Lasofoxifene (CP-336,156), a selective estrogen receptor modulator, prevents bone loss induced by aging and orchidectomy in the adult rat

RuPHOX-Ru Catalyzed Asymmetric Hydrogenation of α-Substituted Tetralones via a Dynamic Kinetic Resolution

The efficient RuPHOX-Ru catalyzed asymmetric hydrogenation of α-substituted tetralones via a dynamic kinetic resolution has been achieved for the synthesis of chiral tetrahydronaphthols. The mechanism study indicated that the hydrogenation...

Selective estrogen receptor modulator lasofoxifene suppresses spondyloarthritis manifestation and affects characteristics of gut microbiota in zymosan-induced SKG mice

Ankylosing spondylitis is a male-predominant disease and previous study revealed that estrogens have an anti-inflammatory effect on the spondyloarthritis (SpA) manifestations in zymosan-induced SKG mice. This study aimed to evaluate the effect of selective estrogen receptor modulator (SERM) lasofoxifene (Laso) on disease activity of SpA. Mice were randomized into zymosan-treated, zymosan + 17β-estradiol (E2)-treated, and zymosan + Laso-treated groups. Arthritis was assessed by ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) small-animal positron emission tomography/computed tomography and bone mineral density (BMD) was measured. Fecal samples were collected and 16S ribosomal RNA gene sequencing was used to determine gut microbiota differences. Both zymosan + E2-treated mice and zymosan + Laso-treated mice showed lower arthritis clinical scores and lower ¹⁸F-FDG uptake than zymosan-treated mice. BMD was significantly higher in zymosan + E2-treated mice and zymosan + Laso-treated mice than zymosan-treated mice, respectively. Fecal calprotectin levels were significantly elevated at 8 weeks after zymosan injection in zymosan-treated mice, but it was not significantly changed in zymosan + E2-treated mice and zymosan + Laso-treated mice. Gut microbiota diversity of zymosan-treated mice was significantly different from zymosan + E2-treated mice and zymosan + Laso-treated mice, respectively. There was no significant difference in gut microbiota diversity between zymosan + E2-treated mice and zymosan + Laso -treated mice. Laso inhibited joint inflammation and enhanced BMD in SKG mice, a model of SpA. Laso also affected the composition and biodiversity of gut microbiota. This study provides new knowledge regarding that selected SpA patients could benefit from SERM treatment.

Selective Estrogen Receptor Modulators: A Potential Option For Non-Binary Gender-Affirming Hormonal Care?

Gender dysphoria describes the distress associated with having a gender identity that differs from one's birth-assigned sex. To relieve this distress, transgender, and gender diverse (henceforth, trans) individuals commonly undergo medical transition involving hormonal treatments. Current hormonal treatment guidelines cater almost exclusively for those who wish to transition from male to female or vice versa. In contrast, there is a dearth of hormonal options for those trans individuals who identify as non-binary and seek an androgynous appearance that is neither overtly male nor female. Though prolonged puberty suppression with gonadotrophin releasing hormone agonists (GnRHa) could in theory be gender-affirming by preventing the development of unwanted secondary sex characteristics, this treatment option would be limited to pre- or peri-pubertal adolescents and likely have harmful effects. Here, we discuss the theoretical use of Selective Estrogen Receptor Modulators (SERMs) for non-binary people assigned male at birth (AMAB) who are seeking an androgynous appearance through partial feminization without breast growth. Given their unique range of pharmacodynamic effects, SERMs may represent a potential gender-affirming treatment for this population, but there is a lack of knowledge regarding their use and potentially adverse effects in this context.

The use of selective estrogen receptor modulators on bone health in men

Selective estrogen receptor modulators (SERMs) represent a class of drugs that act as agonist or antagonist for estrogen receptor in a tissue-specific manner. The SERMs drugs are initially used for the prevention and treatment of osteoporosis in postmenopausal women. Bone health in prostate cancer patients has become a significant concern, whereby patients undergo androgen deprivation therapy is often associated with deleterious effects on bone. Previous preclinical and epidemiological findings showed that estrogens play a dominant role in improving bone health as compared to testosterone in men. Therefore, this evidence-based review aims to assess the available evidence derived from animal and human studies on the effects of SERMs on the male skeletal system. The effects of SERMs on bone mineral density (BMD)/content (BMC), bone histomorphometry, bone turnover, bone strength and fracture risk have been summarized in this review.

Long-Term High-Dose Resveratrol Supplementation Reduces Bone Mass and Fracture Strength in Rats

Resveratrol (RSV) is a natural polyphenolic compound. A recent study suggests a positive effect on BMD in men; however, the underlying changes in microstructure and strength remain unknown. We aimed to investigate the effects of RSV on the skeleton in hindlimb-immobilized and non-immobilized rats. Seventy-two female Wistar rats were divided into six groups. Two baseline (BSL) groups underwent short-term diet intervention for 4 weeks before sacrifice [phytoestrogen-deficient diet (PD) (BSL + PD) or RSV diet (600 mg/kg body weight/day) (BSL + RSV)]. Four groups were injected in the right hindlimb with botulinum toxin (BTX) (immobilized) or saline (non-immobilized), and fed either PD diet or RSV diet 4 weeks pre-injection and 6 weeks post-injection before sacrifice (BTX + PD, BTX + RSV, PD, and RSV, respectively). DXA, µCT, dynamic histomorphometry, and mechanical tests were performed. Short-term RSV treatment did not affect bone parameters, whereas long-term RSV exposure had a consistent negative impact on non-immobilized rats (RSV vs. PD); whole femoral aBMD (p = 0.01) and distal femoral metaphyseal Tb.N (p = 0.01), Tb.Sp (p = 0.02), and BV/TV (p = 0.07). At the femoral mid-diaphysis, RSV increased periosteal resorption (p = 0.01) and increased endosteal formation (p = 0.02), while mineralization was unaffected. In addition, RSV reduced femoral mid-diaphyseal three-point bending strength (p = 0.03) and stiffness (p = 0.04). BTX-induced immobilization resulted in significant bone loss and reduced bone strength; however, RSV supplementation was unable to prevent this. In conclusion, long-term high-dose RSV reduced bone mass and fracture strength and did not prevent immobilization-induced bone loss in rats.

Sclerostin Antibody Reverses Bone Loss by Increasing Bone Formation and Decreasing Bone Resorption in a Rat Model of Male Osteoporosis

Sclerostin antibody (Scl-Ab) restored bone mass and strength in the ovariectomized rat model of postmenopausal osteoporosis. Increased bone mineral density (BMD) and decreased skeletal fragility fracture risk have been reported in postmenopausal osteoporotic women receiving Scl-Ab. In males, loss of androgen leads to rapid decreases in BMD and an increased risk of fragility fractures. We hypothesized that Scl-Ab could reverse the loss of bone mass and strength caused by androgen ablation in the orchiectomized (ORX) rat model of male osteoporosis. We treated 9-month-old ORX Sprague Dawley rats (3 months after ORX) subcutaneously twice weekly with vehicle or Scl-Ab (5 or 25 mg/kg) for 6 weeks (n = 10 per group). Both doses of Scl-Ab fully reversed the BMD deficit in the lumbar spine and femur and tibia in ORX rats. Microcomputed tomography showed that the bone mass in the fifth lumbar vertebral body, femur diaphysis, and femoral neck were dose-dependently restored by Scl-Ab. The bone strength at these sites increased significantly with Scl-Ab to levels matching those of sham-operated controls and correlated positively with improvements in bone mineral content, demonstrating bone quality maintenance. Dynamic histomorphometry of the tibial diaphysis and second lumbar vertebral body demonstrated that Scl-Ab significantly increased bone formation on periosteal, endocortical, and trabecular surfaces and significantly decreased bone resorption on endocortical and trabecular surfaces. The effects of Scl-Ab on increasing bone formation and decreasing bone resorption led to restoration of bone mass and strength in androgen-deficient rats. These findings support the ongoing evaluation of Scl-Ab as a potential therapeutic agent for osteoporosis in men.

Selective estrogen receptor modulators and the vitamin D analogue eldecalcitol block bone loss in male osteoporosis

Rapid increases in the number of elderly people have dramatically increased the number of female and male osteoporosis patients. Osteoporosis often causes bone fragility fractures, and males exhibit particularly poor prognosis after these fractures, indicating that control of osteoporosis is crucial to maintain quality of men's lives. However, osteoporosis therapies available for men have lagged behind advances available for women. Here, we show that three selective estrogen receptor modulators (SERMs), namely, raloxifene, bazedoxifene, and tamoxifen, plus the vitamin D analogue ED71, also called eldecalcitol, completely block orchiectomy-induced, testosterone-depleted bone loss in male mice in vivo. Patients treated with hormone deprivation therapy for prostate cancer also exhibit male osteoporosis, and bone management is critical for these patients. Given that androgen replacement therapy is not an option for these patients, our results represent a novel approach potentially useful to control male osteoporosis.

Selective estrogen receptor modulators: tissue specificity and clinical utility

Selective estrogen receptor modulators (SERMs) are a diverse group of nonsteroidal compounds that function as agonists or antagonists for estrogen receptors (ERs) in a target gene-specific and tissue-specific fashion. SERM specificity involves tissue-specific expression of ER subtypes, differential expression of co-regulatory proteins in various tissues, and varying ER conformational changes induced by ligand binding. To date, the major clinical applications of SERMs are their use in the prevention and treatment of breast cancer, the prevention of osteoporosis, and the maintenance of beneficial serum lipid profiles in postmenopausal women. However, SERMs have also been found to promote adverse effects, including thromboembolic events and, in some cases, carcinogenesis, that have proven to be obstacles in their clinical utility. In this review, we discuss the mechanisms of SERM tissue specificity and highlight the therapeutic application of well-known and emergent SERMs.

The role of activation functions 1 and 2 of estrogen receptor-α for the effects of estradiol and selective estrogen receptor modulators in male mice

Estradiol (E2) is important for male skeletal health and the effect of E2 is mediated via estrogen receptor (ER)-α. This was demonstrated by the findings that men with an inactivating mutation in aromatase or a nonfunctional ERα had osteopenia and continued longitudinal growth after sexual maturation. The aim of the present study was to evaluate the role of different domains of ERα for the effects of E2 and selective estrogen receptor modulators (SERMs) on bone mass in males. Three mouse models lacking either ERαAF-1 (ERαAF-1(0)), ERαAF-2 (ERαAF-2(0)), or the total ERα (ERα(-/-)) were orchidectomized (orx) and treated with E2 or placebo. E2 treatment increased the trabecular and cortical bone mass and bone strength, whereas it reduced the thymus weight and bone marrow cellularity in orx wild type (WT) mice. These parameters did not respond to E2 treatment in orx ERα(-/-) or ERαAF-2(0). However, the effects of E2 in orx ERαAF-1(0) [corrected] were tissue-dependent, with a clear response in cortical bone parameters and bone marrow cellularity, but no response in trabecular bone. To determine the role of ERαAF-1 for the effects of SERMs, we treated orx WT and ERαAF-1(0) mice with raloxifene (Ral), lasofoxifene (Las), bazedoxifene (Bza), or vehicle. These SERMs increased total body areal bone mineral density (BMD) and trabecular volumetric BMD to a similar extent in orx WT mice. Furthermore, only Las increased cortical thickness significantly and only Bza increased bone strength significantly. However, all SERMs showed a tendency toward increased cortical bone parameters. Importantly, all SERM effects were absent in the orx ERαAF-1(0) mice. In conclusion, ERαAF-2 is required for the estrogenic effects on all evaluated parameters, whereas the role of ERαAF-1 is tissue-specific. All evaluated effects of Ral, Las and Bza are dependent on a functional ERαAF-1. Our findings might contribute to the development of bone-specific SERMs in males.

Lasofoxifene (CP-336,156), a novel selective estrogen receptor modulator, in preclinical studies

Estrogen replacement therapy is reported to reduce the incidence of vertebral fractures in postmenopausal women, however, its compliance is limited because of side effects and safety concerns. Estrogen's side effects on breast and uterine tissues leading to the potential increased risk of uterine and breast cancer limit widespread estrogen usage. Thus, there is a significant medical need for a therapy that protects against postmenopausal bone loss but is free of estrogen's negative effects on reproductive tissues. Selective estrogen receptor modulators (SERMs) have been investigated as an alternative to hormone replacement therapy. One such compound, raloxifene, has been approved for the prevention and treatment of osteoporosis. Lasofoxifene (LAS), a new, nonsteroidal, and potent SERM, is an estrogen antagonist or agonist depending on the target tissue. LAS selectively binds with high affinity to human estrogen receptors. In ovariectomized (OVX) rat studies, LAS prevented the decrease in femoral bone mineral density, tibial and lumbar vertebral trabecular bone mass at an ED100 of about 60 μg/kg/day. LAS inhibited the activation of trabecular and endocortical bone resorption and bone turnover in tibial metaphyses and diaphyses, and lumbar vertebral body in OVX rats. In addition, LAS decreased total serum cholesterol, inhibited body weight gain and increased soleus muscle weight in OVX rats. Similarly, LAS prevented bone loss induced by orchidectomy or aging in male rats by decreasing bone resorption and bone turnover while it had no effect in the prostate. Further, LAS decreased total serum cholesterol in intact aged male rats or in orchidectomized male rats. Synergestic skeletal effects were found with LAS in combination with bone anabolic agents such as prostaglandin E2 (PGE2), parathyroid hormone (PTH) or a growth hormone secretagoue (GHS) in OVX rats. In combination with estrogen, LAS inhibited the uterine stimulating effects of estrogen but did not block the bone protective effects of estrogen. In immature and aged female rats, LAS did not affect the uterine weight and uterine histology. In OVX adult female rats, LAS slightly but significantly increased uterine weight. These results demonstrated that LAS produced effects on the skeleton indistinguishable from estrogen in female and male rats. However, unlike estrogen, LAS had little effect on uterine weight and cellular proliferation of uterus in female rats. In preclinical anti-tumor studies, LAS inhibited human breast cancer growth in mice bearing MCF7 tumors, prevented NMU-induced mammary carcinomas and possessed chemotherapeutic effects in NMU-induced carcinomas in rats. Therefore, we conclude that LAS possesses the antiestrogenic effects in breast tissue and estrogenic effects in bone and serum cholesterol, but lacks estrogen's side effects on uterine tissue. These data support the therapeutic potential of LAS for the prevention and treatment of postmenopausal bone loss and mammary carcinomas in humans.

Bazedoxifene exhibits antiestrogenic activity in animal models of tamoxifen-resistant breast cancer: implications for treatment of advanced disease

PURPOSE

There is compelling evidence to suggest that drugs that function as pure estrogen receptor (ER-α) antagonists, or that downregulate the expression of ER-α, would have clinical use in the treatment of advanced tamoxifen- and aromatase-resistant breast cancer. Although such compounds are currently in development, we reasoned, based on our understanding of ER-α pharmacology, that there may already exist among the most recently developed selective estrogen receptor modulators (SERM) compounds that would have usage as breast cancer therapeutics. Thus, our objective was to identify among available SERMs those with unique pharmacologic activities and to evaluate their potential clinical use with predictive models of advanced breast cancer.

EXPERIMENTAL DESIGN

A validated molecular profiling technology was used to classify clinically relevant SERMs based on their impact on ER-α conformation. The functional consequences of these observed mechanistic differences on (i) gene expression, (ii) receptor stability, and (iii) activity in cellular and animal models of advanced endocrine-resistant breast cancer were assessed.

RESULTS

The high-affinity SERM bazedoxifene was shown to function as a pure ER-α antagonist in cellular models of breast cancer and effectively inhibited the growth of both tamoxifen-sensitive and -resistant breast tumor xenografts. Interestingly, bazedoxifene induced a unique conformational change in ER-α that resulted in its proteasomal degradation, although the latter activity was dispensable for its antagonist efficacy.

CONCLUSION

Bazedoxifene was recently approved for use in the European Union for the treatment of osteoporosis and thus may represent a near-term therapeutic option for patients with advanced breast cancer.

Research resource: Transcriptional profiling in a cellular model of breast cancer reveals functional and mechanistic differences between clinically relevant SERM and between SERM/estrogen complexes

Exploitation of the relationship between estrogen receptor (ER) structure and activity has led to the development of 1) selective ER modulators (SERM), compounds whose relative agonist/antagonist activities differ between target tissues; 2) selective ER degraders (SERD), compounds that induce a conformational change in the receptor that targets it for proteasomal degradation; and 3) tissue-selective estrogen complexes (TSEC), drugs in which a SERM and an ER agonist are combined to yield a blended activity that results in distinct clinical profiles. In this study, we have performed a comprehensive head-to-head analysis of the transcriptional activity of these different classes of ERM in a cellular model of breast cancer. Not surprisingly, these studies highlighted important functional differences and similarities among the existing SERM, selective ER degraders, and TSEC. Of particular importance was the identification of genes that were regulated by various TSEC combinations but not by an estrogen or SERM alone. Cumulatively, the findings of this analysis are informative with respect to the mechanisms by which ER is engaged by different enhancers/promoters and highlights how promoter context influences the pharmacological activity of ER ligands.

Diastereoselective Friedel-Crafts alkylation of hydronaphthalenes

An efficient and versatile synthesis of chiral tetralins has been developed using both inter- and intramolecular Friedel-Crafts alkylation as a key step. The readily available hydronaphthalene substrates were prepared via a highly enantioselective metal-catalyzed ring opening of meso-oxabicyclic alkenes followed by hydrogenation. A wide variety of complex tetracyclic compounds have been isolated with high levels of regio-, diastereo-, and enantioselectivity.

Synthesis of Lasofoxifene, Nafoxidine and Their Positional Isomers via the Novel Three-Component Coupling Reaction

A Lewis acid-mediated three-component coupling reaction was successfully applied for the synthesis of lasofoxifene (1), nafoxidine (2), and their positional isomers, inv-lasofoxifene (3) and inv-nafoxidine (4). In the presence of HfCl₄, the desired one-pot coupling reaction among 4-pivaloyloxybenzaldehyde (5), cinnamyltrimethylsilane (6), and anisole proceeded to afford the corresponding 3,4,4-triaryl-1-butene 7 in high yield. The iodocarbocyclization of the coupling product and the successive elimination of hydrogen iodide forming the olefin part, followed by the migration of the double-bond afforded the common synthetic intermediate of lasofoxifene (1) and nafoxidine (2) via a very concise procedure. Additionally, the syntheses of their positional isomers inv-lasofoxifene (3) and inv-nafoxidine (4) were also achieved through very convenient protocols.

Lasofoxifene: Evidence of its therapeutic value in osteoporosis

Introduction:

Osteoporosis is a skeletal disorder characterized by compromised bone strength and increased risk of fracture. It is a common disorder in elderly subjects and represents a major public health problem, affecting up to 40% postmenopausal women and 15% of men. Among the several therapeutical interventions, hormone replacement therapy (HRT) was traditionally seen as the gold standard for preventing osteoporotic fractures in postmenopausal women, as well as for the management of menopausal symptoms. However HRT, especially if administered long-term, may lead to an increased risk of breast and, when unopposed by progestins, endometrial cancers. Alternative therapies include bisphosphonates and raloxifene, a selective estrogen receptor modulator (SERM). While the former have been associated with suboptimal adherence, the latter was considerably less potent than estrogen and its effect in the prevention of nonvertebral fractures remain uncertain.

Aims:

The purpose of this article is to review the clinical trials of lasofoxifene, a new SERM for the treatment of postmenopausal osteoporosis. The medical literature was reviewed for appropriate articles containing the terms “lasofoxifene” and SERMs”.

Evidence review:

There are three (phase II or phase III) clinical trials that clearly demonstrate efficacy and safety of this new SERM in the suppression of bone loss and the prevention of vertebral and nonvertebral fractures. Moreover, lasofoxifene treatment also reduced breast cancer risk and the occurrence of vaginal atrophy.

Place in therapy:

With its increased potency and efficacy on the prevention of nonvertebral fractures lasofoxifene may be an alternative and cost-effective therapy for osteoporosis in postmenopausal women.

Selective estrogen receptor modulator (SERM) for the treatment of osteoporosis in postmenopausal women: focus on lasofoxifene

Selective estrogen receptor modulators (SERMs) represent a class with a growing number of compounds that act as either estrogen receptor agonists or antagonists in a tissue-specific manner. This article reviews lasofoxifene, a new-generation SERM that has completed phase III development for the prevention and treatment of osteoporosis in postmenopausal women. Consistent with preclinical observations, this new SERM demonstrated improved skeletal efficacy over raloxifene and at an oral dose of 0.5 mg/day was effective in the prevention of both vertebral and nonvertebral fractures in postmenopausal women with osteoporosis. At the same dosage, lasofoxifene treatment also reduced estrogen receptor-positive breast cancer risk and the occurrence of vaginal atrophy, but, like the other SERMs, was associated with hot flushes and an increased risk of venous thromboembolic events. With its increased efficacy on the prevention of nonvertebral fractures than current available SERMs and its positive effects on the vagina, this new compound may represent an alternative and cost-effective therapy for osteoporosis in postmenopausal women.

Lasofoxifene for the prevention and treatment of postmenopausal osteoporosis

Lasofoxifene is a selective estrogen receptor modulator (estrogen agonist/antagonist) that has completed phase III trials to evaluate safety and efficacy for the prevention and treatment of osteoporosis and for the treatment of vaginal atrophy in postmenopausal women. In postmenopausal women with low or normal bone mineral density (BMD), lasofoxifene increased BMD at the lumbar spine and hip and reduced bone turnover markers compared with placebo. In women with postmenopausal osteoporosis, lasofoxifene increased BMD, reduced bone turnover markers, reduced the risk of vertebral and nonvertebral fractures, and decreased the risk of estrogen receptor-positive breast cancer. In postmenopausal women with low bone mass, lasofoxifene improved the signs and symptoms of vulvovaginal atrophy. Clinical trials show that lasofoxifene is generally well tolerated with mild to moderate adverse events that commonly resolve even with drug continuation. Lasofoxifene has been associated with an increase in the incidence of venous thromboembolic events, hot flushes, muscle spasm, and vaginal bleeding. It is approved for the treatment of postmenopausal women at increased risk for fracture in some countries and is in the regulatory review process in others.

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.

Pathologic effects of testosterone deprivation

PURPOSE OF REVIEW

Androgen deprivation therapy remains the cornerstone of treatment for advanced prostate cancer. There are significant adverse effects associated with prolonged androgen deprivation therapy, with recent findings associating it with the metabolic syndrome and its associated health risks.

RECENT FINDINGS

A review of the adverse pathologic effects of testosterone deprivation is performed. Recent findings associate androgen deprivation therapy with endocrine and metabolic disarray, specifically the metabolic syndrome, resulting in increased rates of diabetes and myocardial infarction in patients on testosterone deprivation.

SUMMARY

The increased incidence of the metabolic syndrome in patients receiving androgen deprivation therapy and the associated morbidity and possibly mortality require significant investigation into alternatives to complete testosterone deprivation and ways to counteract these adverse effects.

New insights into the metabolism of tamoxifen and its role in the treatment and prevention of breast cancer

The metabolism of tamoxifen is being redefined in the light of several important pharmacological observations. Recent studies have identified 4-hydroxy N-desmethyltamoxifen (endoxifen) as an important metabolite of tamoxifen necessary for antitumor actions. The metabolite is formed through the enzymatic product of CYP2D6 which also interacts with specific selective serotonin reuptake inhibitors (SSRIs) used to prevent the hot flashes observed in up to 45% of patients taking tamoxifen. Additionally, the finding that enzyme variants of CYP2D6 do not promote the metabolism of tamoxifen to endoxifen means that significant numbers of women might not receive optimal benefit from tamoxifen treatment. Clearly these are particularly important issues not only for breast cancer treatment but also for selecting premenopausal women, at high risk for breast cancer, as candidates for chemoprevention using tamoxifen.

Emerging pharmacologic therapies for osteoporosis

Osteoporotic fractures are an important public health problem, contributing substantially to morbidity and mortality in an ageing world population and consuming considerable health resources. Presently available pharmacologic therapies for prevention of fragility fractures are limited in scope, efficacy and acceptability to patients. Considerable efforts are being made to develop new, more effective treatments for osteoporosis, and to refine/optimize existing therapies. These novel treatments include an expanding array of drugs that primarily inhibit osteoclastic bone resorption: estrogenic compounds, bisphosphonates, inhibitors of receptor activator of NF-kappaB ligand signaling, cathepsin K inhibitors, c-src kinase inhibitors, integrin inhibitors and chloride channel inhibitors. The advent of intermittent parathyroid hormone (PTH) therapy has provided proof-of-principle that osteoblast-targeted (anabolic) agents can effectively prevent osteoporotic fractures, and is likely to be followed by the introduction of other therapies based on PTH (orally active PTH analogs, antagonists of the calcium sensing receptor, PTH-related peptide analogs) and/or agents that induce osteoblast anabolism by means of pathways involving key, recently identified, molecular targets (wnt-low-density lipoprotein receptor-related protein 5 signaling, sclerostin and matrix extracellular phosphoglycoprotein).

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.

Biochemical markers in preclinical models of osteoporosis

Although several treatments for osteoporosis exist, further understanding of the mode of action of current treatments, as well as development of novel treatments, are of interest. Thus, preclinical models of osteoporosis are very useful, as they provide the possibility for gaining knowledge about the cellular mechanisms underlying the disease and for studying pharmaceutical prevention or intervention of the disease in simple and strictly controlled systems. In this review, we present a comprehensive collection of studies using biochemical markers of bone turnover for investigation of preclinical models of osteoporosis. These range from pure and simple in vitro systems, such as osteoclast cultures, to ex vivo models, such as cultures of embryonic murine tibiae and, finally, to in vivo models, such as ovariectomy and orchidectomy of rats. We discuss the relevance of the markers in the individual models, and compare their responses to those observed using 'golden standard' methods.

The 2.0 A crystal structure of the ERalpha ligand-binding domain complexed with lasofoxifene

Lasofoxifene is a new and potent selective estrogen receptor modulator (SERM). The structural basis of its interaction with the estrogen receptor has been investigated by crystallographic analysis of its complex with the ligand-binding domain of estrogen receptor alpha at a resolution of 2.0 A. As with other SERMs, lasofoxifene diverts the receptor from its agonist-bound conformation by displacing the C-terminal AF-2 helix into the site at which the LXXLL motif of coactivator proteins would otherwise be able to bind. Lasofoxifene achieves this effect by occupying the space normally filled by residue Leu 540, as well as by modulating the conformation of residues of helix 11 (His 524, Leu 525). A well-defined salt bridge between lasofoxifene and Asp 351 suggests that charge neutralization in this region of the receptor may explain the some of the antiestrogenic effects of lasofoxifene. The results suggest general features of ERalpha/SERM recognition, and add a new dimension to efforts to rationalize differences between the biological activity profiles exhibited by these important pharmacological agents.

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.

Selective Estrogen Receptor Modulators for Postmenopausal Osteoporosis

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.

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.

Lasofoxifene: a third-generation selective estrogen receptor modulator for the prevention and treatment of osteoporosis

This article reviews lasofoxifene, a new-generation selective estrogen receptor modulator (SERM) that is currently in Phase III development for the prevention and treatment of osteoporosis in postmenopausal women. This compound selectively binds to both of the estrogen receptors with a high affinity and a median inhibitory concentration that is similar to that seen with estradiol and > or = 10-fold higher than those reported for other SERMs (raloxifene and tamoxifen). Lasofoxifene has a remarkably improved oral bioavailability with respect to other SERMs due to increased resistance to intestinal wall glucuronidation. In both preclinical and short-term studies, the compound showed a favourable safety profile and demonstrated a proven efficacy in preventing bone loss and lowering cholesterol levels. Dose modelling from Phase II studies allowed the selection of lasofoxifene 0.25 mg/day as the lowest fully effective dose.

Selective estrogen receptor modulators: A possible new treatment of osteoporosis in males

More recently, osteoporosis in men has been recognized as an important public health problem. Bone loss begins in mid life and is associated with the decline of the sex steroids production. Although there is no equivalent of the menopause, gonadal function in men is affected in a slow progressive way leading to hypogonadism. Testosterone, the major androgen in men, exerts its effect on bone by local conversion to 5alpha-dihydrotestosterone or by aromatization to estrogens. Several studies have found that estrogen, rather than testosterone, levels are more closely correlated with BMD in elderly men. Selective estrogen receptor modulator (SERM) raloxifene binds to estrogen receptors and exhibit estrogenic effect in bone, but, contrary to estrogen, without feminizing effect. There are limited numbers of studies investigating the effects of SERMs in males. Animal studies demonstrated that SERMs inhibit bone turnover and prevent bone loss in orchidectomised adult male rats. Raloxifene has been shown to increase bone mineral density of the hip in men receiving androgen deprivation therapy for prostate cancer. Moreover, experimental data demonstrated dramatic increase in cell death in human prostate cancer cell lines after the treatment with raloxifene. All these observations suggest that SERMs may be useful for the prevention and treatment of osteoporosis not only in postmenopausal women but also in elderly men. However, our hypothesis should be tested in a proper designed clinical trial. Several important issues have to be addressed. Does the same drug dose that has been shown to be effective in postmenopausal women should be used in men, too? Does treatment with SERMs reduce the fracture risk in men and is it comparable to that observed in women? Does treatment with SERMs have any beneficial effect on cardiovascular system and prostate cancer? And finally, do men experience adverse events other than women treated with SERMs? Answering to these questions will have great impact in getting the decision of possible SERMs usage in the treatment of osteoporosis in elderly males.

Prevention of bone loss in postmenopausal women treated with lasofoxifene compared with raloxifene

OBJECTIVE

Osteoporosis is a significant health problem in postmenopausal women. Consequently, new and effective therapies are being sought to preserve bone mass and prevent osteoporosis in this population of women. The objective of this study was to compare the effects of lasofoxifene with raloxifene and placebo on indices of bone health in postmenopausal women.

DESIGN

A randomized, double-blind, placebo- and active treatment-controlled study of 2 years duration was conducted. Women included 410 postmenopausal women aged 47 to 74 years. The four treatment groups were: lasofoxifene 0.25 mg/day, or 1.0 mg/day, raloxifene 60 mg/day, or placebo daily. All women received daily calcium and vitamin D supplements. The primary endpoint was percent change from baseline to 2 years in lumbar spine bone mineral density (BMD) in all women having baseline and at least one follow-up bone density measurement. Total hip BMD, biochemical markers of bone turnover, low-density lipoprotein cholesterol, and safety were also evaluated in all women.

RESULTS

Both doses of lasofoxifene significantly increased lumbar spine BMD compared with raloxifene (P < or = 0.05) and with placebo treatment (P < or = 0.05). Least squares mean increases (95% CI) from baseline in lumbar spine BMD, compared with placebo, were 3.6% (1.9, 5.2) for lasofoxifene 0.25 mg/day, 3.9% (2.4, 5.5) for lasofoxifene 1.0 mg/day, and 1.7% (0.3, 3.0) for raloxifene. The two doses of lasofoxifene and raloxifene were equally effective at increasing total hip BMD. Lasofoxifene and raloxifene significantly reduced the levels of biochemical markers of bone turnover compared with placebo. In general, the effects of lasofoxifene were greater than the responses to raloxifene. At 2 years, lasofoxifene significantly (P < or = 0.05) reduced low-density lipoprotein cholesterol levels by 20.6% and 19.7% with 0.25 mg/day and 1 mg/day, respectively, compared with raloxifene (12.1%) and placebo (3.2%). Lasofoxifene and raloxifene had a similar adverse event profile with low rate of discontinuations due to adverse events.

CONCLUSIONS

Lasofoxifene may be an effective and well-tolerated treatment option for the prevention of bone loss in postmenopausal women.

Alcohol-induced bone degradation and its early detection in the alcohol-fed castrated rats

The objective of this study was to examine alcohol-induced changes of bone in hormone-deficient males using the developed method. In the process of bone resorption, type I collagen crosslinking molecules, pyridinoline (PYD), are released into the circulation and cleared by the kidneys. (2)H(2)O as a tracer has been applied to measure the synthesis rates of slow-turnover proteins and successfully applied to bone collagen synthesis in our hormone deficiency rats. This study demonstrated for the first time, the early changes of the femur bone degradation in hormone-deficient male individuals, more influenced by alcohol through histopathological study, serum PYD assay, and (2)H(2)O labeling. We also observed that serum PYD was a sensitive pathological marker of bone degradation in castrated osteoporosis males and the unique features of (2)H(2)O labeling to measure the bone turnover collagen synthesis rates were excellent markers of bone degradation and aging.

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.

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.

Emerging and potential therapies for osteoporosis

Osteoporotic fractures are an important public health problem, contributing substantially to morbidity and mortality in an ageing world population and consuming considerable health resources. Currently available pharmacological therapies for prevention of fragility fractures are limited in scope, efficacy and acceptability to patients. Considerable efforts are being made to develop new, more effective treatments for osteoporosis and to refine/optimise existing therapies. These novel treatments include an expanding array of drugs that primarily inhibit osteoclastic bone resorption; oestrogenic compounds, bisphosphonates, inhibitors of receptor activator of nuclear factor-kappaB ligand signalling, cathepsin K inhibitors, c-src kinase inhibitors, integrin inhibitors and chloride channel inhibitors. The advent of intermittent para-thyroid hormone (PTH) therapy has provided proof-of-principle that osteo-blast-targeted (anabolic) agents can effectively prevent osteoporotic fractures, and is likely to be followed by the introduction of other therapies based upon PTH, such as orally active PTH analogues, antagonists of the calcium sensing receptor, PTH-related peptide analogues, and/or agents that induce osteoblast anabolism via pathways involving key, recently identified, molecular targets (wnt low-density lipoprotein receptor-related protein-5 signalling, sclerostin and matrix extracellular phosphoglycoprotein).

Selective estrogen receptor modulators protect hippocampal neurons from kainic acid excitotoxicity: differences with the effect of estradiol

Neuroprotective effects of estradiol are well characterized in animal experimental models. However, in humans, the outcome of estrogen treatment for cognitive function and neurological diseases is very controversial. Selective estrogen receptor modulators (SERMs) may represent an alternative to estrogen for the treatment or the prevention of neurodegenerative disorders. SERMs interact with the estrogen receptors and have tissue-specific effects distinct from those of estradiol, acting as estrogen agonists in some tissues and as antagonists in others. In this study we have assessed the effect of tamoxifen, raloxifene, lasofoxifene (CP-336,156), bazedoxifene (TSE-424), and 17beta-estradiol on the hippocampus of adult ovariectomized rats, after the administration of the excitotoxin kainic acid. Administration of kainic acid induced the expression of vimentin in reactive astroglia and a significant neuronal loss in the hilus. SERMs did not affect vimentin immunoreactivity in the hilus, while 17beta-estradiol significantly reduced the surface density of vimentin immunoreactive profiles. Estradiol, tamoxifen (0.4-2 mg/kg), raloxifene (0.4-2 mg/kg), and bazedoxifene (2 mg/kg) prevented neuronal loss in the hilus after the administration of kainic acid. Lasofoxifene (0.4-2 mg/kg) was not neuroprotective. These findings indicate that SERMs present different dose-dependent neuroprotective effects. Furthermore, the mechanisms of neuroprotection by SERMs and estradiol are not identical, because SERMs do not significantly affect reactive gliosis while neuroprotection by estradiol is associated with a strong down-regulation of reactive astroglia.

Androgens and bone

Loss of estrogens or androgens increases the rate of bone remodeling by removing restraining effects on osteoblastogenesis and osteoclastogenesis, and also causes a focal imbalance between resorption and formation by prolonging the lifespan of osteoclasts and shortening the lifespan of osteoblasts. Conversely, androgens, as well as estrogens, maintain cancellous bone mass and integrity, regardless of age or sex. Although androgens, via the androgen receptor (AR), and estrogens, via the estrogen receptors (ERs), can exert these effects, their relative contribution remains uncertain. Recent studies suggest that androgen action on cancellous bone depends on (local) aromatization of androgens into estrogens. However, at least in rodents, androgen action on cancellous bone can be directly mediated via AR activation, even in the absence of ERs. Androgens also increase cortical bone size via stimulation of both longitudinal and radial growth. First, androgens, like estrogens, have a biphasic effect on endochondral bone formation: at the start of puberty, sex steroids stimulate endochondral bone formation, whereas they induce epiphyseal closure at the end of puberty. Androgen action on the growth plate is, however, clearly mediated via aromatization in estrogens and interaction with ERalpha. Androgens increase radial growth, whereas estrogens decrease periosteal bone formation. This effect of androgens may be important because bone strength in males seems to be determined by relatively higher periosteal bone formation and, therefore, greater bone dimensions, relative to muscle mass at older age. Experiments in mice again suggest that both the AR and ERalpha pathways are involved in androgen action on radial bone growth. ERbeta may mediate growth-limiting effects of estrogens in the female but does not seem to be involved in the regulation of bone size in males. In conclusion, androgens may protect men against osteoporosis via maintenance of cancellous bone mass and expansion of cortical bone. Such androgen action on bone is mediated by the AR and ERalpha.

Differential effect of short-term etidronate treatment on three cancellous bone sites in orchidectomized adult rats

The aim of the present study was to analyze the effects of short-term treatment with the antiresorptive agent, etidronate, on orchidectomized adult rats, via comparison of three cancellous bone sites, the lumbar vertebral body (LVB), proximal tibial metaphysis (PTM), and distal tibial metaphysis (DTM). Thirty-five male Wistar rats, aged 10 months, were randomly divided into four groups: baseline control (BLC, nF10), age-matched sham-operated control (AMC, nF9), orchidectomy (ORX, nF9), and ORXBetidronate treatment (nF7). Etidronate treatment (10 mg/kg, daily subcutaneous injection) was initiated 2 weeks after surgery and was continued for 2 weeks. Four weeks after surgery, the 5th LVB, PTM, and DTM were processed for histomorphometric analysis of cancellous bone (secondary spongiosa). ORX resulted in a decrease in body weight. No significant difference in cancellous bone volume (BV/TV) was found between the BLC and AMC groups at any skeletal site. The cancellous BV/TV loss was attributable to increased eroded surface (ES/BS) with no significant alteration in the mineral apposition rate (MAR), at all skeletal sites and etidronate treatment in ORX rats significantly decreased ES/BS to a level not significantly different from that in the AMC group, resulting in complete prevention of ORX-induced cancellous BV/TV loss. The MAR was markedly decreased in the PTM and LVB, but maintained in the DTM by etidronate treatment. The present study showed that etidronate treatment could completely prevent ORX-induced cancellous bone loss regardless skeletal sites by suppressing bone resorption. In particular, suppression of bone formation in terms of osteoblastic activity by etidronate treatment was not evident only in the DTM

Coregulator function: a key to understanding tissue specificity of selective receptor modulators

Ligands for the nuclear receptor superfamily control many aspects of biology, including development, reproduction, and homeostasis, through regulation of the transcriptional activity of their cognate receptors. Selective receptor modulators (SRMs) are receptor ligands that exhibit agonistic or antagonistic biocharacter in a cell- and tissue context-dependent manner. The prototypical SRM is tamoxifen, which as a selective estrogen receptor modulator, can activate or inhibit estrogen receptor action. SRM-induced alterations in the conformation of the ligand-binding domains of nuclear receptors influence their abilities to interact with other proteins, such as coactivators and corepressors. It has been postulated, therefore, that the relative balance of coactivator and corepressor expression within a given target cell determines the relative agonist vs. antagonist activity of SRMs. However, recent evidence reveals that the cellular environment also plays a critical role in determining SRM biocharacter. Cellular signaling influences the activity and subcellular localization of coactivators and corepressors as well as nuclear receptors, and this contributes to gene-, cell-, and tissue-specific responses to SRM ligands. Increased understanding of the effect of cellular environment on nuclear receptors and their coregulators has the potential to open the field of SRM discovery and research to many members of the nuclear receptor superfamily.

Pre- and postnatal development studies of lasofoxifene, a selective estrogen receptor modulator (SERM), in Sprague-Dawley rats

BACKGROUND

Lasofoxifene is a nonsteroidal selective estrogen receptor modulator (SERM) developed for the treatment of postmenopausal osteoporosis. The purpose of these studies was to evaluate the effects of lasofoxifene on the postnatal development, behavior, and reproductive performance of offspring of female rats given lasofoxifene during organogenesis and lactation.

METHODS

Two range-finding studies were conducted to determine the effects of lasofoxifene at doses from 0.01-10 mg/kg on parturition and lactation in pregnant rats and on the early postnatal development of the offspring, and to optimize the dosing regimen. Maternal milk and plasma were sampled for concentrations of lasofoxifene on Lactation Days 4, 7, and 14. In the pre- and postnatal development study, lasofoxifene was administered to pregnant and lactating rats by oral gavage at dose levels of 0.01, 0.03, and 0.1 mg/kg on Gestation Days 6-17 and Lactation Days 1-20. Maternal body weight and food consumption were measured throughout pregnancy, and body weight was measured throughout lactation. Parturition was monitored closely. The F1 offspring were measured for viability, body weight, anogenital distance, the appearance of postnatal developmental indices and reflex behaviors, sensory function, in an age-appropriate functional observational battery, motor activity, auditory startle, passive avoidance, and the Cincinnati Water Maze. The F1 generation was assessed for reproductive function, and the F2 offspring were measured for body weight and viability throughout the lactation period.

RESULTS

In the range-finding studies, indications of maternal toxicity included decreased body weight and food consumption, increased length of gestation, prolonged parturition, dystocia, and increased offspring mortality at birth. Concentrations of lasofoxifene in maternal plasma were similar to those in milk, increased with increasing dose, and remained consistent over a 10-day period. In the pre- and postnatal development study, maternal body weights and food consumption were decreased in all treated groups during gestation. Length of gestation was increased, parturition was prolonged, and dystocia was noted in the dams in the 0.1 mg/kg group. There was increased pup mortality in the F1 litters in the 0.1 mg/kg group and all treated groups had decreased offspring body weights beginning at 1 week of age, continuing into the postweaning period and, for the F1 males, into adulthood. Female F1 offspring in the 0.03 and 0.1 mg/kg groups had increased body weights as adults. There were delays in the age of appearance of preputial separation in the males in the 0.1 mg/kg group and vaginal opening in the females in all treated groups. Body temperature was decreased by <0.5 degrees C after weaning for male and female offspring in the 0.1 mg/kg group. The sensory, behavioral, and functional measures, including the tests of learning and memory, were unaffected by treatment. Mating success was lower for the F1 animals in the 0.1 mg/kg group, but there were no effects on the reproductive parameters. Mating, reproduction, and maternal behavior of the F1 animals in the 0.01 and 0.03 mg/kg groups and the survival and body weights of the F2 offspring in all treated groups through Postnatal Day 21 were unaffected by treatment.

CONCLUSION

The maternal findings in this study were related to the pharmacologic activity of lasofoxifene. Inhibition of growth of the F1 offspring after perinatal exposure to lasofoxifene was observed, but there were no significant effects on the sensory, behavioral, or functional measures, including learning and memory. There were no effects on the F2 generation. The findings are consistent with those reported for at least one other SERM. The findings of this study do not suggest increased risk for the primary indication of use in postmenopausal women.

Reproductive toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in male rats

BACKGROUND

Lasofoxifene is a nonsteroidal selective estrogen receptor modulator (SERM) with greater than 100-fold selectivity against all other steroid receptors and is a potentially superior treatment for postmenopausal osteoporosis. The purpose of this study was to evaluate the effects of lasofoxifene on male reproduction in rats in light of the known effects of estrogen modulating compounds on male reproductive ability.

METHODS

Lasofoxifene was administered to adult male rats at doses of 0.1, 1, 10, and 100 mg/kg for 66-70 consecutive days. After 28 days of dosing, male rats were cohabited with untreated female rats. Female rats were euthanized on gestation day 14 and a uterine examination was carried out for evaluation of reproductive parameters and embryo viability. Male rats were euthanized after 66-70 days of dosing and epididymal sperm motility and concentration were assayed. The testes, epididymides, prostate, and seminal vesicles were weighed and microscopically examined.

RESULTS

The duration of cohabitation was increased for 100 mg/kg males by 0.7 days. The number of males copulating and the number of implantation sites produced per copulation were reduced in the 10 and 100 mg/kg groups. Weights of the seminal vesicles and epididymides were reduced for all groups, although the testes weight and epididymal sperm motility and concentration were not affected by treatment. There were no microscopic findings in the male reproductive tissues.

CONCLUSION

The changes in male fertility and reproductive tissue weights after exposure to lasofoxifene are consistent with those previously described for estrogen receptor-modulating compounds.

Embryo/fetal toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in rats and rabbits

BACKGROUND

The purpose of this study was to evaluate the effects of lasofoxifene, a selective estrogen receptor modulator (SERM), on rat and rabbit fetal development.

METHODS

Lasofoxifene was administered orally to rats (1, 10, 100 mg/kg) between gestation days (GD) 6-17, and in rabbits (0.1, 1, 3 mg/kg) between GD 6-18. Maternal body weight and food consumption were monitored throughout pregnancy. Fetuses were delivered by Cesarean section on GD 21 in rats, and GD 28 in rabbits, to evaluate fetal viability, weight, and morphology. Drug concentrations in maternal plasma were measured in a separate cohort of animals at several time points commencing on GD 17 (rats) and 18 (rabbits). On GD 18 (rat) and GD 19 (rabbit) drug concentrations were measured in maternal plasma and in fetal tissue 2 hr post dosing to determine the fetal to maternal drug ratio.

RESULTS

In rats, there were dose-related declines in maternal weight gain and food consumption. Post implantation loss was significantly increased at dosages of 10 and 100 mg/kg, and the number of viable fetuses was decreased at 100 mg/kg. The placental weights increased, whereas fetal weights decreased in a dose-dependent manner. Lasofoxifene-related teratologic findings were noted at 10 and 100 mg/kg and included imperforate anus with hypoplastic tails, dilatation of the ureters and renal pelvis, misaligned sternebrae, hypoflexion of hindpaw, wavy ribs, and absent ossification of sternebrae. In rabbits, neither maternal weight gain nor food consumption were affected during treatment. Between GD 26-28, there was a dose-dependent increased incidence of red discharge beneath the cages. At 1 and 3 mg/kg, resorptions and post-implantation loss increased. There were no significant external or visceral effects, but 3 mg/kg there was an increased incidence of supernumerary ribs. Although the maternal plasma Cmax and AUC(0-24) were dose-dependent, the exposures in the rat were many orders of magnitude greater than in the rabbit even for the same 1 mg/kg dose. The single time point fetal/maternal drug ratio was higher in the rat (1.3-0.78) than in the rabbit (0.21-0.16).

CONCLUSION

In general, both maternal and fetal effects of lasofoxifene were similar to those reported with other SERMs. Although the incidence or severity of these effects was, in some instances, greater in the rat than in the rabbit, the doses and the resultant maternal and fetal exposures were many orders of magnitude higher in the rat, suggesting the rabbit to be more sensitive to the toxicological effects of lasofoxifene.

Reproductive toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in female rats

BACKGROUND

Lasofoxifene is a nonsteroidal selective estrogen receptor modulator (SERM). With high affinity to the alpha and beta human estrogen receptors and greater potency than other SERMs, lasofoxifene is potentially a superior treatment for postmenopausal osteoporosis. In light of the known effects of estrogen-modulating compounds on female reproductive indices, two studies were conducted to evaluate the effects of lasofoxifene on female rat cyclicity, reproduction, and parturition.

METHODS

One study evaluated effects of lasofoxifene on estrous cyclicity, and the second study assessed effects on implantation and parturition. In the cyclicity study, lasofoxifene was administered to female rats at doses of 0.1, 0.3, and 1.0 mg/kg/day for 14 consecutive days. After treatment, there was a 3-week reversibility phase followed by a mating phase. In the implantation study, lasofoxifene was administered to pregnant female rats at doses of 0.01, 0.03, and 0.1 mg/kg/day for 7 consecutive days (gestation day [GD] 0-6). Some animals were euthanized on GD 21, and the remainder of the group was allowed to deliver the F1 generation. Several developmental indices were evaluated in the F1 pups through post-natal day (PND) 21.

RESULTS

In the cyclicity study, all lasofoxifene-treated females were anestrous by Study Day 7 (1.0 mg/kg) or 9 (0.3 and 0.1 mg/kg). The reversibility phase resulted in restoration of normal estrous cycles by the end of 1 (0.1 mg/kg) or 2 weeks (0.3 and 1.0 mg/kg). During the mating phase, no adverse effects occurred in pregnancy success or reproductive parameters. In the implantation study, all doses of lasofoxifene increased pre- and post-implantation losses, increased gestation length, and reduced litter size. None of the developmental parameters measured on the F1 generation was adversely affected.

CONCLUSION

Lasofoxifene reversibly altered the estrous cycle and inhibited implantation, consistent with what would be expected from a member of the SERM class.

Effect of vitamin K2 on cortical and cancellous bones in orchidectomized and/or sciatic neurectomized rats

We examined the effect of vitamin K2 on cortical and cancellous bones in orchidectomized and/or sciatic neurectomized rats. Ninety male Sprague-Dawley rats, 3 months of age, were randomized by stratified weight method into nine groups with 10 rats in each group: baseline control (BLC), age-matched intact control (IN), IN+vitamin K2 administration (K), orchidectomy (ORX), ORX+K, unilateral sciatic neurectomy (NX), NX+K, ORX+NX (ONX), and ONX+K. Vitamin K2 (menatetrenone) was administered orally twice a week at a dose of 30 mg/kg each. After 10 weeks of feeding, the tibial shaft and proximal tibia were processed for cortical and cancellous bone histomorphometric analyses, respectively. An ORX-induced reduction in maturation-related cortical bone gain and ORX-induced cancellous bone loss were attributable to increased endocortical and trabecular bone turnover, respectively. NX- and ONX-induced reductions in maturation-related cortical bone gain were attributable to decreased periosteal bone formation and increased endocortical bone turnover, while NX- and ONX-induced cancellous bone loss was attributable to increased bone resorption and decreased bone formation. ORX-induced cancellous bone loss was more pronounced when combined with immobilization. Vitamin K2 administration did not significantly alter any parameters in IN rats. Vitamin K2 administration in ORX rats suppressed endocortical bone resorption and trabecular bone turnover, retarding a reduction in maturation-related cortical bone gain and cancellous bone loss. This effect on cancellous bone loss was primarily because of prevention of a reduction of trabecular thickness. Vitamin K2 administration in NX and ONX rats suppressed bone resorption and stimulated bone formation (mineralization), with retardation of a reduction of trabecular thickness without any significant effect on cancellous bone mass, and suppressed endocortical bone resorption, retarding a reduction in maturation-related cortical bone gain. The present study provides evidence indicating that vitamin K2 has the potential to suppress bone resorption or bone turnover and/or stimulate bone formation in vivo in ORX and/or NX rats.