Odanacatib,effects of 16-month treatment and discontinuation of therapy on bone mass,turnover and strength in the ovariectomized rabbit model of osteopenia

Odanacatib (ODN) a selective and reversible cathepsin K inhibitor, inhibits bone resorption, increases bone mass and reduces fracture risk in women with osteoporosis. A 16-month (~ 7-remodeling cycles) study was carried out in treatment mode to assess the effects of ODN versus ALN on bone mass, remodeling status and biomechanical properties of lumbar vertebrae (LV) and femur in ovariectomized (OVX) rabbits. This study also evaluated the impact of discontinuing ODN on these parameters. Rabbits at 7.5 months post-OVX were dosed for 16-months with ODN (7.5 μM·h_0–24, in food) or ALN (0.2 mg/kg/wk, s.c.) and compared to vehicle-treated OVX- (OVX + Veh) or Sham-operated animals. After 8 months, treatment was discontinued in half of the ODN group. ODN treatment increased in vivo LV aBMD and trabecular (Tb) vBMD until reaching plateau at month 12 by 16% and 23% vs. baseline, respectively, comparable levels to that in Sham and significantly above OVX + Veh. LV BMD was also higher in ALN that plateaued around month 8 to levels below that in ODN or Sham. ODN treatment resulted in higher BMD, structure and improved biomechanical strength of LV and central femur (CF) to levels similar to Sham. ALN generally showed less robust efficacy compared to ODN. Neither ODN nor ALN influenced material properties at these bone sites following ODN or ALN treatment for 7 remodeling cycles in rabbits. ODN and ALN persistently reduced the bone resorption marker urinary helical peptide over study duration. While ALN reduced the bone formation marker BSAP, ODN treatment did not affect this marker. ODN also preserved histomorphometry-based bone formation indices in LV trabecular, CF endocortical and intracortical surfaces, at the levels of OVX + Veh. Discontinuation of ODN returned bone mass, structure and strength parameters to the comparable respective levels in OVX + Veh. Together, these data demonstrate efficacy and bone safety profile of ODN and suggests the potential long-term benefits of this agent over ALN with respect to accrued bone mass without long-term effects on bone formation.     

Odanacatib increases mineralized callus during fracture healing in a rabbit ulnar osteotomy model

The effects of the cathepsin K inhibitor odanacatib (ODN) on fracture healing were monitored for ～6 and 15 weeks post‐fracture in two separate studies using the unilateral transverse mid‐ulnar osteotomy model in skeletally mature female rabbits. Rabbits were pre‐treated for 3–4 weeks with vehicle (Veh), ODN (2 mg/kg, po, daily), or alendronate (ALN) (0.3 mg/kg, sc, twice‐weekly) prior to osteotomy. In Study 1, the animals were maintained on the same respective treatment for ～6 weeks. In Study 2, the animals were also continued on the same therapy or switched from Veh to ODN or ODN to Veh for 15 weeks. No treatment‐related impairment of fracture union was seen by qualitative histological assessments in the first study. Cartilage retention was detected in the calluses of ALN‐treated rabbits at week‐6, while calluses in the ODN and Veh groups contained bony tissue with significantly less residual cartilage. ODN treatment also markedly increased the number of cathepsin K‐(+) osteoclasts in the callus, indicating enhanced callus remodeling. From the second study, ex vivo DXA and pQCT confirmed that ODN treatment pre‐ and post‐osteotomy increased callus bone mineral content and bone mineral density (BMD) versus Veh (p < 0.001) and discontinuation of ODN post‐surgery returned callus BMD to Veh. Peak load of ODN‐ or ALN‐treated calluses were comparable to Veh. ODN increased callus yield load (20%, p = 0.056) and stiffness (26%, p < 0.05) versus Veh. These studies demonstrated that ODN increased mineralized callus during the early phase of fracture repair without impairing callus formation or biomechanical integrity at the fracture site. © 2015 The Authors. Journal of Orthopaedic Research published by Wiley Periodicals, Inc. on behalf of the Orthopaedic Research Society. J Orthop Res 34:72–80, 2016.     

Odanacatib reduces bone turnover and increases bone mass in the lumbar spine of skeletally mature ovariectomized rhesus monkeys

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K (CatK) currently being developed as a once‐weekly treatment for osteoporosis. In this study, we evaluated the effects of ODN on bone turnover, bone mineral density (BMD), and bone strength in the lumbar spine of estrogen‐deficient, skeletally mature rhesus monkeys. Ovariectomized (OVX) monkeys were treated in prevention mode for 21 months with either vehicle, ODN 6 mg/kg, or ODN 30 mg/kg (p.o., q.d.) and compared with intact animals. ODN treatment persistently suppressed the bone resorption markers (urinary NTx [75% to 90%] and serum CTx [40% to 55%]) and the serum formation markers (BSAP [30% to 35%] and P1NP [60% to 70%]) versus vehicle‐treated OVX monkeys. Treatment with ODN also led to dose‐dependent increases in serum 1‐CTP and maintained estrogen deficiency–elevated Trap‐5b levels, supporting the distinct mechanism of CatK inhibition in effectively suppressing bone resorption without reducing osteoclast numbers. ODN at both doses fully prevented bone loss in lumbar vertebrae (L₁ to L₄) BMD in OVX animals, maintaining a level comparable to intact animals. ODN dose‐dependently increased L₁ to L₄ BMD by 7% in the 6 mg/kg group (p < 0.05 versus OVX‐vehicle) and 15% in the 30 mg/kg group (p < 0.05 versus OVX‐vehicle) from baseline. Treatment also trended to increase bone strength, associated with a positive and highly significant correlation (R = 0.838) between peak load and bone mineral content of the lumbar spine. Whereas ODN reduced bone turnover parameters in trabecular bone, the number of osteoclasts was either maintained or increased in the ODN‐treated groups compared with the vehicle controls. Taken together, our findings demonstrated that the long‐term treatment with ODN effectively suppressed bone turnover without reducing osteoclast number and maintained normal biomechanical properties of the spine of OVX nonhuman primates. © 2012 American Society for Bone and Mineral Research     

Effects of the combination treatment of raloxifene and alendronate on the biomechanical properties of vertebral bone

Raloxifene (RAL) and alendronate (ALN) improve the biomechanical properties of bone by different mechanisms. The goal here was to investigate the effects of combination treatment of RAL and ALN on the biomechanical properties of vertebral bone. Six‐month‐old Sprague‐Dawley rats (n = 80) were randomized into five experimental groups (sham, OVX, OVX + RAL, OVX + ALN, and OVX + RAL + ALN; n = 16/group). Following euthanization, structural and derived material biomechanical properties of vertebral bodies were assessed. Density and dynamic histomorphometric measurements were made on cancellous bone. The results demonstrate that the structural biomechanical properties of vertebral bone are improved with the combination treatment. Stiffness and ultimate load of the OVX + RAL and OVX + ALN groups were significantly lower than those of sham animals, but the combination treatment with RAL + ALN was not significantly different from sham. Furthermore, the OVX + RAL + ALN group was the only agent‐treated group in which the ultimate load was significantly higher than that in OVX animals (p < .05). Cancellous bone fractional volume (BV/TV_canc) and bone mineral density (aBMD) also were improved with the combination treatment. BV/TV_canc of the OVX + RAL + ALN group was 6.7% and 8.7% greater than that of the OVX + RAL (p < .05) and OVX + ALN (p < .05) groups, respectively. Areal BMD of the OVX + RAL or OVX + ALN groups was not significantly different from that in OVX animals, but the value in animals undergoing combination treatment was significantly higher than that in OVX or OVX + RAL animals alone and not significantly different from that in sham‐operated animals. Turnover rates of both the RAL + ALN and ALN alone groups were lower than in the RAL‐treated alone group (p < .05). We conclude that the combination treatment of raloxifene and alendronate has beneficial effects on bone volume, resulting in improvement in the structural properties of vertebral bone. © 2011 American Society for Bone and Mineral Research.     

Antiresorptive therapy conserves some periarticular bone and ligament mechanical properties after anterior cruciate ligament disruption in the rabbit knee

The purpose of this study was to assess, in an osteoarthritic (OA) model, whether bisphosphonate (BP) antiresorptive therapy altered periarticular bone and bone–ligament biomechanics and OA progression. We surgically transected the anterior cruciate ligament (ACLX) in two groups of rabbits; the first group was dosed with BP (risedronate, 0.01 mg/kg s.c. daily for 6 wk), the second group remained untreated, and a third group of normal (unoperated) control rabbits was also evaluated. We measured distal femoral bone mineral density (BMD, Dual Energy X‐ray Absorptiometry [DEXA]), medial collateral ligament (MCL) laxity, and bone mechanical function (bone cores mechanically tested in compression). These measures were related to cartilage/joint gross morphology, histology, and measures of vascular volume (gelatin–dye perfusion) for evidence of inflammatory angiogenesis and early OA. BMD by DEXA in 6 wk ACLX animals was 18% less than normal controls (p < 0.05). In contrast, BP dosing conserved periarticular BMD; risedronate‐treated rabbits had distal femoral BMD only 5% less and not significantly different than normal controls. When the same bone cores were compressed to failure, both ACLX and BP‐dosed animals were significantly weaker than normal controls (p < 0.05). However, the bone energy to failure and elastic modulus of BP‐dosed animals was conserved and not significantly different from normal controls 6 wk after ACLX. Blocking bone resorption with BP also resulted in a significantly improved bone–ligament structural complex. MCL‐complex laxity was significantly less in BP‐dosed animals (1.2 times that of normal controls) compared to untreated ACLX animals (1.7 times that of normal controls; p < 0.05). Blocking bone resorption with risedronate did not suppress osteophytosis and inflammatory angiogenesis, which were significantly increased in the periarticular bone of both untreated and BP treated ACLX animals. Thus, administering BP immediately after ACL loss conserved some periarticular bone and MCL‐complex properties in an early OA model. © 2004 Published by Elsevier Ltd. on behalf of Orthopaedic Research Society.     

Odanacatib in the treatment of postmenopausal women with low bone mineral density: Three‐year continued therapy and resolution of effect

The selective cathepsin K inhibitor odanacatib (ODN) progressively increased bone mineral density (BMD) and decreased bone‐resorption markers during 2 years of treatment in postmenopausal women with low BMD. A 1‐year extension study further assessed ODN efficacy and safety and the effects of discontinuing therapy. In the base study, postmenopausal women with BMD T‐scores between ?2.0 and ?3.5 at the lumbar spine or femur received placebo or ODN 3, 10, 25, or 50 mg weekly. After 2 years, patients (n = 189) were rerandomized to ODN 50 mg weekly or placebo for an additional year. Endpoints included BMD at the lumbar spine (primary), total hip, and hip subregions; levels of bone turnover markers; and safety assessments. Continued treatment with 50 mg of ODN for 3 years produced significant increases from baseline and from year 2 in BMD at the spine (7.9% and 2.3%) and total hip (5.8% and 2.4%). Urine cross‐linked N‐telopeptide of type I collagen (NTx) remained suppressed at year 3 (?50.5%), but bone‐specific alkaline phosphatase (BSAP) was relatively unchanged from baseline. Treatment discontinuation resulted in bone loss at all sites, but BMD remained at or above baseline. After ODN discontinuation at month 24, bone turnover markers increased transiently above baseline, but this increase largely resolved by month 36. There were similar overall adverse‐event rates in both treatment groups. It is concluded that 3 years of ODN treatment resulted in progressive increases in BMD and was generally well tolerated. Bone‐resorption markers remained suppressed, whereas bone‐formation markers returned to near baseline. ODN effects were reversible: bone resorption increased transiently and BMD decreased following treatment discontinuation. © 2011 American Society for Bone and Mineral Research.     

A Short Treatment With an Antibody to Sclerostin Can Inhibit Bone Loss in an Ongoing Model of Colitis

Chronic inflammation leads to bone loss, and increased fracture rates have been reported in a number of human chronic inflammatory conditions. The study reported here investigates the skeletal effects of dosing a neutralizing antibody to the bone regulatory protein sclerostin in a mouse model of chronic colitis. When dosed prophylactically, an antibody to sclerostin (Scl‐AbI) did not reduce the weight loss or histological changes associated with colitis but did prevent inflammation‐induced bone loss. At the end of the experiment, Scl‐AbI–treated animals had a significantly higher femoral BMD (+27%, p < 0.05) than control antibody (Cntrl‐Ab)‐treated animals. In a second experiment, treatment with Scl‐AbI was delayed until colitis had developed, by which time the mechanical properties of femurs in colitic animals were significantly worse than those of healthy age‐matched control mice (maximum load, ?26%, p < 0.05; energy, ?37%, p < 0.05; ultimate strength, ?33%, p < 0.05; elastic modulus, ?17%, p < 0.05). A short treatment with Scl‐AbI halted bone loss and reversed the decline of both intrinsic and extrinsic mechanical properties of the femur such that, after 19 days of treatment, the bone mechanical properties in the Scl‐AbI–treated animals were not significantly different from those of noncolitic age‐matched controls. Serum markers of bone formation and resorption suggested that the antibody to sclerostin stimulated osteoblast activity and inhibited osteoclast‐mediated bone resorption.     

Inhibition of Cathepsin K Increases Modeling‐Based Bone Formation,and Improves Cortical Dimension and Strength in Adult Ovariectomized Monkeys

Treatment with the cathepsin K (CatK) inhibitor odanacatib (ODN) protects against bone loss and maintains normal biomechanical properties in the spine and hip of ovariectomized (OVX) preclinical models. Here, we characterized the effects of ODN on the dynamics of cortical modeling and remodeling, and dimension and strength of the central femur in adult OVX‐rhesus monkeys. Animals were treated with vehicle or ODN (6 or 30 mg/kg, once per day [q.d., p.o.]) in prevention mode for 21 months. Calcein and tetracycline double‐labeling were given at 12 and 21 months, and the femoral cross‐sections were subjected to dynamic histomorphometric and cement line analyses. ODN treatment significantly increased periosteal and endocortical bone formation (BFR/BS), accompanied with an increase in endocortical mineralizing surface (102%, p < 0.01) with the 6 mg/kg dose. ODN at both doses reduced remodeling hemiosteon numbers by 51% and 66% (p < 0.05), respectively, and ODN 30 mg/kg numerically reduced activation frequency without affecting wall thickness. On the same endocortical surface, ODN increased all modeling‐based parameters, while reducing intracortical remodeling, consistent with the observed no treatment effects on cortical porosity. ODN 30 mg/kg markedly increased cortical thickness (CtTh, p < 0.001) and reduced marrow area (p < 0.01). Lastly, ODN treatment increased femoral structural strength (p < 0.001). Peak load was positively correlated with the increases in bone mineral content (BMC) (r² = 0.9057, p < 0.0001) and CtTh (r² = 0.6866, p < 0.0001). Taken together, by reducing cortical remodeling‐based and stimulating modeling‐based bone formation, ODN significantly improved cortical dimension and strength in OVX monkeys. This novel mechanism of CatK inhibition in stimulating cortical formation suggests that ODN represents a novel therapeutic approach for the treatment of osteoporosis. © 2014 American Society for Bone and Mineral Research.     

Differential maintenance of cortical and cancellous bone strength following discontinuation of bone‐active agents

Osteoporotic patients treated with antiresorptive or anabolic agents experience an increase in bone mass and a reduction in incident fractures. However, the effects of these medications on bone quality and strength after a prolonged discontinuation of treatment are not known. We evaluated these effects in an osteoporotic rat model. Six‐month‐old ovariectomized (OVX) rats were treated with placebo, alendronate (ALN, 2 µg/kg), parathyroid hormone [PTH(1–34); 20 µg/kg], or raloxifene (RAL, 2 mg/kg) three times a week for 4 months and withdrawn from the treatments for 8 months. Treatment with ALN, PTH, and RAL increased the vertebral trabecular bone volume (BV/TV) by 47%, 53%, and 31%, with corresponding increases in vertebral compression load by 27%, 51%, and 31%, respectively (p < .001). The resulting bone strength was similar to that of the sham‐OVX control group with ALN and RAL and higher (p < .001) with PTH treatment. After 4 months of withdrawal, bone turnover (BFR/BS) remained suppressed in the ALN group versus the OVX controls (p < .001). The vertebral strength was higher than in the OVX group only in ALN‐treated group (p < .05), whereas only the PTH‐treated animals showed a higher maximum load in tibial bending versus the OVX controls (p < .05). The vertebral BV/TV returned to the OVX group level in both the PTH and RAL groups 4 months after withdrawal but remained 25% higher than the OVX controls up to 8 months after withdrawal of ALN (p < .05). Interestingly, cortical bone mineral density increased only with PTH treatment (p < .05) but was not different among the experimental groups after withdrawal. At 8 months after treatment withdrawal, none of the treatment groups was different from the OVX control group for cortical or cancellous bone strength. In summary, both ALN and PTH maintained bone strength (maximum load) 4 months after discontinuation of treatment despite changes in bone mass and bone turnover; however, PTH maintained cortical bone strength, whereas ALN maintained cancellous bone strength. Additional studies on the long‐term effects on bone strength after discontinuation and with combination of osteoporosis medications are needed to improve our treatment of osteoporosis. © 2011 American Society for Bone and Mineral Research.     

Antiresorptives overlapping ongoing teriparatide treatment result in additional increases in bone mineral density

During teriparatide (TPTD) treatment, high levels of bone formation are accompanied by an increase in bone resorption. The aim of this work was to test if coadministration of raloxifene (RAL) or alendronate (ALN) following 9 months of ongoing TPTD therapy would reopen the anabolic window, thereby exerting additional benefit on bone mineral density (BMD). Postmenopausal women (n = 125) with severe osteoporosis on TPTD treatment for 9 months were randomized into three open‐label groups for a further 9 months: ALN (70 mg/week) in addition to TPTD; RAL (60 mg/d) in addition to TPTD; or no medication in addition to TPTD. Amino‐terminal propeptide of type I procollagen (P1NP) and cross‐linked C‐telopeptide (CTX), and areal and volumetric BMD at the lumbar spine and hip were assessed. During the combination period, P1NP concentrations did not change on TPTD monotherapy (693% ± 371%, p < 0.0001) and decreased in the ALN (360% ± 153%, p < 0.0001) and RAL (482% ± 243%, p < 0.0001) combination groups; whereas CTX did not change on TPTD monotherapy (283% ± 215%, p < 0.0001), decreased to the starting level in the ALN combination group (17% ± 72%, p = 0.39), and remained elevated in the RAL combination group (179% ± 341%, p < 0.0001). The increase in lumbar spine BMD was 5% ± 6.3% in the ALN and 6% ± 5.2% in the RAL combination groups compared with 2.8% ± 9.3% in the TPTD monotherapy group (p = 0.085 and p = 0.033, respectively). The increase of trabecular lumbar spine BMD for both the ALN and RAL combination groups was superior to TPTD monotherapy. Total hip BMD changes were 4% ± 5.3% for the ALN combination group and 1.4% ± 5.1% for the TPTD monotherapy (p = 0.032), and 1.4% ± 3.4% (p = 0.02) for the RAL combination group. With the exception of no differences in the trabecular compartment of femoral neck, volumetric BMD changes in the ALN combination group for all other comparisons were significantly superior to the two other groups. Our data suggest that ALN when added to TPTD 9 months after initiation of TPTD monotherapy results in a more robust increase in BMD, probably due to a reopening of the anabolic window. The clinical relevance of the BMD increase is unknown. © 2013 American Society for Bone and Mineral Research     

Specific evaluation of localized bone mass and bone loss in the rat using dual-energy X-ray absorptiometry subregional analysis

Dual-energy X-ray absorptiometry (DXA), together with the use of ultra-high resolution software, recently appeared as an accurate method for determining bone mineral density (BMD) in the rat. In order to assess the ability of this technique to detect changes in bone mass in the rat rapidly and precisely, we measured BMD at various sites of the femur using DXA subregional analysis. In particular, we studied the BMD of the metaphyseal part of the femur (M-BMD) rich in trabecular bone, and compared the values obtained with the cancellous bone volume measured by histomorphometry. In short-term ovariectomized animals (experiment 1), M-BMD was the only parameter to differentiate statistically between 10 ovariectomized (OVX) and 10 SHAM-operated (SHAM) rats (–11.2%,p<0.01) 9 days after surgery. M-BMD still expressed the greatest variation between OVX and SHAM rats 42 days following ovariectomy (experiment 2) (–16.1%,p<0.001 v –6.2%,p<0.01 for the total femur BMD) and confirmed previous data demonstrating a greater loss of cancellous than cortical bone after cessation of ovarian activity. M-BMD was highly correlated with cancellous bone volume (BV) in normal (r=0.82,p<0.001,n=30), OVX (r=0.77,p<0.001,n=22) and SHAM (r=0.88,p<0.001,n=21) rats. Furthermore, subcutaneous treatment with rat parathyroid hormone fragment (1–34) (r-PTH(1-34)) partially and significantly protected animals from trabecular osteopenia induced by OVX; there was a similar degree of protection of BV and M-BMD (50% and 61% respectively), while BMD of the entire femur achieved complete protection. This M-BMD measurement, specifically reflecting cancellous bone mass as confirmed by the correlation study and the response to PTH treatment, is a sensitve and simple method which can be used to assess any precocious modifications of bone density under physiopathological or therapeutic conditions in experimental rat models of bone loss.     

Odanacatib Restores Trabecular Bone of Skeletally Mature Female Rabbits With Osteopenia but Induces Brittleness of Cortical Bone: A Comparative Study of the Investigational Drug With PTH,Estrogen, and Alendronate

Cathepsin K (CK), a lysosomal cysteine protease, is highly expressed in mature osteoclasts and degrades type 1 collagen. Odanacatib (ODN) is a selective and reversible CK inhibitor that inhibits bone loss in preclinical and clinical studies. Although an antiresorptive, ODN does not suppress bone formation, which led us to hypothesize that ODN may display restorative effect on the osteopenic bones. In a curative study, skeletally mature New Zealand rabbits were ovarectomized (OVX) and after induction of bone loss were given a steady‐state exposure of ODN (9 mM/d) for 14 weeks. Sham‐operated and OVX rabbits treated with alendronate (ALD), 17b‐estradiol (E2), or parathyroid hormone (PTH) served as various controls. Efficacy was evaluated by assessing bone mineral density (BMD), bone microarchitecture (using micro‐computed tomography), fluorescent labeling of bone, and biomechanical strength. Skeletal Ca/P ratio was measured by scanning electron microscopy (SEM) with X‐ray microanalysis, crystallinity by X‐ray diffraction, and bone mineral density distribution (tissue mineralization) by backscattered SEM. Between the sham and ODN‐treated osteopenic groups, lumbar and femur metaphyseal BMD, Ca/P ratio, trabecular microstructure and geometric indices, vertebral compressive strength, trabecular lining cells, cortical parameters (femoral area and thickness and periosteal deposition), and serum P1NP were largely comparable. Skeletal improvements in ALD‐treated or E2‐treated groups fell significantly short of the sham/ODN/PTH group. However, the ODN group displayed reduced ductility and enhanced brittleness of central femur, which might have been contributed by higher crytallinity and tissue mineralization. Rabbit bone marrow stromal cells expressed CK and when treated with ODN displayed increased formation of mineralized nodules and decreased apoptosis in serum‐deficient medium compared with control. In vivo, ODN did not suppress remodeling but inhibited osteoclast activity more than ALD. Taken together, we show that ODN reverses BMD, skeletal architecture, and compressive strength in osteopenic rabbits; however, it increases crystallinity and tissue mineralization, thus leading to increased cortical bone brittleness. © 2015 American Society for Bone and Mineral Research.     

Intermittent Parathyroid Hormone After Prolonged Alendronate Treatment Induces Substantial New Bone Formation and Increases Bone Tissue Heterogeneity in Ovariectomized Rats

Postmenopausal osteoporosis is often treated with bisphosphonates (eg, alendronate, [ALN]), but oversuppression of bone turnover by long‐term bisphosphonate treatment may decrease bone tissue heterogeneity. Thus, alternate treatment strategies after long‐term bisphosphonates are of great clinical interest. The objective of the current study was to determine the effect of intermittent parathyroid hormone (PTH) following 12 weeks of ALN (a bisphosphonate) treatment in 6‐month‐old, ovariectomized (OVX) rats on bone microarchitecture, bone remodeling dynamics, and bone mechanical properties at multiple length scales. By using in vivo μCT and 3D in vivo dynamic bone histomorphometry techniques, we demonstrated the efficacy of PTH following ALN therapy for stimulating new bone formation, and increasing trabecular thickness and bone volume fraction. In healthy bone, resorption and formation are coupled and balanced to sustain bone mass. OVX results in resorption outpacing formation, and subsequent bone loss and reduction in bone tissue modulus and tissue heterogeneity. We showed that ALN treatment effectively reduced bone resorption activity and regained the balance with bone formation, preventing additional bone loss. However, ALN treatment also resulted in significant reductions in the heterogeneity of bone tissue mineral density and tissue modulus. On the other hand, PTH treatment was able to shift the bone remodeling balance in favor of formation, with or without a prior treatment with ALN. Moreover, by altering the tissue mineralization, PTH alleviated the reduction in heterogeneity of tissue material properties induced by prolonged ALN treatment. Furthermore, switching to PTH treatment from ALN improved bone's postyield mechanical properties at both the whole bone and apparent level compared to ALN alone. The current findings suggest that intermittent PTH treatment should be considered as a viable treatment option for patients with prior treatment with bisphosphonates. © 2017 American Society for Bone and Mineral Research.     

Comparison of Skeletal Effects of Ovariectomy Versus Chemically Induced Ovarian Failure in Mice

Bone loss associated with menopause leads to an increase in skeletal fragility and fracture risk. Relevant animal models can be useful for evaluating the impact of ovarian failure on bone loss. A chemically induced model of menopause in which mice gradually undergo ovarian failure yet retain residual ovarian tissue has been developed using the chemical 4‐vinylcyclohexene diepoxide (VCD). This study was designed to compare skeletal effects of VCD‐induced ovarian failure to those associated with ovariectomy (OVX). Young (28 day) C57Bl/6Hsd female mice were dosed daily with vehicle or VCD (160 mg/kg/d, IP) for 15 days (n = 6–7/group) and monitored by vaginal cytology for ovarian failure. At the mean age of VCD‐induced ovarian failure (～6 wk after onset of dosing), a different group of mice was ovariectomized (OVX, n = 8). Spine BMD (SpBMD) was measured by DXA for 3 mo after ovarian failure and OVX. Mice were killed ～5 mo after ovarian failure or OVX, and bone architecture was evaluated by μCT ex vivo. In OVX mice, SpBMD was lower than controls 1 mo after OVX, whereas in VCD‐treated mice, SpBMD was not lower than controls until 2.9 mo after ovarian failure (p < 0.05). Both VCD‐induced ovarian failure and OVX led to pronounced deterioration of trabecular bone architecture, with slightly greater effects in OVX mice. At the femoral diaphysis, cortical bone area and thickness did not differ between VCD mice and controls but were decreased in OVX compared with both groups (p < 0.05). Circulating androstenedione levels were preserved in VCD‐treated mice but reduced in OVX mice relative to controls (p < 0.001). These findings support that (1) VCD‐induced ovarian failure leads to trabecular bone deterioration, (2) bone loss is attenuated by residual ovarian tissue, particularly in diaphyseal cortical bone, and (3) the VCD mouse model can be a relevant model for natural menopause in the study of associated bone disorders.     

Effects of combination treatment with alendronate and vitamin K2 on bone mineral density and strength in ovariectomized mice

Bisphosphonates increase bone mineral density (BMD) by suppressing remodeling space and elongating the duration of mineralization. Menatetrenone (vitamin K₂) reduces the incidence of fractures by improving bone quality through enhanced γ-carboxylation of bone glutamic acid residues of osteocalcin in osteoporotic patients. This study investigated the effects of combination treatment with alendronate (ALN) and vitamin K₂ on BMD and bone strength in ovariectomized (OVX) mice. Thirty-three female mice, 16 weeks of age, were assigned to four groups: (1) OVX-control group; (2) oral vitamin K₂ group; (3) subcutaneous ALN group; and (4) ALN + vitamin K₂ group. The treatment was started 4 weeks after OVX and continued for 4 weeks. BMD, geometric parameters measured by peripheral quantitative computed tomography, and mechanical strength at the femoral metaphysis and mid-diaphysis were evaluated after an 8-week treatment period. ALN alone significantly increased total BMD (20%, P < 0.05) and trabecular BMD (25%, P < 0.05), but not the mechanical parameters of the femur, compared with the OVX-control group. Combination treatment with ALN and vitamin K₂ increased not only total BMD (15%, P < 0.05) and trabecular BMD (32%, P < 0.05) but also maximum load (33%, P < 0.05) and breaking energy (25%, P < 0.05) of compression test at the distal metaphysis, and maximum load (20%, P < 0.05) and breaking force (33%, P < 0.05) of three-point bending test at the mid-diaphysis compared with the OVX-control group. These results suggest that ALN, alone or in combination with vitamin K₂, showed significant improvement in BMD, but that the combination treatment was more effective than ALN alone for improving bone strength in OVX mice.     

Pharmacodynamic responses to combined treatment regimens with the calcium sensing receptor antagonist JTT-305/MK-5442 and alendronate in osteopenic ovariectomized rats

Parathyroid hormone (PTH) is the anabolic standard of care for patients with severe osteoporosis. The CaSR allosteric antagonist JTT-305/MK-5442, a PTH secretagogue, could offer an oral osteoanabolic treatment alternative for postmenopausal women with osteoporosis. Here we disclose the pharmacokinetic profile of JTT-305/MK-5442 and its activity on bone remodeling in ovariectomized (OVX) osteopenic rats. Daily treatments (0.3 to 2.4 mg/kg/d) for 12 weeks resulted in plateaued BMD increases (3.8 to 5.3%) at axial and appendicular skeletal sites. However, treatment effects were not statistically significant, in agreement with effects seen in animals treated with low dose PTH (1-84) (5 μg/kg/d). In a consecutive study we tested JTT-305/MK-5442 effects on bone formation in OVX-rats challenged with combined alendronate (ALN) treatment paradigms. At 7 month, JTT-305/MK-5442 treatment significantly increased BMD in lumbar vertebrae (LV), while no change in BMD was observed in femora or tibiae. ALN add-on co-treatment produced incremental increases in LV, distal femur (DF) and proximal tibia (PT) BMD over the respective ALN control. Histological analyses confirmed modest increases in mineralized surface (MS/BS) and bone formation rate (30.5±1.9%) on trabecular surfaces by JTT-305/MK-5442. As expected, ALN administration profoundly reduced bone formation, however, JTT-305/MK-5442 significantly stimulated MS/BS and BFR in ALN treated groups. In summary, JTT-305/MK-5442 acts as a PTH secretagogue in the osteopenic OVX-rat, eliciting consistent, though modest effects on remediation of BMD due to estrogen depletion. Induction of bone formation by JTT-305/MK-5442 at trabecular bone surfaces appears to be resilient to ALN-mediated suppression of bone formation. This study provides for the first time, a mechanistic evaluation of combination treatment of a PTH secretagogue with ALN.     

Effect of odanacatib on bone turnover markers,bone density and geometry of the spine and hip of ovariectomized monkeys: A head-to-head comparison with alendronate

Odanacatib (ODN) is a selective and reversible Cathepsin K (CatK) inhibitor currently being developed as a once weekly treatment for osteoporosis. Here, effects of ODN compared to alendronate (ALN) on bone turnover, DXA-based areal bone mineral density (aBMD), QCT-based volumetric BMD (vBMD) and geometric parameters were studied in ovariectomized (OVX) rhesus monkeys. Treatment was initiated 10 days after ovariectomy and continued for 20 months. The study consisted of four groups: L-ODN (2 mg/kg, daily p.o.), H-ODN (8/4 mg/kg daily p.o.), ALN (15 μg/kg, twice weekly, s.c.), and VEH (vehicle, daily, p.o.). L-ODN and ALN doses were selected to approximate the clinical exposures of the ODN 50-mg and ALN 70-mg once-weekly, respectively. L-ODN and ALN effectively reduced bone resorption markers uNTx and sCTx compared to VEH. There was no additional efficacy with these markers achieved with H-ODN. Conversely, ODN displayed inversely dose-dependent reduction of bone formation markers, sP1NP and sBSAP, and L-ODN reduced formation to a lesser degree than ALN. At month 18 post-OVX, L-ODN showed robust increases in lumbar spine aBMD (11.4%, p < 0.001), spine trabecular vBMD (13.7%, p < 0.001), femoral neck (FN) integral (int) vBMD (9.0%, p < 0.001) and sub-trochanteric proximal femur (SubTrPF) int vBMD, (6.4%, p < 0.001) compared to baseline. L-ODN significantly increased FN cortical thickness (Ct.Th) and cortical bone mineral content (Ct.BMC) by 22.5% (p < 0.001) and 21.8% (p < 0.001), respectively, and SubTrPF Ct.Th and Ct.BMC by 10.9% (p < 0.001) and 11.3% (p < 0.001) respectively. Compared to ALN, L-ODN significantly increased FN Ct. BMC by 8.7% (p < 0.05), and SubTrPF Ct.Th by 7.6% (p < 0.05) and Ct.BMC by 6.2% (p < 0.05). H-ODN showed no additional efficacy compared to L-ODN in OVX-monkeys in prevention mode. Taken together, the results from this study have demonstrated that administration of ODN at levels which approximate clinical exposure in OVX-monkeys had comparable efficacy to ALN in DXA-based aBMD and QCT-based vBMD. However, FN cortical mineral content clearly demonstrated superior efficacy of ODN versus ALN in this model of estrogen-deficient non-human primates.     

Novel EP4 Receptor Agonist‐Bisphosphonate Conjugate Drug (C1) Promotes Bone Formation and Improves Vertebral Mechanical Properties in the Ovariectomized Rat Model of Postmenopausal Bone Loss

Current treatments for postmenopausal osteoporosis aim to either promote bone formation or inhibit bone resorption. The C1 conjugate drug represents a new treatment approach by chemically linking the antiresorptive compound alendronate (ALN) with the anabolic agent prostanoid EP4 receptor agonist (EP4a) through a linker molecule (LK) to form a conjugate compound. This enables the bone‐targeting ability of ALN to deliver EP4a to bone sites and mitigate the systemic side effects of EP4a, while also facilitating dual antiresorptive and anabolic effects. In vivo hydrolysis is required to release the EP4a and ALN components for pharmacological activity. Our study investigated the in vivo efficacy of this drug in treating established bone loss using an ovariectomized (OVX) rat model of postmenopausal osteopenia. In a curative experiment, 3‐month‐old female Sprague‐Dawley rats were OVX, allowed to lose bone for 7 weeks, then treated for 6 weeks. Treatment groups consisted of C1 conjugate at low and high doses, vehicle‐treated OVX and sham, prostaglandin E₂ (PGE₂), and mixture of unconjugated ALN‐LK and EP4a to assess the effect of conjugation. Results showed that weekly administration of C1 conjugate dose‐dependently increased bone volume in trabecular bone, which partially or completely reversed OVX‐induced bone loss in the lumbar vertebra and improved vertebral mechanical strength. The conjugate also dose‐dependently stimulated endocortical woven bone formation and intracortical resorption in cortical bone, with high‐dose treatment increasing the mechanical strength but compromising the material properties. Conjugation between the EP4a and ALN‐LK components was crucial to the drug's anabolic efficacy. To our knowledge, the C1 conjugate represents the first time that a combined therapy using an anabolic agent and the antiresorptive compound ALN has shown significant anabolic effects which reversed established osteopenia. © 2014 American Society for Bone and Mineral Research.     

Comparable Effects of Alendronate and Strontium Ranelate on Femur in Ovariectomized Rats

This study compared the effects of alendronate (ALN) and strontium ranelate (SR) on bone mineral density (BMD), bone histomorphometry, and biomechanics in ovariectomized (OVX) rats. We randomly assigned 48 3-month-old female Sprague–Dawley rats to four groups: sham, OVX, ALN, and SR. Rats in the OVX, ALN, and SR groups received bilateral OVX. Rats in the ALN and SR groups were orally administrated ALN (7 mg/kg/week) and SR (500 mg/kg/day). Rats in the sham and OVX groups were treated with saline. All treatments continued for 12 weeks. Femoral BMD examination, distal femoral bone histomorphometry analysis, and biomechanical tests at the femoral diaphysis and metaphysis were performed to evaluate the effects of treatments in OVX rats. Results showed that both ALN and SR significantly increased femoral BMD (total femur, diaphyseal BMD, and distal metaphyseal BMD), distal femoral bone histomorphometric parameters (BV/TV, Tb.N, and Tb.Th), and femoral biomechanical parameters (maximum load, failure load, stiffness) compared with the OVX group (P < 0.05). No differences were found between ALN and SR in increasing femoral BMD, distal femoral bone histomorphometric parameters (BV/TV, Tb.N, and Tb.Th), and femoral diaphysis biomechanical parameters (maximum load, failure load, stiffness) (P > 0.05). The SR group was inferior to the ALN group in femoral metaphysis biomechanical parameters (P < 0.05). In conclusion, ALN (7 mg/kg/week) and SR (500 mg/kg/day) have similar effects by increasing BMD, distal femoral bone histomorphometric parameters, and femoral metaphysis biomechanical properties. Although ALN has greater effects than SR on distal femoral metaphysis biomechanical properties, in general, ALN and SR have comparable effects on the femur in OVX rats.