Third-generation Selective Estrogen Receptor Modulator Research Articles

Bazedoxifene Inhibits Cell Viability, Colony-Forming Activity, and Cell Migration in Human Non-Small Cell Lung Cancer Cells and Improves the Treatment Efficacy of Paclitaxel and Gemcitabine.

Bazedoxifene is a third-generation selective estrogen receptor modulator that inhibits the IL6/IL6R/GP130 signaling pathway by inhibiting IL6-induced homodimerization of GP130. Considering that the IL6/IL6R/GP130 signaling pathway is important in tumorigenesis and metastasis, bazedoxifene is thought to have an antitumor effect, which has been proven preliminarily in breast cancer and pancreatic cancer but has not yet been studied in non-small cell lung cancer (NSCLC). This study is aimed at evaluating the antitumor effect of bazedoxifene in NSCLC. A549 and H1299 NSCLC cell lines were employed and exposed to various concentrations of bazedoxifene, paclitaxel, gemcitabine, and their combinations for cell viability, colony formation, and wound healing assays to demonstrate the antitumor effect of bazedoxifene with or without paclitaxel or gemcitabine. MTT cell viability, colony formation, and wound healing assays showed that bazedoxifene was capable of inhibiting cell viability, colony formation, and cell migration in a dose-dependent manner. In addition, bazedoxifene was capable of working with paclitaxel or gemcitabine synergistically to inhibit cell viability, colony formation, and cell migration. This study demonstrated the potential antitumor effect of bazedoxifene and its ability to improve the treatment efficacy of paclitaxel and gemcitabine.

Modulation of Estrogen Receptor Alpha (ERα) and Tumor Suppressor Gene BRCA1 in Breast Cancer Cells by Bazedoxifene Acetate (BZA).

Selective estrogen receptor modulators (SERMs) are steroid analogs with dual functionality, acting as partial estrogen receptor agonists to preserve postmenopausal bone density and as estrogen receptor antagonists in breast tissue. Bazedoxifene acetate (BZA) is an FDA-approved, third-generation SERM used in the treatment of osteoporosis in women. It demonstrates potential as a therapeutic option for breast cancer patients undergoing endocrine therapy. Our study aimed to assess BZA's effects on Estrogen Receptor Alpha (ERα) and tumor suppressor gene BRCA1 in T-47D and MCF-7 breast cancer cells, using Western blots, cellular viability, apoptosis assays, and RT-qPCR. Cells were cultured in 5% charcoal-stripped fetal bovine serum for six days to deplete endogenous steroids. Following a 24 h exposure to 2 µM BZA (optimal concentration determined from 1 nM-2 µM studies), Western blot analyses revealed reduced ERα and BRCA1 protein levels in both cell lines. ERα decreased by 48-63% and BRCA1 by 61-64%, indicating sensitivity to antiestrogens. Cytolocalization of ERα and BRCA1 remained unchanged after BZA and 17-β-estradiol (E2) treatment. ESR1 mRNA expression correlated with Western blot findings. Image cytometric analysis using the stain, propidium iodide, detected decreased cellular proliferation in T-47D and MCF-7 cells following a 6-day treatment ranging from 1 nM to 2 µM BZA. BZA treatment alone led to a tenfold reduction in cellular proliferation compared to estrogen-treated cells, suggesting antiproliferative effects. Understanding BZA's modulation of BRCA1 and ERα, along with their mechanistic interactions, is vital for comprehending its impact on breast cancer tumor suppressors and hormone receptors.

Investigating Lasofoxifene Efficacy Against the Y537S + F404V Double-Mutant Estrogen Receptor Alpha Using Molecular Dynamics Simulations.

Estrogen receptor alpha (ERα) plays a critical role in breast cancer (BC) progression, with endocrine therapy being a key treatment for ERα + BC. However, resistance often arises due to somatic mutations in the ERα ligand-binding domain (LBD). Lasofoxifene, a third-generation selective estrogen receptor modulator, has shown promise against Y537S and D538G mutations. However, the emergence of a novel F404 mutation in patients with pre-existing LBD mutations raises concerns about its impact on lasofoxifene efficacy. This study investigates the impact of the dual Y537S and F404V mutations on lasofoxifene's efficacy. Using molecular dynamics simulations and molecular mechanics/Poisson-Boltzmann surface area (MM-PBSA) free energy calculations, we found that the dual mutation reduces lasofoxifene binding affinity and binding free energy, disrupts crucial protein-ligand interactions, and induces significant conformational changes in the ligand-binding pocket. These alterations are likely due to the loss of the pi-pi stacking interaction in the F404V mutation. These findings suggest a potential reduction in lasofoxifene efficacy due to the dual mutation. Further experimental validation is required to confirm these results and fully understand the impact of dual mutations on lasofoxifene's effectiveness in ERα + metastatic BC.

Solid-liquid phase equilibrium and thermodynamic properties analysis of Bazedoxifene acetate in fifteen kinds of mono-solvents

Crystallization is widely used for the isolation and purification of active pharmaceutical ingredients (APIs) in the final manufacturing stage. Bazedoxifene (BZD) acetate, classified as a third-generation selective estrogen receptor modulator, is employed in the treatment of postmenopausal osteoporosis. This work reports the equilibrium solubility data of BZD acetate in fifteen different mono-solvents, including methanol, ethanol, n-propanol, i-propanol, n-butanol, ethyl formate, methyl acetate, ethyl acetate, acetone, 2-butanone, cyclohexanone, tetrahydrofuran (THF), 2-methyltetrahydrofurane (2-MeTHF), 1,4-dioxane and acetonitrile (ACN), within the temperature range “T = 283.15–323.15 K” under p = 0.1 MPa. The solubilities of BZD acetate in various solvents increase with increasing temperature. Among the alcoholic solvents, the solubility order is as follows: methanol > ethanol > n-propanol > n-butanol > i-propanol. In esters solvent, the solubility of BZD acetate decreases in the following order: methyl acetate > ethyl acetate > ethyl formate. For ketones solvent, the solubility decreases in the following order: cyclohexanone > acetone > 2-butanone. The maximum value of BZD acetate solubility was 0.011 mol·mol−1 in tetrahydrofuran at T = 323.15 K, but the least data was found in ethyl formate at 283.15 K. Four thermodynamic models, i.e., the Yaws model, modified Apelblat model, λh model, and Wilson model were applied to fit the solubility data of BZD acetate in different solvents. Among them, the Wilson model represents the most accurate fitting outcomes. Finally, the thermodynamic functions of mixing (including enthalpy, entropy, and Gibbs energy) were calculated, and the results indicate a mixing process that is both spontaneous and driven by entropy. The solubility data, correlated models, and derived thermodynamic functions present essential thermodynamic fundamentals for the industrial production of BZD acetate crystallization, facilitating efficient separation and purification.

Expert opinion on the treatment of vulvovaginal atrophy with ospemifene based on new evidence

Vulvovaginal atrophy (VVA) is an underdiagnosed and undertreated chronic condition resulting in physiological and histological changes in the genitourinary tract of postmenopausal women. Treatment of moderate to severe VVA includes local estrogens, dehydroepiandrosterone (DHEA) and oral ospemifene, a third-generation selective estrogen receptor modulator (SERM). Due to venous thromboembolism (VTE) safety concerns classically associated with the SERM class, and as part of its original marketing authorization approval (MAA), the European Medicines Agency (EMA) requested the performance of a 5-year post-authorization safety study (PASS) to study the incidence rate of VTE among women receiving ospemifene. The results have led to important regulatory changes to ospemifene’s labeling, extending its indication and eliminating concerted risk management measures. A panel of experts discussed and reached consensus on the impact of these regulatory changes on clinical practice, reflecting on the reassurance of ospemifene’s benefit–risk balance and recommending its positioning as a first-line pharmacological treatment option for moderate to severe VVA together with local therapies. In a scenario where different treatments present similar efficacy and safety profiles, a shared decision between clinician and patient, according to her needs and preferences over time, is fundamental to improve adherence and persistence with sequential treatment, contributing to the achievement of health outcomes.

Open-label, phase 2, multicenter study of lasofoxifene (LAS) combined with abemaciclib (Abema) for treating pre- and postmenopausal women with locally advanced or metastatic ER+/HER2− breast cancer and an ESR1 mutation after progression on prior therapies.

1022 Background: Resistance to endocrine therapy can develop when treating estrogen receptor positive (ER+), metastatic breast cancer (mBC). Treatment with aromatase inhibitors can lead to acquired mutations in the estrogen receptor 1 ( ESR1), which can constitutively activate the ER, leading to endocrine resistance and worse disease prognosis. Treatment options for mBC patients with an ESR1 mutation are limited. Further, data suggest that patients could derive clinical benefit from Abema after progression on prior cyclin-dependent kinase 4/6 inhibitor (CDK4/6i). LAS, a third-generation selective estrogen receptor modulator, as monotherapy or combined with a CDK4/6i, was shown to have superior efficacy over fulvestrant (FVT) in preclinical breast cancer models expressing ESR1 mutations. Based on these results, a phase 2 clinical trial of LAS combined with Abema was initiated in mBC patients with ESR1 mutations. Methods: ELAINE 2 is an open-label, phase 2, multicenter trial evaluating the safety and efficacy of LAS combined with the CDK4/6i, Abema. Study participants were pre- and postmenopausal women with ER+/HER2- mBC with acquired ESR1 mutation (identified by ctDNA testing), whose disease had progressed on one or two lines of hormonal therapy for metastatic disease with or without a CDK4/6i (including Abema). Patients took oral LAS 5 mg/day and Abema 150 mg BID. Treatment continued until evidence of disease progression, death, unacceptable toxicity, or withdrawal from the study. The primary endpoint was safety, and secondary endpoints were progression free survival (PFS), objective response rate (ORR), and clinical benefit rate (CBR). Results: 29 patients were enrolled at 16 US sites (Oct 2020 to June 2021). Mean age was 58.3 y (35-79 y); 86% were Caucasian. Most had progressed with at least 2 previous hormonal treatments (80%). All except 1 patient received a prior CDK4/6i and 72% had received prior FVT; 48% had chemotherapy in the metastatic setting. Four patients discontinued the trial due to adverse events (AEs, n = 2), consent withdrawal (n = 1), or investigator withdrawal (n = 1). No deaths occurred during the study and few Grade 3/4 AEs were observed. Most common AEs were diarrhea, nausea, and leukopenia. Five patients had an Abema dose reduction from 150 mg to 100 mg BID. To date, 11 patients have progressed and 14 continue treatment. The censored median PFS was 13.9 mos (95% CI, 8.0‒NE), the ORR 33.3% (95% CI, 16.3‒56.3) with 6 confirmed partial responses, and the CBR 62.1% (95% CI, 44.0‒77.3). Conclusions: LAS combined with Abema in the ELAINE 2 trial was well tolerated and demonstrated robust and meaningful efficacy in women with ER+/HER2- mBC and an ESR1 mutation who had progressed on previous CDK4/6i therapies. Clinical trial information: NCT04432454.

Abstract 648: Effects of bazedoxifene and lapatinib in the prevention of estrogen receptor positive (ER+) and negative (ER-) mammary cancers

Abstract Bazedoxifene is a third-generation selective estrogen receptor modulator (SERM) that has been clinically approved in Europe for the prevention and treatment of postmenopausal osteoporosis. Our research previously showed that this agent (at a dose of 5 mg/kg diet) would decrease ER+ mammary cancers in rats by 73%. Lapatinib, an epidermal growth factor receptor (EGFR) inhibitor, is commonly used to treat patients with HER2+ breast cancer. We have also shown that the compound inhibits the development of ER+ mammary cancers in rats and ER- mammary cancers in mice at a dose of 75 mg/kg BW/day. The present studies were done to determine if lower doses and different treatment regimens designed to reduce possible toxicity would also be effective in preventing mammary cancers. Bazeodxifene was added directly to the diet (Teklad, 4% fat), while lapatinib was given by oral gavage. When evaluated in rats receiving methylnitrosourea (MNU), lapatinib given daily at doses of 75, 50 and 25 mg/kg BW/day reduced mammary cancer multiplicity by 93, 84 and 67%, respectively. Equivalent doses given 1x/week caused reductions of 87, 56, and 40%. When lapatinib was given to dimethylbenzanthracene (DMBA) treated MMTV/Neu mice at dose levels of 250, 125, and 63 mg/kg BW, 5x/week, mammary cancer multiplicity was reduced by 89, 60 and 80%, respectively. When equivalent doses were given 1x/week, the number of cancers were reduced by 82, 61, and 70%. Bazedoxifene given at 5.0 and 2.5 mg/kg diet to female MMTV/Neu mice also receiving DMBA caused reduction of mammary cancers by 73 and 51%. In a biomarker study lasting two weeks, bazedoxifene at the 5.0 mg/kg BW/day dose decreased the proliferation rate of normal mammary epithelial cells in MMTV/Neu mice by 60%. Additional studies to determine why this SERM is having a preventive effect against ER- mammary cancers are warranted. Studies to evaluate the efficacy of the combination of low doses of bazedoxifene and lapatinib in prevention of ER+ and ER- mammary cancers are in progress and will be presented. Supported by the NCI contract number HHSN261201500036I, Task Order HHSN26100005. Citation Format: Clinton J. Grubbs, Altaf Mohammed, Shizuko Sei, Robert H. Shoemaker. Effects of bazedoxifene and lapatinib in the prevention of estrogen receptor positive (ER+) and negative (ER-) mammary cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 648.

Bazedoxifene for the treatment of osteoporosis

ABSTRACTIntroduction: Bazedoxifene (BZD) is a third-generation selective estrogen receptor modulator approved for the treatment of postmenopausal osteoporosis with additional favorable effects in lipids, uterine and breast tissue.Areas covered: In this review, the authors outline clinical data regarding the efficacy, safety, and tolerability of continuous BZD administration up to seven years in randomized, placebo-controlled, phase III clinical trials. Long-term treatment with BZD for postmenopausal osteoporosis is generally safe and well tolerated. BZD achieves small but significant increases in the bone mineral density of the lumbar spine but not the total hip. In addition, BZD reduces significantly the risk of vertebral fractures but not of non-vertebral and hip fractures, with the exception of high fracture risk postmenopausal women in whom BZD significantly reduces non-vertebral fractures.Expert opinion: BZD does not seem to offer significant advantages over the other available antiresorptive agents. However, considering the need for long-term management of osteoporosis, BZD may have a place in the long-term therapeutic planning of the disease.

Bazedoxifene protects cerebral autoregulation after traumatic brain injury and attenuates impairments in blood-brain barrier damage: involvement of anti-inflammatory pathways by blocking MAPK signaling.

Traumatic brain injury (TBI) is a significant cause of death and long-term deficits in motor and cognitive functions for which there are currently no effective chemotherapeutic drugs. Bazedoxifene (BZA) is a third-generation selective estrogen receptor modulator (SERM) and has been investigated as a treatment for postmenopausal osteoporosis. It is generally safe and well tolerated, with favorable endometrial and breast safety profiles. Recent findings have shown that SERMs may have therapeutic benefits; however, the role of BZA in the treatment of TBI and its molecular and cellular mechanisms remain poorly understood. The aim of the present study was to examine the neuroprotective effects of BZA on early TBI in rats and to explore the underlying mechanisms of these effects. TBI was induced using a modified weight-drop method. Neurological deficits were evaluated according to the neurological severity score (NSS). Morris water maze and open-field behavioral tests were used to test cognitive functions. Brain edema was measured by brain water content, and impairments in the blood-brain barrier (BBB) were evaluated by expression analysis of tight junction-associated proteins, such as occludin and zonula occludens-1 (ZO-1). Neuronal injury was assessed by hematoxylin and eosin (H&E) staining. LC-MS/MS analysis was performed to determine the ability of BZA to cross the BBB. Our results indicated that BZA attenuated the impaired cognitive functions and the increased BBB permeability of rats subjected to TBI through activation of inflammatory cascades. In vivo experiments further revealed that BZA provided this neuroprotection by suppressing TBI-induced activation of the MAPK/NF-κB signaling pathway. Thus, mechanically, the anti-inflammatory effects of BZA in TBI may be partially mediated by blocking the MAPK signaling pathway. These findings suggest that BZA might attenuate neurological deficits and BBB damage to protect against TBI by blocking the MAPK/NF-κB signaling pathway.

Down-regulating IL-6/GP130 targets improved the anti-tumor effects of 5-fluorouracil in colon cancer.

Recent studies have confirmed that IL-6/GP130 targets are closely associated with tumor growth, metastasis and drug resistance. 5-Fluorouracil (5-FU) is the most common chemotherapeutic agent for colon cancer but is limited due to chemoresistance and high cytotoxicity. Bazedoxifene (BZA), a third-generation selective estrogen receptor modulator, was discovered by multiple ligand simultaneous docking and drug repositioning approaches to have a novel function as an IL-6/GP130 target inhibitor. Thus, we speculated that in colon cancer, the anti-tumor efficacy of 5-FU might be increased in combination with IL-6/GP130 inhibitors. CCK8 assay and colony formation assay were used to detect the cell proliferation and colony formation. We measured the IC50 value of 5-FU alone and in combination with BZA by cell viability inhibition. Cell migration and invasion ability were tested by scratch migration assays and transwell invasion assays. Flow cytometric analysis for cell apoptosis and cell cycle. Quantitative real-time PCR was used to detect Bad, Bcl-2 and Ki-67 mRNA expression and western blotting (WB) assay analyzed protein expression of Bad/Bcl-2 signaling pathway. Further mechanism study, WB analysis detected the key proteins level in IL-6/GP130 targets and JAK/STAT3, Ras/Raf/MEK/ERK, and PI3K/AKT/mTOR signaling pathway. A colon cancer xenograft model was used to further confirm the efficacy of 5-FU and BZA in vivo. The GP130, P-STAT3, P-AKT, and P-ERK expression levels were detected by immunohistochemistry in the xenograft tumor. BZA markedly potentiates the anti-tumor function of 5-FU in vitro and in vivo. Conversely, 5-FU activation is reduced following exogenous IL-6 treatment in cells. Further mechanistic studies determined that BZA treatment enhanced 5-FU anti-tumor activation by inhibiting the IL-6/GP130 signaling pathway and the phosphorylation status of the downstream effectors AKT, ERK and STAT3. In contrast, IL-6 can attenuate 5-FU function via activating IL-6R/GP130 signaling and the P-AKT, P-ERK and P-STAT3 levels. This study firstly verifies that targeting IL-6/GP130 signaling can increase the anti-tumor function of 5-FU; in addition, this strategy can sensitize cancer cell drug sensitivity, implying that blocking IL-6/GP130 targets can reverse chemoresistance. Therefore, combining 5-FU and IL-6/GP130 target inhibitors may be a promising approach for cancer treatment.

Abstract P5-14-02: Effects of bazedoxifene and/or letrozole in the prevention of chemically-induced mammary cancers

Abstract Bazedoxifene is described as a third-generation selective estrogen receptor modulator (SERM) that has been approved in Europe for the prevention and treatment of postmenopausal osteoporosis. The agent has also been shown to have therapeutic activity against estrogen receptor positive (ER+) breast cancer. Our laboratory has evaluated bazedoxifene for chemopreventive efficacy against mammary cancers when given alone or in combination with the aromatase inhibitor letrozole. Initially, the agents were evaluated alone to determine effective chemopreventive doses in the methylnitrosourea (MNU) ER+ mammary cancer model using female Sprague-Dawley rats. Bazedoxifene was mixed directly into a standard (Teklad, 4% fat) diet, while letrozole was gavaged 7x/week (vehicle was ethanol: PEG 400, 10:90, v/v). When evaluated alone in rats receiving MNU at 50 days of age, bazedoxifene (started one week after MNU) at doses of 100 and 30 mg/kg diet decreased mammary cancer multiplicity by 93 and 88%, respectively. In a similar protocol, letrozole at a dose of 0.1 mg/kg BW/day reduced cancer multiplicity by 89%, while a dose of 0.05 mg/kg BW/day reduced the number by 47%. In a separate study evaluating lower doses of bazedoxifene (5 mg/kg diet) and letrozole (0.04 mg/kg BW/day), mammary cancer multiplicity was decreased by 73% by both agents. When the agents were given in combination at these lower dose levels, cancer number was reduced by 91%. It is obvious that bazedoxifene is as effective as letrozole in the prevention of ER+ mammary cancers. Furthermore, administration of the agents in combination suggests an additive effect. The large increase in body weight gain generally noted in letrozole treated rats was not observed in rats receiving bazedoxifene; of interest, rats receiving the combination also had no increase in body weights. Several published invitro studies suggested that bazedoxifene might also be effective in preventing ER- mammary cancers; e.g., the agent is a novel inhibitor of IL-6/GP130 protein-protein interactions using multiple ligand simultaneous docking and drug repositioning approaches that result in apoptosis. In an initial study using MMTV/Neu mice (N=21/group) that received dimethylbenzanthracene (DMBA), we showed that administering bazedoxifene (15 mg/kg diet) would reduce the mammary tumor multiplicity from 5.4/mouse in controls to 1.1/mouse (an 80% decrease). These studies suggested that bazedozxifene is superior to other similar agents in that both ER+ and ER- mammary cancers are prevented at non-toxic doses. Supported by NCI contract HHSN261201200021I, Task Order HHSN26100007. Citation Format: Dunn BK, Grubbs CJ. Effects of bazedoxifene and/or letrozole in the prevention of chemically-induced mammary cancers [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P5-14-02.

The antagonist properties of Bazedoxifene after acute treatment are shifted to stimulatory action after chronic exposure in the liver but not in the uterus.

A promising alternative to conventional hormone therapy for postmenopausal symptoms is treatment combining Bazedoxifene (BZA), a third-generation selective estrogen receptor modulator (SERM), and conjugated equine estrogen (CE). This combination is also known as a tissue-selective estrogen complex (TSEC). Understanding the tissue-specific actions of SERMs and the TSEC remains a major challenge to try to predict their clinical effects. The aim of this study was to compare acute versus chronic treatment with BZA, CE or CE+BZA in two major targets of estrogens, the uterus and the liver. In these two tissues, acute treatment with CE, but not with BZA, induced similar gene expression change than the most important endogenous estrogen, 17-β estradiol (E2). Acute induction of gene expression by E2 or by CE was antagonized by the addition of BZA. Concomitantly, BZA alone or in combination with E2 or CE induced a partial degradation of ERα protein after acute exposure. In uterus, chronic treatment of BZA alone had no impact on tissue weight gain or on epithelial cell proliferation, and also antagonized CE-effect in uterus, thereby mimicking the acute effect. By contrast, in the liver, chronic BZA and CE+BZA elicited agonistic transcriptional effects similar to those of CE alone. In addition, at variance to BZA acute effect, no change in ERα protein abundance was observed after chronic treatment in this tissue. These experimental invivo data highlight a new aspect of the time-dependent tissue-specific action of BZA or TSEC, i.e. they can act acutely as antagonists but become agonists after chronic treatment. This shift was observed in liver tissue, but not in proliferative sex target such as the uterus.

Abstract 5246: Effects of bazedoxifene either alone or in combination with letrozole in the prevention of chemically induced mammary cancers

Abstract Bazedoxifene is a third-generation selective estrogen receptor modulator (SERM) that has been clinically approved in Europe for the prevention and treatment of postmenopausal osteoporosis. The agent has also been shown to have therapeutic activity against estrogen receptor positive (ER+) breast cancer. Our laboratory is currently evaluating bazedoxifene for chemopreventive efficacy when given alone or in combination with the aromatase inhibitor (AI) letrozole. Initially, the agents were evaluated alone to determine effective chemopreventive doses in the methylnitrosourea (MNU) ER+mammary cancer model using female Sprague-Dawley rats. Bazedoxifene was mixed directly into a standard (Teklad, 4% fat) diet, while letrozole was gavaged 7x/week (vehicle was ethanol: PEG 400, 10:90, v/v). When evaluated alone in rats receiving MNU at 50 days of age, bazedoxifene (started one week after MNU) at doses of 100 and 30 mg/kg diet decreased mammary cancer multiplicity by 93 and 88%, respectively. In a similar protocol, letrozole at a dose of 0.1 mg/kg BW/day reduced cancer number (multiplicity) by 89%, while a dose of 0.05 mg/kg BW/day reduced the number by 47%. In a separate study evaluating lower doses (MNU also given to rats at 50 days of age), bazedoxifene at a dose of 5 mg/kg diet and letrozole at a dose of 0.04 mg/kg BW/day both decreased mammary tumor multiplicity by 73%. When the agents were given in combination at these lower dose levels, cancer number was reduced by 91%. An additional study was done in which the agents were given to rats receiving MNU at an older age (100 days). Rats receiving the agents at the original doses beginning one week after MNU (bazedoxifene at 30 mg/kg diet; letrozole at 0.1 mg/kg BW/day) had identical decreases in mammary tumor development (96%). It is obvious that bazedoxifene is as effective as letrozole in the prevention of mammary cancers even when initiated in older rats. Furthermore, administration of the agents in combination suggests an additive effect. The large increase in body weight gain generally noted in letrozole treated rats was not observed in rats receiving bazedoxifene; of interest, rats receiving the combination also had no increase in body weights. These studies indicate that bazedoxifene may be superior to other SERMs in that chemopreventive efficacy is achieved at low doses, which may be associated with less toxicity. Supported by NCI contract HHSN261201200021I, Task Order HHSN26100007. Citation Format: Barbara K. Dunn, Chen Suen, Ronald A. Lubet, Vernon E. Steele, Clinton J. Grubbs. Effects of bazedoxifene either alone or in combination with letrozole in the prevention of chemically induced mammary cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5246. doi:10.1158/1538-7445.AM2017-5246

Ospemifene: A Novel Option for the Treatment of Vulvovaginal Atrophy.

Ospemifene—a third-generation selective estrogen receptor modulator approved by the Food and Drug Administration in 2013—is an oral medication for the treatment of dyspareunia. In postmenopausal women with vulvovaginal atrophy, ospemifene significantly improves the structure and pH levels of the vagina, reducing dyspareunia. It is available as a 60-mg tablet; hence, women who may have had prior difficulty with vaginal administration or on-demand use of nonprescription lubricants and moisturizers would likely prefer this form of treatment. Preclinical studies demonstrated that ospemifene has an estrogen agonist action on the bone, reducing the cell proliferation of ductal carcinoma in an in situ model. Studies evaluating the safety of treatment for up to 52 weeks have shown that ospemifene is a safe medication with minimal impact on the endometrium. Further studies with larger number of subjects are necessary to better conclude its effects and long-term safety.

Bazedoxifene and Conjugated Equine Estrogen: A Combination Product for the Management of Vasomotor Symptoms and Osteoporosis Prevention Associated with Menopause.

Bazedoxifene (BZA), a third-generation selective estrogen receptor modulator (SERM), has been combined with conjugated equine estrogen (CE) to create a tissue selective estrogen complex (TSEC) for the management of vasomotor symptoms (VMS) and the prevention of osteoporosis (OP) associated with menopause. Both of these outcomes of menopause contribute to significant negative effects on quality of life and increases in utilization of health care resources and dollars. Current treatment modalities for VMS and OP include estrogen therapy that requires the use of progestin in women who have a uterus to reduce the risk of endometrial hyperplasia and resultant cancer. However, progestin use results in nuisance bleeding as well as a further increased risk of breast cancer when combined with estrogen. And while SERMs can be used to prevent OP, their use alone has been shown to increase hot flashes. The combination of BZA and CE does not require progestin treatment with CE as the BZA component acts as an antagonist on endometrial tissue. The U.S. Food and Drug Administration approval of BZA/CE in 2013 was based on a series of five phase 3 studies known as the Selective estrogens, Menopause And Response to Therapy (SMART) trials. These trials, in their entirety, evaluated the impact of BZA/CE on VMS frequency and severity, bone mineral density, bone turnover markers, vaginal symptoms, lipid profiles, sleep, quality of life, breast density, and endometrial safety. The approved dose of BZA/CE is 20 mg BZA and 0.45 mg CE. Although this TSEC manages VMS while opposing breast and endometrial proliferation, preventing bone resorption, and improving lipid profiles, long-term experience with BZA/CE is currently lacking.

Effect of selective estrogen receptor modulators on metabolic homeostasis.

Selective estrogen receptor modulators (SERMs) are estrogen receptor (ER) ligands that exhibit either estrogen agonistic or antagonistic activity in a tissue-specific manner. The first and second generation SERMs, tamoxifen and raloxifene, are used for treatment of ER positive breast cancer and postmenopausal osteoporosis respectively. The third-generation SERM, bazedoxifene (BZA), effectively prevents osteoporosis while blocking the estrogenic stimulation in breast and uterus. Notably, BZA combined with conjugated estrogens (CE) in a tissue-selective estrogen complex (TSEC) is a new menopausal treatment. Postmenopausal estrogen deficiency predisposes to metabolic syndrome and type 2 diabetes, and therefore the effects of SERMs and TSECs on metabolic homeostasis are gaining attention. In this article, we summarize current knowledge about the impact of SERMs on metabolic homeostasis and metabolic disorders in animal models and postmenopausal women.

Bazedoxifene/conjugated estrogens combination for the treatment of the vasomotor symptoms associated with menopause and for prevention of osteoporosis in postmenopausal women.

The decrease of estrogen in postmenopausal women has been associated with the presence of different symptoms such as vasomotor symptoms, vulvovaginal atrophy, bone loss, sleep disturbances, and mood and sexual activity alterations. Hormone replacement therapy with estrogen and progestins has been used to improve menopausal symptoms; however, there are still concerns regarding its safety and tolerability, as some progestins have been shown to increase breast cancer and cardiovascular risk. Bazedoxifene is a third-generation selective estrogen receptor modulator (SERM) used for osteoporosis management in postmenopausal women at fracture risk that has demonstrated a powerful antiestrogenic effect on the endometrium. Today we have a new alternative called the tissue-selective estrogen complex (TSEC), which combines bazedoxifene and conjugated estrogens and is designed not only to improve menopausal symptoms and vulvovaginal atrophy but also to prevent bone loss. Therefore, it maintains the benefits of estrogen therapy while antagonizing the stimulation effects on the endometrium and mammary gland without the effects associated with progestins.

Raloxifene hydrochloride treatment leads to better outcomes than medroxyprogesterone acetate when paired with estrogen in ovariectomized cholesterol-fed rabbits.

The benefits of estrogen in cardiovascular system include a reduction in low-density lipoprotein cholesterol (LDL-C), decrease in LDL oxidation, and enhancement of vascular function [1]. Estrogen replacement therapy, however, has been linked to an increased risk of tissue-specific side effects including breast cancer and uterine cancer [2]. These issues have led to the development of hormone replacement therapy (HRT) which combines estrogen and progestin. Progestin can reverse endometrial hyperplasia induced by estrogen. The most commonly used progestin in HRT is medroxyprogesterone acetate (MPA), a synthetic progestin, although there is some evidence that the administration of MPA is not as beneficial as natural progesterone [3]. Findings from randomized placebo-controlled trials have demonstrated that the combination of estrogen and MPA does not confer cardiac protection and may increase the risk of coronary heart disease among healthy postmenopausal women, especially in the first year after initiation of hormone therapy. Furthermore, an increase in the risk of breast cancer was also found with this therapy [4]. Although the role of progestin remains poorly defined, it is possible that the coadministration of progestin could counteract the cardioprotective effects of estrogen [5]. In an effort to obtain the beneficial effects and reduce the risks associated with HRT, new replacement therapy formulations including selective estrogen receptor modulators (SERMs) have been developed. However, in a preclinical trial, treatment with bazedoxifene acetate (BZA), a new third-generation SERM, and conjugated equine estrogen (CEE) in combination did not show significant effects on plasma lipid profiles, and BZA treatment had no adverse

Ospemifene for the treatment of dyspareunia in postmenopausal women.

Ospemifene is a third-generation selective estrogen receptor modulator (SERM), structurally closely related to toremifene. Clinical studies in postmenopausal women with vulvovaginal atrophy demonstrated that it produced significant improvements in the structure of the vagina and its pH, and significantly reduced dyspareunia, the main complaint of the women treated. Preclinical studies demonstrated that ospemifene, unlike tamoxifen, did not produce DNA adducts, suggesting that it has less carcinogenic potential than tamoxifen. Preclinical and clinical studies showed that ospemifene has an agonist action on bone and reduced the growth of all breast cancer models in animal studies, providing they expressed estrogen receptor-α. Ospemifene had minimal effects on the endometrium of postmenopausal women. Ospemifene 60 mg once a day was approved by the U.S. Food and Drug Administration in February 2013 for women with moderate to severe dyspareunia.

CB2 cannabinoid receptor is a novel target for third-generation selective estrogen receptor modulators bazedoxifene and lasofoxifene

The purpose of the current study was to investigate the ability of the third-generation selective estrogen receptor modulators (SERMs) bazedoxifene and lasofoxifene to bind and act on CB2 cannabinoid receptor. We have identified, for the first time, that CB2 is a novel target for bazedoxifene and lasofoxifene. Our results showed that bazedoxifene and lasofoxifene were able to compete for specific [3H]CP-55,940 binding to CB2 in a concentration-dependent manner. Our data also demonstrated that by acting on CB2, bazedoxifene and lasofoxifene concentration-dependently enhanced forskolin-stimulated cAMP accumulation. Furthermore, bazedoxifene and lasofoxifene caused parallel, rightward shifts of the CP-55,940, HU-210, and WIN55,212-2 concentration–response curves without altering the efficacy of these cannabinoid agonists on CB2, which indicates that bazedoxifene- and lasofoxifene-induced CB2 antagonism is most likely competitive in nature. Our discovery that CB2 is a novel target for bazedoxifene and lasofoxifene suggests that these third-generation SERMs can potentially be repurposed for novel therapeutic indications for which CB2 is a target. In addition, identifying bazedoxifene and lasofoxifene as CB2 inverse agonists also provides important novel mechanisms of actions to explain the known therapeutic effects of these SERMs.