Unlocking estrogen receptor: Structural insights into agonists and antagonists for glioblastoma therapy.

Glioblastoma (GBM), a malignant brain tumor originating in glial cells, is one of the most common primary brain malignancies, affecting one in 100,000 people, typically in the frontal lobe. Estrogens, like estradiol-17 (E2), significantly influence GBM progression, metastasis, and angiogenesis. Estrogen receptors (ERs) are crucial in signal transduction and physiology, making them potential therapeutic targets. However, their roles in GBM pathogenesis remain unclear. This review explores ERs in GBM, focusing on their involvement in tumor immune evasion, modulation of the tumor microenvironment, and the mechanisms underlying GBM progression. Additionally, therapeutic opportunities targeting ERs for GBM treatment are discussed. Estrogen, synthesized primarily in ovaries and in smaller amounts by adrenal glands and fat tissues, regulates reproductive systems, bone density, skin health, and cardiovascular function. The invasive nature and heterogeneity of GBM complicate therapy development. Preclinical findings suggest that endocrine therapy with hormone receptor agonists or antagonists can extend patient survival and improve post-treatment quality of life. The ERß pathway, in particular, shows tumor-suppressive potential, limiting glioma progression with fewer side effects. ERß agonists could become a novel drug class for GBM treatment. Identifying biomarkers and specific therapeutic targets is crucial for early detection and improved prognosis. Estrogen and its receptors are advantageous for GBM treatment due to their regulation of numerous biological processes, ability to penetrate the blood-brain barrier, and genomic and non-genomic control of transcription, making them promising targets for GBM therapy.

Structure-based design and synthesis of conformationally constrained derivatives of methyl-piperidinopyrazole (MPP) with estrogen receptor (ER) antagonist activity.

Nuclear Estrogen receptors (ER) are cytoplasmic proteins; translocated to the nucleus to induce transcriptional signals after getting bound to the estrogen hormone. ER activation implicated in cancer cell proliferation of female reproductive organs. Thus, the discovery of ER antagonists is a reliable strategy to combat estrogen-dependent breast cancer. Endometrial carcinoma is one of the complications encountered upon long-term therapy by selective estrogen receptor modulators (SERMs) like Tamoxifen (TMX) and methyl piperidinopyrazole (MPP). Thus, the ER-full antagonist is a solution to improve the safety of this class of therapeutics during the treatment of breast cancer. We selected MPP as a lead structure to design conformationally constrained analogs. Structural rigidification is a proven strategy to transform the SERMs into full antagonists. Accordingly, we synthesized 7-methoxy-3-(4-methoxyphenyl)-4,5-dihydro-2H-benzo[g]indazoles (4), (6a-c),(8-12) along with the biphenolic counterparts(13-19)that are the anticipated active metabolites. The 4-nitrophenyl derivative(4)is with the most balanced profile regardingthe in vivoanti-uterotrophic potential (EC50 = 4.160 µM); and the cytotoxicity assay of the corresponding active metabolite(13)against ER+ breast cancer cell lines (MCF-7 IC50 = 7.200 µM, T-47D IC50 = 11.710 µM). The inconsiderable uterotrophic activities of the elaborated ER-antagonists and weak antiproliferative activity of the compound(13)against ovarian cancer (SKOV-3 IC50 = 29.800 µM) highlighted it as a good start point to elaborate potential ER-full antagonists devoid of endometrial carcinoma. Extending the pendant chain that protrudes from the 2-(4-(substituted)-phenyl) ring of the new benzo-indazoles is recommended for enhancing the potency based on the binding mode of compound(13)in the ligand-binding domain (LBD) of ER.

Human estrogen receptor α antagonists, part 2: Synthesis driven by rational design, in vitro antiproliferative, and in vivo anticancer evaluation of innovative coumarin-related antiestrogens as breast cancer suppressants.

New twelve in silico designed coumarin-based ERα antagonists, namely 3DQ-1a to 3DQ-1е, were synthesized and confirmed as selective ERα antagonists, showing potencies ranging from single-digit nanomolar to picomolar. The hits were confirmed as selective estrogen receptor modulators and validated as antiproliferative agents using MCF-7 breast cancer cell lines exerting from picomolar to low nanomolar potency, at the same time showing no agonistic activity within endometrial cell lines. Their mechanism of action was inspected and revealed to be through the inhibition of the Raf-1/MAPK/ERK signal transduction pathway, preventing hormone-mediated gene expression on either genomic direct or genomic indirect level, and stopping the MCF-7 cells proliferation at G0/G1 phase. In vivo experiments, by means of the per os administration to female Wistar rats with pre-induced breast cancer, distinguished six derivatives, 3DQ-4a, 3DQ-2a, 3DQ-1a, 3DQ-1b, 3DQ-2b, and 3DQ-3b, showing remarkable potency as tumor suppressors endowed with optimal pharmacokinetic profiles and no significant histopathological profiles. The presented data indicate the new compounds as potential candidates to be submitted in clinical trials for breast cancer therapy.

GDC-9545 (Giredestrant): A Potent and Orally Bioavailable Selective Estrogen Receptor Antagonist and Degrader with an Exceptional Preclinical Profile for ER+ Breast Cancer.

Breast cancer remains a leading cause of cancer death in women, representing a significant unmet medical need. Here, we disclose our discovery efforts culminating in a clinical candidate, 35 (GDC-9545 or giredestrant). 35 is an efficient and potent selective estrogen receptor degrader (SERD) and a full antagonist, which translates into better antiproliferation activity than known SERDs (1, 6, 7, and 9) across multiple cell lines. Fine-tuning the physiochemical properties enabled once daily oral dosing of 35 in preclinical species and humans. 35 exhibits low drug-drug interaction liability and demonstrates excellent in vitro and in vivo safety profiles. At low doses, 35 induces tumor regressions either as a single agent or in combination with a CDK4/6 inhibitor in an ESR1Y537S mutant PDX or a wild-type ERα tumor model. Currently, 35 is being evaluated in Phase III clinical trials.

Design and synthesis of novel benzothiophene analogs as selective estrogen receptor covalent antagonists against breast cancer.

Endocrine therapy (ET) has benefited patients with estrogen receptor alpha (ERα) positive breast cancer for decades. Selective estrogen receptor modulator (SERM) such as Tamoxifen represents the clinical standard of care (SoC). Despite the therapeutic importance of current SoC agents, 30-50% of prolonged treatment patients inevitably generated resistant tumor cells, usually eventually suffered tumor relapse and developed into metastatic breast cancer (MBC), which was the leading cause of female cancer-related mortality. Among these, most resistant tumors remained dependent on ERα signaling, which reignited the need for the next generation of ERα related agents. We hypothesized that selective estrogen receptor covalent antagonists targeting ERα would provide a therapeutic alternative. In the current work, series of novel benzothiophene hybrids bearing electrophile moieties were synthesized and biologically evaluated. The representative analogue 15c exhibited potent anti-proliferative effect in MCF-7 cell lines in vitro, and further mechanism studies confirmed the necessity of covalent bonding. More importantly, 15c could attenuate the expression of TFF-1, GREB-1 and downregulate the levels of cellular ERα protein.

Development of bivalent triarylalkene- and cyclofenil-derived dual estrogen receptor antagonists and downregulators.

Up to 80% of mammary carcinoma initially exhibit estrogen-dependent growth, which can be treated by aromatase inhibitors or SERMs/SERDs. To increase the options after failure of the hormonal therapy with these drugs, the search for alternatives with a different mode of action to prevent estrogen action is of high relevance. Therefore, this study focused on the inhibition of coactivator recruitment at the estrogen receptor (ER) by targeted attachment of bivalent compounds at the coactivator binding site besides the primary binding at the ligand binding domain. Eight homodimeric 4-[1-(4-hydroxyphenyl)-2-phenyl-1-butenyl]cinnamic acid (GW7604)- or cyclofenilacrylic acid-based ER ligands with diaminoalkane linkers (C2-C5) were synthesized and their effects on the ER subtypes were assessed in vitro. All compounds possessed full antagonistic potency at ERα/ß as determined in a transactivation assay. Furthermore, they exerted medium downregulatory effects dependent on the spacer length and did not stimulate the ER expression as observed for 4-hydroxytamoxifen. The cyclofenil-derived dimer with C4 spacer (15b) showed the highest binding affinity to ERα (RBA = 79.2%) and downregulated the ER content in MCF-7 cells with an efficiency of 38% at 1 µM.

Bisphenol AF: Halogen bonding effect is a major driving force for the dual ERα-agonist and ERß-antagonist activities.

17ß-Estradiol (E2) is a natural steroid ligand for the structurally and physiologically independent estrogen receptors (ERs) ERα and ERß. We recently observed that CF3-containing bisphenol AF (BPAF) works as an agonist for ERα but as an antagonist for ERß. Similar results were also observed for the CCl3-containing bisphenol designated as HPTE. Both BPAF and HPTE are comprised of a tri-halogenated methyl group in the central alkyl moiety of their bisphenol structures, which strongly suggests that halogens contribute directly to the agonist/antagonist dual biological functions. We conducted this study to investigate the structure-activity relationships by assessing together newly synthesized CF3- and CBr3-containing bisphenol E analogs (BPE-X). We first tested bisphenols for their receptor binding ability and then for their transcriptional activities. Halogen-containing bisphenols were found to be fully active for ERα, but almost completely inactive for ERß. When we examined these bisphenols for their inhibitory activities for E2 in ERß, we observed that they worked as distinct antagonists. The ascending order of agonist/antagonist dual biological functions was BPE-F < BPE-Cl (HPTE) ≤ BPAF < BPE-Br, demonstrating that the electrostatic halogen bonding effect is a major driving force of the bifunctional ERα agonist and ERß antagonist activities of BPAF.

[Academic Detailing from the Viewpoint of Chemical Structural Formulas].

In order to implement academic detailing, it is extremely important to understand the pharmacological activity of drugs based on their chemical structures. To construct a database for academic detailing, a viewpoint for clinically utilizing the fundamental pharmacological features of a drug is required. These fundamental pharmacological features include chemical characteristics such as chemical structures, physical characteristics such as pharmaceutical formulations for efficient drug delivery to target organs, and a pharmacological viewpoint, which is a mechanism by which a drug is determined to be effective. In addition, in vivo kinetics are included in a drug's pharmacological features, i.e., a drug's excretion through urine and feces via the kidneys, its side effects due to differences in enzyme type when the drug is metabolized in the liver, as well as the capacity of the patient's current enzyme profile. This review describes academic detailing based on the chemical structure of drugs for breast cancer hormone therapy, as an example.

Estrogen Receptor α (ERα)-targeting Compounds and Derivatives: Recent Advances in Structural Modification and Bioactivity.

Breast cancer is the most common cancer suffered by female, and the second highest cause of cancer-related death among women worldwide. At present, hormone therapy is still the main treatment route and can be divided into three main categories: selective estrogen receptor modulators (SERMs), selective estrogen receptor downregulators (SERDs), and aromatase inhibitors (AIs). However, breast cancer is difficult to cure even after several rounds of anti-estrogen therapy and most drugs have serious side-effects. Here, we review the literature published over the past five years regarding the isolation and synthesis of analogs and their derivatives.

Novel Hybrid Conjugates with Dual Suppression of Estrogenic and Inflammatory Activities Display Significantly Improved Potency against Breast Cancer.

In this work, we developed a small library of novel OBHS-RES hybrid compounds with dual inhibition activities targeting both the estrogen receptor α (ERα) and NF-κB by incorporating resveratrol (RES), a known inhibitor of NF-κB, into a privileged indirect antagonism structural motif (OBHS, oxabicycloheptene sulfonate) of estrogen receptor (ER). The OBHS-RES conjugates could bind well to ER and showed remarkable ERα antagonistic activity, and they also exhibited excellent NO inhibition in macrophage RAW 264.7 cells. Compared with 4-hydroxytamoxifen, some of them showed better antiproliferative efficacy in MCF-7 cell lines with IC50 up to 3.7 µM. In vivo experiments in a MCF-7 breast cancer model in Balb/c nude mice indicated that compound 26a was more potent than tamoxifen. Exploration of the compliancy of the structure against ER specificity utilizing these types of isomeric three-dimensional ligands indicated that one enantiomer had much better biological activity than the other.

Discovery of Selective Estrogen Receptor Covalent Antagonists for the Treatment of ERαWT and ERαMUT Breast Cancer.

Mutations in estrogen receptor alpha (ERα) that confer resistance to existing classes of endocrine therapies are detected in up to 30% of patients who have relapsed during endocrine treatments. Because a significant proportion of therapy-resistant breast cancer metastases continue to be dependent on ERα signaling, there remains a critical need to develop the next generation of ERα antagonists that can overcome aberrant ERα activity. Through our drug-discovery efforts, we identified H3B-5942, which covalently inactivates both wild-type and mutant ERα by targeting Cys530 and enforcing a unique antagonist conformation. H3B-5942 belongs to a class of ERα antagonists referred to as selective estrogen receptor covalent antagonists (SERCA). In vitro comparisons of H3B-5942 with standard-of-care (SoC) and experimental agents confirmed increased antagonist activity across a panel of ERαWT and ERαMUT cell lines. In vivo, H3B-5942 demonstrated significant single-agent antitumor activity in xenograft models representing ERαWT and ERαY537S breast cancer that was superior to fulvestrant. Lastly, H3B-5942 potency can be further improved in combination with CDK4/6 or mTOR inhibitors in both ERαWT and ERαMUT cell lines and/or tumor models. In summary, H3B-5942 belongs to a class of orally available ERα covalent antagonists with an improved profile over SoCs.Significance: Nearly 30% of endocrine therapy-resistant breast cancer metastases harbor constitutively activating mutations in ERα. SERCA H3B-5942 engages C530 of both ERαWT and ERαMUT, promotes a unique antagonist conformation, and demonstrates improved in vitro and in vivo activity over SoC agents. Importantly, single-agent efficacy can be further enhanced by combining with CDK4/6 or mTOR inhibitors. Cancer Discov; 8(9); 1176-93. ©2018 AACR.This article is highlighted in the In This Issue feature, p. 1047.

Pharmacophore modeling for identification of anti-IGF-1R drugs and in-vitro validation of fulvestrant as a potential inhibitor.

Insulin-like growth factor 1 receptor (IGF-1R) is an important therapeutic target for breast cancer treatment. The alteration in the IGF-1R associated signaling network due to various genetic and environmental factors leads the system towards metastasis. The pharmacophore modeling and logical approaches have been applied to analyze the behaviour of complex regulatory network involved in breast cancer. A total of 23 inhibitors were selected to generate ligand based pharmacophore using the tool, Molecular Operating Environment (MOE). The best model consisted of three pharmacophore features: aromatic hydrophobic (HyD/Aro), hydrophobic (HyD) and hydrogen bond acceptor (HBA). This model was validated against World drug bank (WDB) database screening to identify 189 hits with the required pharmacophore features and was further screened by using Lipinski positive compounds. Finally, the most effective drug, fulvestrant, was selected. Fulvestrant is a selective estrogen receptor down regulator (SERD). This inhibitor was further studied by using both in-silico and in-vitro approaches that showed the targeted effect of fulvestrant in ER+ MCF-7 cells. Results suggested that fulvestrant has selective cytotoxic effect and a dose dependent response on IRS-1, IGF-1R, PDZK1 and ER-α in MCF-7 cells. PDZK1 can be an important inhibitory target using fulvestrant because it directly regulates IGF-1R.

Design and synthesis of estrogen receptor ligands with a 4-heterocycle-4-phenylheptane skeleton.

The estrogen receptor (ER), a member of the nuclear receptor (NR) family, is involved in the regulation of physiological effects such as reproduction and bone homeostasis. Approximately 70% of human breast cancers are hormone-dependent and ERα-positive, and, thus, ER antagonists are broadly used in breast cancer therapy. We herein designed and synthesized a set of ER antagonists with a 4-heterocycle-4-phenylheptane skeleton.

A Computational Assay of Estrogen Receptor α Antagonists Reveals the Key Common Structural Traits of Drugs Effectively Fighting Refractory Breast Cancers.

Somatic mutations of the Estrogen Receptor α (ERα) occur with an up to 40% incidence in ER sensitive breast cancer (BC) patients undergoing prolonged endocrine treatments. These polymorphisms are implicated in acquired resistance, disease relapse, and increased mortality rates, hence representing a current major clinical challenge. Here, multi-microseconds (12.5 µs) molecular dynamics simulations revealed that recurrent ERα polymorphisms (i. e. L536Q, Y537S, Y537N, D538G) (mERα) are constitutively active in their apo form and that they prompt the selection of an agonist (active)-like conformation even upon antagonists binding. Interestingly, our simulations rationalize, for the first time, the efficacy profile of (pre)clinically used Selective Estrogen Receptor Modulators/Downregulators (SERMs/SERDs) against these variants, enlightening, at atomistic level of detail, the key common structural traits needed by drugs able to effectively fight refractory BC types. This knowledge represents a key advancement for mechanism-based therapeutics targeting resistant ERα isoforms, potentially allowing the community to move a step closer to 'precision medicine' calibrated on patients' genetic profiles and disease progression.

Selective estrogen receptor modulators (SERMs) and selective estrogen receptor degraders (SERDs) in cancer treatment.

Breast cancer is the most frequently diagnosed cancer in women, with estrogen receptor positive (ER+) breast cancer making up approximately 75% of all breast cancers diagnosed. Given the dependence on active ER signaling in these tumors, the predominant treatment strategy has been to inhibit various aspects of this pathway including directly antagonizing ER with the use of selective estrogen receptor modulators (SERMs) and selective estrogen receptor degraders (SERDs). Interestingly, the dependence on ER for breast cancer growth is often retained even after progression through several lines of antiestrogen therapy, making ER a bonafide biomarker for this cancer subtype and driving the continued research and development of novel ER-targeted therapeutics to treat this patient population. This, combined with the continuous discovery of mechanisms underlying endocrine resistance, is resulting in a continually evolving treatment landscape for ER+ breast cancer. This review discusses various ER antagonists investigated for the treatment of breast cancer, outlining their pharmacological and tissue-specific mechanisms of action as well as their specified use within the ER+ breast cancer setting. In addition, mechanisms of resistance to SERMs and SERDs, the use of ER antagonists in combination therapy strategies, and the ongoing development of novel drugs are also reviewed in the context of the changing clinical landscape of ER+ breast cancer. Lastly, the role of SERMs and SERDs in non-breast cancer indications is also discussed.

New estrogen receptor antagonists. 3,20-Dihydroxy-19-norpregna-1,3,5(10)-trienes: Synthesis, molecular modeling, and biological evaluation.

New estrogen receptor α (ERα) antagonists - 3,20-dihydroxy-19-norpregna-1,3,5(10)-trienes containing an additional carbocyclic ring D' at the 16α,17α positions - were synthesized. The effects of the new compounds on the MCF-7 breast cancer cells and ERα activation were investigated. All the steroids studied were synthesized starting from estrone methyl ether. The scaffold of compounds containing the six-membered ring D' was constructed via the Diels-Alder reaction of butadiene with 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5. The hydrogenation of primary 16α,17α-cyclohexeno-adduct 7 followed by 3-demethylation (by HBr-AcOH) and reduction of 20-oxo group (by LiAlH4) or in one step by DIBAH gave target mono- and dihydroxy steroids 9-11. The Corey-Chaykovsky reaction of the same 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5 gave 16α,17α-methylene-substituted compound. The reaction of the latter with DIBAH immediately yielded 3,20-dihydroxy-16α,17α-methyleno-19-norpregna-1,3,5(10)-triene 13. The same procedures using 3-methoxy-19-norpregna-1,3,5(10),16-tetraen-20-one 5 produced corresponding 3,20-dihydroxy-16,17-19-norpregna-1,3,5(10)-triene 16 and 3,20-dihydroxy-19-norpregna-1,3,5(10),16-tetraene 17. All compounds were fully characterized by 1D and 2D NMR, HRMS, and X-ray diffraction. The molecular docking showed that the target compounds can bind to ER, their binding mode being similar to that of natural estradiol. 16α,17α-Methylene- or unsubstituted compounds exhibit the highest cytotoxicity against MCF-7 cells, being simultaneously relatively weak ERα inhibitors. 3,20-Dihydroxy steroids containing the six-membered ring D' proved to be the most effective ERα inhibitors. These compounds displayed moderate cytotoxicity comparable of that of tamoxifen and showed no toxic effect on MCF-10A normal, nontumorigenic epithelial cells. The new ER antagonists were found to be good candidates for further testing as agents for the treatment and prevention of ERα-positive breast cancers.

Oxabicycloheptene Sulfonate Protects Against ß-Amyloid-induced Toxicity by Activation of PI3K/Akt and ERK Signaling Pathways Via GPER1 in C6 Cells.

Oxabicycloheptene sulfonate (OBHS) is a novel bicyclic core selective estrogen receptor modulator (SERM) with estrogen receptor (ER) antagonistic-activity and anti-inflammatory activity. However, little is known about protective action of OBHS on neurodegenerative disorders. In the present study, OBHS demonstrated a remarkably protective effect against amyloid beta (Aß) induced cytotoxicity via G-protein-coupled estrogen receptor 1 (GPER1) in rat astroglial cell line (C6). The C6 cell death induced by Aß was decreased by OBHS (1 µM) treatment for 45 min. This rapid protective action was blocked by GPER1 specific antagonist or siRNA knockdown. Inhibitors of phosphatidylinositol 3-kinase (PI3k)/Akt and extracellular signal-regulated kinase (ERK) activation also exhibited similar effects as GPER1 antagonist in blocking the protective effects of OBHS. Moreover, the expression of anti-apoptotic protein Bcl-2 was also increased by OBHS as a consequence of the activation of GPER1-PI3K/Akt and ERK pathways. Additionally, the phenyl sulfonate moiety of OBHS played a vital role in producing GPER1's agonist property according to the molecular docking analysis. These findings suggest that OBHS provide protection directed at enhancing glial cell survival through the activation of GPER1, which, in turn, offers a novel insight into the molecular mechanisms behind the potential application of OBHS in treating Alzheimer's disease (AD).

Expression of ER-α and ER-ß during peri-implantation period in uterus is essential for implantation and decidualization in golden hamster.

AIMS: The role of estrogen in embryo implantation in golden hamster (Mesocricetus auratus) is still ambiguous. In order to clarify it, we investigated the spatial distribution and expression of estrogen receptors, ER-α and ER-ß in the uterus of pregnant hamster during peri-implantation period and identified the effect of estrogen receptor antagonist ICI-182,780 on the embryo implantation. MAIN METHODS: We performed in vivo experiments on early pregnant hamsters involving treatment with ICI-182,780, an estrogen receptor antagonist. Immunohistochemistry, western blot analysis and quantitative PCR were employed to evaluate the spatio-temporal distribution and expression of ER-α and ER-ß in the uterus of normal early pregnant and treated hamsters. KEY FINDINGS: Results showed that embryo implantation was completely absent in ICI-182,780 treated uterine horn while, normal implantation occurred in control and vehicle treated horns. Both the receptors were differentially expressed in the uterus of hamster from day 1 (D1) to day7 (D7). In contrast, treated horns without any implantation site showed no trace of any receptors. Protein and mRNA expression of both the receptors were high around the day of implantation while, ER-ß expression was up-regulated on D7 of embryo implantation. P value˂0.05 is considered significant. SIGNIFICANCE: Spatio-temporal expression of ERs in the uterus during peri-implantation period have crucial role for endometrium receptivity and implantation in hamster. Recurrent implantation failure is the devastating problem among the desirable couple and is mainly due to defect in endometrium receptivity. This study may provide a new insight to manage the problem of idiopathic infertility.

Structure-activity relationships for the antifungal activity of selective estrogen receptor antagonists related to tamoxifen.

Cryptococcosis is one of the most important invasive fungal infections and is a significant contributor to the mortality associated with HIV/AIDS. As part of our program to repurpose molecules related to the selective estrogen receptor modulator (SERM) tamoxifen as anti-cryptococcal agents, we have explored the structure-activity relationships of a set of structurally diverse SERMs and tamoxifen derivatives. Our data provide the first insights into the structural requirements for the antifungal activity of this scaffold. Three key molecular characteristics affecting anti-cryptococcal activity emerged from our studies: 1) the presence of an alkylamino group tethered to one of the aromatic rings of the triphenylethylene core; 2) an appropriately sized aliphatic substituent at the 2 position of the ethylene moiety; and 3) electronegative substituents on the aromatic rings modestly improved activity. Using a cell-based assay of calmodulin antagonism, we found that the anti-cryptococcal activity of the scaffold correlates with calmodulin inhibition. Finally, we developed a homology model of C. neoformans calmodulin and used it to rationalize the structural basis for the activity of these molecules. Taken together, these data and models provide a basis for the further optimization of this promising anti-cryptococcal scaffold.

Induction of UDP-glucuronosyltransferase 2B15 gene expression by the major active metabolites of tamoxifen, 4-hydroxytamoxifen and endoxifen, in breast cancer cells.

We previously reported upregulation of UGT2B15 by 17ß-estradiol in breast cancer MCF7 cells via binding of the estrogen receptor α (ERα) to an estrogen response unit (ERU) in the proximal UGT2B15 promoter. In the present study, we show that this ERα-mediated upregulation was significantly reduced by two ER antagonists (fulvestrant and raloxifene) but was not affected by a third ER antagonist, 4-hydroxytamoxifen (4-OHTAM), a major active tamoxifen (TAM) metabolite. Furthermore, we found that, similar to 17ß-estradiol, 4-OHTAM and endoxifen (another major active TAM metabolite) elevated UGT2B15 mRNA levels, and that this stimulation was significantly abrogated by fulvestrant. Further experiments using 4-OHTAM revealed a critical role for ERα in this regulation. Specifically; knockdown of ERα expression by anti-ERα small interfering RNA reduced the 4-OHTAM-mediated induction of UGT2B15 expression; 4-OHTAM activated the wild-type but not the ERU-mutated UGT2B15 promoter; and chromatin immunoprecipitation assays showed increased ERα occupancy at the UGT2B15 ERU in MCF7 cells upon exposure to 4-OHTAM. Together, these data indicate that both 17ß-estradiol and the antiestrogen 4-OHTAM upregulate UGT2B15 in MCF7 cells via the same ERα-signaling pathway. This is consistent with previous observations that both 17ß-estradiol and TAM upregulate a common set of genes in MCF7 cells via the ER-signaling pathway. As 4-OHTAM is a UGT2B15 substrate, the upregulation of UGT2B15 by 4-OHTAM in target breast cancer cells is likely to enhance local metabolism and inactivation of 4-OHTAM within the tumor. This represents a potential mechanism that may reduce TAM therapeutic efficacy or even contribute to the development of acquired TAM resistance.