Raloxifene (LY139481 HCI) prevents bone loss and reduces serum cholesterol without causing uterine hypertrophy in ovariectomized rats

Effect of raloxifene on the ovarian circulation in women after menopause

OBJECTIVE

We sought to determine whether raloxifene effects the ovarian circulation in women after menopause.

STUDY DESIGN

The resistance indices of the ovarian blood flow were assessed in 130 women after menopause who were randomly assigned to receive either 60 mg of raloxifene, a continuous combined estrogen-progestin tablet daily, or neither treatment for 24 months.

RESULTS

The women who received raloxifene or hormonal replacement therapy had a significant time-related decrease in the resistance index of the ovarian artery blood flow compared to baseline values (resistance index, 0.91) starting after 12 and 18 months of treatment (resistance index, 0.88 and 0.89, respectively; P <.002 and.001, respectively). Whereas significant increases in the resistance index respective to the prestudy values were observed in the nontreated women at 24 months (resistance index, 0.93; P <.0001). The mean (+/-SD) resistance index of the ovarian blood flow at the end of the study (resistance index, 0.89) was significantly lower in the women who were treated with raloxifene than in the women who were treated with hormone replacement therapy (P <.002). No changes in the ovarian dimensions or appearance were noticed during the entire study.

CONCLUSION

Daily therapy with raloxifene has significant ovarian vascular-relaxing effect in women after menopause. This potentially important direct vasculoprotective long-term effect of raloxifene on cardiovascular disease deserves further investigation.

Directions of drug discovery in osteoporosis

Osteoporosis is a condition of increasing importance and prevalence in all parts of the world and particularly in Asia. Recent advances have led to the introduction of effective drugs that decrease bone resorption and stabilize bone mass. However, these drugs have been identified by serendipity rather than rational drug design and are not ideal because of limited bioavailability, mode of administration, or other unwanted effects. There is still a place for even more suitable and effective resorption inhibitors than those currently available. The more compelling need in this field is an acceptable drug that is anabolic for bone, that safely and acceptably increases bone mass and improves the disturbances in bone microarchitecture that characterize established and advanced osteoporosis. Possible approaches to identifying more effective resorption inhibitors and new anabolic agents are discussed.

Growth-stimulatory and transcriptional activation properties of raloxifene in human endometrial Ishikawa cells

Raloxifene (Ral) has estrogenic activity in bone and cardiovascular tissues, but is antiestrogenic in breast and has limited uterotrophic activity in mice. Here we report that Ral stimulates the growth of human endometrial Ishikawa tumors implanted in the mammary fat pad of nude ovariectomized mice. In cultured Ishikawa cells, Ral has agonist effects on transcription mediated by the progesterone receptor, an endogenous estrogen target gene, and on expression of reporter genes containing estrogen response elements (EREs). Both Ral and tamoxifen (Tam), but not estradiol, stimulated transcription mediated by the activator protein 1 at micromolar concentrations. However, this effect correlated with induction of cellular death at high concentrations of Ral or Tam and was not observed at lower concentrations. Our results suggest that Ral has stimulatory effects in Ishikawa cells on both cellular growth and gene transcription, and that EREs can mediate some of these effects.

Characterization of selective estrogen receptor modulator (SERM) activity in two triarylethylene oxybutyric acids

Previously we identified 4-[1-(4-hydroxyphenyl)-2-phenylbuten-1-yl]phenoxy-n-butyric acid (4HBA) and its des-hydroxy analog (BA) as potential selective estrogen receptor modulators (SERMs) in the ovariectomized (OVX) rat. The aim of the present study was to characterize comprehensively the effects of 4HBA and BA in both the OVX rat and in estrogen-responsive cells. Thus, 4HBA was found to be an estrogen antagonist with partial agonist efficacy in estrogen-responsive reporter gene and estrogen-dependent proliferation assays (MVLN cells and MCF-7 human breast cancer cells, respectively). In the OVX rat, 4HBA and BA were equally effective and comparable to other known SERMs regarding (a) serum cholesterol reduction and suppression of serum markers of excessive bone metabolism, and (b) partial agonist efficacy in reproductive tissue relative to steroidal estrogens. Like steroidal estrogens, both compounds increased serum triglyceride levels, with BA being more effective in this regard. The maximal effects of 4HBA on all of these parameters except cholesterol lowering were seen at oral doses of 0.4 micromol/kg/day; maximal cholesterol lowering required doses of 10 micromol/kg/day. In OVX rat liver 9S fraction, BA was found to be efficiently converted to a single hydroxylated metabolite, 4HBA. These results suggest that the effects of BA in the OVX rat might, in part, be a consequence of biotransformation to 4HBA, and that those of 4HBA and BA in the OVX rat and in estrogen-responsive cells are qualitatively similar to those of SERMs such as tamoxifen and raloxifene.

Efficacy of raloxifene for treatment of menopause: a systematic review

PURPOSE

To critically appraise recent randomized controlled trials (RCT) of raloxifene and its effects on the long-term consequences of menopause.

DATA SOURCES

All RCTs of greater than six months duration in post-menopausal women found in MEDLINE through July 2000.

CONCLUSIONS

Raloxifene lowered lipids, but estrogen had a more beneficial effect on HDL and fibrinolytic markers. Raloxifene had a more beneficial effect on triglycerides, inflammatory and thrombogenic markers. Compared to placebo, raloxifene reduced vertebral fractures but had a similar although lesser effect on bone mineral density and markers of bone turnover than estrogen. Estrogen receptor positive breast cancer was reduced by 90% with no increase in the incidence of endometrial cancer with raloxifene. The most serious side effect of raloxifene was an increased incidence of deep vein thromboses and pulmonary emboli.

IMPLICATIONS

Raloxifene has been shown to be beneficial using cardiovascular and osteoporosis end-points in studies of short duration. More RCTs of longer duration with comparisons to other traditional treatments are needed before raloxifene becomes the treatment of choice.

The evolution of tamoxifen therapy in breast cancer: selective oestrogen-receptor modulators and downregulators

Tamoxifen is the most widely used hormonal treatment for all stages of breast cancer and has been approved for the prevention of breast cancer in high-risk women. The observation that tamoxifen acts as an antioestrogen on the breast but has paradoxical oestrogenic effects on bones and lipids heralded the development of the selective oestrogen-receptor modulators (SERM). Raloxifene, another of these drugs, is being used to prevent osteoporosis in postmenopausal women, but it seems, like tamoxifen, to prevent breast cancer. The molecular basis for these target-site-specific actions remains unclear but may involve the relative expressions of coregulatory proteins in target tissues. Several new SERM agents are in clinical development in an attempt to decrease the unwanted effects. Furthermore, two different classes of hormonal agents, the aromatase inhibitors and oestrogen-receptor downregulators, which have no oestrogen-like properties at any site, are promising new treatments for breast cancer.

Structure-function relationships of the raloxifene-estrogen receptor-alpha complex for regulating transforming growth factor-alpha expression in breast cancer cells

Amino acid Asp-351 in the ligand binding domain of estrogen receptor alpha (ERalpha) plays an important role in regulating the estrogen-like activity of selective estrogen receptor modulator-ERalpha complexes. 4-Hydroxytamoxifen is a full agonist at a transforming growth factor alpha target gene in situ in MDA-MB-231 human breast cancer cells stably transfected with the wild-type ERalpha. In contrast, raloxifene (Ral), which is also a selective estrogen receptor modulator, is a complete antiestrogen in this system. Because D351G ERalpha allosterically silences activation function-1 activity in the 4-hydroxytamoxifen-ERalpha complex with the complete loss of estrogen-like activity, we examined the converse interaction of amino acid 351 and the piperidine ring of the antiestrogen side chain of raloxifene to enhance estrogen-like action. MDA-MB-231 cells were either transiently or stably transfected with Asp-351 (the wild type), D351E, D351Y, or D351F ERalpha expression vectors. Profound differences in the agonist and antagonist actions of Ralcenter dotERalpha complexes were noted only in stable transfectants. The agonist activity of the Ralcenter dotERalpha complex was enhanced with D351E and D351Y ERalpha, but raloxifene lost its agonist activity with D351F ERalpha. The distance between the piperidine nitrogen of raloxifene and the negative charge of amino acid 351 was critical for estrogen-like actions. The role of the piperidine ring in neutralizing Asp-351 was addressed using compound R1h, a raloxifene derivative replacing the nitrogen on its piperidine ring with a carbon to form cyclohexane. The derivative was a potent agonist with wild type ERalpha. These results support the concept that the side chain of raloxifene shields and neutralizes the Asp-351 to produce an antiestrogenic ERalpha complex. Alteration of either the side chain or its relationship with the negative charge at amino acid 351 controls the estrogen-like action at activating function 2b of the selective estrogen receptor modulator ERalpha complex.

Effects of 3-phenyl-4-[[4-[2-(1-piperidinyl)ethoxy]phenyl]methyl]- 2H-1-benzopyran-7-ol (CHF 4056), a novel nonsteroidal estrogen agonist/antagonist, on reproductive and nonreproductive tissue

We have discovered a new, nonsteroidal, estrogen agonist/antagonist, 3-phenyl-4-[[4-[2-(1-piperidinyl)ethoxy]phenyl] methyl]-2H-1-benzopyran-7-ol (CHF 4056). The aim of this study was to determine the effects of CHF 4056 on a series of parameters (body weight, uteri, serum cholesterol, and bones) that were previously shown to be sensitive to estrogens and to selective estrogen receptor modulators (SERMs). CHF 4056 is a benzopyran derivative that binds with high affinity to the human estrogen receptors alpha and beta (dissociation constant K(i) of 0.041 and 0.157 nM, respectively). In immature rats, CHF 4056 induced a full estrogen antagonism (half-maximal efficacious dose = 0.33 mg/kg x day p.o.) coupled with a lack of uterine stimulatory activity, whereas the structurally related SERM levormeloxifene demonstrated a maximal partial agonist effect of approximately 65% that of 17alpha-ethynyl estradiol (EE2). In ovariectomized (OVX) rats, CHF 4056 (0.1-1 mg/kg x day p.o. for 4 weeks) significantly reduced OVX-induced bone loss in the lumbar spine L1-4 and OVX-induced increase in serum osteocalcin. These protective effects on bone tissue were comparable with those of 0.1 mg/kg x day EE2. In the same experimental conditions, serum cholesterol was significantly lower in the CHF 4056-treated animals, compared with vehicle-treated OVX rats. In line with the results observed in immature rats, also in OVX rats CHF 4056 diverged dramatically from EE2 and levormeloxifene in its lack of significant estrogenic effects on uterine tissue. In conclusion, CHF 4056 is a new SERM that produces beneficial effects on bone and cholesterol levels, while maintaining antagonist effects on the uterus.

Tissue-specific estrogenic response and molecular mechanisms

Estrogens exert profound effects on growth, differentiation, and function of many reproductive tissues. They also affect other tissues, including bone, liver, cardiovascular system, and brain. In the last few years it has been demonstrated that several synthetic estrogens can act in a tissue-specific manner. The first example of such a selective estrogen receptor modulator (SERM) was tamoxifen, for which an estrogen agonist-like activity in the endometrium and bone was seen to occur simultaneously with an estrogen antagonist activity in the breast. The mechanisms by which the same compound can exert tissue-specific agonist and antagonist actions are still being investigated. Important aspects include the interaction of the ligand with the two estrogen receptor subtypes and the interaction of these ligand-receptor complexes with effectors, which include different DNA response elements and important coregulator proteins. In addition to well-documented effects on gene transcription, there is evidence that estrogen receptors and other estrogen binding proteins are involved in some rapid, non-genomic effects of estrogens in target cells. For these reasons it is important to point out that a toxicological evaluation of endocrine modulators should include an analysis of potential SERM-like properties.

Effects of raloxifene after tamoxifen on breast and endometrial tumor growth in athymic mice

BACKGROUND

In patients with early-stage breast cancer, 5 years of treatment with the selective estrogen receptor modulator (SERM) tamoxifen reduces breast cancer recurrence and mortality, whereas more than 5 years of tamoxifen does not further reduce breast cancer recurrence and doubles the risk of endometrial cancer. We evaluated the effects on tumor growth of raloxifene, another SERM, after tamoxifen treatment in mouse models of breast and endometrial cancers.

METHODS

Athymic, ovariectomized mice were bitransplanted with tumors derived from human breast cancer and endometrial cancer cells that either were tamoxifen-naive or had been exposed to tamoxifen for short (6 months) or long (>5 years) terms. The effects of raloxifene (two dose levels) and tamoxifen on tumor growth in the presence and absence of low-dose estrogen were evaluated. All statistical tests were two-sided.

RESULTS

Raloxifene was less effective than tamoxifen in blocking the stimulatory effects of low-dose estrogen on the growth of tamoxifen-naive breast (P<.001) and endometrial (P =.001) tumors. Raloxifene and tamoxifen had similar inhibitory effects on the growth of short-term tamoxifen-exposed breast tumors. Raloxifene and tamoxifen had similar stimulatory effects on the growth of breast and endometrial tumors that had been exposed to at least 5 years of tamoxifen. However, neither drug blocked the stimulatory effects of estrogen on the growth of these tumors. Raloxifene was less effective than tamoxifen (P<.001) in blocking the stimulatory effects of estrogen on endometrial tumors that had been exposed to tamoxifen in the past.

CONCLUSIONS

Raloxifene and tamoxifen had similar effects on these mouse models of tamoxifen-naive and tamoxifen-resistant breast and endometrial cancer. Treatment with raloxifene following 5 years of adjuvant tamoxifen may not further decrease breast cancer recurrence and may increase endometrial cancer incidence.

Raloxifene enhances nitric oxide release in rat aorta via increasing endothelial nitric oxide mRNA expression

We report the modulatory effects of chronic oral LY139481 (raloxifene) on basal release of nitric oxide (NO) and mRNA levels of endothelial NO synthase (eNOS) in rat thoracic aorta. Constrictor dose-response curves to phenylephrine were generated before and after pretreatment with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NO synthase. Aortic segments were obtained from four groups of rats gavaged orally for 21 days: (i) ovariectomized, (ii) sham, (iii) ovariectomized estradiol-treated, and (iv) ovariectomized raloxifene-treated. Intact aortic rings from sham rats and ovariectomized rats receiving raloxifene and estrogen showed a greater potentiation of the phenylephrine responses after L-NAME. Semi-quantitative reverse transcription-polymerase chain reaction indicated a gender-based difference in eNOS mRNA expression in thoracic aorta. Moreover, we demonstrated that eNOS mRNA expression in the upper thoracic aorta was significantly higher in treatment groups. These results show that chronically administered raloxifene is exerting a potentially important vasculo-protective effect by stimulating eNOS expression.

Synthesis and biological evaluation of novel thio-substituted chromanes as high-affinity partial agonists for the estrogen receptor

Synthesis of (+/-)-cis-7-hydroxy-3-phenyl-4-(4-(2-piperidinoethanethio)phenyl)chromane (13) and (+/-)-cis-7-hydroxy-3-phenyl-4-(4-(2-pyrrolidinoethanethio)phenyl)chromane (15) is presented. These compounds are representatives of a novel class of compounds with high in vitro binding affinity for the estrogen receptor (IC(50)=7-10 nM), and very low in vitro uterotrophic activity (max stim.=5-17% rel to moxestrol; EC(50)=0.5-1.8 nM).

Selective estrogen receptor modulators: tissue actions and potential for CNS protection

Significant physiologic changes occur during menopause. Evidence exists to suggest that estrogen may be neuroprotective under specific conditions. However, there are limitations in the neuroprotection afforded by standard hormone therapy. Accordingly, alternative agents with selected estrogenic effects may hold even greater promise rather than conventional hormone replacement therapy for the prevention and treatment of CNS injury. Recently, a variety of selective estrogen receptor modulators (SERMs) have been developed to retain the favorable and minimize the adverse side effects of estrogens. This review focuses on the CNS and known neuroprotective effects of two specific SERMs, raloxifene and arzoxifene. Recent studies hint that raloxifene and arzoxifene are neuroprotective and may preserve some elements of cognitive function. However, the mechanism of action is not well described and it is unclear if the beneficial effects of SERMs rely on activation of estrogen receptors.

Selective estrogen receptor modulators (SERMs) and retinoids in breast cancer chemoprevention

Tamoxifen has been shown to decrease the risk of invasive breast cancer by 49% and noninvasive breast cancer by 50%. Tamoxifen is also associated with a threefold increased risk of endometrial cancer. Raloxifene, a second-generation selective estrogen receptor modulator (SERM), has not been associated with endometrial cancer risk, and is currently under study in a large, multi-institutional, randomized Study of Tamoxifen and Raloxifene (STAR) for breast cancer prevention in postmenopausal women. A pilot trial of raloxifene in premenopausal women to assess the safety, tolerability, effects on bone mineral density, mammographic density, and other biological endpoints is ongoing. The retinoids have been shown to decrease mammary tumors in rodent carcinogenesis models. The Italian trial of fenretinide (4-HPR) in women with stage I breast cancer randomized women to fenretinide or no intervention. This study did not show an overall effect of decreasing the risk of contralateral breast cancer. However, a protective effect was suggested in premenopausal women. It has been suggested that this effect may be related to insulin-like growth factor 1 (IGF-1), which has been shown to be modulated by fenretinide in premenopausal but not postmenopausal women. Pilot studies of SERMs alone and in combination with retinoids or other agents provide a model for testing the safety and tolerability, pharmacokinetics and pharmacodynamics, and biomarker modulation in high-risk women. These studies can provide information as to both the pathophysiology of carcinogenesis and the mechanism of action of chemopreventive agents, and help select agents and doses for testing in large randomized studies.

Chemoprevention with antiestrogens: the beginning of the end for breast cancer. Daniel G. Miller Lecture

In the 1960s, compounds known as nonsteroidal antiestrogens were identified as potential contraceptives, but the drugs caused the induction of ovulation in subfertile women. Tamoxifen and clomiphene were marketed for this indication. However, tamoxifen was advanced for the treatment of breast cancer in the 1970s through a close cooperation between the laboratory and the clinical trials community. The extensive use of long-term adjuvant tamoxifen has resulted in saving the lives of 400,000 women with breast cancer. Tamoxifen is a selective estrogen receptor modulator (SERM) that produces antiestrogenic actions in the breast but estrogen-like actions in bone and lowers serum cholesterol. These properties not only allowed the application of tamoxifen as the first chemopreventive in high-risk pre- and postmenopausal women but also the development of raloxifene to prevent osteoporosis with the potential to prevent breast cancer in postmenopausal women. The future development of SERMs holds the promise of preventing osteoporosis and coronary heart disease as well as breast and endometrial cancer.

Hormone replacement therapy at the threshold of 21st century

The management of postmenopausal women has become a major focus for the medical profession. The menopause era should progress from a period of "chaos" to an orderly understanding of the many issues related to the menopause and hormone replacement therapy (HRT). Although HRT has beneficial clinical effect and positive benefit/risk ratio, understanding of the side effects and weight gain, and, especially, a fear of cancer limit compliance. New data from long-term, controlled, prospective studies on the effects of different HRT schedules on cancer, cardiovascular disease and osteoporotic fracture risk are needed. HRT should be considered either as for prevention or for individualized care since women experience menopause as individuals, care should be taken not to make inappropriate generalizations. The priority should be the administration of appropriate medication to women with the best result in order to improve health care and quality of life. New therapeutic options will offer substantial medical advancement for the treatment of postmenopausal women.

EM-652 (SCH57068), a pure SERM having complete antiestrogenic activity in the mammary gland and endometrium

In order to minimize the risks of endometrial cancer and the development of resistance to antiestrogen therapy, we have synthesized the orally active antiestrogen EM-652 which is the most potent of the known antiestrogens and exerts pure antiestrogenic activity in the mammary gland and endometrium. EM-652 inhibits the AF-1 and AF-2 functions of both ERalpha and beta while the inhibitory action of OH-TAM is limited to AF-2. EM-652, thus, inhibits Ras-induced transcriptional activity and blocks SRC-1-stimulated activity of the two receptors. The absence of blockade of AF-1 by OH-TAM could explain why resistance develops to Tamoxifen treatment. Not only the development, but also the growth of established DMBA-induced mammary carcinoma is inhibited by treatment with EM-800, the prodrug of EM-652. EM-652 is the most potent antiestrogen to inhibit the growth of human breast cancer ZR-75-1, MCF-7 and T-47D cells in vitro. When incubated with human Ishikawa endometrial carcinoma cells, EM-800 has no stimulatory effect on the estrogen-sensitive parameter alkaline phosphatase activity. When administered to ovariectomized animals, EM-800 prevents bone loss, and lowers serum cholesterol and triglyceride levels. EM-800 has shown benefits in women with breast cancer who had failed Tamoxifen. The above-summarized preclinical and clinical data clearly suggest the interest of studying this compounds in the neoadjuvant and adjuvant settings and, most importantly, for the prevention of breast and uterine cancer.

The effect of SERMs on the endometrium

Tamoxifen, the first clinically available SERM, was developed in 1966 and approved by the FDA (United States Food and Drug Administration) in 1978. It is the most prescribed antineoplastic drug in the world, with approximately 10 million women-use-years of experience. Tamoxifen has proved efficacious in all settings of breast cancer. However, in the mid-to-late 1980s, a series of letters to the editor and case reports announced an association between tamoxifen therapy in women with breast cancer and the development of endometrial carcinoma. Subsequently, in 1998, the observation of a significant 49% reduction in invasive breast cancer relative to placebo in a cohort of women at increased risk for the disease resulted in the early stopping of the National Surgical Adjuvant Breast and Bowel Project's (NSABP) P-1: Breast Cancer Prevention Trial (BCPT). Importantly, this was the first time that information became available about the effects of tamoxifen in healthy women, that is, women who did not already have breast cancer. In this healthy population, the relative risk of developing endometrial carcinoma in the tamoxifen arm was 2.54, although when stratified by age, in women over 50, the risk grew to 4.01. Thus, the risk appears to be confined to women over 50 because, in contrast, in women under 50 there was no statistically significant increase in the risk of endometrial carcinoma.

Selective estrogen receptor modulator effects on serum lipoproteins and vascular function in postmenopausal women and in hypercholesterolemic men

Epidemiological observations, clinical mechanistic studies, and basic laboratory research suggest that estrogen therapy is associated with beneficial cardiovascular effects in postmenopausal women. Estrogen has a multitude of biological effects that may account for this apparent benefit (which remains to be proved in randomized clinical trials), including favorable effects on the lipid profile, increased endothelial nitric oxide bioactivity, and enhanced fibrinolysis. However, long-term estrogen therapy increases the risk of breast and endometrial cancers. Raloxifene, a benzothiophene derivative that binds to the estrogen receptor, is a selective estrogen receptor modulator, producing estrogen-agonist effects in some tissues (liver, bone) and estrogen-antagonistic effects in others (breast, uterus), and may prove to be an option for women with atherosclerosis or its risk factors. This review updates the current knowledge of the biological effects of selective estrogen receptor modulators of potential cardiovascular importance in postmenopausal women.

Capitalizing on the complexities of estrogen receptor pharmacology in the quest for the perfect SERM

The term Selective Estrogen Receptor Modulators (SERMs) has been used of late to describe a group of pharmaceuticals that manifest estrogen receptor (ER) agonist activity in some tissues, but that oppose estrogen action in others. Whereas the name describing this class of drugs is new, the concept is not. Indeed, compounds exhibiting tissue-selective ER agonist/antagonist properties have been around for nearly 40 years. What is new is the idea that it may be possible to capitalize on the paradoxical activities of these drugs and develop them as treatments for estrogenopathies where it is desirable to direct therapy to a specific estrogen-responsive target organ. This realization has provided the impetus for research in this area and has pushed the development and clinical use of this class of drugs. The objective of this review is to describe how the medical need for SERMs arose and how recent studies of the mechanism of action of the currently available drugs are paving the way for the development of novel drugs with improved selectivity.

Increasing the sensitivity of the rodent uterotrophic assay to estrogens, with particular reference to bisphenol A

The gravimetric uterotrophic assay is currently the most well-established, short-term rodent estrogenicity assay. Increasing attention is being paid to the extent to which use of morphometric or molecular changes in the uterus could act as surrogates for the gravimetric end point of the assay, thereby perhaps increasing the sensitivity of the assay. In this paper I discuss the available data, paying particular attention to studies on bisphenol A (BPA) because it offers the largest database for consideration. I conclude that the case has yet to be made for augmenting the gravimetric end point of the uterotrophic assay. To resolve this important question, it will be necessary to conduct detailed dose-response studies where the no-observed-effect level (NOEL) for the proposed surrogate end points are compared with the NOEL for the gravimetric end point. Currently, few such studies exist, and among those that do no clear message emerges. The general trend to increasing use of molecular assays in toxicology (multigene microarrays and real-time polymerase chain reaction) emphasizes the need for clear criteria for comparing the performance of individual markers of toxicity.

Evidence for an estrogen-like action of raloxifene upon the hypothalamic-pituitary unit: raloxifene inhibits luteinizing hormone secretion and stimulates prolactin secretion in ovariectomized female rats

Selective estrogen receptor modulators (SERMs) constitute a new family of drugs with growing interest in the management of estrogen-associated pathology. Raloxifene is a SERM that is used to treat and prevent osteoporosis in postmenopausal women. The actions of raloxifene on bone, breast, uterus and serum cholesterol have been widely analyzed, but very few studies have been carried out to evaluate whether raloxifene has an estrogenic activity upon the hypothalamic-pituitary axis in the rat. For this purpose, adult female rats were ovariectomized or sham ovariectomized. One week later, the rats were implanted with intracardiac canullae and 24 h after injected daily with raloxifene (500 microg/rat/day) or vehicle for 5 days. One hour after the last injection, blood samples were obtained at 5 min intervals for a 3 h. period (10:00-13:00 h). Our results indicate that raloxifene inhibits the pulsatile nature of the post-ovariectomy hypersecretion of luteinizing hormone (LH) and increases prolactin (PRL) secretion in ovariectomized animals. These effects are suggestive of an estrogenic activity of raloxifene on LH and PRL secretion in ovariectomized females.

Ameliorative effects of Anoectochilus formosanus extract on osteopenia in ovariectomized rats

The purpose of this study was to determine ameliorative effects of crude aqueous extract of Anoectochilus formosanus (AFE) on osteopenia in ovariectomized (OVX) rats. First, all of the rats were divided into sham and OVX groups. The OVX rats were allowed to lose bone for 6 weeks. At 6 weeks post-OVX, the OVX rats were divided into four groups treated with water, 17beta-estradiol (30 microg/kg, daily s.c. injection) or AFE (0.5, 2 g/kg, daily, orally) for 12 weeks. In OVX rats, the increases of body weight and serum total cholesterol were significantly decreased by AFE or 17beta-estradiol treatment. In OVX rats, atrophy of uterus and vagina was preserved by treatment with 17beta-estradiol, but not by AFE. The decreased weight of pituitary was increased by treatment with both 17beta-estradiol and AFE. There were decreases in bone density and calcium content including the right femur and the fourth lumbar vertebra, when compared with the sham control rats. Treatment with either 17beta-estradiol or AFE ameliorated these changes induced by OVX. In addition, ovariectomy increased serum alkaline phosphatase levels. The increases were suppressed by the treatment with 17beta-estradiol and AFE. Our results demonstrated that AEF could ameliorate ovariectomy-induced osteopenia.

Randomized, double-blind, placebo-controlled study on effects of raloxifene and hormone replacement therapy on plasma no concentrations, endothelin-1 levels, and endothelium-dependent vasodilation in postmenopausal women

The endothelium is thought to play an important role in the genesis of atherosclerosis, and several lines of evidence suggest that the effect of an intervention on endothelial function might predict its involvement in coronary disease progression and in the rate of cardiovascular events. Estrogen has direct effects on the blood vessel wall, indicating that vascular endothelium may play a key role in the cardiovascular protective effects of hormone replacement therapy (HRT). Raloxifene relaxes coronary arteries in vitro by an estrogen receptor-dependent and NO-dependent mechanism, thus suggesting that this selective estrogen receptor modulator could also have beneficial effects on endothelial function. This study compared the effects of HRT and raloxifene on NO products, endothelin-1 plasma levels, and endothelium-dependent vasodilatation in postmenopausal women. Healthy postmenopausal women (n=90) were enrolled in a double-blind, randomized, placebo-controlled, 6-month trial. Women were randomly assigned to receive continuous HRT (1 mg 17beta-estradiol combined with 0.5 mg norethisterone acetate), raloxifene (60 mg/d), or placebo for 6 months. Flow-mediated endothelium-dependent vasodilation of the brachial artery, plasma NO concentrations, and endothelin levels were measured at baseline and after 6 months of therapy. The mean baseline level of NO breakdown products was 26.5+/-10.7 micromol/L and increased to 36.3+/-11.4 micromol/L after 6 months of treatment with raloxifene. The mean baseline plasma endothelin level was 17.3+/-8.9 pg/mL and decreased to 11.5+/-2.1 pg/mL after 6 months of treatment with the selective estrogen receptor modulator. The mean baseline ratio of NO (breakdown products) to endothelin was also significantly increased at the end of treatment with raloxifene. Postmenopausal women treated with HRT had similar changes in plasma nitrites/nitrates and endothelin levels as well as in the ratio of NO to endothelin. In contrast, these markers of endothelial function did not change in the placebo-treated women. Flow-mediated endothelium-dependent vasodilation of the brachial artery was 8.3+/-2.1% at baseline and increased to 12.3+/-2.1% after 6 months of treatment with raloxifene. HRT also caused a significant and similar increase in flow-mediated endothelium-dependent vasodilation. No change in flow-mediated vasodilation was observed in the participants treated with placebo. We conclude that raloxifene therapy and HRT influence endothelial function and improve flow-mediated endothelium-dependent vasodilation to a comparable extent in healthy postmenopausal women at least after a 6-month treatment period. However, further investigation is warranted to enhance our understanding of the mechanisms of the effect of raloxifene on vascular function and to determine whether its effect on endothelial function may contribute to the reduction in cardiovascular-related morbidity and mortality.

Neuroprotective properties of 17beta-estradiol, progesterone, and raloxifene in MPTP C57Bl/6 mice

Previous work from our laboratory showed prevention of 1-methyl-4-phenyl-1,2,3,6 tetrahydropyridine (MPTP) induced dopamine depletion in striatum of C57Bl/6 mice by 17beta-estradiol, progesterone, and raloxifene, whereas 17alpha-estradiol had no effect. The present study investigated the mechanism by which these compounds exert their neuroprotective activity. The hormonal effect on the dopamine transporter (DAT) was examined to probe the integrity of dopamine neurons and glutamate receptors in order to find a possible excitotoxic mechanism. Drugs were injected daily for 5 days before MPTP (four injections, 15 mg/kg ip at 2-h intervals) and drug treatment continued for 5 more days. MPTP induced a decrease of striatal DAT-specific binding (50% of control) and DAT mRNA in the substantia nigra (20% of control), suggesting that loss of neuronal nerve terminals was more extensive than cell bodies. This MPTP-induced decrease of striatal [(125)I]RTI-121 specific binding was prevented by 17beta-estradiol (2 microg/day), progesterone (2 microg/day), or raloxifene (5 mg/kg/day) but not by 17alpha-estradiol (2 microg/day) or raloxifene (1 mg/kg/day). No treatment completely reversed the decreased levels of DAT mRNA in the substantia nigra. Striatal [(125)I]RTI-121 specific binding was positively correlated with dopamine concentrations in intact, saline, or hormone-treated MPTP mice. Striatal NMDA-sensitive [(3)H]glutamate or [(3)H]AMPA specific binding remained unchanged in intact, saline, or hormone-treated MPTP mice, suggesting the unlikely implication of changes of glutamate receptors in an excitotoxic mechanism. These results show a stereospecific neuroprotection by 17beta-estradiol of MPTP neurotoxicity, which is also observed with progesterone or raloxifene treatment. The present paradigm modeled early DA nerve cell damage and was responsive to hormones.

Effects of raloxifene treatment on uterine leiomyomas in postmenopausal women

OBJECTIVE

To evaluate the effects of raloxifene administration on uterine and uterine leiomyoma sizes in postmenopausal women.

DESIGN

Prospective randomized, double-blind, placebo-controlled clinical trial.

SETTING

Department of Gynecology, Obstetrics, and Pathophysiology of Human Reproduction, University of Naples "Federico II", Italy.

PATIENT(S)

Seventy spontaneous postmenopausal women affected by uterine leiomyomas.

INTERVENTION(S)

Twelve cycles (of 28 days each) of treatment with raloxifene (60 mg daily per os) or placebo.

MAIN OUTCOME MEASURE(S)

At entry and at every 3 cycles, uterine and uterine leiomyoma dimensions were measured by means of transvaginal ultrasound. The difference between uterine and leiomyoma volumes (Delta size) was calculated in all subjects. The characteristics of uterine bleeding and the side effects of the treatments were assessed using a daily diary.

RESULT(S)

After 6, 9, and 12 cycles of therapy, in subjects treated with raloxifene, the mean uterine and uterine leiomyoma size were significantly decreased, and the mean Delta size significantly increased in comparison with basal values and the placebo group. No significant differences in uterine bleeding were detected between the two groups.

CONCLUSION(S)

In postmenopausal women raloxifene appears to act selectively on uterine leiomyomas, reducing their size.

Clinical use of selective estrogen receptor modulators

The concept of selective estrogen receptor modulators (SERMs) is derived from the observation that tamoxifen, an effective adjuvant therapy of breast cancer that has an antiestrogenic effect on breast tissue, has estrogen-like effects on the skeleton and on plasma lipoproteins. Raloxifene is a SERM that has undergone extensive clinical investigation in the prevention and treatment of postmenopausal osteoporosis. It prevents bone loss at all skeletal sites, and in a large trial in osteoporotic women, the incidence of vertebral fractures was significantly decreased (relative risk 0.64) after up to 4 years of treatment with raloxifene 60 mg. The decrease of nonvertebral fractures did not reach the level of significance. Raloxifene decreased significantly the incidence of breast cancer (relative risk 0.28) and has no effect on the risk of endometrial cancer. SERMs are likely to play an important role in the management of postmenopausal women.

Levormeloxifene prevents increased bone turnover and vertebral bone loss following ovariectomy in cynomolgus monkeys

Levormeloxifene, a nonsteroidal selective estrogen receptor modulator (SERM), has been evaluated for its effects on bone in cynomolgus monkeys (Macaca fascicularis). Adult female monkeys were imported from Indonesia and randomized into six groups of 25-28 animals each (n = 158). Animals in one group were sham ovariectomized (sham) and received vehicle. Animals in the remaining five groups were ovariectomized and received either vehicle (ovx); 17beta-estradiol at 0.016 mg/kg (est); or levormeloxifene at 0.5 (L1), 1 (L2), or 5 (L3) mg/kg. Lumbar spine and whole body bone mass were measured by dual-energy X-ray absorptiometry (DXA) pretreatment and at 6 and 12 months following the initiation of treatment. Bone mass at the femoral neck was measured by peripheral quantitative computed tomography (pQCT) at 0 and 12 months. Serum markers of bone turnover, including bone-specific alkaline phosphatase (BSAP), osteocalcin (BGP), tartrate-resistant acid phosphatase (TRAP), and urinary collagen C-terminal extension peptides (CrossLaps), were measured at 0, 6, and 12 months. Ovariectomy resulted in an increase in these markers; the increase was prevented by estradiol or levormeloxifene. Estradiol or levormeloxifene inhibited loss of lumbar spine bone mineral density (BMD) following ovariectomy compared with untreated monkeys (ovx -5.0%; sham -0.4%; est +0.2%; L1 -3.6%, L2 -2.0%, L3 -2.5%). Estradiol, but not levormeloxifene, prevented loss of BMD at the femoral neck (ovx -7.4%; sham -3.1%; est -3.6%; L1 -8.0%, L2 -6.5%, L3 -7.8%), and whole body bone mineral content (BMC) (ovx -7.6%; sham -1.9%, est -2.9%; L1 -6.2%, L2 -6.1%, L3 -6.7%). Bone loss at each site was correlated with bone turnover as measured by serum and urine biomarkers. There was no dose effect of levormeloxifene.

A non-calcemic analog of 1 alpha,25 dihydroxy vitamin D(3) (JKF) upregulates the induction of creatine kinase B by 17 beta estradiol in osteoblast-like ROS 17/2.8 cells and in rat diaphysis

We have reported that multiple treatments with so-called 'non-hypercalcemic' analogs of 1 alpha,25(OH)(2) vitamin D(3) (1,25(OH)(2)D(3)) stimulate the specific activity of creatine kinase BB (CK) in ROS 17/2.8 osteoblast-like cells, and that pretreatment with these analogs upregulates responsiveness and sensitivity to 17 beta estradiol (E(2)) for the induction of CK. However, since the analogs showed toxicity in vivo, we have now studied the action of a demonstrably non-calcemic hybrid analog of vitamin D in ROS 17/2.8 cells, and prepubertal rats. The analog JKF was designed to separate its calcemic activity from other biological activities by combining a calcemic-lowering 1-hydroxymethyl group with a potentiating C, D-ring side chain modification including 24 difluoronation. Treatment with 1 pM JKF alone significantly stimulated CK specific activity at 4 h by 30+/-10%. However after three daily pretreatments, JKF upregulated the extent of induction by 30 nM E(2) by 33% at 1 pM and by 97% at 1 nM; the E(2) dose needed for a significant stimulation of CK activity was lowered to 30 pM. The action of the SERMS tamoxifen, tamoxifen methiodide and raloxifene, at 3 microM, was also upregulated by three daily pretreatments with 1 nM JKF; unexpectedly, this pretreatment prevented the inhibition of E(2) stimulation by the SERMS. Upregulation of E(2) action by 1 nM JKF was inhibited by 1 nM ZK159222, an inhibitor of the nuclear action of 1,25(OH)(2)D(3). In vivo, three daily injections of 0.05 ng/g body weight of JKF augmented the response of prepubertal female rat diaphysis and epiphysis to E(2). Therefore, demonstrably non-calcemic analogs of 1,25(OH)(2)D(3) may have potential for use in combination with estrogens or SERMS in the prevention and/or treatment of metabolic bone diseases such as postmenopausal osteoporosis.

Identification of new triarylethylene oxyalkanoic acid analogues as bone selective estrogen mimetics

Previously, the estrogen receptor (ER) ligand 4-[1-(p-hydroxyphenyl)-2-phenylethyl]phenoxyacetic acid (5) was found to have differential bone loss suppressive effects in the ovariectomized (OVX) rat approaching those of selective ER modulators (SERMs) such as tamoxifen. In an effort to improve efficacy, analogues of this compound were prepared which incorporated features designed to reduce polarity/ionizability. Thus, the acetic acid side chain of 5 was replaced by n-butanoic acid and 1H-tetrazol-4-ylmethyl moieties, to give 8 and 10, respectively. Also, the phenolic hydroxyl of 5 was replaced, giving deoxy analogue 9. We also developed new methods for the synthesis of triarylethylene variants of 5 and 9, namely 4-([1-(p-hydroxyphenyl)-2-phenyl-1-butenyl]phenoxy)-n-butanoic acid (6) and its des-hydroxy counterpart (7), because the former of these had in vitro antiestrogenic effects characteristic of known SERMs. In the OVX rat, 6 and 7 were as effective as 17 beta-estradiol in suppressing serum markers of bone resorption/turnover, namely osteocalcin and deoxypyridinoline, but had only 30% of the uterotrophic efficacy of 17 beta-estradiol. This study has thus identified two triarylethylene oxybutyric acids, 6 and 7, that have differential bone/uterus effects like those of known SERMs.

From adjuvant therapy to breast cancer prevention: BCPT and STAR

The continued widespread prevalence of breast cancer supports placing a high priority on research aimed at its primary prevention, particularly among women who are at increased risk for developing this disease. The suggestion of potential agents for the primary chemoprevention of breast cancer evolved out of the treatment setting. Extensive experience with tamoxifen, a first-generation selective estrogen receptor modulator (SERM) showing efficacy, first, in the treatment of advanced breast cancer and, subsequently, as adjuvant therapy for early stage disease established the safety of this agent. Cumulative data from multiple adjuvant studies documented the efficacy of tamoxifen in reducing second primary breast cancers in the contralateral breast, supporting its potential as a chemopreventive agent for breast cancer. The safety and second primary data on tamoxifen, together with extensive information on its pharmacokinetics, metabolism, and antitumor effects, as well as its potentially beneficial effects on lipid metabolism and osteoporosis, led the National Surgical Adjuvant Breast and Bowel Project (NSABP) to select tamoxifen for testing in the first prospective randomized phase III trial of the efficacy of a chemopreventive agent for preventing breast cancer in women at increased risk of the disease. Accordingly, in 1992 the NSABP started the Breast Cancer Prevention Trial (P-1) in which 13,388 women > or = 35 years of age who were at increased risk of breast cancer according to Gail model risk factors [family history, age, and personal history (i.e., age at first birth, age at menarche, previous breast biopsies)] were randomized to tamoxifen 20 mg/day or placebo for 5 years. Through 69 months of follow-up tamoxifen reduced the risk of invasive breast cancer, primarily estrogen receptor-positive tumors, by 49% (two-sided p < 0.00001). Tamoxifen reduced the risk of noninvasive breast cancer by 50% (two-sided p < 0.002). In addition, tamoxifen reduced fractures of the hip, radius, and spine, but it had no effect on the rate of ischemic heart disease. As previously shown, the rates of endometrial cancer and vascular events increased with tamoxifen. With the P-1 results establishing tamoxifen as the standard of care for the primary chemoprevention of breast cancer in high-risk women, concern over the side effects of tamoxifen has prompted a continuing search for an agent that displays a more desirable efficacy/toxicity profile. Raloxifene, a second-generation SERM approved for the prevention of osteoporosis in postmenopausal women, displays antiestrogenic properties in the breast and possibly the endometrium, and estrogenic effects in the bone and on the lipid profile, suggesting it as a candidate for comparison with the chemopreventive standard, tamoxifen. Raloxifene will be compared to tamoxifen in an equivalency trial, the Study of Tamoxifen and Raloxifene (STAR) NSABP P-2, which began in July 1999 at almost 500 centers in North America. The plan is to randomize 22,000 postmenopausal women > or = 35 years of age at increased risk of breast cancer by Gail criteria to tamoxifen 20 mg/day or raloxifene 60 mg/day for 5 years. Study endpoints include invasive and noninvasive breast cancer, cardiovascular disease, endometrial cancer, bone fractures, and vascular events.

Soybean ethanol extract increases the function of osteoblastic MC3T3-E1 cells

To investigate the bioactivities of soybean, which act on bone metabolism, we studied the effect of a soybean ethanol extract on the activity of osteoblast MC3T3-E1 cells. Soy extract (0.01-0.1 g/l) dose-dependently increased survival (P<0.05) and DNA synthesis (P<0.05) of MC3T3-E1 cells. In addition, soy extract (0.05 g/l) increased alkaline phosphatase activity (P<0.05) and collagen synthesis (P<0.05) of MC3T3-E1 cells. Moreover, the anti-estrogen tamoxifen eliminated the stimulation of MC3T3-E1 cells on the proliferation, ALP activity and collagen synthesis by soy extract, indicating that the main action of the soy extract on osteoblastic MC3T3-E1 cells is similar to that of estrogen effects. Treatment with soy extract prevented apoptosis, as assessed by a one-step sandwich immunoassay and DNA gel electrophoresis studies. This effect may be associated with the activation of the estrogen receptor, since we observed soy extract-mediated survival against apoptosis was blocked by the estrogen receptor antagonist tamoxifen in cells, further supporting a receptor-mediated mechanism of cell survival. These results suggest that osteoblast function is promoted by soy extract and that the estrogen receptor is involved in the response, thereby playing an important role in bone remodeling. In conclusion, soy extract has a direct stimulatory effect on bone formation in cultured osteoblastic cell in vitro. Presumably, dietary soy products are useful in the prevention of osteoporosis.

Lasofoxifene (CP-336,156) protects against the age-related changes in bone mass, bone strength, and total serum cholesterol in intact aged male rats

The purpose of this study was to evaluate if long-term (6 months) treatment with lasofoxifene (LAS), a new selective estrogen receptor modulator (SERM), can protect against age-related changes in bone mass and bone strength in intact aged male rats. Sprague-Dawley male rats at 15 months of age were treated (daily oral gavage) with either vehicle (n = 12) or LAS at 0.01 mg/kg per day (n = 12) or 0.1 mg/kg per day (n = 11) for 6 months. A group of 15 rats was necropsied at 15 months of age and served as basal controls. No significant change was found in body weight between basal and vehicle controls. However, an age-related increase in fat body mass (+42%) and decrease in lean body mass (-8.5%) was observed in controls. Compared with vehicle controls, LAS at both doses significantly decreased body weight and fat body mass but did not affect lean body mass. No significant difference was found in prostate wet weight among all groups. Total serum cholesterol was significantly decreased in all LAS-treated rats compared with both the basal and the vehicle controls. Both doses of LAS treatment completely prevented the age-related increase in serum osteocalcin. Peripheral quantitative computerized tomography (pQCT) analysis at the distal femoral metaphysis indicated that the age-related decrease in total density, trabecular density, and cortical thickness was completely prevented by treatment with LAS at 0.01 mg/kg per day or 0.1 mg/kg per day. Histomorphometric analysis of proximal tibial cancellous bone showed an age-related decrease in trabecular bone volume (TBV; -46%), trabecular number (Tb.N), wall thickness (W.Th), mineral apposition rate, and bone formation rate-tissue area referent. Moreover, an age-related increase in trabecular separation (Tb.Sp) and eroded surface was observed. LAS at 0.01 mg/kg per day or 0.1 mg/kg per day completely prevented these age-related changes in bone mass, bone structure, and bone turnover. Similarly, the age-related decrease in TBV and trabecular thickness (Tb.Th) and the age-related increase in osteoclast number (Oc.N) and osteoclast surface (Oc.S) in the third lumbar vertebral cancellous bone were completely prevented by treatment with LAS at both doses. Further, LAS at both doses completely prevented the age-related decrease in ultimate strength (-47%) and stiffness (-37%) of the fifth lumbar vertebral body. These results show that treatment with LAS for 6 months in male rats completely prevents the age-related decreases in bone mass and bone strength by inhibiting the increased bone resorption and bone turnover associated with aging. Further, LAS reduced total serum cholesterol and did not affect the prostate weight in these rats. Our data support the potential use of a SERM for protecting against the age-related changes in bone and serum cholesterol in elderly men.

Mechanism of action of estrogens and selective estrogen receptor modulators

Estrogen, one of several sex steroid hormones, mediates its actions through the estrogen receptor. The estrogen receptor (ER) has two subtypes, ER alpha and ER beta, each of which predominates in specific tissues and organs. Cofactor proteins interact with the ER to maximize ligand-dependent transactivation of target-gene promoters. The estrogen response element is the final step in estrogen-mediated gene regulation, and current research is focused on alternate response elements. The resulting biologic action can vary according to the specific type of ER, cofactor milieu, response element, and ligand. Selective estrogen receptor modulators (SERMs) exhibit tissue-specific estrogen agonist or antagonist activity. The SERM raloxifene, which binds to ER and targets a distinct DNA element, may distinguish agonist vs antagonist activity by ER subtype and has unique activity among other SERMs because of its molecular conformation. Phytoestrogens, a potential alternative to hormone replacement therapy and for cancer prevention, do not consistently mimic estrogen's activity. Different types of phytoestrogens have different potencies, and taking high-dose supplements after menopause may not emulate the apparent benefits of lifelong consumption of phytoestrogen-rich diets. In conclusion, the complexity of estrogen action--through different ER subtypes, with various cofactors, on alternate response element--is further enhanced by ligands with selective estrogen activity. Additional research is needed to elucidate these pathways and the resulting biological effects.

Structural insights into the mode of action of a pure antiestrogen

BACKGROUND

Estrogens exert their effects on target tissues by binding to a nuclear transcription factor termed the estrogen receptor (ER). Previous structural studies have demonstrated that each class of ER ligand (agonist, partial agonist, and SERM antagonist) induces distinctive orientations in the receptor's carboxy-terminal transactivation helix. The conformation of this portion of the receptor determines whether ER can recruit and interact with the components of the transcriptional machinery, thereby facilitating target gene expression.

RESULTS

We have determined the structure of rat ERbeta ligand binding domain (LBD) in complex with the pure antiestrogen ICI 164,384 at 2.3 A resolution. The binding of this compound to the receptor completely abolishes the association between the transactivation helix (H12) and the rest of the LBD. The structure reveals that the terminal portion of ICI's bulky side chain substituent protrudes from the hormone binding pocket, binds along the coactivator recruitment site, and physically prevents H12 from adopting either its characteristic agonist or AF2 antagonist orientation.

CONCLUSIONS

The binding mode adopted by the pure antiestrogen is similar to that seen for other ER antagonists. However, the size and resultant positioning of the ligand's side chain substituent produces a receptor conformation that is distinct from that adopted in the presence of other classes of ER ligands. The novel observation that binding of ICI results in the complete destabilization of H12 provides some indications as to a possible mechanism for pure receptor antagonism.

The role of selective estrogen receptor modulators in the prevention and treatment of osteoporosis

Osteoporosis can affect almost everyone in the population, and although clinical outcome of fracture is manifested in late life, the disease process begins in the early postmenopausal years in women. The pharmacologic agents currently available for osteoporosis prevention and treatment act by inhibiting bone resorption, and include estrogen or hormone replacement therapy (estrogen with progestin), bisphosphonates, salmon calcitonin nasal spray, and selective estrogen receptor modulators (SERMs). Raloxifene is a benzothiophene SERM that has estrogen against effects in bone and on serum lipid metabolism and estrogen antagonist effects on breast and uterine tissue. This article summarizes the effects of these antiresorptive agents, as measured by changes in bone mineral density, biochemical markers of bone turnover, and incident fractures in postmenopausal osteoporosis.

Hormone replacement therapy and fractures in older adults

Estrogen deficiency in women is associated with accelerated bone loss, and estrogen replacement therapy has been proven to be effective in preventing osteoporosis and fractures in postmenopausal women. The introduction of selective estrogen receptor modulators that have an estrogen-like effect on the skeleton but have a different pattern of effects on other tissues may have an important role in the management of osteoporosis in women in the near future. In men, androgen deficiency has been shown to be associated with osteoporosis. Although androgen replacement in hypogonadal men may decrease bone resorption and increase bone mass, long-term placebo-controlled trials are needed to better define the benefits and risks of such therapy before it can be recommended. Sex hormone deficiency is linked to the development of osteoporosis in both women and men. In women, hormonal replacement by estrogen or the newly developed selective estrogen receptor modulators may prevent the development of osteoporosis and its related fractures. In men, there is early evidence that testosterone replacement therapy may enhance bone mass in hypogonadal men.

Raloxifene and estrogen reduces progression of advanced atherosclerosis--a study in ovariectomized, cholesterol-fed rabbits

The present study investigated the effect of raloxifene, a selective estrogen receptor modulator (SERM), on aortic atherosclerosis in 80 ovariectomized, cholesterol-fed rabbits with pre-induced atherosclerosis. The animals were fed an atherogenic diet containing 240 mg cholesterol/day for 15 weeks, after this period a baseline control group was sacrificed. Thereafter, oral treatment was initiated with either estradiol 4 mg/day (n=20), raloxifene (210 mg/day) or placebo (n=20). In the treatment period of 39 weeks, the dietary cholesterol content was reduced to 80 mg cholesterol/day. Postmortem evaluation showed a significantly increased uterine weight induced by estradiol treatment (10.3+/-1.2 g), whereas raloxifene intervention caused a decreased uterus weight (1.21+/-0.1 g) when compared to placebo (2.48+/-0.47 g). Throughout the study, serum lipids increased in all groups to levels seen in very high risk humans. After 58 weeks the cholesterol content in the aorta was 3.18+/-0.54 micromol/cm(2) (38% reduction) in the estradiol group, 3.66+/-0.52 micromol/cm(2) (29% reduction) in the raloxifene group and 5.12+/-0.60 micromol/cm(2) in the placebo group. Analyses of the aortic cholesterol content corrected for time-averaged serum cholesterol revealed that both estradiol and raloxifene therapy significantly reduced the progression of atherosclerosis (P<0.01 for both) as compared to placebo.

Sex steroids and bone

Sex steroids are essential for skeletal development and the maintenance of bone health throughout adult life, and estrogen deficiency at menopause is a major pathogenetic factor in the development of osteoporosis in postmenopausal women. The mechanisms by which the skeletal effects of sex steroids are mediated remain incompletely understood, but in recent years there have been considerable advances in our knowledge of how estrogens and, to a lesser extent androgens, influence bone modeling and remodeling in health and disease. New insights into estrogen receptor structure and function, recent discoveries about the development and activity of osteoclasts, and lessons learned from human and animal genetic mutations have all contributed to increased understanding of the skeletal effects of estrogen, both in males and females. Studies of untreated and treated osteoporosis in postmenopausal women have also contributed to this knowledge and have provided unequivocal evidence for the potential of high-dose estrogen therapy to have anabolic skeletal effects. The development of selective estrogen receptor modulators has provided a new approach to the prevention of osteoporosis and other major diseases of menopause and has implications for the therapeutic use of other steroid hormones, including androgens. Further elucidation of the mechanisms by which sex steroids affect bone thus has the potential to improve the clinical management not only of osteoporosis, both in men and women, but also of a number of other diseases related to sex hormone status.

Paradoxical interactions among estrogen receptors, estrogens and SERMS: mutual annihilation and synergy

The phenomenon of mutual annihilation of action between 17beta estradiol (E(2)) and a selective estrogen receptor modulator (SERM), previously described in prepubertal rat diaphysis, epiphysis and uterus, has been investigated in ROS 17/2.8 rat osteoblastic cells and in transiently co-transfected cells in culture. In ROS 17/2.8 cells, the estrogen-induced marker enzyme creatine kinase B (CKB) was stimulated by raloxifene, tamoxifen and tamoxifen methiodide to a specific activity equal to or greater than that induced by 10 nM E(2). However, when a fully inhibitory dose of any of these SERMS was given simultaneously with E(2), no stimulation of CK activity resulted. Therefore, SERMS can be full agonists when acting alone, but complete antagonists to a super-physiological dose of estrogen. It is expected that excess tamoxifen would prevent the action of a SERM, but that the agonist activity of a SERM is abolished by 1000-fold less estrogen is a phenomenon without obvious explanation by classical pharmacology of competitive inhibition. To probe the mechanism of this interaction further, a ckb-CAT reporter plasmid, plus the human receptor expression plasmid, HEO, was transfected transiently into several cell types. In MCF-7 cells, a 1:10 ratio of E(2) to tamoxifen produced mutual annihilation, but the same ratio in ROS 17/2.8 or HeLa cells led to synergistic stimulation. In HeLa cells, co-transfected with the more efficient wild-type estrogen receptor plasmid, HEGO, synergy was demonstrated only at sub-saturation levels of HEGO. We speculate that, in the presence of estradiol and a SERM, not only active homodimers would be formed, but also hetero-dimers of estrogen-liganded and tamoxifen-liganded receptor monomers, depending on the molar ratio of their ligands and their relative affinities. The resulting hetero-dimer conformation would change the specific receptor surface for interactions with the growing number of co-activators and co-repressors, structural changes which could help to explain the mutual annihilation and synergy phenomena and their cell selectivity.

Cardiovascular effects of raloxifene hydrochloride

Raloxifene hydrochloride binds to the estrogen receptor and shows tissue-selective effects; thus, it belongs to a class of drugs recently described as selective estrogen receptor modulators (SERMs). Tissue selectivity of raloxifene may be achieved through several mechanisms: the ligand structure, interaction of the ligand with different receptor subtypes in various tissues, and intracellular events after ligand binding. Raloxifene has estrogen-agonist effects on bone and lipids and estrogen antagonist effects on the breast and uterus. In addition to its well established effects on osteoporosis, recent preclinical and clinical findings suggest that raloxifene also possesses beneficial effects on the cardiovascular system. These findings indicated that raloxifene may have cardioprotective properties without an increased risk of cancer or other side effects. Raloxifene has been shown to reduce total and low-density lipoprotein cholesterol concentrations in plasma, an effect similar to that produced by estrogens. Unlike estrogens, however, raloxifene does not increase high-density lipoprotein cholesterol and triglyceride levels in plasma. Endothelium is thought to play an important role in the genesis of atherosclerosis. Several lines of evidence suggest that an intervention with endothelial function might influence the progression of coronary disease and the incidence of cardiovascular events. Raloxifene increases the nitric oxide/endothelin-1 ratio, and improves endothelium-dependent vasomotion in post-menopausal women to the same extent as estrogens. Furthermore, in two randomized trials on post-menopausal women raloxifene reduced homocysteine levels, another independent risk factor for the development of cardiovascular disease. Although estrogens remain the drugs of choice in the hormonal therapy of most postmenopausal women, raloxifene may represent and alternative in women who are at risk of coronary artery disease.

Mechanism of action and preclinical profile of raloxifene, a selective estrogen receptor modulation

Raloxifene possesses a complex pharmacology with tissue-selective estrogen agonist and antagonist effects. At the center of these effects resides the high affinity interaction of raloxifene with the ER. The ability of raloxifene to compete with estrogen for ER binding accounts for the estrogen antagonist effects of raloxifene in uterine and mammary tissue. Since the precise mechanism for the agonist effect of estrogen on the skeleton remains uncertain, it is difficult to unequivocally cite a single estrogen-like mechanism for raloxifene in bone. However, multiple lines of evidence clearly indicate that the estrogen agonist effect of raloxifene on bone is also mediated via an interaction with ER. The data showing non-additivity of raloxifene and estrogen effects in bone, and those showing the requirement for a pituitary hormone in the anti-estrogenic action of raloxifene and estrogen are particularly important. Thus, global evaluation of the similarities and parallel responses of raloxifene and estrogen in bone and the cardiovascular system, as summarized above, strongly support a similar mechanistic basis for the agonist effects of these agents on the skeleton.