The Structure-Function Relationship of Angular Estrogens and Estrogen Receptor Alpha to Initiate Estrogen-Induced Apoptosis in Breast Cancer Cells

Estrogen Receptor Alpha Mutations, Truncations, Heterodimers, and Therapies

Annual breast cancer (BCa) deaths have declined since its apex in 1989 concomitant with widespread adoption of hormone therapies that target estrogen receptor alpha (ERα), the prominent nuclear receptor expressed in ∼80% of BCa. However, up to ∼50% of patients who are ER+ with high-risk disease experience post endocrine therapy relapse and metastasis to distant organs. The vast majority of BCa mortality occurs in this setting, highlighting the inadequacy of current therapies. Genomic abnormalities to ESR1, the gene encoding ERα, emerge under prolonged selective pressure to enable endocrine therapy resistance. These genetic lesions include focal gene amplifications, hotspot missense mutations in the ligand binding domain, truncations, fusions, and complex interactions with other nuclear receptors. Tumor cells utilize aberrant ERα activity to proliferate, spread, and evade therapy in BCa as well as other cancers. Cutting edge studies on ERα structural and transcriptional relationships are being harnessed to produce new therapies that have shown benefits in patients with ESR1 hotspot mutations. In this review we discuss the history of ERα, current research unlocking unknown aspects of ERα signaling including the structural basis for receptor antagonism, and future directions of ESR1 investigation. In addition, we discuss the development of endocrine therapies from their inception to present day and survey new avenues of drug development to improve pharmaceutical profiles, targeting, and efficacy.

The adverse outcome pathway for breast cancer: a knowledge management framework bridging biomedicine and toxicology

Breast cancer is the most common cancer worldwide, with an estimated 2.3 million new cases diagnosed every year. Effective measures for cancer prevention and cancer therapy require a detailed understanding of the individual key disease mechanisms involved and their interactions at the molecular, cellular, tissue, organ, and organism level. In that regard, the rapid progress of biomedical and toxicological research in recent years now allows the pursuit of new approaches based on non-animal methods that provide greater mechanistic insight than traditional animal models and therefore facilitate the development of Adverse Outcome Pathways (AOPs) for human diseases. We performed a systematic review of the current state of published knowledge with regard to breast cancer to identify relevant key mechanisms for inclusion into breast cancer AOPs, i.e. decreased cell stiffness and decreased cell adhesion, and to concurrently map non-animal methods addressing these key events. We conclude that the broader sharing of expertise and methods between biomedical research and toxicology enabled by the AOP knowledge management framework can help to coordinate global research efforts and accelerate the transition to advanced non-animal methods, which, when combined into powerful method batteries, closely mimic human physiology and disease states without the need for animal testing.

AIB1/SRC-3/NCOA3 function in estrogen receptor alpha positive breast cancer

The estrogen receptor alpha (ERα) is a steroid receptor that is pivotal in the initiation and progression of most breast cancers. ERα regulates gene transcription through recruitment of essential coregulators, including the steroid receptor coactivator AIB1 (Amplified in Breast Cancer 1). AIB1 itself is an oncogene that is overexpressed in a subset of breast cancers and is known to play a role in tumor progression and resistance to endocrine therapy through multiple mechanisms. Here we review the normal and pathological functions of AIB1 in regard to its ERα-dependent and ERα-independent actions, as well as its genomic conservation and protein evolution. We also outline the efforts to target AIB1 in the treatment of breast cancer.

Hormonal and Genetic Regulatory Events in Breast Cancer and Its Therapeutics: Importance of the Steroidogenic Acute Regulatory Protein

Estrogen promotes the development and survival of the majority of breast cancers (BCs). Aromatase is the rate-limiting enzyme in estrogen biosynthesis, and it is immensely expressed in both cancerous and non-cancerous breast tissues. Endocrine therapy based on estrogen blockade, by aromatase inhibitors, has been the mainstay of BC treatment in post-menopausal women; however, resistance to hormone therapy is the leading cause of cancer death. An improved understanding of the molecular underpinnings is the key to develop therapeutic strategies for countering the most prevalent hormone receptor positive BCs. Of note, cholesterol is the precursor of all steroid hormones that are synthesized in a variety of tissues and play crucial roles in diverse processes, ranging from organogenesis to homeostasis to carcinogenesis. The rate-limiting step in steroid biosynthesis is the transport of cholesterol from the outer to the inner mitochondrial membrane, a process that is primarily mediated by the steroidogenic acute regulatory (StAR) protein. Advances in genomic and proteomic technologies have revealed a dynamic link between histone deacetylases (HDACs) and StAR, aromatase, and estrogen regulation. We were the first to report that StAR is abundantly expressed, along with large amounts of 17β-estradiol (E2), in hormone-dependent, but not hormone-independent, BCs, in which StAR was also identified as a novel acetylated protein. Our in-silico analyses of The Cancer Genome Atlas (TCGA) datasets, for StAR and steroidogenic enzyme genes, revealed an inverse correlation between the amplification of the StAR gene and the poor survival of BC patients. Additionally, we reported that a number of HDAC inhibitors, by altering StAR acetylation patterns, repress E2 synthesis in hormone-sensitive BC cells. This review highlights the current understanding of molecular pathogenesis of BCs, especially for luminal subtypes, and their therapeutics, underlining that StAR could serve not only as a prognostic marker, but also as a therapeutic candidate, in the prevention and treatment of this life-threatening disease.

BARD1 mystery: tumor suppressors are cancer susceptibility genes

The full-length BRCA1-associated RING domain 1 (BARD1) gene encodes a 777-aa protein. BARD1 displays a dual role in cancer development and progression as it acts as a tumor suppressor and an oncogene. Structurally, BARD1 has homologous domains to BRCA1 that aid their heterodimer interaction to inhibit the progression of different cancers such as breast and ovarian cancers following the BRCA1-dependant pathway. In addition, BARD1 was shown to be involved in other pathways that are involved in tumor suppression (BRCA1-independent pathway) such as the TP53-dependent apoptotic signaling pathway. However, there are abundant BARD1 isoforms exist that are different from the full-length BARD1 due to nonsense and frameshift mutations, or deletions were found to be associated with susceptibility to various cancers including neuroblastoma, lung, breast, and cervical cancers. This article reviews the spectrum of BARD1 full-length genes and its different isoforms and their anticipated associated risk. Additionally, the study also highlights the role of BARD1 as an oncogene in breast cancer patients and its potential uses as a prognostic/diagnostic biomarker and as a therapeutic target for cancer susceptibility testing and treatment.

Mechanistic Effects of Estrogens on Breast Cancer

PURPOSE

Current concepts regarding estrogen and its mechanistic effects on breast cancer in women are evolving. This article reviews studies that address estrogen-mediated breast cancer development, the prevalence of occult tumors at autopsy, and the natural history of breast cancer as predicted by a newly developed tumor kinetic model.

METHODS

This article reviews previously published studies from the authors and articles pertinent to the data presented.

RESULTS

We discuss the concepts of adaptive hypersensitivity that develops in response to long-term deprivation of estrogen and results in both increased cell proliferation and apoptosis. The effects of menopausal hormonal therapy on breast cancer in postmenopausal women are interpreted based on the tumor kinetic model. Studies of the administration of a tissue selective estrogen complex in vitro, in vivo, and in patients are described. We review the various clinical studies of breast cancer prevention with selective estrogen receptor modulators and aromatase inhibitors. Finally, the effects of the underlying risk of breast cancer on the effects of menopausal hormone therapy are outlined.

DISCUSSION

The overall intent of this review is to present data supporting recent concepts, discuss pertinent literature, and critically examine areas of controversy.

Estrogen Receptor Complex to Trigger or Delay Estrogen-Induced Apoptosis in Long-Term Estrogen Deprived Breast Cancer

Antiestrogen therapy of breast cancer has been a "gold standard" of treatment of estrogen receptor (ER)-positive breast cancer for decades. Resistance to antiestrogen therapy may develop, however, a vulnerability in long-term estrogen deprived (LTED) breast cancer cells was discovered. LTED breast cancer cells may undergo estrogen-induced apoptosis within a week of treatment with estrogen in vitro. This phenomenon has been also validated in vivo and in the clinic. The molecular ER-mediated mechanism of action of estrogen-induced apoptosis was deciphered, however, the relationship between the structure of estrogenic ligands and the activity of the ER in LTED breast cancer cells remained a mystery until recently. In this review we provide an overview of the structure-activity relationship of various estrogens with different chemical structures and the modulation of estrogen-induced apoptosis in LTED breast cancer cells resistant to antihormone therapy. We provide analysis of evidence gathered over more than a decade of structure-activity relationship studies by our group on the role of the change in the conformation of the estrogen receptor and the biological activities of different classes of estrogens and the receptor as well in LTED breast cancer.

Association of SNPs within TMPRSS6 and BMP2 genes with iron deficiency status in Saudi Arabia

BACKGROUND

Globally, iron-deficiency anemia (IDA) remains a major health obstacle. This health condition has been identified in 47% of pre-school students (aged 0 to 5 years), 42% of pregnant females, and 30% of non-pregnant females (aged 15 to 50 years) worldwide according to the WHO. Environmental and genetic factors play a crucial role in the development of IDA; genetic testing has revealed the association of a number of polymorphisms with iron status and serum ferritin.

AIM

The current study aims to reveal the association of TMPRSS6 rs141312 and BMP2 rs235756 with the iron status of females in Saudi Arabia.

METHODS

A cohort of 108 female university students aged 18-25 years was randomly selected to participate: 50 healthy and 58 classified as iron deficient. A 3-5 mL sample of blood was collected from each one and analyzed based on hematological and biochemical iron status followed by genotyping by PCR.

RESULTS

The genotype distribution of TMPRSS6 rs141312 was 8% (TT), 88% (TC) and 4% (CC) in the healthy group compared with 3.45% (TT), 89.66% (TC) and 6.89% (CC) in the iron-deficient group (P = 0.492), an insignificant difference in the allelic distribution. The genotype distribution of BMP2 rs235756 was 8% (TT), 90% (TC) and 2% (CC) in the healthy group compared with 3.45% (TT), 82.76% (TC) and 13.79% (CC) in iron-deficient group (P = 0.050) and was significantly associated with decreased ferritin status (P = 0.050). In addition, TMPRSS6 rs141312 is significantly (P<0.001) associated with dominant genotypes (TC+CC) and increased risk of IDA while BMP2 rs235756 is significantly (P<0.026) associated with recessive homozygote CC genotypes and increased risk of IDA.

CONCLUSION

Our finding potentially helps in the early prediction of iron deficiency in females through the genetic testing.

Turning scientific serendipity into discoveries in breast cancer research and treatment: a tale of PhD students and a 50-year roaming tamoxifen team

PURPOSE

This retrospective, about a single "mobile" laboratory in six locations on two continents, is intended as a case study in discovery for trainees and junior faculty in the medical sciences. Your knowledge of your topic is necessary to expect the unexpected.

HISTORICAL METHOD

In 1972, there was no tamoxifen, only ICI 46, 474, a non-steroidal anti-estrogen with little chance of clinical development. No one would ever be foolish enough to predict that the medicine, 20 years later, would achieve legendary status as the first targeted treatment for breast cancer, and millions of women would benefit from long-term adjuvant tamoxifen therapy. The secret of tamoxifen's success was a translational research strategy proposed in the mid 1970's. This strategy was to treat only patients with estrogen receptor (ER)-positive breast cancer and deploy 5 or more years of adjuvant tamoxifen therapy to prevent recurrence. Additionally, tamoxifen prevented mammary cancer in animals. Could the medicine prevent breast cancer in women?

RESULTS

Tamoxifen and the failed breast cancer drug raloxifene became the first selective estrogen receptor modulators (SERMs): a new drug group, discovered at the University of Wisconsin, Comprehensive Cancer Center. Serendipity can play a fundamental role in discovery, but there must be a rigorous preparation for the investigator to appreciate the possibility of a pending discovery. This article follows the unanticipated discoveries when PhD students "get the wrong answer." The secret of success of my six Tamoxifen Teams was their technical excellence to create models, to decipher mechanisms, that drove the development of new medicines. Discoveries are listed that either changed women's health or allowed an understanding of originally opaque mechanisms of action of potential therapies. These advances in women's health were supported entirely by government-sponsored peer-reviewed funding and major philanthropy from the Lynn Sage Breast Cancer Foundation, the Avon Foundation, and the Susan G. Komen Breast Cancer Foundation. The resulting lives saved or extended, families aided in a time of crisis and the injection of billions of dollars into national economies by drug development, is proof of the value of Federal or philanthropic investment into unencumbered research aimed at saving millions of lives.

In silico modeling of the interaction between TEX19 and LIRE1, and analysis of TEX19 gene missense SNPs

BACKGROUND

Testis expressed 19 (TEX19) is a specific human stem cell gene identified as cancer-testis antigen (CTA), which emerged as a potential therapeutic drug target. TEX19.1, a mouse paralog of human TEX19, can interact with LINE-1 retrotransposable element ORF1 protein (LIRE1) and subsequently restrict mobilization of LINE-1 elements in the genome.

AIM

This study aimed to predict the interaction of TEX19 with LIRE1 and analyze TEX19 missense polymorphisms. TEX19 model was generated using I-TASSER and the interaction between TEX19 and LIRE1 was studied using the HADDOCK software.

METHODS

The stability of the docking formed complex was studied through the molecular dynamic simulation using GROMACS. Missense SNPs (n=102) of TEX19 were screened for their potential effects on protein structure and function using different software.

RESULTS

Outcomes of this study revealed amino acids that potentially stabilize the predicted interaction interface between TEX19 and LIRE1. Of these SNPs, 37 were predicted to play a probably damaging role for the protein, three of them (F35S, P61R, and E55L) located at the binding site of LIRE1 and could disturb this binding affinity.

CONCLUSION

This information can be verified by further in vitro and in vivo experimentations and could be exploited for potential therapeutic targets.

Nitric Oxide Synthase Potentiates the Resistance of Cancer Cell Lines to Anticancer Chemotherapeutics

BACKGROUND

Despite the advancement in the fields of medical science and molecular biology, cancer is still the leading cause of death worldwide. Chemotherapy is a choice for treatment; however, the acquisition of chemo-resistance is a major impediment to cancer management. Many mechanisms have been postulated regarding the acquisition of chemo-resistance in breast cancer the impact on cellular signaling and the induction of apoptosis in tumour cells. The mechanism of the apoptotic mutation of p53 and bcl-2 proteins is commonly associated with increased resistance to apoptosis and, therein, to chemotherapy.

OBJECTIVES

The current study was aimed to investigate A172 and MDA-MB-231 cancer cells' sensitivity against chemotherapeutic drugs, including cisplatin, doxorubicin, and paclitaxel with different doses. Moreover, it estimates the resistance of cancer cells by evaluating nitric oxide synthase (NOS) expression and evaluate its correlation with the expression profile proteins of the apoptosis regulating Bcl-2 family.

METHODS

Dose-dependent sensitivity to cisplatin, doxorubicin, or paclitaxel was evaluated on spheroid cultured A172 and MDA-MB-231 cells lines as measured by time-lapse microscopy over a 72h period. Expressions of two nitric oxides (NO) synthases isoforms (iNOS, eNOS), anti-apoptotic (Bcl-2, phospho-Bcl-2, Mcl-1, and Bcl-xL), and pro-apoptotic (BID, Bim, Bok, Bad, Puma, and Bax) were evaluated by Western blot. The effect of NO modulation on anti- and pro-apoptotic molecule expression was also studied using Western blot.

RESULT

A172 cells show more resistance to chemotherapy drugs than MDA-MB-231 cancer cells. Therefore, they need higher doses for apoptosis. Resistance of gliomas might be returned to the higher significant expression of endothelial eNOS expression. It was clear that there is not a significant effect of NO modulation on the expression of pro-and anti-apoptotic proteins on both cell lines.

CONCLUSION

The present work provides a putative mechanism for the acquisition of drug resistance in breast cancer and glioma, which might be significant for clinical outcomes.

Prostate cancer and therapeutic challenges

Prostate cancer (PC) is the most prevalent type of cancer in men worldwide. In Saudi Arabia, the rate of PC is increasing annually. The sex steroid hormones androgens and their receptors have critical roles in PC development and progression. Additionally, apoptosis-related proteins such as heat-shock proteins are vital molecules in PC development. Steroid hormone-deprivation therapies remain the essential treatment for patients with metastatic PCs; however, acquired resistance to hormone deprivation and the transition to PC androgen independence is a major health obstacle. In this review, we aim to detail the roles of androgens, androgen receptors and sex steroid hormones in inducing apoptosis in PC.

Rapid Induction of the Unfolded Protein Response and Apoptosis by Estrogen Mimic TTC-352 for the Treatment of Endocrine-Resistant Breast Cancer

Patients with long-term estrogen-deprived breast cancer, after resistance to tamoxifen or aromatase inhibitors develops, can experience tumor regression when treated with estrogens. Estrogen's antitumor effect is attributed to apoptosis via the estrogen receptor (ER). Estrogen treatment can have unpleasant gynecologic and nongynecologic adverse events; thus, the development of safer estrogenic agents remains a clinical priority. Here, we study synthetic selective estrogen mimics (SEM) BMI-135 and TTC-352, and the naturally occurring estrogen estetrol (E₄), which are proposed as safer estrogenic agents compared with 17β-estradiol (E₂), for the treatment of endocrine-resistant breast cancer. TTC-352 and E₄ are being evaluated in breast cancer clinical trials. Cell viability assays, real-time PCR, immunoblotting, ERE DNA pulldowns, mass spectrometry, X-ray crystallography, docking and molecular dynamic simulations, live cell imaging, and Annexin V staining were conducted in 11 biologically different breast cancer models. Results were compared with the potent full agonist E₂, less potent full agonist E₄, the benchmark partial agonist triphenylethylene bisphenol (BPTPE), and antagonists 4-hydroxytamoxifen and endoxifen. We report ERα's regulation and coregulators' binding profiles with SEMs and E₄ We describe TTC-352's pharmacology as a weak full agonist and antitumor molecular mechanisms. This study highlights TTC-352's benzothiophene scaffold that yields an H-bond with Glu353, which allows Asp351-to-helix 12 (H12) interaction, sealing ERα's ligand-binding domain, recruiting E₂-enriched coactivators, and triggering rapid ERα-induced unfolded protein response (UPR) and apoptosis, as the basis of its anticancer properties. BPTPE's phenolic OH yields an H-Bond with Thr347, which disrupts Asp351-to-H12 interaction, delaying UPR and apoptosis and increasing clonal evolution risk.

Pharmacology and Molecular Mechanisms of Clinically Relevant Estrogen Estetrol and Estrogen Mimic BMI-135 for the Treatment of Endocrine-Resistant Breast Cancer

Long-term estrogen deprivation (LTED) with tamoxifen (TAM) or aromatase inhibitors leads to endocrine-resistance, whereby physiologic levels of estrogen kill breast cancer (BC). Estrogen therapy is effective in treating patients with advanced BC after resistance to TAM and aromatase inhibitors develops. This therapeutic effect is attributed to estrogen-induced apoptosis via the estrogen receptor (ER). Estrogen therapy can have unpleasant gynecologic and nongynecologic adverse events. Here, we study estetrol (E4) and a model Selective Human ER Partial Agonist (ShERPA) BMI-135. Estetrol and ShERPA TTC-352 are being evaluated in clinical trials. These agents are proposed as safer estrogenic candidates compared with 17β-estradiol (E2) for the treatment of endocrine-resistant BC. Cell viability assays, real-time polymerase chain reaction, luciferase reporter assays, chromatin immunoprecipitation, docking and molecular dynamics simulations, human unfolded protein response (UPR) RT2 PCR profiler arrays, live cell microscopic imaging and analysis, and annexin V staining assays were conducted. Our work was done in eight biologically different human BC cell lines and one human endometrial cancer cell line, and results were compared with full agonists estrone, E2, and estriol, a benchmark partial agonist triphenylethylene bisphenol (BPTPE), and antagonists 4-hydroxytamoxifen and endoxifen. Our study shows the pharmacology of E4 and BMI-135 as less-potent full-estrogen agonists as well as their molecular mechanisms of tumor regression in LTED BC through triggering a rapid UPR and apoptosis. Our work concludes that the use of a full agonist to treat BC is potentially superior to a partial agonist given BPTPE's delayed induction of UPR and apoptosis, with a higher probability of tumor clonal evolution and resistance. SIGNIFICANCE STATEMENT: Given the unpleasant gynecologic and nongynecologic adverse effects of estrogen treatment, the development of safer estrogens for endocrine-resistant breast cancer (BC) treatment and hormone replacement therapy remains a priority. The naturally occurring estrogen estetrol and Selective Human Estrogen-Receptor Partial Agonists are being evaluated in endocrine-resistant BC clinical trials. This work provides a comprehensive evaluation of their pharmacology in numerous endocrine-resistant BC models and an endometrial cancer model and their molecular mechanisms of tumor regression through the unfolded protein response and apoptosis.

Long noncoding RNA LINC00844-mediated molecular network regulates expression of drug metabolizing enzymes and nuclear receptors in human liver cells

Noncoding RNAs, such as long noncoding RNAs (lncRNAs) and microRNAs (miRNAs), regulate gene expression in many physiological and pathological processes, including drug metabolism. Drug metabolizing enzymes (DMEs) are critical components in drug-induced liver toxicity. In this study, we used human hepatic HepaRG cells treated with 5 or 10 mM acetaminophen (APAP) as a model system and identified LINC00844 as a toxicity-responsive lncRNA. We analyzed the expression profiles of LINC00844 in different human tissues. In addition, we examined the correlations between the levels of LINC00844 and those of key DMEs and nuclear receptors (NRs) for APAP metabolism in humans. Our results showed that lncRNA LINC00844 is enriched in the liver and its expression correlates positively with mRNA levels of CYP3A4, CYP2E1, SULT2A1, pregnane X receptor (PXR), and hepatocyte nuclear factor (HNF) 4α. We demonstrated that LINC00844 regulates the expression of these five genes in HepaRG cells using gain- and loss-of-function assays. Further, we discovered that LINC00844 is localized predominantly in the cytoplasm and acts as an hsa-miR-486-5p sponge, via direct binding, to protect SULT2A1 from miRNA-mediated gene silencing. Our data also demonstrated a functional interaction between LINC00844 and hsa-miR-486-5p in regulating DME and NR expression in HepaRG cells and primary human hepatocytes. We depicted a LINC00844-mediated regulatory network that involves miRNA and NRs and influences DME expression in response to APAP toxicity.