Kristin L. Chidsey-Frink

Effects of CP-336,156, a New, Nonsteroidal Estrogen Agonist/Antagonist, on Bone, Serum Cholesterol, Uterus, and Body Composition in Rat Models.

We have discovered a new, nonsteroidal, potent estrogen agonist/antagonist, CP-336,156. CP-336,156 binds selectively and with high affinity to the human estrogen receptor-α with a half-inhibition concentration of 1.5 nm, which is similar to that seen with estradiol (4.8 nm). When given orally to immature (3-week-old) female Sprague-Dawley rats for 3 days at doses of 0.1, 1.0, 10, or 100 μg/kg·day, unlike 17α-ethynyl estradiol, CP-336,156 had no effect on uterine wet or dry weight. Similarly, no uterine hypertrophy was observed in aged (17-month-old) female rats treated (po) with CP-336,156 at 10 or 100 μg/kg·day for 28 days. We also found that CP-336,156 decreased total serum cholesterol and fat body mass and had no effect on lean body mass in these aged female rats. In 5-month-old ovariectomized (OVX) Sprague-Dawley female rats, CP-336,156 completely prevented OVX-induced increases in body weight gain, total serum cholesterol, and serum osteocalcin at doses between 10 and 1000 μg/kg·day after 4 weeks. At...

Comparative effects of droloxifene, tamoxifen, and estrogen on bone, serum cholesterol, and uterine histology in the ovariectomized rat model

The purpose of this study was to compare the effects of droloxifene (DRO), tamoxifen (TAM), and 17 alpha-ethynyl estradiol (EE) on bone mineral density, bone histomorphometry, total serum cholesterol, and uterine histology in the ovariectomized (ovx) rat model. Sprague-Dawley female rats at five months of age were sham-operated and treated orally with vehicle (n = 8), or ovx (n = 56) and treated (p.o.) with either vehicle, DRO at 0.1 or 1.0 mg/kg daily, TAM at 0.1 or 1 mg/kg daily, or EE at 3 or 30 micrograms/kg daily for 4 weeks. The uterine wet weight and uterine histologic parameters (cross-sectional tissue area, stromal thickness, and luminal epithelial thickness) were determined. Femoral and lumbar vertebral bone mineral density was determined ex vivo using dual energy x-ray absorptiometry. Static and dynamic cancellous bone histomorphometry was performed on double-labeled, undecalcified longitudinal sections from proximal tibial metaphyses. Furthermore, the changes in total serum cholesterol and body weight gain were also determined. Compared to sham controls, ovx for four weeks significantly decreased uterine weight (-72%), uterine cross-sectional tissue area (-74%), stromal thickness (-52%), and luminal epithelial thickness (-53%). ovx rats treated with EE at 30 micrograms/kg/day maintained these parameters at the levels of sham controls. Uterine weight and uterine cross-sectional tissue area in 3 micrograms/kg/day of EE treated ovx rats were higher than that of vehicle-treated ovx rats. In ovx rats treated with TAM at both 0.1 and 1 mg/kg/day, these parameters were significantly less than sham controls but significantly higher than ovx controls. DRO at 0.1 mg/kg/day had no effects on all above parameters. Uterine weight and cross-sectional tissue area in 1 mg/kg/day of DRO treated ovx rats was slightly but significantly higher than that in ovx controls. However, DRO at 1 mg/kg/day had no effects on uterine stromal thickness and luminal epithelial thickness compared to ovx controls. The ovx-induced decrease in femoral and lumbar vertebral bone mineral density was prevented by treatment with EE at 30 micrograms/kg/day, TAM at both 0.1 and 1 mg/kg/day, or DRO at 1 mg/kg/day. Similarly, the decrease in bone mass and the increase in bone resorption and bone turnover in proximal tibial metaphyses were prevented by treatment with EE at 30 micrograms/kg/day or TAM at both 0.1 and 1 mg/kg/day, or DRO at 1 mg/kg/day. Total serum cholesterol decreased significantly in ovx rats treated with either EE, DRO, or TAM at all dose levels compared to vehicle treated ovx controls (-32% to -56%). The ovx-induced body weight gain was completely prevented by EE at 30 micrograms/kg/day, and partially prevented by DRO at 1 mg/kg/day. TAM at both 0.1 and 1 mg doses caused a significant decrease in body weight compared to both sham and ovx controls. Our results indicated that DRO prevented ovx-induced bone loss and lowered total serum cholesterol with an ED50 less than 1 mg/kg/day. The bone protective and cholesterol lowering effects of DRO were comparable to those observed with TAM and EE. However, DRO differed from TAM and EE in its lack of significant estrogenic effects on uterine tissue at doses which were bone protective. These data suggest that DRO may be a significant alternative to EE and TAM for prevention and treatment of postmenopausal 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.

Prostaglandin E2 increases bone strength in intact rats and in ovariectomized rats with established osteopenia

It is well documented that prostaglandin E2 (PGE2) has the ability to stimulate bone formation, improve bone structure, and increase bone mass in intact or osteopenic rat models. However, the effects of PGE2 on the mechanical properties of bone have not been investigated previously. The purpose of our study was to determine the effects of PGE2 on the mechanical strength of bones in rapidly growing, adult, and ovariectomized rat models. In study I, PGE2 at 3 mg/kg per day, or vehicle, was given by daily subcutaneous injections for 30 days to rapidly growing (3-month-old) intact male rats. Compared with controls, PGE2 significantly increased initial maximal load and stiffness of cancellous bone at the distal femoral metaphysis (DFM) as determined by an indentation test. As determined by a compression test, rats treated with PGE2 showed a significant increase in maximal load, and a nonsignificant increase in stiffness in the fifth lumbar vertebral body (L5) when compared with controls. In study II, PGE2 at 3 mg/kg per day, or vehicle, was given by daily subcutaneous injection for 30 days to mature (10-month-old) intact male rats. PGE2 treatment significantly increased initial maximal load and stiffness of the DFM and L5. PGE2 induced a significant increase in maximal load, but not stiffness, in the femoral neck (FN), as determined by a cantilever compression test. There was an increase in maximal load in a three-point bending test at the femoral shaft (FS) although the increase did not achieve statistical significance. No change in stiffness in the FS was found after PGE2 treatment. In study III, 3-month-old female rats were sham-operated or ovariectomized (ovx) for 30 days. Thereafter, PGE, at 1 or 3 mg/kg, or vehicle, were given by daily subcutaneous injection to these rats for 30 days. After 30 and 60 days, ovx induced a significant decrease in initial maximal load and stiffness of cancellous bone at the DFM as compared with sham controls. In ovx rats with established osteopenia, PGE2 at 1 mg/kg per day nonsignificantly increased the initial maximal load and stiffness, whereas, at 3 mg/kg per day, PGE2 completely restored the initial maximal load and stiffness of DFM to sham control levels. Similarly, maximal load and stiffness of L5 decreased significantly in ovx rats compared with sham controls at 30 days postsurgery. PGE2 at 1 mg/kg per day partially restored the maximal load, whereas, at 3 mg/kg per day, it completely restored the maximal load and stiffness of L5 in the established osteopenia, ovx rats. At the FS, PGE2 at 3 mg/kg per day nonsignificantly increased maximal load (+11%) and significantly increased stiffness (+25%) compared with ovx controls. Neither ovx nor PGE2 treatment caused a significant change in the maximal load and stiffness of the FN in this study. These results reveal that PGE2 significantly increased the mechanical strength at various skeletal sites in rapidly growing and mature male rats, although the increase in femoral shafts was not statistically different. Furthermore, PGE2 completely restored mechanical strength to the cancellous bone in ovx rats with established osteopenia.

Pyrazolinone-piperidine dipeptide growth hormone secretagogues (GHSs) : Discovery of capromorelin

Novel pyrazolinone-piperidine dipeptide derivatives were synthesized and evaluated as growth hormone secretagogues (GHSs). Two analogues, capromorelin (5, CP-424391-18, hGHS-R1a K(i)=7 nM, rat pituicyte EC(50)=3 nM) and the des-methyl analogue 5c (hGHS-R1a K(i)=17 nM, rat pituicyte EC(50)=3 nM), increased plasma GH levels in an anesthesized rat model, with ED(50) values less than 0.05 mg/kg iv. Capromorelin showed enhanced intestinal absorption in rodent models and exhibited superior pharmacokinetic properties, including high bioavailabilities in two animal species [F(rat)=65%, F(dog)=44%]. This short-duration GHS was orally active in canine models and was selected as a development candidate for the treatment of musculoskeletal frailty in elderly adults.

Discovery and biological characterization of capromorelin analogues with extended half-lives

New tert-butyl, picolyl and fluorinated analogues of capromorelin (3), a short-acting growth hormone secretagogue (GHS), were prepared as part of a program to identify long-acting GHSs that increase 24-h plasma IGF-1 levels. Compounds 4c and 4d (ACD LogD values >or=2.9) displayed extended plasma elimination half-lives in dogs, primarily due to high volumes of distribution, but showed weak GH secretagogue activities in rats (ED(50)s>10 mg/kg). A less lipophilic derivative 4 (ACD LogD=1.6) exhibited a shorter canine half-life, but stimulated GH secretion in two animal species. Repeat oral dosing of 4 in dogs for 29 days (6 mg/kg) resulted in a significant down-regulation of the post dose GH response and a 60 and 40% increase in IGF-1 levels relative to pre-dose levels at the 8- and 24-h post dose time points. Compound 4 (CP-464709-18) has been selected as a development candidate for the treatment of frailty.

Droloxifene does not blunt bone anabolic effects of prostaglandin E2, but maintains prostaglandin E2-restored bone in aged, ovariectomized rats

Droloxifene (DRO) is a selective estrogen receptor modulator that prevents bone loss by inhibition of bone turnover associated with estrogen deficiency in both growing and aged female rats. The purposes of this study were to test: (a) whether DRO can maintain prostaglandin E2 (PGE2)-restored bone after discontinuation of PGE2 in aged, ovariectomized (ovx) rats; (b) if an inhibition of bone turnover by DRO reduces bone anabolic effects of PGE2; and (c) whether bone mass restored by PGE2 plus DRO can be maintained after discontinuation of both agents. Female rats at 12 months of age were sham-operated (sham) or ovx. Three months postsurgery, ovx rats were treated with either PGE2 (3 mg/kg per day, subcutaneously [s.c.]) alone, or PGE2 plus DRO (10 mg/kg per day, per os [p.o.]) for 2 months. Thereafter, the PGE2 or PGE2 plus DRO treatment was withdrawn and the rats were then treated with either vehicle or DRO for another 1.5 months. Using dual-energy X-ray absorptiometry (DXA), total lumbar vertebral bone mineral density (LV-BMD) was determined in vivo at months 0, 3, 5, and 6.5. At the end of the study, the rats were autopsied, and BMD of total femur, femoral shaft, distal femoral metaphysis, and proximal femur was determined ex vivo by DXA. Standard static and dynamic bone histomorphometric parameters were determined on the fourth lumbar vertebral body (L-4). At 3, 5, or 6.5 months postsurgery, LV-BMD decreased significantly (-15%, -19%, and -19%, respectively) in the vehicle-treated ovx rats compared with sham. Beginning at 3 months post-ovx, PGE2 alone or in combination with DRO for 2 months completely restored LV-BMD back to the sham level. There was no difference in LV-BMD in PGE2 alone or PGE2 plus DRO. Upon cessation of PGE2 treatment, a significant decrease in LV-BMD was observed in the PGE2-alone group (-12%). On the other hand, when DRO treatment was given after discontinuation of PGE2, the PGE2-restored LV-BMD was completely maintained. In the PGE2 plus DRO group, no loss in LV-BMD was observed after cessation of either PGE2 alone or both PGE2 and DRO. However, treatment with DRO following 2 months of PGE2 plus DRO further increased LV-BMD (+10%). At the end of the study, ex vivo femoral BMD data confirmed the observation in lumbar vertebrae. Histomorphometric results of L-4 indicated that loss in bone mass after cessation of PGE2 in PGE2 alone group was associated with increased bone turnover. Treatment with DRO in the maintenance phase inhibited bone turnover and prevented bone loss induced by withdrawal of PGE2. Trabecular bone mass was maintained in the PGE2 plus DRO followed by vehicle group and further increased in the PGE2 plus DRO followed by DRO groups. We found that: (a) DRO is efficacious in maintaining PGE2-restored bone after discontinuation of PGE2; (b) DRO did not blunt the anabolic effects of PGE2; (c) bone loss occurred after cessation of treatment in the PGE2-alone group, whereas it was maintained after cessation of treatment in PGE2 plus DRO group; and (d) an additional anabolic effect was found in ovx rats treated with PGE2 plus DRO followed by DRO.