The Role of ERα36 in Development and Tumor Malignancy

Rat Models of Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) breast cancer (BC) is the most common type of breast cancer among women worldwide, accounting for 70-80% of all invasive cases. Patients with HR+ BC are commonly treated with endocrine therapy, but intrinsic or acquired resistance is a frequent problem, making HR+ BC a focal point of intense research. Despite this, the malignancy still lacks adequate in vitro and in vivo models for the study of its initiation and progression as well as response and resistance to endocrine therapy. No mouse models that fully mimic the human disease are available, however rat mammary tumor models pose a promising alternative to overcome this limitation. Compared to mice, rats are more similar to humans in terms of mammary gland architecture, ductal origin of neoplastic lesions and hormone dependency status. Moreover, rats can develop spontaneous or induced mammary tumors that resemble human HR+ BC. To date, six different types of rat models of HR+ BC have been established. These include the spontaneous, carcinogen-induced, transplantation, hormone-induced, radiation-induced and genetically engineered rat mammary tumor models. Each model has distinct advantages, disadvantages and utility for studying HR+ BC. This review provides a comprehensive overview of all published models to date.

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.

Icariin, a phytoestrogen, exerts rapid estrogenic actions through crosstalk of estrogen receptors in osteoblasts

Icariin, a flavonoid glycoside derived from Epimedium brevicornum Maxim, exerts bone protective effects via estrogen receptors (ERs). This study aimed to investigate the role of ER-α66, ER-α36, and GPER in bone metabolism in osteoblasts following treatment with icariin. Human osteoblastic MG-63 cells and osteoblast-specific ER-α66 knockout mice were employed. The ERs crosstalk in the estrogenic action of icariin was evaluated in ER-α66-negative human embryonic kidney HEK293 cells. Icariin, like E2, regulated ER-α36 and GPER protein expression in osteoblasts by downregulating them and upregulating ER-α66. ER-α36 and GPER suppressed the actions of icariin and E2 in bone metabolism. However, the in vivo administration of E2 (2 mg/kg/day) or icariin (300 mg/kg/day) restored bone conditions in KO osteoblasts. ER-α36 and GPER expression increased significantly and rapidly activated and translocated in KO osteoblasts after treatment with E2 or icariin. ER-α36 overexpression in KO osteoblasts further promoted the OPG/RANKL ratio induced by E2 or icariin treatment. This study showed icariin and E2 elicit rapid estrogenic responses in bone through recruiting ER-α66, ER-α36, and GPER. Notably, in osteoblasts lacking ER-α66, ER-α36, and GPER mediate the estrogenic effects of icariin and E2, while in intact osteoblasts, ER-α36 and GPER act as negative regulators of ER-α66.

Risk of estrogen receptor-specific breast cancer by family history of estrogen receptor subtypes and other cancers

BACKGROUND

The extent to which the risk of estrogen receptor (ER)-specific breast cancer is associated with ER status of breast cancer and other cancers among first-degree relatives is unclear.

METHODS

This population-based cohort included 464 707 cancer-free women in Stockholm, Sweden, during 1978-2019. For ER-negative and ER-positive breast cancers, we estimated hazard ratios (HRs) associated with ER status of female first-degree relatives with breast cancer and of other cancers in all first-degree relatives. Associations between ER-negative and ER-positive status by family cancer history were estimated using logistic regression in a case-only design.

RESULTS

Women with familial ER-positive breast cancer had 1.87 times (95% confidence interval [CI] = 1.77 to 1.97) higher risk of ER-positive subtype, whereas the corresponding hazard ratio for ER-negative was 2.54 (95% CI = 2.08 to 3.10) when having familial ER-negative breast cancer. The risk increased with an increasing number of female first-degree relatives having concordant subtypes and younger age at diagnosis (Ptrend <.001 for both). Nonbreast cancers among first-degree relatives were associated with both ER-positive (HR = 1.14, 95% CI = 1.10 to 1.17) and ER-negative (HR = 1.08, 95% CI = 1.01 to 1.16) breast cancers. Compared with women with ER-positive breast cancer, women with ER-negative breast cancer were more likely to have family history of liver (odds ratio [OR] = 1.33, 95% CI = 1.05 to 1.67), ovary (OR = 1.28, 95% CI = 1.01 to 1.61), and testicle cancer (OR = 1.79, 95% CI = 1.01 to 3.16) but less likely to have family history of endometrial cancer (OR = 0.77, 95% CI = 0.60 to 1.00) and leukemia (OR = 0.72, 95% CI = 0.56 to 0.91).

CONCLUSIONS

Risk of ER-specific breast cancer differs according to ER status of female first-degree relatives with breast cancer and some other cancers of first-degree relatives. This family history information should be considered in the individual risk prediction for ER subtypes.

Local production of active vitamin D3 metabolites in breast cancer cells by CYP24A1 and CYP27B1

The role of vitamin D3 and its metabolites in cancer and especially as a treatment option has been widely disputed. Clinicians noting low serum 25-hydroxyvitamin D3 [25(OH)D3] levels in their patients, recommend vitamin D3 supplementation as a method of reducing the risk of cancer; however, data supporting this are inconsistent. These studies rely on systemic 25(OH)D3 as an indicator of hormone status, but 25(OH)D3 is further metabolized in the kidney and other tissues under regulation by several factors. This study examined if breast cancer cells also possess the ability to metabolize 25(OH)D3, and if so, whether the resulting metabolites are secreted locally; if this ability reflects ERα66 status; and if they possess vitamin D receptors (VDR). To address this question, estrogen receptor alpha (ERα) positive (MCF-7) and ERα negative (HCC38 and MDA-MB-231) breast cancer cell lines were examined for expression of ERα66, ERα36, CYP24A1, CYP27B1, and VDR as well as for local production of 24,25-dihydroxyvitamin D3 [24,25(OH)2D3] and 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] after treatment with 25(OH)D3. The results showed that independent of ER status, breast cancer cells express the enzymes CYP24A1 and CYP27B1, which are responsible for converting 25(OH)D3 into its dihydroxylated forms. Moreover, these metabolites are produced at levels comparable to the levels observed in blood. They are positive for VDR, indicating that they can respond to 1α,25(OH)2D3, which can upregulate CYP24A1. These findings suggest that vitamin D metabolites may contribute to the tumorigenicity of breast cancer via autocrine and/or paracrine mechanisms.

Calycosin inhibits triple-negative breast cancer progression through down-regulation of the novel estrogen receptor-α splice variant ER-α30-mediated PI3K/AKT signaling pathway

BACKGROUND

Triple-negative breast cancer (TNBC) is a heterogeneous carcinoma characterized by the most aggressive phenotype among all breast cancer subtypes. However, therapeutic options for TNBC patients have limited clinical efficacy due to lack of specific target and efficient targeted therapeutics.

AIM

To investigate the biological characteristics of a novel estrogen receptor (ER)-α splice variant ER-α30 in breast cancer cells, and its possible role in the anticancer effects of calycosin, a typical phytoestrogen derived from the herbal plant Astragalus membranaceus, against TNBC. This may also provide a better understanding of the inhibitory activity of calycosin on TNBC progression.

METHODS

Breast cancer tissues and para-cancer tissues were collected and analyzed for the expression levels of ER-α30 using immunohistochemistry (IHC), and its expression in two TNBC cell lines (MDA-MB-231 and BT-549) was detected by western blot and qRT-PCR assays. Then the alteration of cell viability, apoptosis, migration, invasion and epithelial-mesenchymal transition (EMT) in response to overexpression or knockdown of ER-α30 was separately determined by CCK-8, Hoechst 33258, wound healing, transwell and western blot assays in two TNBC cell lines. Next, the anticancer effects of calycosin on MDA-MB-231 cells were evaluated through CCK-8, colony formation, flow cytometry, Hoechst 33258 and western blot assays, along with the role of ER-α30 in these effects and the possible downstream targets of ER-α30. In addition, the in vivo experiments were carried out using MDA-MB-231 xenograft model intraperitoneally treated with calycosin. The volume and weight of xenograft tumor were measured to evaluate the in vivo anticancer activities of calycosin, while the corresponding changes of ER-α30 expression in tumor tissues were detected by IHC.

RESULTS

It was demonstrated that the novel ER-α splice variant ER-α30 was primarily distributed in the nucleus of TNBC cells. Compared with normal breast tissues, ER-α30 expression was found in significantly higher levels in breast cancer tissues of ER- and progesterone receptor (PR)-negative subtype, so did in TNBC cell lines (MDA-MB-231 and BT-549) when compared to normal breast cell line MCF10A. Moreover, ER-α30 overexpression strikingly enhanced cell viability, migration, invasion and EMT progression and reduced apoptosis in TNBC cells, whereas shRNA-mediated knockdown of ER-α30 revealed the opposite results. Notably, calycosin suppressed the expression of ER-α30 in a dose-dependent manner, accompanied with the inhibition of TNBC growth and metastasis. A similar finding was observed for the xenografts generated from MDA-MB-231 cells. The treatment with calycosin suppressed the tumor growth and decreased ER-α30 expression in tumor tissues. Furthermore, this inhibition by calycosin was more pronounced in ER-α30 knockdown cells. Meanwhile, we found a positive relationship between ER-α30 and the activity of PI3K and AKT, which could also be inactivated by calycosin treatment.

CONCLUSION

For the first time, it is demonstrated that the novel estrogen receptor-α splice variant ER-α30 could function as pro-tumorigenic factor in the context of TNBC by participating in cell proliferation, apoptosis, invasion and metastasis, thus it may serve as a potential therapeutic target for TNBC therapy. Calycosin could reduce the activation of ER-α30-mediated PI3K/AKT pathway, thereby inhibited TNBC development and progression, suggesting that calycosin may be a potential therapeutic option for TNBC.

How Driver Oncogenes Shape and Are Shaped by Alternative Splicing Mechanisms in Tumors

The development of RNA sequencing methods has allowed us to study and better understand the landscape of aberrant pre-mRNA splicing in tumors. Altered splicing patterns are observed in many different tumors and affect all hallmarks of cancer: growth signal independence, avoidance of apoptosis, unlimited proliferation, invasiveness, angiogenesis, and metabolism. In this review, we focus on the interplay between driver oncogenes and alternative splicing in cancer. On one hand, oncogenic proteins-mutant p53, CMYC, KRAS, or PI3K-modify the alternative splicing landscape by regulating expression, phosphorylation, and interaction of splicing factors with spliceosome components. Some splicing factors-SRSF1 and hnRNPA1-are also driver oncogenes. At the same time, aberrant splicing activates key oncogenes and oncogenic pathways: p53 oncogenic isoforms, the RAS-RAF-MAPK pathway, the PI3K-mTOR pathway, the EGF and FGF receptor families, and SRSF1 splicing factor. The ultimate goal of cancer research is a better diagnosis and treatment of cancer patients. In the final part of this review, we discuss present therapeutic opportunities and possible directions of further studies aiming to design therapies targeting alternative splicing mechanisms in the context of driver oncogenes.

A Basic Review on Estrogen Receptor Signaling Pathways in Breast Cancer

Breast cancer is the most common cancer and the deadliest among women worldwide. Estrogen signaling is closely associated with hormone-dependent breast cancer (estrogen and progesterone receptor positive), which accounts for two-thirds of tumors. Hormone therapy using antiestrogens is the gold standard, but resistance to these treatments invariably occurs through various biological mechanisms, such as changes in estrogen receptor activity, mutations in the ESR1 gene, aberrant activation of the PI3K pathway or cell cycle dysregulations. All these factors have led to the development of new therapies, such as selective estrogen receptor degraders (SERDs), or combination therapies with cyclin-dependent kinases (CDK) 4/6 or PI3K inhibitors. Therefore, understanding the estrogen pathway is essential for the treatment and new drug development of hormone-dependent cancers. This mini-review summarizes current literature on the signalization, mechanisms of action and clinical implications of estrogen receptors in breast cancer.

Estrogen Receptor Alpha Splice Variants, Post-Translational Modifications, and Their Physiological Functions

The importance of estrogenic signaling for a broad spectrum of biological processes, including reproduction, cancer development, energy metabolism, memory and learning, and so on, has been well documented. Among reported estrogen receptors, estrogen receptor alpha (ERα) has been known to be a major mediator of cellular estrogenic signaling. Accumulating evidence has shown that the regulations of ERα gene transcription, splicing, and expression across the tissues are highly complex. The ERα promoter region is composed of multiple leader exons and 5′-untranslated region (5′-UTR) exons. Differential splicing results in multiple ERα proteins with different molecular weights and functional domains. Furthermore, various post-translational modifications (PTMs) further impact ERα cellular localization, ligand affinity, and therefore functionality. These splicing isoforms and PTMs are differentially expressed in a tissue-specific manner, mediate certain aspects of ERα signaling, and may work even antagonistically against the full-length ERα. The fundamental understanding of the ERα splicing isoforms in normal physiology is limited and association studies of the splicing isoforms and the PTMs are scarce. This review aims to summarize the functional diversity of these ERα variants and the PTMs in normal physiological processes, particularly as studied in transgenic mouse models.

RNA splicing dysregulation and the hallmarks of cancer

Dysregulated RNA splicing is a molecular feature that characterizes almost all tumour types. Cancer-associated splicing alterations arise from both recurrent mutations and altered expression of trans-acting factors governing splicing catalysis and regulation. Cancer-associated splicing dysregulation can promote tumorigenesis via diverse mechanisms, contributing to increased cell proliferation, decreased apoptosis, enhanced migration and metastatic potential, resistance to chemotherapy and evasion of immune surveillance. Recent studies have identified specific cancer-associated isoforms that play critical roles in cancer cell transformation and growth and demonstrated the therapeutic benefits of correcting or otherwise antagonizing such cancer-associated mRNA isoforms. Clinical-grade small molecules that modulate or inhibit RNA splicing have similarly been developed as promising anticancer therapeutics. Here, we review splicing alterations characteristic of cancer cell transcriptomes, dysregulated splicing's contributions to tumour initiation and progression, and existing and emerging approaches for targeting splicing for cancer therapy. Finally, we discuss the outstanding questions and challenges that must be addressed to translate these findings into the clinic.

Role of Estradiol Hormone in Human Life and Electrochemical Aptasensing of 17β-Estradiol: A Review

Estradiol is known as one of the most potent estrogenic endocrine-disrupting chemicals (EDCs) that may cause various health implications on human growth, metabolism regulation, the reproduction system, and possibly cancers. The detection of these EDCs in our surroundings, such as in foods and beverages, is important to prevent such harmful effects on humans. Aptamers are a promising class of bio-receptors for estradiol detection due to their chemical stability and high affinity. With the development of aptamer technology, electrochemical aptasensing became an important tool for estradiol detection. This review provides detailed information on various technological interventions in electrochemical estradiol detection in solutions and categorized the aptasensing mechanisms, aptamer immobilization strategies, and electrode materials. Moreover, we also discussed the role of estradiol in human physiology and signaling mechanisms. The level of estradiol in circulation is associated with normal and diseased conditions. The aptamer-based electrochemical sensing techniques are powerful and sensitive for estradiol detection.

Molecular Mechanisms of Anti-Estrogen Therapy Resistance and Novel Targeted Therapies

Breast cancer (BC) is the most commonly diagnosed cancer in women, constituting one-third of all cancers in women, and it is the second leading cause of cancer-related deaths in the United States. Anti-estrogen therapies, such as selective estrogen receptor modulators, significantly improve survival in estrogen receptor-positive (ER+) BC patients, which represents about 70% of cases. However, about 60% of patients inevitably experience intrinsic or acquired resistance to anti-estrogen therapies, representing a major clinical problem that leads to relapse, metastasis, and patient deaths. The resistance mechanisms involve mutations of the direct targets of anti-estrogen therapies, compensatory survival pathways, as well as alterations in the expression of non-coding RNAs (e.g., microRNA) that regulate the activity of survival and signaling pathways. Although cyclin-dependent kinase 4/6 and phosphatidylinositol 3-kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) inhibitors have significantly improved survival, the efficacy of these therapies alone and in combination with anti-estrogen therapy for advanced ER+ BC, are not curative in advanced and metastatic disease. Therefore, understanding the molecular mechanisms causing treatment resistance is critical for developing highly effective therapies and improving patient survival. This review focuses on the key mechanisms that contribute to anti-estrogen therapy resistance and potential new treatment strategies alone and in combination with anti-estrogen drugs to improve the survival of BC patients.

ERα-LBD, an isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance

Estrogen receptor alpha (ERα) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of an ERα isoform, ERα-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ERα-LBD is found to promote breast cancer growth and resistance to the ERα antagonist fulvestrant. ERα-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ERα-LBD expression and function does not appear to be restricted to cancers that express full length ERα but also promotes growth of triple-negative breast cancers and ERα-LBD transcript (ESR1-LBD) is also present in BC samples from both ERα(+) and ERα(-) human tumors. These findings point to ERα-LBD as a potential mediator of breast cancer progression and therapy resistance.

Estrogen Receptors-Mediated Apoptosis in Hormone-Dependent Cancers

It is known that estrogen stimulates growth and inhibits apoptosis through estrogen receptor(ER)-mediated mechanisms in many cancer cell types. Interestingly, there is strong evidence that estrogens can also induce apoptosis, activating different ER isoforms in cancer cells. It has been observed that E2/ERα complex activates multiple pathways involved in both cell cycle progression and apoptotic cascade prevention, while E2/ERβ complex in many cases directs the cells to apoptosis. However, the exact mechanism of estrogen-induced tumor regression is not completely known. Nevertheless, ERs expression levels of specific splice variants and their cellular localization differentially affect outcome of estrogen-dependent tumors. The goal of this review is to provide a general overview of current knowledge on ERs-mediated apoptosis that occurs in main hormone dependent-cancers. Understanding the molecular mechanisms underlying the induction of ER-mediated cell death will be useful for the development of specific ligands capable of triggering apoptosis to counteract estrogen-dependent tumor growth.

Regulation of Bcl-2 Family Proteins in Estrogen Receptor-Positive Breast Cancer and Their Implications in Endocrine Therapy

Estrogen receptor (ER)-positive breast cancer accounts for around two-thirds of breast cancer occurrences, with endocrine therapy serving as first-line therapy in most cases. Targeting estrogen signaling pathways, which play a central role in regulating ER+ breast cell proliferation and survival, has proven to improve patient outcomes. However, despite the undeniable advantages of endocrine therapy, a subset of breast cancer patients develop acquired or intrinsic resistance to ER-targeting agents, limiting their efficacy. The activation of downstream ER signaling pathways upregulates pro-survival mechanisms that have been shown to influence the response of cells to endocrine therapy. The Bcl-2 family proteins play a central role in cell death regulation and have been shown to contribute to endocrine therapy resistance, supporting the survival of breast cancer cells and enhancing cell death evasion. Due to the overexpression of anti-apoptotic Bcl-2 proteins in ER-positive breast cancer, the role of these proteins as potential targets in hormone-responsive breast cancer is growing in interest. In particular, recent advances in the development of BH3 mimetics have enabled their evaluation in preclinical studies with ER+ breast cancer models, and BH3 mimetics have entered early ER+ breast cancer clinical trials. This review summarizes the molecular mechanisms underlying the regulation of Bcl-2 family proteins in ER+ breast cancer. Furthermore, an overview of recent advances in research regarding the efficacy of BH3 mimetics in ER+ breast cancer has been provided.

Segregation of nuclear and membrane-initiated actions of estrogen receptor using genetically modified animals and pharmacological tools

Estrogen receptor alpha (ERα) and beta (ERβ) are members of the nuclear receptor superfamily, playing widespread functions in reproductive and non-reproductive tissues. Beside the canonical function of ERs as nuclear receptors, in this review, we summarize our current understanding of extra-nuclear, membrane-initiated functions of ERs with a specific focus on ERα. Over the last decade, in vivo evidence has accumulated to demonstrate the physiological relevance of this ERα membrane-initiated-signaling from mouse models to selective pharmacological tools. Finally, we discuss the perspectives and future challenges opened by the integration of extra-nuclear ERα signaling in physiology and pathology of estrogens.

Non-genomic signaling of steroid receptors in cancer

Steroid receptors (SRs) are members of the nuclear receptor family, which are ligand-activated transcription factors. SRs regulate many physiological functions including development and reproduction, though they can also be involved in several pathologies, especially cancer. Highly controlled cellular responses to steroids involve transcriptional regulation (genomic activity) combined with direct activation of signaling cascades (non-genomic activity). Non-genomic signaling has been extensively studied in cancer, mainly in breast cancer for ER and PR, and prostate cancer for AR. Even though most of the studies have been conducted in cells, some of them have been confirmed in vivo, highlighting the relevance of this pathway in cancer. This review provides an overview of the current and emerging knowledge on non-genomic signaling with a focus on breast and prostate cancers and its clinical relevance. A thorough understanding of ER, PR, AR and GR non-genomic pathways may open new perspectives for the development of therapeutic strategies.

ERα36-GPER1 Collaboration Inhibits TLR4/NFκB-Induced Pro-Inflammatory Activity in Breast Cancer Cells

Inflammation is important for the initiation and progression of breast cancer. We have previously reported that in monocytes, estrogen regulates TLR4/NFκB-mediated inflammation via the interaction of the Erα isoform ERα36 with GPER1. We therefore investigated whether a similar mechanism is present in breast cancer epithelial cells, and the effect of ERα36 expression on the classic 66 kD ERα isoform (ERα66) functions. We report that estrogen inhibits LPS-induced NFκB activity and the expression of downstream molecules TNFα and IL-6. In the absence of ERα66, ERα36 and GPER1 are both indispensable for this effect. In the presence of ERα66, ERα36 or GPER1 knock-down partially inhibits NFκB-mediated inflammation. In both cases, ERα36 overexpression enhances the inhibitory effect of estrogen on inflammation. We also verify that ERα36 and GPER1 physically interact, especially after LPS treatment, and that GPER1 interacts directly with NFκB. When both ERα66 and ERα36 are expressed, the latter acts as an inhibitor of ERα66 via its binding to estrogen response elements. We also report that the activation of ERα36 leads to the inhibition of breast cancer cell proliferation. Our data support that ERα36 is an inhibitory estrogen receptor that, in collaboration with GPER1, inhibits NFκB-mediated inflammation and ERα66 actions in breast cancer cells.

Estrogen receptor-α signaling in post-natal mammary development and breast cancers

17β-estradiol controls post-natal mammary gland development and exerts its effects through Estrogen Receptor ERα, a member of the nuclear receptor family. ERα is also critical for breast cancer progression and remains a central therapeutic target for hormone-dependent breast cancers. In this review, we summarize the current understanding of the complex ERα signaling pathways that involve either classical nuclear “genomic” or membrane “non-genomic” actions and regulate in concert with other hormones the different stages of mammary development. We describe the cellular and molecular features of the luminal cell lineage expressing ERα and provide an overview of the transgenic mouse models impacting ERα signaling, highlighting the pivotal role of ERα in mammary gland morphogenesis and function and its implication in the tumorigenic processes. Finally, we describe the main features of the ERα-positive luminal breast cancers and their modeling in mice.

Potentiating Therapeutic Effects of Epidermal Growth Factor Receptor Inhibition in Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is a subset of breast cancer with aggressive characteristics and few therapeutic options. The lack of an appropriate therapeutic target is a challenging issue in treating TNBC. Although a high level expression of epidermal growth factor receptor (EGFR) has been associated with a poor prognosis among patients with TNBC, targeted anti-EGFR therapies have demonstrated limited efficacy for TNBC treatment in both clinical and preclinical settings. However, with the advantage of a number of clinically approved EGFR inhibitors (EGFRis), combination strategies have been explored as a promising approach to overcome the intrinsic resistance of TNBC to EGFRis. In this review, we analyzed the literature on the combination of EGFRis with other molecularly targeted therapeutics or conventional chemotherapeutics to understand the current knowledge and to provide potential therapeutic options for TNBC treatment.

Systems pharmacology dissection of Epimedium targeting tumor microenvironment to enhance cytotoxic T lymphocyte responses in lung cancer

The clinical notably success of immunotherapy fosters an enthusiasm in developing drugs by enhancing antitumor immunity in the tumor microenvironment (TME). Epimedium, is a promising herbal medicine for tumor immunotherapy due to the pharmacological actions in immunological function modulation and antitumor. Here, we developed a novel systems pharmacology strategy to explore the polypharmacology mechanism of Epimedium involving in targeting TME of non-small cell lung cancer (NSCLC). This strategy integrates the active compounds screening, target predicting, network pharmacology analysis and onco-immune interacting to predict the potential active compounds that trigger the antitumor immunity. Icaritin (ICT), a major active ingredient of Epimedium, was predicted to have good drug-like properties and target immune microenvironment in NSCLC via regulating multiple targets and pathways. Then, we evidenced that the ICT effectively inhibited tumor growth in LLC tumor-bearing mice and increases the infiltration of CD8+ T cells in TME. In addition, we demonstrated that ICT promotes infiltration of CD8⁺ T cells in TME by downregulating the immunosuppressive cytokine (TNF-α, IL10, IL6) and upregulating chemotaxis (CXCL9 and CXCL10). Overall, the systems pharmacology strategy offers an important paradigm to understand the mechanism of polypharmacology of natural products targeting TME.

Anti-Hepatocellular Carcinoma Effect and Molecular Mechanism of the Estrogen Signaling Pathway

There are significant gender differences in the incidence and mortality of hepatocellular carcinoma (HCC). Compared with men, the incidence and mortality of HCC in women are relatively low. The estrogen signaling pathway, composed of estrogen and estrogen receptors, has been postulated to have a protective effect on the occurrence and development of HCC. There have been multiple studies that have supported anti-HCC effects of the estrogen signaling pathways, including direct and indirect pathways such as genomic pathways, rapid transduction pathways, non-coding RNA, tumor microenvironment, estrogen metabolites, and inhibition of hepatitis infection and replication. Based on the evidence of an anti-HCC effect of the estrogen signaling pathway, a number of strategies have been investigated to determine the potential therapeutic effect. These have included estrogen replacement therapy, targeting the estrogen receptor, key molecules, inflammatory mediators, and regulatory pathways of the estrogen signaling pathway. In this review, we have systematically summarized the latest developments in the complex functions and molecular mechanisms of the estrogen signaling pathway in liver cancer. Furthermore, we have highlighted the potential targets of treatment strategies based on the estrogen signaling pathway in the treatment of liver cancer and the principal obstacles currently encountered for future investigation.

Astrocytoma: A Hormone-Sensitive Tumor?

Astrocytomas and, in particular, their most severe form, glioblastoma, are the most aggressive primary brain tumors and those with the poorest vital prognosis. Standard treatment only slightly improves patient survival. Therefore, new therapies are needed. Very few risk factors have been clearly identified but many epidemiological studies have reported a higher incidence in men than women with a sex ratio of 1:4. Based on these observations, it has been proposed that the neurosteroids and especially the estrogens found in higher concentrations in women's brains could, in part, explain this difference. Estrogens can bind to nuclear or membrane receptors and potentially stimulate many different interconnected signaling pathways. The study of these receptors is even more complex since many isoforms are produced from each estrogen receptor encoding gene through alternative promoter usage or splicing, with each of them potentially having a specific role in the cell. The purpose of this review is to discuss recent data supporting the involvement of steroids during gliomagenesis and to focus on the potential neuroprotective role as well as the mechanisms of action of estrogens in gliomas.