Long-term dosing of arzoxifene lowers cholesterol, reduces bone turnover, and preserves bone quality in ovariectomized rats

Selective Estrogen-Receptor Modulators and Aromatase Inhibitors: Promising New Medical Therapies for Endometriosis?

Endometriosis is an estrogen-dependent disease and estrogen-related pathways are imbalanced in women with endometriosis. One of the key enzymes in estrogen synthesis is aromatase. Inhibiting this pathway at several points is a promising idea for the treatment of endometriosis. The third generation of aromatase inhibitors is becoming more potent in efficacy, with fewer side effects than previous generations, but cotreatment with other hormones is needed to inhibit ovarian stimulation. Other components that promote estrogen synthesis such as COX-2 can also be potentially targeted. Selective estrogen-receptor modulators could also be interesting in view of their tissue-specific effect. However, all these new drugs are still in an early phase of development. At present, it is too early to conclude that aromatase inhibitors, COX-2 inhibitors or selective estrogen-receptor modulators really present any added value compared with the existing drugs that can be used to achieve hormonal suppression in the medical treatment of endometriosis.

The discovery and development of selective estrogen receptor modulators (SERMs) for clinical practice

Selective estrogen receptor modulators (SERMs) are structurally different compounds that interact with intracellular estrogen receptors in target organs as estrogen receptor agonists or antagonists. These drugs have been intensively studied over the past decade and have proven to be a highly versatile group for the treatment of different conditions associated with postmenopausal women's health, including hormone responsive cancer and osteoporosis. Tamoxifen, a failed contraceptive is currently used to treat all stages of breast cancer, chemoprevention in women at high risk for breast cancer and also has beneficial effects on bone mineral density and serum lipids in postmenopausal women. Raloxifene, a failed breast cancer drug, is the only SERM approved internationally for the prevention and treatment of postmenopausal osteoporosis and vertebral fractures. However, although these SERMs have many benefits, they also have some potentially serious adverse effects, such as thromboembolic disorders and, in the case of tamoxifen, uterine cancer. These adverse effects represent a major concern given that long-term therapy is required to prevent osteoporosis or prevent and treat breast cancer. The search for the 'ideal' SERM, which would have estrogenic effects on bone and serum lipids, neutral effects on the uterus, and antiestrogenic effects on breast tissue, but none of the adverse effects associated with current therapies, is currently under way. Ospemifene, lasofoxifene, bazedoxifene and arzoxifene, which are new SERM molecules with potentially greater efficacy and potency than previous SERMs, have been investigated for use in the treatment and prevention of osteoporosis. These drugs have been shown to be comparably effective to conventional hormone replacement therapy in animal models, with potential indications for an improved safety profile. Clinical efficacy data from ongoing phase III trials are available or are awaited for each SERM so that a true understanding of the therapeutic potential of these compounds can be obtained. In this article, we describe the discovery and development of the group of medicines called SERMs. The newer SERMs in late development: ospemifene, lasofoxifene, bazedoxifene, are arzoxifene are described in detail.

Nuclear receptors and their selective pharmacologic modulators

Nuclear receptors are ligand-activated transcription factors and include the receptors for steroid hormones, lipophilic vitamins, sterols, and bile acids. These receptors serve as targets for development of myriad drugs that target a range of disorders. Classically defined ligands that bind to the ligand-binding domain of nuclear receptors, whether they are endogenous or synthetic, either activate receptor activity (agonists) or block activation (antagonists) and due to the ability to alter activity of the receptors are often termed receptor "modulators." The complex pharmacology of nuclear receptors has provided a class of ligands distinct from these simple modulators where ligands display agonist/partial agonist/antagonist function in a tissue or gene selective manner. This class of ligands is defined as selective modulators. Here, we review the development and pharmacology of a range of selective nuclear receptor modulators.

Metabolomic profiles delineate signature metabolic shifts during estrogen deficiency-induced bone loss in rat by GC-TOF/MS

Postmenopausal osteoporosis is a complicated and multi-factorial disease. To study the metabolic profiles and pathways activated in osteoporosis, Eight rats were oophorectomized (OVX group) to represent postmenopausal osteoporosis and the other eight rats were sham operated (Sham group) to be the control. The biochemical changes were assessed with metabolomics using a gas chromatography/time-of-flight mass spectrometry. Metabolomic profile using serial blood samples obtained prior to and at different time intervals after OVX were analyzed by principal component analysis (PCA) and Partial least squares-discriminant analysis (PLS-DA). The conventional indicators (bone mineral density, serum Bone alkaline phosphatase (B-ALP) and N-telopeptide of type I collagen (NTx) of osteoporosis in rats were also determined simultaneously. In OVX group, the metabolomics method could describe the endogenous changes of the disease more sensitively and systematically than the conventional criteria during the progression of osteoporosis. Significant metabolomic difference was also observed between the OVX and Sham groups. The metabolomic analyses of rat plasma showed that levels of arachidonic acid, octadecadienoic acid, branched-chain amino acids (valine, leucine and isoleucine), homocysteine, hydroxyproline and ketone bodies (3-Hydroxybutyric Acid) significantly elevated, while levels of docosahexaenoic acid, dodecanoic acid and lysine significantly decreased in OVX group compared with those in the homeochronous Sham group. Considering such metabolites are closely related to the pathology of the postmenopausal osteoporosis, the results suggest that potential biomarkers for the early diagnosis or the pathogenesis of osteoporosis might be identified via metabolomic study.

Rational therapeutic combinations with histone deacetylase inhibitors for the treatment of cancer

Histone deacetylases (HDACs) regulate the acetylation of a variety of histone and nonhistone proteins, controlling the transcription and regulation of genes involved in cell cycle control, proliferation, survival, DNA repair and differentiation. Unsurprisingly, HDAC expression is frequently altered in hematologic and solid tumor malignancies. Two HDAC inhibitors (vorinostat and romidepsin) have been approved by the US FDA for the treatment of cutaneous T-cell lymphoma. As single agents, treatment with HDAC inhibitors has demonstrated limited clinical benefit for patients with solid tumors, prompting the investigation of novel treatment combinations with other cancer therapeutics. In this article, the rationales and clinical progress of several combinations with HDAC inhibitors are presented, including DNA-damaging chemotherapeutic agents, radiotherapy, hormonal therapies, DNA methyltransferase inhibitors and various small-molecule inhibitors. The future application of HDAC inhibitors as a treatment for cancer is discussed, examining current hurdles to overcome before realizing the potential of this new approach.

Current, new and future treatments of osteoporosis

Osteoporosis as a common chronic disease is challenging human health. Although different therapeutic options are routinely used for prevention/treatment of osteoporosis, their side effects and benefits are under question. Increasing our knowledge about signaling pathways in bone and osteocytes as well as osteoblasts and osteoclasts will help us in designing new therapeutic modalities for osteoporosis. In the present study, all new therapeutic measures of osteoporosis have been reviewed. For this purpose, search engines like Pubmed, Web of Science, Scopus, Google Scholar were searched and all relevant articles were found. The study was limited to the year 1998-2010. Bisphosphonates are the cornerstone of osteoporosis treatment, but there are not enough relevant studies that investigated their equivalencies in comparison with each other or the other medications. Therefore, medication selection is empirical and subjective. Furthermore, no eminent study has compared certain combinations. There are new hopes for treatment of osteoporosis, which are more specific with less harm. Our results show that new and emerging therapies are more potent and target specified which more individualize osteoporosis treatment; however, more investigations on their safety and efficacy in comparison with current medications are highly recommended.

Developing drugs to treat osteoporosis: lessons learned?

BACKGROUND

Selective estrogen-receptor modulators (SERMs) are drugs that act as estrogen receptor agonists or antagonists depending on the target tissue. Theoretically this class of agents would be an ideal substitute for hormone replacement therapy (HRT), if their effects on the skeleton matched those of estrogen while their actions on other tissues were either neutral or beneficial.

OBJECTIVE

To evaluate a Phase III trial of a new SERM, arzoxefine, for prevention of osteoporosis in younger postmenopausal women.

METHODS/RESULTS

Arzoxifene induced modest but significant increases in bone mineral density versus a control group during 2 years of therapy, with minor adverse events. However, fracture efficacy and other patient-specific outcomes were not evaluated.

CONCLUSION

Despite a positive study of surrogate end points (bone density and biochemical markers of bone turnover), arzoxifene was withdrawn from further FDA evaluation, principally because of long-term side effects and lack of non-vertebral fracture efficacy in the companion Phase III fracture study. Each SERM has a unique profile on bone and other tissues. Regulatory approval of this class of agents may remain problematic for the immediate future.

Current and emerging pharmacologic therapies for the management of postmenopausal osteoporosis

Postmenopausal osteoporosis is an asymptomatic skeletal disease that is often underdiagnosed and undertreated. Osteoporotic fractures are associated with substantial morbidity and mortality and impaired quality of life-socially, emotionally, and financially. Considering the growing burden of osteoporotic fractures worldwide, there remains an ongoing need for progress in the diagnosis of osteoporosis, identification of individuals at high fracture risk, and treatment to prevent fractures. Adequate intake of calcium and vitamin D is recommended as baseline therapy for osteoporosis prevention and treatment. Available pharmacological agents for the management of postmenopausal osteoporosis may not be appropriate for all women. Oral bisphosphonates are generally considered first-line therapy for patients with osteoporosis, but their use may be limited by gastrointestinal side effects. Other agents include hormone therapy, the selective estrogen receptor modulator (SERM) raloxifene, salmon calcitonin, teriparatide (human recombinant parathyroid hormone), and strontium ranelate (in some countries). Factors that may contribute to poor compliance and persistence with current osteoporosis therapies include drug intolerance, complexity of dosing regimens, and poor understanding of the relative benefit and risk with treatment. Emerging therapies for postmenopausal osteoporosis include novel SERMs (bazedoxifene, lasofoxifene, ospemifene, arzoxifene) and denosumab. Because SERMs can display mixed functional estrogen receptor agonist or antagonist activity depending on the target tissue, they may confer beneficial effects on bone with limited stimulation of other tissues (e.g., breast, endometrium). Clinical investigation of these promising new agents is ongoing to evaluate efficacy and safety, with the goal of developing effective strategies to maximize long-term tolerance, compliance, and persistence with therapy.

Identification and structure-activity relationships of chromene-derived selective estrogen receptor modulators for treatment of postmenopausal symptoms

As part of a program aimed at the development of selective estrogen receptor modulators (SERMs), novel chromene scaffolds, benzopyranobenzoxapanes, were discovered. Many compounds showed binding affinity as low as 1.6-200 nM, displayed antagonist behaviors in the MCF-7 human breast adenocarcinoma cell line as well in Ishikawa cell line with IC(50) values in the range 0.2-360 nM. On the basis of the side chain substitution, various compounds demonstrated strong inhibitory activity in anti-uterotropic assay. Compound 7-(R) and its major metabolites 5-(R) and 6-(R) were evaluated in several in vivo models of estrogen action. Relative to a full estrogen agonist (ethynyl estradiol) and the SERM raloxifene, 7-(R) was found to be a potent SERM that behaved as antagonist in the uterus and exhibited estrogen agonistic activity on bone, plasma lipids, hot flush, and vagina. The overall pharmacokinetic profile and stability were significantly improved compared to those of the phase 2 development compound 9-(R).

Pharmacology and clinical applications of selective estrogen receptor modulators

Compounds that can be described as selective estrogen receptor modulators (SERMs) have expanded dramatically over the past two decades. The ability of SERMs to act as estrogens in certain tissues while remaining inert or acting as an anti-estrogen in other tissues has opened up opportunities for treating specific estrogen-modulated diseases without accepting the risk of systemic estrogen activity. SERM development has resulted in significant therapeutic advances for breast cancer, osteoporosis and potentially other diseases associated with the menopause. After the publication of the Women's Health Initiative, interest in compound selectivity that reduces menopausal symptoms while protecting bone, breast, uterus and the heart has increased. Future SERMs may also have a therapeutic profile that can be tailored to specific patient populations, including men. This review paper summarizes the characteristics of different SERMs from various pharmacological categories and the feasibility and scope of their use for a large range of disease/health conditions.

Effects of arzoxifene on bone mineral density and endometrium in postmenopausal women with normal or low bone mass

INTRODUCTION

Arzoxifene, a benzothiophene estrogen agonist/antagonist, is being developed for prevention and treatment of osteoporosis and for risk reduction of invasive breast cancer in postmenopausal women.

METHODS

The effects of arzoxifene 20 mg/d on bone mineral density (BMD), uterine safety, and overall safety were studied in the FOUNDATION study, a 2-yr randomized, placebo-controlled trial including 331 postmenopausal women with normal to low bone mass.

RESULTS

Compared to placebo, arzoxifene significantly increased lumbar spine (+2.9%) and total hip (+2.2%) BMD. Arzoxifene decreased biochemical markers of bone metabolism compared to placebo. Changes in breast density were neutral or slightly decreased in the arzoxifene vs. placebo group. There was no evidence of endometrial hyperplasia or carcinoma in the arzoxifene group as assessed by central review of baseline and follow-up endometrial biopsies. There was no significant change between the groups in endometrial thickness assessed by transvaginal ultrasound. The incidence of uterine polyps and vaginal bleeding was not significantly different between the groups. Vulvovaginal mycotic infection was the only adverse event significantly increased in the arzoxifene vs. placebo group. Hot flushes were not significantly different between the groups.

CONCLUSION

In postmenopausal women with normal to low bone mass, arzoxifene 20 mg/d increased BMD at the spine and hip and had a neutral effect on the uterus and endometrium.

Phase III Double-Blind Trial of Arzoxifene Compared With Tamoxifen for Locally Advanced or Metastatic Breast Cancer

Purpose

To compare the efficacy of arzoxifene with tamoxifen for the treatment of locally advanced or metastatic breast cancer.

Patients and Methods

Women with estrogen- or progesterone-receptor–positive breast cancer who had not received prior systemic therapy, or who had relapsed more than 12 months after stopping adjuvant hormonal therapy, were randomly assigned to receive 20 mg arzoxifene or 20 mg tamoxifen daily. Each treatment arm was to have 240 patients enrolled. The primary end point was progression-free survival. Secondary end points included other measures of tumor response, overall survival, and safety.

Results

Enrollment was stopped when a planned interim analysis of the first 200 patients suggested arzoxifene to be significantly inferior to tamoxifen. The median progression-free survival for the 352 patients who had been randomly assigned when enrollment was stopped was 4.0 months (95% CI, 3.4 to 5.6 months) for the arzoxifene group and 7.5 months (95% CI, 5.9 to 8.8 months) for the tamoxifen group. On-study progression-free survival (P = .011) and time to treatment failure (P = .029) also favored tamoxifen. Overall tumor response rate and median response duration were comparable between the groups. Adverse events were similar between the treatments, except for nausea (more frequent with arzoxifene) and vaginal discharge (more frequent with tamoxifen).

Conclusion

Tamoxifen produced significantly longer progression-free survival and time to treatment failure compared with arzoxifene in the treatment of locally advanced and metastatic breast cancer. There were no significant differences between tumor response rate, clinical benefit rate, or median response duration.

Selective estrogen receptor modulators (SERMS)

Hormone receptors and, specifically, estrogen receptors were described about four decades ago. For estrogens, there are two receptors, estrogen receptor alpha (ERalpha) and estrogen receptor beta (ERbeta). The two receptors are coded by different genes and their tissue expression varies across organs. ERalpha is predominantly expressed in reproductive tissues (uterus, breast, ovaries) liver and central nervous system, whereas ERbeta is expressed in other tissues such as bone, endothelium, lungs, urogenital tract, ovaries, central nervous system and prostate. More than seventy molecules that belong to the SERMS class have been described. There are 5 chemical groups: triphenylethylenes, benzotiophenes, tetrahydronaphtylenes, indoles and benzopyrans. All of these non-hormonal compounds are capable of activating the ER, reduce bone turnover rate and, as an antiresorptive, clearly improve bone density. Estrogens reduce bone turnover rate and, as an antiresorptive, clearly improve bone density. They are also beneficial for the relief of menopausal symptoms. An ongoing debate that extends over the decades, relates to to overall benefit/risk profile of estrogen or estrogen-progestin therapy since these therapies can increase the risk of serious health disorders, such as breast cancer. SERMs have increased our understanding of hormone-receptor regulatory mechanisms. Their development has permitted a targeted efficacy profile avoiding some of the side effects of the hormone therapy. Their clinical utility relies today mostly on the effects on breast cancer and bone.

Selective estrogen receptor modulators for postmenopausal osteoporosis: current state of development

Selective estrogen receptor modulators (SERMs) are structurally different compounds that interact with intracellular estrogen receptors in target organs as estrogen receptor agonists and antagonists. These drugs have been intensively studied over the past decade and have proven to be a highly versatile group for the treatment of different conditions associated with aging, including hormone-responsive cancer and osteoporosis. Tamoxifen and toremifene are currently used to treat advanced breast cancer and also have beneficial effects on bone mineral density and serum lipids in postmenopausal women. Raloxifene is the only SERM approved worldwide for the prevention and treatment of postmenopausal osteoporosis and vertebral fractures. However, although these SERMs have many benefits, they may also be responsible for some potentially very serious adverse effects, such as thromboembolic disorders and, in the case of tamoxifen, uterine cancer. These adverse effects represent a major concern given that long-term therapy is required to prevent osteoporosis. Moreover, both preclinical and clinical reports suggest that tamoxifen, toremifene and raloxifene are considerably less potent than estrogen. The search for the 'ideal' SERM, which would have estrogenic effects on bone and serum lipids, neutral effects on the uterus, and antiestrogenic effects on breast tissue, but none of the adverse effects associated with current therapies, is currently under way. Ospemifene, lasofoxifene, bazedoxifene and arzoxifene, which are new SERM molecules with potential greater efficacy and potency than previous SERMs, are currently under investigation for use in the treatment and prevention of osteoporosis. These drugs have been shown to be comparably effective to conventional hormone replacement therapy in animal models of osteoporosis, with potential indications for an improved safety profile. Clinical efficacy data from ongoing phase III trials are awaited so that a true understanding of the therapeutic potential of these compounds can be obtained.

Quantitative Microcomputed Tomography Assessment of Intratrabecular, Intertrabecular, and Cortical Bone Architecture in a Rat Model of Severe Renal Osteodystrophy

OBJECTIVE

To determine the effects of renal osteodystrophy (ROD) on bone microarchitecture in growing rats.

METHODS

A total of 24 rats underwent 5/6 nephrectomy (NX) and were fed a high-phosphorus diet to induce ROD; another 6 underwent sham NX. In vitro microcomputed tomography images (GEMS, London, Ontario, Canada) were obtained in the femoral metaphysis and midshaft.

RESULTS

Trabecular and cortical bone volume/total volume (BV/TV) were significantly lower in NX specimens because of pores within the trabeculae and along the endosteal surface. Topological analysis using component labeling in 3-dimensions verified that trabecular pores connected to the marrow space. After the trabecular pores were filled using a morphological filter, trabecular thickness was significantly increased in NX. In contrast, cortical thickness was significantly decreased in NX compared with controls; however, after filling the endocortical pores, thickness did not differ.

CONCLUSIONS

The ROD resulted in decreased cortical and trabecular BV/TV, increased porosity, and increased trabecular thickness. Advanced image processing algorithms demonstrated the effects of cortical and trabecular porosity on BV/TV and structure in ROD.

Postmenopausal osteoporosis: an update on current and future therapeutic options

Recent advances in osteoporosis have dramatically changed the management and treatment of this disease. This article reviews the safety and efficacy of US FDA-approved drugs for prevention and treatment of postmenopausal osteoporosis, as well as studies on combination, sequential or intermittent use of these agents. A review of promising agents for osteoporosis therapy is provided.

Developments in the pharmacotherapeutic management of osteoporosis

During the last two decades, several medications have been granted a marketing authorisation for the management of osteoporosis. Bisphosphonates are the most widely prescribed drugs in this area, worldwide. Alendronate and risedronate are given daily or weekly and have demonstrated their ability to reduce fracture rates at the spine and hip. Ibandronate has demonstrated spine antifracture efficacy with intervals between dosings greater than weekly. New developments in this class include intravenous administration of ibandronate or zoledronate, once every three months or once yearly. Raloxifene, a selective estrogen-receptor modulator, reduces spine fractures and, in post-hoc analyses, non-spine fractures in high-risk subjects. New selective estrogen-receptor modulators, including lasofoxifene, bazedoxifene and arzoxifene, are expected to demonstrate antifracture efficacy at the hip level, whilst retaining the extra-skeletal benefits (such as in the breast) that are obtained with raloxifene. The peptides from the parathyroid hormone family are potent stimulators of bone formation. Teriparatide (1 - 34 amino acid fragment of the parathyroid hormone) reduces spine and non-spine fractures, an effect that is sustained for up to 30 months after the withdrawal of treatment. The intact hormone (1 - 84 amino acids) showed similar results on spine fractures, and more data are requested to evaluate its effect on non-spine or hip fractures. Strontium ranelate is suggested to be the first medication to uncouple bone formation from bone resorption. It has shown antifracture efficacy at all sites in a large number of postmenopausal women. New developments include: denosumab, an antibody against receptor activator of NF-kappaB ligand (RANKL); a cytokine that is responsible for osteoclastogenesis; and inhibitors of cathepsin K, a cysteine protease that is involved in the cleavage of collagen.

[SERMs for treatment of osteoporosis: state-of-the-art and perspectives]

Every year in France, we observe 60,000 vertebral fractures, 50,000 hip fractures and 35,000 wrist fractures. However, only 20% of these patients receive adequate pharmacologic therapy to prevent new fractures and their complications. At the present time, clinicians have not a perfect knowledge of the therapeutic class of SERMs (Selective Estrogen Receptor Modulators). In this paper, the authors show the strong capacity of these drugs to produce, in osteoporotic postmenopausal women, major therapeutic effects on bone (reduction of fracture risk), on breast (reduction of cancer risk), and without any side effects on arterial diseases except an increased risk of venous thromboembolism.

Arzoxifene: the development and clinical outcome of an ideal SERM

Hormone-sensitive tumours are among the most common cancers in women. Specific inhibition of the estrogen receptor by selective estrogen receptor downregulators or selective estrogen receptor modulators (SERMs) is effective for the treatment of breast and endometrial cancers and may be used for the prevention of breast cancer. Due to differential recruitment of co-activators and corepressors, SERMs are tissue specific and may have antiestrogenic effects in some tissues, with estrogen agonist activity in others. The ideal SERM would have antiestrogenic effects on the breast and endometrium, but pro-estrogenic effects on bone and lipids. The SERM, arzoxifene (LY-353381.HCl) meets all of these criteria. This review summarises the development, preclinical studies and the clinical outcome of arzoxifene and places it in context with other modalities in the treatment of hormone receptor-positive tumours.

Emerging Selective Estrogen Receptor Modulators

Menopause, regardless of age at onset, is associated with a marked increase in coronary heart disease (CHD) risk. On the basis of epidemiological studies that demonstrated mainly positive effects of postmenopausal hormone therapy on CHD as well as on risk markers of CHD, it has been suggested that CHD could be prevented in postmenopausal women with long-term hormone therapy. However, since the publications of the Heart and Estrogen/progestin Replacement Study and the Women's Health Initiative trial, prescription of hormone therapy for the prevention of CHD has become controversial. Major efforts have been made to identify alternatives for hormone therapy. Compounds suggested have included selective estrogen receptor modulators (SERMs), which represent a class with a growing number of compounds that act as either estrogen receptor agonists or antagonists in a tissue-specific manner. This pharmacological profile may offer the opportunity to dissociate favourable estrogenic effects on the bone and cardiovascular system from unfavourable stimulatory effects on the breast and endometrium. Two SERMs presently on the market are tamoxifen and raloxifene. The only data available regarding the effects of tamoxifen on cardiovascular events in postmenopausal women are from breast cancer trials. These trials found fewer fatal myocardial events in women randomly assigned to tamoxifen compared with women assigned to placebo. Raloxifene is a second-generation SERM that has been shown to prevent osteoporotic fractures, is safe for the endometrium and holds high promise for the prevention of breast cancer. The effect of raloxifene on CHD is still uncertain. On the basis of the MORE (Multiple Outcomes of Raloxifene Evaluation) trial, raloxifene may offer some protection to women with CHD or to those who are at high risk of CHD. Proof that raloxifene reduces the risk of CHD requires a clinical trial with hard clinical endpoints. Such a study is currently underway. Next-generation SERMs taken into clinical development include idoxifene, droloxifene, ospemifene, arzoxifene, acolbifene/EM-800, levormeloxifene, lasofoxifene, bazedoxifene and HMR 3339. The aim is to find a compound with the ideal profile, that is, alleviation of climacteric symptoms and prevention of osteoporotic fractures, but without an adverse effect on the breast and endometrium, and no negative effect or even a beneficial effect on the cardiovascular system and the brain. Currently, limited data are available with regard to these next-generation SERMs and CHD. Nevertheless, some of these novel agents provide arguments for continuing the search for an ideal SERM.

Selective estrogen receptor modulators (SERMs): mechanisms of anticarcinogenesis and drug resistance

Despite the beneficial effects of estrogens in women's health, there is a plethora of evidence that suggest an important role for these hormones, particularly 17beta-estradiol (E(2)), in the development and progression of breast cancer. Most estrogenic responses are mediated by estrogen receptors (ERs), either ERalpha or ERbeta, which are members of the nuclear receptor superfamily of ligand-dependent transcription factors. Selective estrogen receptor modulators (SERMs) are ER ligands that in some tissues (i.e. bone and cardiovascular system) act like estrogens but block estrogen action in others. Tamoxifen is the first SERM that has been successfully tested for the prevention of breast cancer in high-risk women and is currently approved for the endocrine treatment of all stages of ER-positive breast cancer. Raloxifene, a newer SERM originally developed for osteoporosis, also appears to have preventive effect on breast cancer incidence. Numerous studies have examined the molecular mechanisms for the tissue selective action of SERMs, and collectively they indicate that different ER ligands induce distinct conformational changes in the receptor that influence its ability to interact with coregulatory proteins (i.e. coactivators and corepressors) critical for the regulation of target gene transcription. The relative expression of coactivators and corepressors, and the nature of the ER and its target gene promoter also affect SERM biocharacter. This review summarizes the therapeutic application of SERMs in medicine; particularly breast cancer, and highlights the emerging understanding of the mechanism of action of SERMs in select target tissues, and the inevitable development of resistance.

A new selective estrogen receptor modulator, CHF 4227.01, preserves bone mass and microarchitecture in ovariectomized rats

A new SERM, CHF 4227.01, given to 6-month-old female rats immediately after ovariectomy, preserved bone mass and bone microarchitecture without affecting uterus weight. It also decreased serum cholesterol and fat mass in estrogen-deficient rats.

INTRODUCTION

We tested the effect of a new benzopyran derivative, CHF 4227.01, with selective estrogen receptor modulator (SERM) activity on bone mass and biomechanics in ovariectomized (OVX) female rats in comparison with 17alpha-ethinylestradiol (EST), raloxifene (RLX), and lasofoxifene (LFX).

MATERIALS AND METHODS

Four doses of CHF 4227.01 (0.001, 0.01, 0.1, and 1 mg/kg body weight [bw]/day) were administered in OVX animals daily by gavage 5 days/week for 4 months. EST was administered at a dose of 0.1 mg/kg bw/day, whereas RLX and LSX were administered at doses of 1 and 0.1 mg/kg bw/day, respectively, by gavage. In one group (Sham), rats were operated but the ovaries not removed; another OVX group was treated only with placebo.

RESULTS AND CONCLUSIONS

Treatment with CHF 4227.01 (1.0 and 0.1 mg/kg bw), EST (0.1 mg/kg bw), LFX (0.1 mg/kg bw), or RLX (1.0 mg/kg bw) prevented bone loss on the lumbar spine and the proximal femur assessed in vivo by DXA. Volumetric BMD obtained by pQCT ex vivo confirmed protection from bone loss in the spine and proximal femur among rats treated with CHF 4227.01. This effect was associated with strong inhibition of bone resorption both histologically and biochemically. Furthermore, CHF 4227.01 preserved trabecular microarchitecture, analyzed by muCT, and maintained biomechanical indices of bone strength in the spine and proximal femur, effects also observed for RLX, whereas LSX was less protective of microarchitecture. CHF 4227.01 treatment did not affect uterine weight, prevented the increase in body weight and fat mass seen in OVX animals, and decreased serum cholesterol to below the average of intact animals. In conclusion, CHF 4227.01 exhibits a promising therapeutic and safety profile as a new SERM on both skeletal and extraskeletal outcomes.

A new selective estrogen receptor modulator HMR-3339 fully corrects bone alterations induced by ovariectomy in adult rats

The selective estrogen receptor modulator (SERM) raloxifene has been shown to reduce the risk of vertebral fracture, but without significant effect on nonvertebral fractures. However, there is a need for SERMs capable of improving mechanical competence and reducing the risk of fractures at multiple skeletal sites, with minimal side effects. We investigated the effects of a new steroidal SERM, HMR-3339, compared to raloxifene, on bone strength and its determinants (BMD, microarchitecture, dimensions) at various skeletal sites (lumbar spine, tibia, and femur) of adult ovariectomized rats in both prevention and intervention protocols. In a prevention study, HMR-3339 and raloxifene treatments fully prevented alterations of bone strength. In an intervention protocol, where treatment was started 8 weeks after ovariectomy, HMR-3339 fully restored mechanical properties by influencing both areal BMD and outer diameter. This effect was observed at skeletal sites formed of cancellous and cortical bone or of cortical bone only. In contrast, raloxifene positively influenced structures containing mainly cancellous bone. In HMR-3339-treated rats, IGF-I plasma levels were higher than in ovariectomized controls; this was not observed with raloxifene. In conclusion, these results indicate that HMR-3339 increased not only bone mineral mass, but also restored bone mechanical strength at multiple sites in adult osteoporotic rats. In contrast to raloxifene, HMR-3339 also influenced skeletal sites predominantly formed of cortical bone.