]. Primary endpoint was objective response rate (ORR) in each cohort. We hypothesized that ORR would be ≥20% against null of 5% using Simon two-stage design. At least one response was required in 1 of 13 patients per cohort to continue accrual to 27 per cohort (type I error, 4%; power, 90%).Results: There was one partial response among 27 women with hormone-resistant disease (ORR = 4%; 95% CI, 0-19), and none in 13 women with TNBC. One additional partial response was observed in the OC phase in the hormone-resistant cohort (n = 12). Mandatory tumor samples were obtained pre- and posttreatment (58% paired) with either up- or downregulation of ER observed in approximately 50% of posttreatment biopsies in the hormone-resistant, but not TNBC cohort.Conclusions: Combination epigenetic therapy was well tolerated, but our primary endpoint was not met. OC phase results suggest that some women benefit from epigenetic therapy and/or reintroduction of endocrine therapy beyond progression, but further study is needed. Clin Cancer Res; 23(11); 2691-701. ©2016 AACR.

Oestrogen receptor negativity in breast cancer: a cause or consequence?

Endocrine resistance, which occurs either by de novo or acquired route, is posing a major challenge in treating hormone-dependent breast cancers by endocrine therapies. The loss of oestrogen receptor α (ERα) expression is the vital cause of establishing endocrine resistance in this subtype. Understanding the mechanisms that determine the causes of this phenomenon are therefore essential to reduce the disease efficacy. But how we negate oestrogen receptor (ER) negativity and endocrine resistance in breast cancer is questionable. To answer that, two important approaches are considered: (1) understanding the cellular origin of heterogeneity and ER negativity in breast cancers and (2) characterization of molecular regulators of endocrine resistance. Breast tumours are heterogeneous in nature, having distinct molecular, cellular, histological and clinical behaviour. Recent advancements in perception of the heterogeneity of breast cancer revealed that the origin of a particular mammary tumour phenotype depends on the interactions between the cell of origin and driver genetic hits. On the other hand, histone deacetylases (HDACs), DNA methyltransferases (DNMTs), miRNAs and ubiquitin ligases emerged as vital molecular regulators of ER negativity in breast cancers. Restoring response to endocrine therapy through re-expression of ERα by modulating the expression of these molecular regulators is therefore considered as a relevant concept that can be implemented in treating ER-negative breast cancers. In this review, we will thoroughly discuss the underlying mechanisms for the loss of ERα expression and provide the future prospects for implementing the strategies to negate ER negativity in breast cancers.

FOXK2 Elicits Massive Transcription Repression and Suppresses the Hypoxic Response and Breast Cancer Carcinogenesis

Although clinically associated with severe developmental defects, the biological function of FOXK2 remains poorly explored. Here we report that FOXK2 interacts with transcription corepressor complexes NCoR/SMRT, SIN3A, NuRD, and REST/CoREST to repress a cohort of genes including HIF1β and EZH2 and to regulate several signaling pathways including the hypoxic response. We show that FOXK2 inhibits the proliferation and invasion of breast cancer cells and suppresses the growth and metastasis of breast cancer. Interestingly, FOXK2 is transactivated by ERα and transrepressed via reciprocal successive feedback by HIF1β/EZH2. Significantly, the expression of FOXK2 is progressively lost during breast cancer progression, and low FOXK2 expression is strongly correlated with higher histologic grades, positive lymph nodes, and ERα^-/PR^-/HER2^- status, all indicators of poor prognosis.