The selective estrogen receptor modulator, raloxifene: a segment II/III delivery study in rats

Current and evolving approaches to individualizing estrogen receptor-based therapy for menopausal women

CONTEXT

Adding progestogens to estrogens changes the risk profile of hormonal therapy for menopausal women, and recent data support the need for progestogen-free options. Several current and evolving approaches to managing estrogen deficiency allow for progestogen omission. We review the mechanisms of estrogen activity and provide an overview of emerging and available estrogen receptor (ER)-based therapies.

EVIDENCE ACQUISITION

PubMed was searched for relevant English-language articles using keywords pertaining to estrogen deficiency, menopause, hormone therapy, and estrogen-only therapy. Pivotal or recent randomized controlled trials, large observational studies, comprehensive meta-analyses, and established therapeutic guidelines were compiled.

EVIDENCE SYNTHESIS

Advances in our understanding of ER pharmacology have led to therapies designed to optimize ER activity, including selective ER modulators (SERMs) and tissue-selective estrogen complexes (TSECs). Each estrogen, SERM, and TSEC exhibits a unique profile of tissue-specific activity, spanning the spectrum from ER agonism to antagonism. Systemic estrogens unopposed by progestogens effectively manage menopausal symptoms in hysterectomized postmenopausal women but require progestogen use in postmenopausal women with a uterus. SERMs are effective for managing certain aspects of estrogen deficiency in postmenopausal women, but data suggest that pairing a SERM with estrogens to form a TSEC provides a more optimal therapeutic profile for women with a uterus.

CONCLUSIONS

Treating signs and symptoms of estrogen deficiency requires an individualized approach based on a woman's goals and the purported risks of different therapies. New and emerging agents have demonstrated efficacy in postmenopausal women with a uterus, while allowing these women to avoid progestogens and their possible adverse effects.

Lasofoxifene: Evidence of its therapeutic value in osteoporosis

Introduction:

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

Aims:

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

Evidence review:

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

Place in therapy:

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

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

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

Effects of in utero and lactational exposure to tamoxifen in SD rats

Pregnant CD (SD) IGS rats were given tamoxifen (TMX) orally at doses of 0.12, 0.6, or 3 microg/kg/day from gestational day 6 to postnatal day 21, and the effects of TMX exposure on all offspring were examined 10 weeks after birth; the reproductive performance of the offspring was also evaluated. Although the body weights of the dams treated with TMX remained normal from gestational day 6 until the day of autopsy (postnatal day 21), three dams in the 3 microg/kg/day group died during the pregnancy or partum periods. These deaths were regarded as the toxicological effects of TMX. No changes were detected in the reproductive parameters of all the TMX groups except for a decrease in the number of newborns/live newborns in the 3 microg/kg/day group. No abnormal clinical signs, body weight change, ano-genital distance, vaginal opening, or organ weight changes were detected in any of TMX groups, but the day of preputial separation was prolonged in the male offspring of all TMX groups and cleft phallus was detected in the female offspring of the 0.6 and 3 microg/kg/day groups. No abnormalities were detected in the reproductive performance of the male and female offspring.

Effects of in utero and lactational exposure to flutamide in SD rats: comparison of the effects of administration periods

Pregnant CD(SD) IGS rats were given flutamide (FLUT) orally at doses of 0.4, 2, or 10 mg/kg/day from gestational day 6 to postnatal day (PND) 20, and the effects of FLUT exposure on male offspring were examined 10 weeks after birth, and compared to the effects in offspring treated after weaning and in offspring untreated after weaning. Although the body weight of the dams treated with FLUT remained normal, two dams in the 10 mg/kg/day group were killed because of abnormal parturition periods and loss of all the pups. The number of stillborns and dead newborns at birth was significantly higher in the 10 mg/kg/day group than in the control groups. No abnormalities in the reproductive parameters of the other dams treated with FLUT were detected. The body weights of the male offspring in each group remained normal from birth until the end of the study. The ano-genital distance was significantly shortened in 2 and 10 mg/kg/day groups. Changes in the organ weights and gross findings were detected in the 2 and/or 10 mg/kg/day groups with or without the continuous administration of FLUT after weaning; these changes were more appreciable in groups treated with FLUT after weaning than in groups untreated after weaning. The prolongation of preputial separation was observed in the 0.4 and 2 mg/kg/day groups treated with FLUT after weaning, but this change was not detected in the same dose groups untreated after weaning. The testosterone levels were higher in the 10 mg/kg/day group treated with FLUT after weaning. The present data demonstrated that the endocrine-mediated effects on rats were more appreciable in offspring treated with FLUT after weaning than in offspring untreated after weaning.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSION

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

Raloxifene effects upon the neuronal system controlling sexual receptivity in 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 mimics estrogen action on bone and blood lipid concentration but whether it acts as estrogen in the central nervous system remains to be fully established. In the present communication, we aimed at evaluating the estrogenic/antiestrogenic effects of raloxifene upon organization and activation of sexual receptivity, an estrogen-dependent event, in female rats. To this end, the effects of raloxifene, administered during the neonatal period, were compared with those of estrogen in terms of disruption of sexual receptivity in estrogen-progesterone-primed ovariectomized (OVX) female rats. In addition, the ability of raloxifene to induce sexual receptivity in progesterone-primed OVX females was analyzed. Similarly, the effects of the combined administration of estrogen and raloxifene were studied. Our results suggest that raloxifene does not act as estrogen upon the organization of the neuronal system involved in the control of sexual receptivity in female rats and exerted an antiestrogenic action in adult OVX estrogen-primed female rats.

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.

The selective estrogen receptor modulator, raloxifene: segment II studies in rats and rabbits

Raloxifene is a nonsteroidal, selective estrogen receptor modulator developed by Eli Lilly and Company primarily as a therapeutic agent for postmenopausal osteoporosis. Two Segment II studies were conducted that examined maternal reproductive parameters and fetal outcome following gestational exposure to raloxifene. Pregnant CD rats (25/group) and New Zealand white rabbits (20/group) were dosed once daily by oral gavage with 0, 0.1, 1, or 10 mg/kg on Gestation Days (GD) 6 through 17 and 7 through 19, respectively. Maternal body weight and food consumption were monitored throughout pregnancy. Caesarean sections were performed on GD 20 and GD 28 for rats and rabbits, respectively, to evaluate fetal viability, weight, and morphology. In rats, maternal body weight, body weight gain, and food consumption were reduced in all raloxifene treatment groups. Fetal viability was depressed in the 10-mg/kg group and was often associated with signs of hemorrhaging from the vagina. Fetal growth retardation was indicated in the 1- and/or 10-mg/kg groups by increased incidences of fetal runts and the developmental deviations, wavy ribs and kidney cavitation. There was no evidence of treatment-related malformations in rat fetuses. In rabbits, depressions in body weight gain and food consumption occurred in the 10-mg/kg group, and a single abortion occurred in the 1-mg/kg group. Fetal viability and weights were not affected in any of the raloxifene treatment groups. The overall proportions of fetuses with malformations, deviations, or variations were not affected by treatment with raloxifene; however, one fetus each from the 0.1-, 1-, and 10-mg/kg groups had incomplete closure of the interventricular septum. Therefore, maternal and fetal no-effect levels were not obtained in this study of raloxifene.

The selective estrogen receptor modulator, raloxifene: reproductive assessments in adult male rats

Raloxifene HCl is a nonsteroidal, selective estrogen receptor modulator developed for postmenopausal osteoporosis. Reproductive toxicity of raloxifene was examined in adult male CD rats after the oral administration of doses of 0, 10, 30, or 100 mg/kg/d. In the first study, males (12/group) were treated for 2 weeks followed by 2 weeks without treatment. After dose administration on Day 13, 6 males/group were cohabited with untreated females (1:2) for up to 7 d. Males were killed on Day 14 or 28 (6/group each day). Sperm were collected from the right cauda epididymis and evaluated for relative concentration, motion characteristics, and breakage. The kinetics of spermatogenesis were examined by DNA flow cytometry. The left testis and epididymis were preserved for histopathologic evaluation. Females were examined for reproductive status on Gestation Day 13. In a second study, males (20/group) were treated for 7 weeks (4 weeks prior to cohabitation during a 2-week cohabitation period, and for 1 additional week). Treated males were cohabited with untreated females (1:1). On Gestation Day 20, untreated females were examined for reproductive status and fetuses were examined for viability, weight, gender, and morphology. At necropsy, male reproductive tissues were collected, weighed, and preserved for histopathologic evaluation. In both studies, male body weight gain and food consumption were depressed at all dose levels. There was no indication in either study that raloxifene caused important changes in sperm production, sperm quality, or male reproductive performance at doses as high as 100 mg/kg/d.

The selective estrogen receptor modulator, raloxifene: reproductive assessments following premating exposure in female rats

Raloxifene HCl is a nonsteroidal, selective estrogen receptor modulator developed as a therapeutic agent for postmenopausal osteoporosis. Two studies were conducted that examined the effects of premating exposure to raloxifene HCl. In the first study, adult female CD rats (20/group) were given diets containing 0, 0.01, or 0.1% raloxifene (providing an average of 0, 6, or 63 mg/kg/d, respectively) for 2 weeks, after which the treated diets were replaced with control diet. Following a 2-week period without treatment, each female that had displayed at least three conversions in vaginal cytology from cornified cells to leukocytes was cohabited for 1 to 2 d with an untreated male as she entered proestrus. Females were killed at midgestation and examined for evidence of pregnancy. In the second study, adult female CD rats (40/group) were given oral gavage doses of raloxifene (0, 0.1, 1, or 10 mg/kg/d) for 4 weeks. Immediately or following a 2-week period without treatment, 20 females/group were cohabited with untreated males (1:1) for up to 3 weeks. The females were allowed to deliver and rear their offspring until Postpartum Day 21. Progeny survival, growth, and development were evaluated. Maternal body weight, body weight gain, and food consumption were depressed in all raloxifene treatment groups. Doses > or =1 mg/kg caused disruptions in estrous cycles. In Study 1, 90% of the females treated with raloxifene resumed normal cycling, and fertility was not significantly affected. Although there were no statistically significant differences in time-to-mating, fertility, or liveborn indices in Study 2, females in the 10-mg/kg immediate-cohabitation group had slightly increased gestation lengths and smaller litter sizes. Progeny from these litters were larger on Postpartum Day 1 and had advanced incisor eruption and eye opening. In addition, slight delays were seen in physical landmark appearance in the 0.1- and 1-mg/kg immediate-cohabitation groups and in the 1- and 10-mg/kg delayed-cohabitation groups. Progeny viability, growth, and negative geotactic performance were not adversely affected. In these studies of maternal premating exposure to raloxifene, findings were consistent with established pharmacologic activity of the test chemical. Reproductive effects (disrupted estrous cycles and decreased litter size) occurred at doses > or =1 mg/kg and were generally reversible. Effects on offspring were seen at doses > or =0.1 mg/kg, were of minor importance, and were resolved during the lactation period.

The selective estrogen receptor modulator, raloxifene: reproductive assessments following preimplantation exposure in mated female rats

Raloxifene is a nonsteroidal, selective estrogen receptor modulator being developed for postmenopausal osteoporosis. As part of an integrated reproductive toxicity assessment, two studies were conducted in which raloxifene was administered orally to CD rats during Gestation Days (GD) 0 through 5. In each study, animals received daily raloxifene doses of 0, 0.1, 1, or 10 mg/kg. In Study 1, GD 20 evaluations of maternal reproductive parameters identified dose-related increases in pre- and postimplantation loss, reductions in the numbers of corpora lutea and live conceptuses, and reduced fetal weight. The low fetal weights were consistent with an extent of morphologic development that corresponded to developmental ages up to 8 d younger than GD 20. Study 2 characterized the potential impact of this disrupted and apparently delayed implantation on gestation length, parturition, and progeny viability. Dams were allowed to deliver and rear their offspring through Postpartum Day 21. Gestation lengths were extended up to 1 week, and litter sizes were reduced in a dose-dependent manner. Nevertheless, parturition occurred normally and pup morphology, survival, and physical and behavioral development were unaffected.