The selective oestrogen receptor modulator, LY362321, is not neuroprotective in a rat model of transient focal ischaemia.

Selective oestrogen receptor modulators (SERMs) may offer improved alternatives to oestrogen as neuroprotectants in experimental stroke. The present study investigated the role of a novel SERM, LY362321, in a rat model of transient middle cerebral artery occlusion (MCAO). Female Sprague-Dawley rats were ovariectomised and began receiving daily s.c. injections of either 1 mg/kg (n = 13), 10 mg/kg (n = 14) of LY362321, or vehicle (n = 13). The left MCA was temporarily occluded (90 min), with cortical blood flow monitoring, at 12 days post ovariectomy. Sensorimotor function was assessed using a neurological score prior to the MCAO and daily for 3 days following the MCAO. Tissue was processed for infarct volume assessment using 2,3,5-triphenyltetra-zolium chloride staining. The results indicated that there were no significant differences amongst groups in cortical blood flow during the MCAO. Furthermore, there was no significant difference in infarct size amongst vehicle, 1, and 10 mg/kg treated animals: 22.9 +/- 5.0, 16.7 +/- 4.2, and 21.1 +/- 4.1, respectively, one-way anova [F(2,32) = 0.542, P = 0.587]. The MCAO induced a significant decline in neurological score in the vehicle group (from 14 to 7 at 24 h post-MCAO) but this was not significantly affected by LY362321 at either dose. In conclusion, pretreatment with a low or high dose of the novel SERM LY362321 did not significantly influence cerebral blood flow, infarct volume, or sensorimotor function in rats exposed to transient MCAO.

Inhibition of glycinamide ribonucleotide formyltransferase results in selective inhibition of macrophage cytokine secretion in vitro and in vivo efficacy in rat adjuvant arthritis.

OBJECTIVE: To determine the effects of a glycinamide ribonucleotide formyltransferase (GARFT) inhibitor on macrophage inflammatory processes and in vivo in rat adjuvant arthritis. METHODS: GARFT inhibitors, LY309886 (6S-2',5'-thienyl-5, 10-dideazatetrahydrofolic acid) and LY329201 (R)-N-[[5-[2-(2-amino-1,4,5,6,7,8-hexahydro-4-oxopyrido[2,3-d]pyrimidin-6-yl)ethyl]-2-thienyl]carbonyl]-L-glutamatic acid disodium salt, were investigated in vitro and ex vivo on primary murine peritoneal macrophages and in the RAW macrophage cell line for both purine depletion and inhibition of LPS induced monokine secretion. In vivo efficacy following GARFT inhibition was evaluated in modified rat adjuvant arthritis. RESULTS: LY309886 inhibited purine biosynthesis in the RAW cell line with an EC50 of 90 nM, an effect readily reversible with exogenous hypoxanthine. LY309886 and LY329201 also inhibited LPS induced TNF alpha and MIP1 alpha in these cells and in primary macrophages. A similar effect could be demonstrated ex vivo with mice dosed for two days with 3 mg/kg of LY329201. LY329201 as well as methotrexate demonstrated a dose dependent reduction in both paw and spleen weight and improved joint histology following 2 weeks of dosing in a rat adjuvant arthritis study. CONCLUSION: These results suggest that GARFT inhibitors should be tested in the treatment of rheumatoid arthritis by considering their mechanism of action, here successfully tested on activated macrophages.

The nongenotropic synthetic ligand 4-estren-3alpha17beta-diol is a high-affinity genotropic androgen receptor agonist.

The nongenotropic ligand estren (Science 298:843-846, 2002) was evaluated for its transcriptional activity mediated by the human androgen receptor (AR). Our results show that estren can bind, translocate, transactivate, and regulate two known target genes of AR in androgen-responsive cell lines. Estren binds recombinant AR with 10-fold higher affinity than either estrogen receptor (ER)-alpha or ERbeta. Estren-bound AR can translocate AR to the nucleus and stimulate the androgen response element-luciferase reporter activity with an efficacy similar to that of androgen. Estren also increased the expression of prostate-specific antigen (PSA) in a dose-dependent manner in human LnCaP cells. Using chromatin immunoprecipitation analysis, we show that the estren-bound AR coimmunoprecipitates with a region of the PSA gene promoter. Therefore, cotreatment with an AR antagonist, bicalutamide, blocked the estren-induced increase in PSA expression. In contrast, phosphoinositol 3-kinase inhibitor wortmannin, or extracellular signal-regulated kinase inhibitor 1,4-diamino-2,3-dicyano-1,4-bis(2-aminophynyltio)butadiene (U0126), and ER antagonist ICI-182780 failed to block the effects of estren. In vivo analysis of estren's action on male-orchidectomized ICR mice revealed estren's AR agonist actions on the levator ani and seminal vesicle target tissues. Taken together, our results reveal the hitherto unidentified genotropic action of estren mediated by AR in androgen-responsive cells and tissues.

Differential effects of estrogen and raloxifene on messenger RNA and matrix metalloproteinase 2 activity in the rat uterus.

A detailed analysis of the differential effects of estrogen (E) compared to raloxifene (Ral), a selective estrogen receptor modulator (SERM), following estrogen receptor (ER) binding in gynecological tissues was conducted using gene microarrays, Northern blot analysis, and matrix metalloproteinase (MMP) 2 activity studies. We profiled gene expression in the uterus following acute (1 day) and prolonged daily (5 wk) treatment of E and Ral in ovariectomized rats. Estrogen regulated twice as many genes as Ral, largely those associated with catalysis and metabolism, whereas Ral induced genes associated with cell death and negative cell regulation. Follow-up studies confirmed that genes associated with matrix integrity were differentially regulated by Ral and E at various time points in uterine and vaginal tissues. Additional experiments were conducted to determine the levels of MMP2 activity in uterus explants from ovariectomized rats following 2 wk of treatment with E, Ral, or one of two additional SERMs: lasofoxifene, and levormeloxifene. Both E and lasofoxifene stimulated uterine MMP2 activity to a level twofold that of Ral, whereas levormeloxifene elevated MMP2 activity to a level 12-fold that of Ral. These data show that one of the significant differences between E and Ral signaling in the uterus is the regulation of genes and proteins associated with matrix integrity. This may be a potential key difference between the action of SERMs in the uterus of postmenopausal women.

Central and peripheral temperature changes in sheep following ovariectomy.

OBJECTIVES: To determine if ovariectomized ewes undergo periodic body temperature rises (hot flashes) similar to women at menopause. METHODS: Eighteen mature ewes were assigned to ovariectomy (OVX), ovariectomy+17 beta-estradiol implant (OVXE) or Sham. Electronic temperature loggers placed subcutaneously over the carotid artery and within the abdomen (core) and subcutaneously in the thigh and axilla (peripheral) were programmed to record body temperatures every 2.5 min for 59 days. Circadian rhythm changes were avoided by dividing readings into 1 h intervals. Hot flashes were defined as a 0.2 or 0.4 degrees C increase over the minimum temperature recorded for a 1 h interval for each sheep. RESULTS: Logger placement did not reflect core and peripheral temperatures. The carotid and abdominal sites were most useful. The percentage of readings considered HF at the carotid site was 63% OVX, 54% OVXE and 37% Sham (P<0.001), and at the abdominal site were 32% OVX, 15% OVE and 17% Sham (P<0.001). When only the first 7 days after ovariectomy were analyzed, the percentage of readings considered to be HF at the carotid site was 75% OVX, 63% OVXE, and 49% Sham (P<0.001), and at the abdominal site was 35% OVX, 15% OVXE and 17% Sham (P<0.001). CONCLUSIONS: Ovariectomy in the ewe does illicit changes in body temperature compared with control ewes, which may be interpreted as HF. However, shifts in the circadian rhythm were not apparent. Estradiol treatment led to milder and less frequent HF. Periodic HF in species other than rats have heretofore not been reported.

Arzoxifene, a new selective estrogen receptor modulator for chemoprevention of experimental breast cancer.

Arzoxifene ([6-hydroxy-3-[4-[2-(1-piperidinyl)-ethoxy]phenoxy]-2-(4-methoxyphenyl)]benzo[b]thiophene) is a selective estrogen receptor modulator (SERM) that is a potent estrogen antagonist in mammary and uterine tissue while acting as an estrogen agonist to maintain bone density and lower serum cholesterol. Arzoxifene is a highly effective agent for prevention of mammary cancer induced in the rat by the carcinogen nitrosomethylurea and is significantly more potent than raloxifene in this regard. Arzoxifene is devoid of the uterotrophic effects of tamoxifen, suggesting that, in contrast to tamoxifen, it is unlikely that the clinical use of arzoxifene will increase the risk of developing endometrial carcinoma.

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.

Photochemical synthesis of N-arylbenzophenanthridine selective estrogen receptor modulators (serms).

Selective estrogen receptor modulators are an emerging class of pharmaceutically important molecules. Many compounds in this class contain an aminoethoxyaryl moiety attached to a polycyclic framework at an asymmetric carbon atom. To assess whether this carbon atom can be replaced by nitrogen, we have employed a Ninomiya enamide photocyclization for the rapid synthesis of a novel N-arylbenzophenanthridine framework, 4. Further elaboration of 4 into a new structural class of achiral, nonsteroidal estrogen receptor modulators is described.

The effect of raloxifene on coronary arteries in aged ovariectomized ewes.

BACKGROUND: Ovariectomized sheep are a useful model of postmenopausal osteoporosis and other postmenopausal conditions. Estrogen may have a protective effect on the coronary arteries in postmenopausal women. The effects of raloxifene, a selective estrogen receptor modulator, on coronary arteries in aged ovariectomized ewes was investigated. METHODS AND RESULTS: Forty eight aged ewes were randomly assigned to undergo sham surgery (Sham, n = 7), ovariectomy (OVX, n = 10), ovariectomy with estradiol supplementation (OVXE, n = 8), ovariectomy with raloxifene supplementation, 0.02 mg/kg per day (RAL1, n = 10), or ovariectomy with raloxifene supplementation, 0.10 mg/kg per day (RAL2, n = 13). Contrast coronary angiography was performed 6 months after intervention. Diameters of the right main and left anterior descending coronary arteries in the RAL1, RAL2 and Sham groups were not different from each other, but were significantly greater than the OVX and OVXE groups. Intracoronary nitroglycerin did not affect the relationships of the diameters in any group. There were no differences in vascular remodeling between the groups. CONCLUSIONS: The results indicate that raloxifene in this sheep model allows greater dilation of coronary arteries than estrogen. Raloxifene may provide a significant protective functional effect on coronary arteries in postmenopausal heart disease.

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.

Raloxifene and estradiol benzoate both fully restore hippocampal choline acetyltransferase activity in ovariectomized rats.

Selective estrogen receptor modulators (SERMs) demonstrate tissue-specific estrogen receptor (ER) agonist or antagonist properties. Raloxifene, a prototypical SERM, has ER agonist properties in bone and on cholesterol metabolism but full antagonist properties in the uterus and breast. To characterize the ER agonist/antagonist profile of raloxifene in the brain, we have examined its effect on the activity of a known estrogen-responsive gene product, choline acetyltransferase (ChAT), in the hippocampus and other brain regions of 6-month-old ovariectomized (OVX) Sprague-Dawley rats. Three weeks post-ovariectomy, animals received estradiol benzoate (EB, 0.03 mg or 0.3 mg kg(-1) day(-1) for 3 or 10 days); raloxifene HCl (3.0 mg kg(-1) day(-1) for 3 or 10 days), tamoxifen (3.0 mg kg(-1) day(-1) for 10 days) or vehicle (20% CDX). As previously reported, ChAT activity decreased by approximately 20%-50% in the hippocampus of OVX compared with SHAM-operated control rats with no change in ChAT activity observed in the hypothalamus. Raloxifene or EB reversed the OVX-induced decrease in ChAT activity in the hippocampus but did not change ChAT activity in the hypothalamus. Animals that received combined EB (0.03 mg/kg) plus raloxifene (1 mg/kg) or tamoxifen alone (3.0 or 10 mg/kg) also showed increased hippocampal ChAT activity. Raloxifene failed to increase uterine weight and blocked the estrogen-induced increase in uterine weight, while another SERM, tamoxifen, increased uterine weight. These data demonstrate that raloxifene has estrogen-like properties on hippocampal ChAT activity in vivo, and suggest that benzothiophene SERMs may exert estrogen-like beneficial effects on cholinergic neurotransmission in brain without producing peripheral stimulation of breast or uterine tissue.

An estrogen receptor basis for raloxifene action in bone.

Although controversy remains regarding direct effects of estrogen on bone, in vivo data clearly show that estrogens suppress bone turnover, resulting in decreased bone resorption and formation activity. Selective estrogen receptor modulators (SERMs), such as raloxifene, produce effects on bone which are very similar to those of estrogen. In vitro, both raloxifene and estrogen inhibit mammalian osteoclast differentiation and bone resorption activity, but only in the presence of IL-6. Data from a number of ovariectomized rat model manipulations (i.e. hypophysectomy, low calcium diet and drug combinations) demonstrate a strong parallel between the antiosteopenic effects of raloxifene and estrogen. A characteristic action of estrogens on the skeleton is inhibition of longitudinal bone growth, an effect which is not observed with other resorption inhibitors, including calcitonin and bisphosphonates. Consistent with an estrogen-like mechanism on bone, raloxifene inhibits longitudinal bone growth in growing rats. In addition to the overall similarity of the bone activity profile in animals, estrogen and raloxifene also produce similar effects on various signaling pathways relative to the antiosteopenic effect of these two agents. For example, IL-6, a cytokine involved in high turnover bone resorption following estrogen deficiency in rats, is suppressed by both raloxifene and estrogen. Raloxifene and estrogen also produce a similar activation of TGF-beta3 (a cytokine associated with inhibition of osteoclast differentiation and activity) in ovariectomized rats. Like 17beta-estradiol, raloxifene binds with high affinity to both estrogen receptor-alpha (ER alpha) and estrogen receptor-beta (ER beta). Crystal structure analyses have shown that 17beta-estradiol and raloxifene bind to ER alpha with small, but important, differences in three dimensional structure. These subtle differences in the conformation of the ligand:receptor complex are likely the basis for the key pharmacological differences between estrogens and the various SERMs (i.e. raloxifene vs tamoxifen). Raloxifene also produces estrogen-like effects on serum cholesterol metabolism and the vasculature. Thus, while raloxifene exhibits a complete estrogen antagonist in mammary tissue and the uterus, it produces beneficial effects on the cardiovascular system and prevents bone loss via an estrogen receptor mediated mechanism.

Selective estrogen receptor modulators: tissue selectivity and differential uterine effects.

Selective estrogen receptor modulators (SERMs) are compounds that bind to estrogen receptors and produce estrogen-like (agonist) effects in some tissues and estrogen-blocking (antagonist) effects in other tissues. One of the goals of SERM research has been to develop compounds that provide the potential benefits of estrogen in the skeleton and cardiovascular system, but avoid the negative effects of estrogen in other tissues. Estrogen therapy has been consistently associated with endometrial stimulation, including glandular proliferation, hyperplasia and cancer. In contrast, the presence or degree of endometrial stimulation observed with SERMs varies by compound. The purpose of this review is to differentiate the endometrial effects of compounds that display a SERM-like profile. Molecular mechanisms involving SERM binding to estrogen receptors, preclinical uterine effects in both tissue culture and animal models, and endometrial findings in clinical experience are discussed. There are several SERMs commercially available or in development. The favorable safety profile of raloxifene in the uterus differentiates it from the others. Future SERM development will continue to focus on finding compounds that exhibit minimal endometrial stimulation.

LY353381.HCl: a novel raloxifene analog with improved SERM potency and efficacy in vivo.

Body weight, uteri, serum cholesterol and bones were shown previously in vivo to be sensitive to circulating levels of estrogen, as well as to synthetic, nonsteroidal ligands termed selective estrogen receptor modulators (SERM). In this study, we examined the in vivo effects of a new potent SERM on these tissues in 6-month-old, ovariectomized rats that were orally dosed with 0.0001-10 mg/kg/day LY353381.HCl for 5 weeks. LY353381.HCl prevented the ovariectomy-induced increase in body weight and serum cholesterol levels of treated rats and lowered them to below sham levels in a dose dependent manner, with maximum efficacy similar to estrogen or raloxifene. However, LY353381.HCl was consistently more potent than raloxifene, with a half maximal efficacious dose of 0.001 mg/kg for the reduction of body weight and cholesterol. In the uterus, LY353381.HCl had marginal effects on uterine weight compared to ovariectomized controls (OVX) like raloxifene, but unlike estrogen. Histological examination of uterine epithelial cell height showed little to no stimulatory effect of LY353381.HCl on the endometrium. Quantitative computed tomographic analyses (pQCT) of tibiae showed that LY353381.HCl prevented loss of bone due to ovariectomy with an ED50 of about 0.01 mg/kg with maximal efficacy observed at 0.1-1 mg/kg/day. Maximally attainable bone mineral density and content with LY353381.HCl were not significantly different from Sham or ovariectomized rats treated with estrogen or raloxifene. Interestingly, assessment of bone quality by biomechanical analyses showed that LY353381.HCl preserved the strength of the femora neck and midshaft, while improving the Young's modulus of cortical bone to beyond estrogen, raloxifene or sham levels. In uteri of immature rats treated with estrogen, LY353381.HCl antagonized the estrogen-induced elevation in uterine weight down to vehicle-dosed control levels with ED50 of 0.03 mg/kg/day. Therefore, LY353381.HCl was 30-100 times more potent than raloxifene in preventing ovariectomy effects on body weight, serum cholesterol and bone, while maintaining estrogen antagonist effects on the uterus. These animal data suggest that LY353381.HCl may have advantages over estrogen or raloxifene in the prevention of bone loss and treatment of other tissues in postmenopausal women.

Differential responses of estrogen target tissues in rats including bone to clomiphene, enclomiphene, and zuclomiphene.

The substituted triphenylethylene antiestrogen clomiphene (CLO) prevents cancellous bone loss in ovariectomized (OVX'd) rats. However, CLO is a mixture of two stereoisomers, enclomiphene (ENC) and zuclomiphene (ZUC), which have distinctly different activities on reproductive tissues and tumor cells. The purpose of the present dose response study was to determine the effects of ENC and ZUC on nonreproductive estrogen target tissues. These studies were performed in 7-month-old female rats with moderate cancellous osteopenia that was established by ovariectomizing rats 1 month before initiating treatment. OVX resulted in increases in body weight, serum cholesterol, endocortical resorption, and indices of cancellous bone turnover, as well as decreases in uterine weight, uterine epithelial cell height, bone mineral density, bone strength, and cancellous bone area. Estrogen treatment for 3 months restored body weight, uterine histology, dynamic bone measurements, and osteoblast and osteoclast surfaces in OVX'd rats to the levels found in the age-matched sham-operated rats. In contrast, estrogen only partially restored cancellous bone volume and uterine weight, and it reduced serum cholesterol to subnormal values. CLO was a weak estrogen agonist on uterine measurements and a much more potent agonist on body weight, serum cholesterol, and dynamic bone measurements. CLO increased trabecular thickness in osteopenic rats and was the most effective treatment in improving cancellous bone volume and architecture. ZUC was a potent estrogen agonist on all tissues investigated and had dose-dependent effects. In contrast, ENC had dose-dependent effects on most measurements similar to CLO and decreased the uterotrophic effects of ZUC. It is concluded that ENC antagonizes the estrogenic effects of ZUC on the uterus but that the beneficial effects of CLO on nonreproductive tissues in OVX'd rats is conferred by both isomers. Furthermore, the combined actions of the two isomers on bone volume and architecture were more beneficial than either isomer given alone.

The selective estrogen receptor modulator, raloxifene: an overview of nonclinical pharmacology and reproductive and developmental testing.

Raloxifene is a nonsteroidal, selective estrogen receptor modulator being developed by Eli Lilly and Company as a therapeutic agent for postmenopausal osteoporosis. In the ovariectomized (OVX) rat, raloxifene prevents the loss of bone at the distal metaphysis of the femur, proximal tibia, and vertebrae; reduces cancellous bone resorption; and reduces serum cholesterol, but does not cause any significant changes in stromal eosinophilia or uterine epithelium. In estrogen-stimulated OVX rats, raloxifene prevents the morning lowering of serum luteinizing hormone levels, produces a reduction in afternoon serum prolactin levels, antagonizes pituitary weight increase, and antagonizes stimulation of mammary gland development. Raloxifene also has been shown to exhibit antiestrogenic activity in several in vivo and in vitro mammary tumor models. Raloxifene treatment results in regression of endometriosis in both a surgically prepared, rat uterine explant model and in Rhesus macaques diagnosed with spontaneous endometriosis before exposure. Also, uterine leiomyomas in estrogen-stimulated OVX guinea pigs regress after the onset of raloxifene treatment. Raloxifene antagonizes testosterone-induced increases in prostate weight of castrated rats, but does not bind to androgen receptors or affect prostatic 5-alpha-reductase or testicular steroid 17-alpha-hydroxylase activity. A series of preclinical toxicology studies was designed to characterize reproductive and developmental outcomes following various schedules of raloxifene treatment in rats or rabbits. Studies of female reproduction and developmental outcome were conducted primarily at pharmacologic doses (0.1, 1, or 10 mg/kg/d); male reproductive studies used higher doses (10, 30, or 100 mg/kg/d). In this series of studies, male reproductive end points were not affected, whereas embryo implantation, fetal rabbit morphology, and several aspects of offspring development were disrupted by the lowest dose of maternal raloxifene treatment, a profile consistent with estrogen antagonist activity.

Synthesis and pharmacology of conformationally restricted raloxifene analogues: highly potent selective estrogen receptor modulators.

The 2-arylbenzothiophene raloxifene, 1, is a selective estrogen receptor modulator (SERM) which is currently under clinical evaluation for the prevention and treatment of postmenopausal osteoporosis. In vivo structure-activity relationships and molecular modeling studies have indicated that the orientation of the basic amine-containing side chain of 1, relative to the stilbene plane, is an important discriminating factor for the maintenance of tissue selectivity. We have constructed a series of analogues of 1 in which this side chain is held in an orientation which is orthogonal to the stilbene plane, similar to the low-energy conformation predicted for raloxifene. Herein, we report on the synthesis of these compounds and on their activity in a series of in vitro and in vivo biological assays reflective of the SERM profile. In particular, we describe their ability to (1) bind the estrogen receptor, (2) antagonize estrogen-stimulated proliferation of MCF-7 cells in vitro, (3) stimulate TGF-beta3 gene expression in cell culture, (4) inhibit the uterine effects of ethynyl estradiol in immature rats, and (5) potently reduce serum cholesterol and protect against osteopenia in ovariectomized (OVX) rats without estrogen-like stimulation of uterine tissue. These data demonstrate that one of these compounds, LY357489,4, is among the most potent SERMs described to date with in vivo efficacy on bone and cholesterol metabolism in OVX rats at doses as low as 0.01 mg/kg/d.