A 50-gene biomarker identifies estrogen receptor-modulating chemicals in a microarray compendium.

High throughput transcriptomics (HTTr) profiling has the potential to rapidly and comprehensively identify molecular targets of environmental chemicals that can be linked to adverse outcomes. We describe here the construction and characterization of a 50-gene expression biomarker designed to identify estrogen receptor (ER) active chemicals in HTTr datasets. Using microarray comparisons, the genes in the biomarker were identified as those that exhibited consistent directional changes when ER was activated (4 ER agonists; 4 ESR1 gene constitutively active mutants) and opposite directional changes when ER was suppressed (4 antagonist treatments; 4 ESR1 knockdown experiments). The biomarker was evaluated as a predictive tool using the Running Fisher algorithm by comparison to annotated gene expression microarray datasets including those evaluating the transcriptional effects of hormones and chemicals in MCF-7 cells. Depending on the reference dataset used, the biomarker had a predictive accuracy for activation of up to 96%. To demonstrate applicability for HTTr data analysis, the biomarker was used to identify ER activators in a set of 15 chemicals that are considered potential bisphenol A (BPA) alternatives examined at up to 10 concentrations in MCF-7 cells and analyzed by full-genome TempO-Seq. Using benchmark dose (BMD) modeling, the biomarker genes stratified the ER potency of BPA alternatives consistent with previous studies. These results demonstrate that the ER biomarker can be used to accurately identify ER activators in transcript profile data derived from MCF-7 cells.

Autophagy and senescence facilitate the development of antiestrogen resistance in ER positive breast cancer.

Estrogen receptor positive (ER+) breast cancer is the most common breast cancer diagnosed annually in the US with endocrine-based therapy as standard-of-care for this breast cancer subtype. Endocrine therapy includes treatment with antiestrogens, such as selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). Despite the appreciable remission achievable with these treatments, a substantial cohort of women will experience primary tumor recurrence, subsequent metastasis, and eventual death due to their disease. In these cases, the breast cancer cells have become resistant to endocrine therapy, with endocrine resistance identified as the major obstacle to the medical oncologist and patient. To combat the development of endocrine resistance, the treatment options for ER+, HER2 negative breast cancer now include CDK4/6 inhibitors used as adjuvants to antiestrogen treatment. In addition to the dysregulated activity of CDK4/6, a plethora of genetic and biochemical mechanisms have been identified that contribute to endocrine resistance. These mechanisms, which have been identified by lab-based studies utilizing appropriate cell and animal models of breast cancer, and by clinical studies in which gene expression profiles identify candidate endocrine resistance genes, are the subject of this review. In addition, we will discuss molecular targeting strategies now utilized in conjunction with endocrine therapy to combat the development of resistance or target resistant breast cancer cells. Of approaches currently being explored to improve endocrine treatment efficacy and patient outcome, two adaptive cell survival mechanisms, autophagy, and "reversible" senescence, are considered molecular targets. Autophagy and/or senescence induction have been identified in response to most antiestrogen treatments currently being used for the treatment of ER+ breast cancer and are often induced in response to CDK4/6 inhibitors. Unfortunately, effective strategies to target these cell survival pathways have not yet been successfully developed. Thus, there is an urgent need for the continued interrogation of autophagy and "reversible" senescence in clinically relevant breast cancer models with the long-term goal of identifying new molecular targets for improved treatment of ER+ breast cancer.

Increased Rate of Mesh Erosion in Breast Cancer Survivors Taking Antiestrogen Therapy.

IMPORTANCE: There are no current data investigating the relationship between mesh-exposure complications after midurethral sling surgery and antiestrogen therapy. OBJECTIVES: We sought to determine if there are increased mesh-exposure complications between a breast cancer population versus a noncancer population particularly in conjunction with hormone suppression (HS) therapy. STUDY DESIGN: A retrospective chart review was performed on patients with a history of breast cancer undergoing tension-free vaginal tape (TVT) surgery at our institution between 2013 and 2021. A group of patients who underwent TVT surgery without a history of cancer served as our control. Univariate and multivariate logistic regression analyses were performed to identify predictors of mesh exposure complications. RESULTS: One hundred twenty-one patients with breast cancer had TVT surgery. Two hundred ninety-seven patients without cancer had TVT surgery during the same period. Baseline characteristics across all groups were similar. Twenty-nine patients (6.9%) experienced mesh exposure. This occurred at a higher rate in our cancer (15.7%) versus the noncancer population (3.4%). Women with breast cancer taking HS therapy had a higher rate of mesh exposure complications compared with those not taking HS therapy (25.0% versus 6.6%; P = 0.005). The highest rate of mesh exposure complications occurred in the cohort taking estrogen receptor modulators, selective estrogen receptor modulator (10/36 [27.8%]) versus aromatase inhibitors (5/24 [20.8%]) versus no HS therapy (4/61 [6.6%]; P = 0.014). On multivariate analysis, HS therapy use (odds ratio, 1.57; P = 0.007) and diabetes mellitus (odds ratio, 4.53; P = 0.018) were associated with increased TVT-related complications. CONCLUSION: Women with breast cancer had a higher rate of mesh exposure complications from TVT surgery compared with women without cancer, particularly those taking antiestrogenic therapy.

EB1089 Increases the Antiproliferative Response of Lapatinib in Combination with Antiestrogens in HER2-Positive Breast Cancer Cells.

HER2-positive breast cancer is associated with aggressive behavior and reduced survival rates. Calcitriol restores the antiproliferative activity of antiestrogens in estrogen receptor (ER)-negative breast cancer cells by re-expressing ERα. Furthermore, calcitriol and its analog, EB1089, enhance responses to standard anti-cancer drugs. Therefore, we aimed to investigate EB1089 effects when added to the combined treatment of lapatinib and antiestrogens on the proliferation of HER2-positive breast cancer cells. BT-474 (ER-positive/HER2-positive) and SK-BR-3 (ER-negative/HER2-positive) cells were pre-treated with EB1089 to modulate ER expression. Then, cells were treated with EB1089 in the presence of lapatinib with or without the antiestrogens, and proliferation, phosphorylation array assays, and Western blot analysis were performed. The results showed that EB1089 restored the antiproliferative response to antiestrogens in SK-BR-3 cells and improved the inhibitory effects of the combination of lapatinib with antiestrogens in the two cell lines. Moreover, EB1089, alone or combined, modulated ERα protein expression and reduced Akt phosphorylation in HER2-positive cells. EB1089 significantly enhanced the cell growth inhibitory effect of lapatinib combined with antiestrogens in HER2-positive breast cancer cells by modulating ERα expression and Akt phosphorylation suppression. These results highlight the potential of this therapeutic approach as a promising strategy for managing HER2-positive breast cancer.

Synthesis, biological evaluation, and stability studies of raloxifene mono- and bis-sulfamates as dual-targeting agents.

All three possible sulfamate derivatives of the selective estrogen receptor modulator Raloxifene (bis-sulfamate 7 and two mono-sulfamates 8-9) were synthesized and evaluated as inhibitors of the clinical drug target steroid sulfatase (STS), both in cell-free and in cell-based assays, and also as estrogen receptor (ER) modulators. Bis-sulfamate 7 was the most potent STS inhibitor with an IC50 of 12.2 nM in a whole JEG3 cell-based assay, with the two mono-sulfamates significantly weaker. The estrogen receptor-modulating activities of 7-9 showed generally lower affinities compared to Raloxifene HCl, diethylstilbestrol and other known ligands, with mono-sulfamate 8 being the best ligand (Ki of 1.5 nM) for ERα binding, although 7 had a Ki of 13 nM and both showed desirable antagonist activity. The antiproliferative activities of the sulfamate derivatives against the T-47D breast cancer cell line showed 7 as most potent (GI50 = 7.12 µM), comparable to that of Raloxifene. Compound 7 also showed good antiproliferative potency in the NCI-60 cell line panel with a GI50 of 1.34 µM against MDA-MB-231 breast cancer cells. Stability testing of 7-9 showed that bis-sulfamate 7 hydrolyzed by desulfamoylation at a surprisingly rapid rate, initially leading selectively to 8 and finally to Raloxifene 3 without formation of 9. The mechanisms of these hydrolysis reactions could be extensively rationalized. Conversion of Raloxifene (3) into its bis-sulfamate (7) thus produced a promising drug lead with nanomolar dual activity as an STS inhibitor and ERα antagonist, as a potential candidate for treatment of estrogen-dependent breast cancer.

Investigation of the potential effects of estrogen receptor modulators on immune checkpoint molecules.

Immune checkpoints regulate the immune system response. Recent studies suggest that flavonoids, known as phytoestrogens, may inhibit the PD-1/PD-L1 axis. We explored the potential of estrogens and 17 Selective Estrogen Receptor Modulators (SERMs) as inhibiting ligands for immune checkpoint proteins (CTLA-4, PD-L1, PD-1, and CD80). Our docking studies revealed strong binding energy values for quinestrol, quercetin, and bazedoxifene, indicating their potential to inhibit PD-1 and CTLA-4. Quercetin and bazedoxifene, known to modulate EGFR and IL-6R alongside estrogen receptors, can influence the immune checkpoint functionality. We discuss the impact of SERMs on PD-1 and CTLA-4, suggesting that these SERMs could have therapeutic effects through immune checkpoint inhibition. This study highlights the potential of SERMs as inhibitory ligands for immune checkpoint proteins, emphasizing the importance of considering PD-1 and CTLA-4 inhibition when evaluating SERMs as therapeutic agents. Our findings open new avenues for cancer immunotherapy by exploring the interaction between various SERMs and immune checkpoint pathways.

MYSM1 acts as a novel co-activator of ERα to confer antiestrogen resistance in breast cancer.

Endocrine resistance is a crucial challenge in estrogen receptor alpha (ERα)-positive breast cancer (BCa). Aberrant alteration in modulation of E2/ERα signaling pathway has emerged as the putative contributor for endocrine resistance in BCa. Herein, we demonstrate that MYSM1 as a deubiquitinase participates in modulating ERα action via histone and non-histone deubiquitination. MYSM1 is involved in maintenance of ERα stability via ERα deubiquitination. MYSM1 regulates relevant histone modifications on cis regulatory elements of ERα-regulated genes, facilitating chromatin decondensation. MYSM1 is highly expressed in clinical BCa samples. MYSM1 depletion attenuates BCa-derived cell growth in xenograft models and increases the sensitivity of antiestrogen agents in BCa cells. A virtual screen shows that the small molecule Imatinib could potentially interact with catalytic MPN domain of MYSM1 to inhibit BCa cell growth via MYSM1-ERα axis. These findings clarify the molecular mechanism of MYSM1 as an epigenetic modifier in regulation of ERα action and provide a potential therapeutic target for endocrine resistance in BCa.

Tibolone and Breast Tissue: a Review.

The safety profile of hormone replacement therapy (HRT) on breast is still controversial. Tibolone is an option of treatment for climacteric syndrome of postmenopausal women. Its risk profile on breast is debated. This is an updated narrative review focusing on the impact of tibolone on breast. Particularly, we will report data from major preclinical and clinical studies regarding the effects of the use of this compound on breast tissue and breast density. Moreover, we will analyze and discuss the most relevant findings of the principal studies evaluating the relationship between tibolone and breast cancer risk. Our purpose is making all clinicians who are particularly involved in women's health more aware of the effects of this compound on breast and, thus, more experienced in the management of menopausal symptoms with this drug. According to the available literature, tibolone seems to be characterized by an interesting safety profile on breast tissue.

Network pharmacology and topological analysis on tibolone metabolites and their molecular mechanisms in traumatic brain injury.

Traumatic brain injury (TBI) is a pathology of great social impact, affecting millions of people worldwide. Despite the scientific advances to improve the management of TBI in recent years, we still do not have a specific treatment that controls the inflammatory process after mechanical trauma. The discovery and implementation of new treatments is a long and expensive process, making the repurpose of approved drugs for other pathologies a clinical interest. Tibolone is a drug in use for the treatment of symptoms associated with menopause and has been shown to have a broad spectrum of actions by regulating estrogen, androgen and progesterone receptors, whose activation exerts potent anti-inflammatory and antioxidant effects. In the present study, we aimed to investigate the therapeutic potential of the tibolone metabolites 3α-Hydroxytibolone, 3ß-Hydroxytibolone, and Δ4-Tibolone as a possible therapy in TBI using network pharmacology and network topology analysis. Our results demonstrate that the estrogenic component mediated by the α and ß metabolites can regulate synaptic transmission and cell metabolism, while the Δ metabolite may be involved in modulating the post-TBI inflammatory process. We identified several molecular targets, including KDR, ESR2, AR, NR3C1, PPARD, and PPARA, which are known to play critical roles in the pathogenesis of TBI. Tibolone metabolites were predicted to regulate the expression of key genes involved in oxidative stress, inflammation, and apoptosis. Overall, the repurposing of tibolone as a neuroprotective treatment for TBI holds promise for future clinical trials. However, further studies are needed to confirm its efficacy and safety in TBI patients.

Discovery of highly potent proapoptotic antiestrogens in a series of androst-5,16-dienes D-modified with imidazole-annulated pendants.

Heterocyclic derivatives of steroid hormones are potent anticancer agents, which are used in the chemotherapy of breast and prostate cancers. Here, we describe a novel series of androstenes, D-modified with imidazole-annulated pendants, with significant anticancer activity. Novel C17-linked imidazole-annulated heterocyclic derivatives of dehydropregnenolone acetate were synthesized by the cyclocondensation with amidines using 3ß-acetoxy-21-bromopregna-5,16-dien-20-one as the substrate. The antiproliferative potency of all the synthesized compounds was evaluated against human prostate (22Rv1) and human breast (MCF7) cancer cell lines and cytochromes P450. The lead compound, imidazo[1,2-a]pyridine derivative 3h, was revealed to be a promising candidate for future anticancer drug design, particularly against ERα-positive breast cancer. Lead compound 3h was found to be selective against MCF7 cells with IC50 of 0.1 µM and to act as both a potent selective agent blocking estrogen receptor α, which is involved in the stimulation of breast cancer growth, and an effective apoptosis inducer. The potential ability of compound 3h to bind to ERα was studded using molecular docking and molecular dynamics simulation. The selectivity analysis showed that lead steroid 3h produces no effects on cytochromes P450 CYP17A1, CYP7A1, and CYP21A2.

Impact of Acupuncture on Hot Flashes in Breast Cancer Patients Receiving Adjuvant Antiestrogen Therapy with Tamoxifen: A Randomized Controlled Trial.

Objectives: The aim of this study was to evaluate the impact of acupuncture on hot flashes in breast cancer patients taking tamoxifen as an adjuvant antiestrogen therapy in Korea. Design: This trial was a randomized, no-treatment-controlled, single-blind, multi-center trial. Participants were randomized 1:1 into the acupuncture group or into the no-treatment control group. Location: This trial was conducted at Daegu Catholic University Hospital and Daegu Haany University Korean Medicine Hospital in Daegu, Republic of Korea. Participants: Patients with moderate to severe symptoms of hot flashes while receiving adjuvant antiestrogen therapy using tamoxifen after surgery for breast cancer were included. Interventions: In the acupuncture group, acupuncture was performed three times a week for 4 consecutive weeks at five predetermined points. The control group received no treatment during the study period. Study Outcome Measures: As a primary outcome, the severity of hot flashes was measured on the visual analogue scale (VAS) and total hot flash score. In addition, the quality of life (QoL) of participants was assessed as a secondary outcome. Results: A total of 30 patients were included in this study, 15 each in the acupuncture group and the control group. The participants in the acupuncture group significantly decreased the severity of hot flashes evaluated with both VAS and total hot flash scores compared with participants in the control group. Also, the acupuncture group showed improved score of a global health status/QoL scale and functional scales assessed with the European Organisation for Research and Treatment of Cancer QoL questionnaire-core questionnaire, compared with those in the control group. This trend was maintained 4 weeks after acupuncture treatment. No adverse events have been reported in this study. Conclusions: Acupuncture was effective and safe in improving hot flashes in Korean breast cancer patients receiving adjuvant antiestrogen therapy with tamoxifen, and it improved the QoL. Clinical Trial Registration: KCT0007829.

ERß1 Sensitizes and ERß2 Desensitizes ERα-Positive Breast Cancer Cells to the Inhibitory Effects of Tamoxifen, Fulvestrant and Their Combination with All-Trans Retinoic Acid.

Adjuvant endocrine therapy (AET) is the treatment of choice for early-stage estrogen receptor alpha (ERα)-positive breast cancer (BC). However, almost 40% of tamoxifen-treated cases display no response or a partial response to AET, thus increasing the need for new treatment options and strong predictors of the therapeutic response of patients at high risk of relapse. In addition to ERα, BC research has focused on ERß1 and ERß2 (isoforms of ERß), the second ER isotype. At present, the impact of ERß isoforms on ERα-positive BC prognosis and treatment remains elusive. In the present study, we established clones of MCF7 cells constitutively expressing human ERß1 or ERß2 and investigated their role in the response of MCF7 cells to antiestrogens [4-hydroxytamoxifen (OHΤ) and fulvestrant (ICI182,780)] and retinoids [all-trans retinoic acid (ATRA)]. We show that, compared to MCF7 cells, MCF7-ERß1 and MCF7-ERß2 cells were sensitized and desensitized, respectively, to the antiproliferative effect of the antiestrogens, ATRA and their combination and to the cytocidal effect of the combination of OHT and ATRA. Analysis of the global transcriptional changes upon OHT-ATRA combinatorial treatment revealed uniquely regulated genes associated with anticancer effects in MCF7-ERß1 cells and cancer-promoting effects in MCF7-ERß2 cells. Our data are favorable to ERß1 being a marker of responsiveness and ERß2 being a marker of resistance of MCF7 cells to antiestrogens alone and in combination with ATRA.

Expression patterns and clinical significance of estrogen receptor in non-small cell lung cancer.

BACKGROUND: Lung cancer death remains the highest among all malignancies. Gender differences show women have an increased cancer incidence while men have worse outcomes. These observations identified that some lung carcinomas express estrogen receptors (ER). This is a promising target as antiestrogen drugs can reduce tumors and improve survival. However, there is a limited understanding of ER distribution and its clinical significance to properly design antiestrogen drug clinical trials. Thus, we comprehensively analyzed ERα and ERß expression patterns by gender, cancer cell type, and receptor location in lung cancer. METHODS: We conducted a systematic review using the PubMed database from all-time through October 2022, using MeSH terms with the keywords "lung cancer," "estrogen receptor," and "immunohistochemistry." We identified 120 studies with 21 reports being evaluated based on our inclusion criteria. RESULTS: We examined 4874 lung cancers from 5011 patients. ERß is the predominant form of ER expressed, mainly found in the nucleus. The ERß positivity rate is 51.5% in males versus 55.5% in females and was not statistically different. In contrast, ERα is predominately extranuclear in location, and ERα expression varies by gender. Males had a positivity rate of 31% versus 26.6% in females, which is statistically different. ERα is associated with a worse prognosis in some studies, while it had no effect in others. Overall, ERß was associated with a better prognosis. CONCLUSION: We characterized ER expression patterns in 4874 lung cancers. Over 50% expressed ERß with equal rates in both sexes and was associated with a better prognosis. ERα expression was slightly higher in males (31%) than females (26.6%) and was associated with a poor prognosis. Our findings suggest estrogen signaling may be a promising drug target in lung cancer.

Upregulation of the EGFR/MEK1/MAPK1/2 signaling axis as a mechanism of resistance to antiestrogen­induced BimEL dependent apoptosis in ER+ breast cancer cells.

The epidermal growth factor receptor (EGFR) is commonly upregulated in multiple cancer types, including breast cancer. In the present study, evidence is provided in support of the premise that upregulation of the EGFR/MEK1/MAPK1/2 signaling axis during antiestrogen treatment facilitates the escape of breast cancer cells from BimEL­dependent apoptosis, conferring resistance to therapy. This conclusion is based on the findings that ectopic BimEL cDNA overexpression and confocal imaging studies confirm the pro­apoptotic role of BimEL in ERα expressing breast cancer cells and that upregulated EGFR/MEK1/MAPK1/2 signaling blocks BimEL pro­apoptotic action in an antiestrogen­resistant breast cancer cell model. In addition, the present study identified a pro­survival role for autophagy in antiestrogen resistance while EGFR inhibitor studies demonstrated that a significant percentage of antiestrogen­resistant breast cancer cells survive EGFR targeting by pro­survival autophagy. These pre­clinical studies establish the possibility that targeting both the MEK1/MAPK1/2 signaling axis and pro­survival autophagy may be required to eradicate breast cancer cell survival and prevent the development of antiestrogen resistance following hormone treatments. The present study uniquely identified EGFR upregulation as one of the mechanisms breast cancer cells utilize to evade the cytotoxic effects of antiestrogens mediated through BimEL­dependent apoptosis.

Short-term PI3K Inhibition Prevents Breast Cancer in Preclinical Models.

Antiestrogen medication is the only chemoprevention currently available for women at a high risk of developing breast cancer; however, antiestrogen therapy requires years to achieve efficacy and has adverse side effects. Therefore, it is important to develop an efficacious chemoprevention strategy that requires only a short course of treatment. PIK3CA is commonly activated in breast atypical hyperplasia, the known precancerous precursor of breast cancer. Targeting PI3K signaling in these precancerous lesions may offer a new strategy for chemoprevention. Here, we first established a mouse model that mimics the progression from precancerous lesions to breast cancer. Next, we demonstrated that a short-course prophylactic treatment with the clinically approved PI3K inhibitor alpelisib slowed early lesion expansion and prevented cancer formation in this model. Furthermore, we showed that alpelisib suppressed ex vivo expansion of patient-derived atypical hyperplasia. Together, these data indicate that the progression of precancerous breast lesions heavily depends on the PI3K signaling, and that prophylactic targeting of PI3K activity can prevent breast cancer. PREVENTION RELEVANCE: PI3K protein is abnormally high in breast precancerous lesions. This preclinical study demonstrates that the FDA-approved anti-PI3K inhibitor alpelisib can prevent breast cancer and thus warrant future clinical trials in high-risk women.

The AF-2 cofactor binding region is key for the selective SUMOylation of estrogen receptor alpha by antiestrogens.

Antiestrogens (AEs) are used to treat all stages of estrogen receptor (ER)-positive breast cancer. Selective estrogen receptor modulators such as tamoxifen have tissue-specific partial agonist activity, while selective estrogen receptor downregulators such as fulvestrant (ICI182,780) display a more complete antiestrogenic profile. We have previously observed that fulvestrant-induced ERα SUMOylation contributes to transcriptional suppression, but whether this effect is seen with other AEs and is specific to ERα is unclear. Here we show that several AEs induce SUMOylation of ERα, but not ERß, at different levels. Swapping domains between ERα and ERß indicates that the ERα identity of the ligand-binding domain helices 3 and 4 (H3-H4 region), which contribute to the static part of the activation function-2 (AF-2) cofactor binding groove, is sufficient to confer fulvestrant-induced SUMOylation to ERß. This region does not contain lysine residues unique to ERα, suggesting that ERα-specific residues in H3-H4 determine the capacity of the AE-bound ERα ligand-binding domain to recruit the SUMOylation machinery. We also show that the SUMO E3 ligase protein inhibitor of activated STAT 1 increases SUMOylation of ERα and of ERß containing the H3-H4 region of ERα, but not of ERß. Together, these results shed new light on the molecular basis for the differential capacity of selective estrogen receptor modulators and selective estrogen receptor downregulators to suppress transcription by ERα.

A Nursing Educational Intervention to Improve Antiestrogen Adherence and Self-Management of Side Effects.

Antiestrogens prescribed to reduce breast cancer risk or recurrence can have undesirable musculoskeletal side effects that may lead to early discontinuation of therapy. Previous studies have not focused on nurse-led assessmen.

The novel estrogen receptor modulator STX attenuates Amyloid-ß neurotoxicity in the 5XFAD mouse model of Alzheimer's disease.

Based on previous evidence that the non-steroidal estrogen receptor modulator STX mitigates the effects of neurotoxic Amyloid-ß (Aß) in vitro, we have evaluated its neuroprotective benefits in a mouse model of Alzheimer's disease. Cohorts of 5XFAD mice, which begin to accumulate cerebral Aß at two months of age, were treated with orally-administered STX starting at 6 months of age for two months. After behavioral testing to evaluate cognitive function, biochemical and immunohistochemical assays were used to analyze key markers of mitochondrial function and synaptic integrity. Oral STX treatment attenuated Aß-associated mitochondrial toxicity and synaptic toxicity in the brain, as previously documented in cultured neurons. STX also moderately improved spatial memory in 5XFAD mice. In addition, STX reduced markers for reactive astrocytosis and microgliosis surrounding amyloid plaques, and also unexpectedly reduced overall levels of cerebral Aß in the brain. The neuroprotective effects of STX were more robust in females than in males. These results suggest that STX may have therapeutic potential in Alzheimer's Disease.

Clinical Translation: Targeting the Estrogen Receptor.

Estrogen Receptor alpha (ERα) stands as one of the most successfully prosecuted drug targets in oncology, beginning with the approval of tamoxifen for women with ERα positive (ER+) breast cancer over 40 years ago. The field continued to advance with the development of aromatase inhibitors and the pure antiestrogen fulvestrant. With multiple endocrine therapies approved for the treatment of ER+ breast cancer, efforts to generate novel ERα-targeted therapeutics somewhat diminished in the early 2000s. Today however, there are at least eight new molecular entities targeting ERα under active clinical investigation, each with the aim of bringing further benefit to patients. This remarkable re-energizing of the field was spurred in part by the discovery of highly prevalent ERα mutations as a mechanism of resistance to standard-of-care therapies, which provided unequivocal evidence of the continued, and broad, dependence of tumors on ERα, despite relapsing after earlier lines of endocrine therapy. Re-engagement of the pharmaceutical and biotechnology industries with ERα as a drug target has been further underpinned by the impressive advances made in medicinal chemistry, enabling desirable mechanistic features - high potency full ERα antagonism - to be combined with improved drug-like properties - oral bioavailability and optimized pharmacokinetics. In this chapter, we describe the rich history and science behind the currently evolving landscape of ERα targeting in breast cancer.