Bone density, turnover, and estimated strength in postmenopausal women treated with odanacatib: a randomized trial

Efficacy and safety of odanacatib in the treatment of postmenopausal women with osteoporosis: a meta-analysis

BACKGROUND

Osteoporosis, a systemic skeletal disease, seriously affects the quality of life in postmenopausal women. As one type of cathepsin K (CatK) inhibitor, odanacatib (ODN) is a fresh medication for osteoporosis. Considering the potential of ODN, we further examined the effect and safety of ODN for postmenopausal osteoporosis (PMOP) with a meta-analysis.

METHODS

PubMed, EMBASE, Cochrane Library, and Web of Science were searched for eligible studies from inception to December 29th, 2023. After that, we conducted a comprehensive meta-analysis following PRISMA guidelines. Risk of bias was meticulously investigated with the Cochrane Collaboration's tool. Efficacy was assessed with bone mineral density (BMD) at different sites (lumbar spine, trochanter, radius, femoral neck) and biomarkers of bone turnover (P1NP, uNTx/Cr, s-CTx, BSAP). Safety was evaluated by analyzing total, serious, other, and skin adverse events (AEs).

RESULTS

Four random clinical trials (RCTs) were involved in our research. All trials were rated as having high quality and met the eligibility criteria. In the current research, ODN was found to elevate BMD at lumbar spine, femoral neck, total hip, trochanter and forearm, while it decreased the levels of serum C-telopeptides of type I collagen (s-CTx) as well as urinary N-telopeptide/creatinine ratio (uNTx/Cr). No significant differences were observed in AEs between the ODN group and the control group.

CONCLUSIONS

ODN is a promising alternative for the treatment of PMOP on account of its excellent efficacy and credible safety. Unclear links between ODN and cardiovascular AEs require further research to clarify.

Inhibition of cysteine protease disturbs the topological relationship between bone resorption and formation in vitro

INTRODUCTION

Osteoporosis is a global health issue. Bisphosphonates that are commonly used to treat osteoporosis suppress both bone resorption and subsequent bone formation. Inhibition of cathepsin K, a cysteine proteinase secreted by osteoclasts, was reported to suppress bone resorption while preserving or increasing bone formation. Analyses of the different effects of antiresorptive reagents such as bisphosphonates and cysteine proteinase inhibitors will contribute to the understanding of the mechanisms underlying bone remodeling.

MATERIALS AND METHODS

Our team has developed an in vitro system in which bone remodeling can be temporally observed at the cellular level by 2-photon microscopy. We used this system in the present study to examine the effects of the cysteine proteinase inhibitor E-64 and those of zoledronic acid on bone remodeling.

RESULTS

In the control group, the amount of the reduction and the increase in the matrix were correlated in each region of interest, indicating the topological and quantitative coordination of bone resorption and formation. Parameters for osteoblasts, osteoclasts, and matrix resorption/formation were also correlated. E-64 disrupted the correlation between resorption and formation by potentially inhibiting the emergence of spherical osteoblasts, which are speculated to be reversal cells in the resorption sites.

CONCLUSION

These new findings help clarify coupling mechanisms and will contribute to the development of new drugs for osteoporosis.

Metabolic bone disorders and the promise of marine osteoactive compounds

Metabolic bone disorders and associated fragility fractures are major causes of disability and mortality worldwide and place an important financial burden on the global health systems. These disorders result from an unbalance between bone anabolic and resorptive processes and are characterized by different pathophysiological mechanisms. Drugs are available to treat bone metabolic pathologies, but they are either poorly effective or associated with undesired side effects that limit their use. The molecular mechanism underlying the most common metabolic bone disorders, and the availability, efficacy, and limitations of therapeutic options currently available are discussed here. A source for the unmet need of novel drugs to treat metabolic bone disorders is marine organisms, which produce natural osteoactive compounds of high pharmaceutical potential. In this review, we have inventoried the marine osteoactive compounds (MOCs) currently identified and spotted the groups of marine organisms with potential for MOC production. Finally, we briefly examine the availability of in vivo screening and validation tools for the study of MOCs.

Development and application of decatungstate catalyzed C-H 18F- and 19F-fluorination, fluoroalkylation and beyond

Over the past few decades, photocatalytic C-H functionalization reactions have received increasing attention due to the often mild reaction conditions and complementary selectivities to conventional functionalization processes. Now, photocatalytic C-H functionalization is a widely employed tool, supporting activities ranging from complex molecule synthesis to late-stage structure-activity relationship studies. In this perspective, we will discuss our efforts in developing a photocatalytic decatungstate catalyzed C-H fluorination reaction as well as its practical application realized through collaborations with industry partners at Hoffmann-La Roche and Merck, and extension to radiofluorination with radiopharmaceutical chemists and imaging experts at TRIUMF and the BC Cancer Agency. Importantly, we feel that our efforts address a question of utility posed by Professor Tobias Ritter in "Late-Stage Fluorination: Fancy Novelty or Useful Tool?" (ACIE, 2015, 54, 3216). In addition, we will discuss decatungstate catalyzed C-H fluoroalkylation and the interesting electrostatic effects observed in decatungstate-catalyzed C-H functionalization. We hope this perspective will inspire other researchers to explore the use of decatungstate for the purposes of photocatalytic C-H functionalization and further advance the exploitation of electrostatic effects for both rate acceleration and directing effects in these reactions.

Relative Effects of Radiation-Induced Changes in Bone Mass, Structure, and Tissue Material on Vertebral Strength in a Rat Model

The observed increased risk of fracture after cancer radiation therapy is presumably due to a radiation-induced reduction in whole-bone strength. However, the mechanisms for impaired strength remain unclear, as the increased fracture risk is not fully explained by changes in bone mass. To provide insight, a small animal model was used to determine how much of this whole-bone weakening effect for the spine is attributable to changes in bone mass, structure, and material properties of the bone tissue and their relative effects. Further, because women have a greater risk of fracture after radiation therapy than men, we investigated if sex had a significant influence on bone's response to irradiation. Fractionated in vivo irradiation (10 × 3 Gy) or sham irradiation (0 Gy) was administered daily to the lumbar spine in twenty-seven 17-week-old Sprague-Dawley rats (n = 6-7/sex/group). Twelve weeks after final treatment, animals were euthanized, and lumbar vertebrae (L4 and L5 ) were isolated. Using a combination of biomechanical testing, micro-CT-based finite element analysis, and statistical regression analysis, we separated out the effect of mass, structural, and tissue material changes on vertebral strength. Compared with the sham group (mean ± SD strength = 420 ± 88 N), the mean strength of the irradiated group was lower by 28% (117 N/420 N, p < 0.0001). Overall, the response of treatment did not differ with sex. By combining results from both general linear regression and finite element analyses, we calculated that mean changes in bone mass, structure, and material properties of the bone tissue accounted for 56% (66 N/117 N), 20% (23 N/117 N), and 24% (28 N/117 N), respectively, of the overall change in strength. As such, these results provide insight into why an elevated clinical fracture risk for patients undergoing radiation therapy is not well explained by changes in bone mass alone. © 2023 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Efficacy and safety of odanacatib for osteoporosis treatment: a systematic review and meta-analysis

PURPOSE

Osteoporosis is a metabolic bone disease that commonly results in middle-aged and elderly people following fractures. Odanacatib (ODN), a potential osteoporosis medication, was stopped in the Long-term Odanacatib Fracture Trial (LOFT) phase III study because it increased the risk of stroke. Herein, we conducted a systematic review and meta-analysis to further assess the efficacy and safety of ODN in osteoporosis treatment.

METHODS

We searched the PubMed, EMBASE, Cochrane Library, and Web of Science, using the core search terms "osteoporosis" and "odanacatib." The primary outcomes were the percentage change in markers of bone turnover and bone formation as well as that in the bone mineral density (BMD) of the lumbar spine, hip, femoral neck, and greater trochanter. The secondary outcome was the risk of adverse events (AEs), used to explore the safety of ODN.

RESULTS

Ten articles-all double-blinded, randomized, placebo-controlled trials-were included. All trials were considered to be of high quality if they met the inclusion and exclusion criteria. We found that ODN increases BMD in the lumbar spine, total hip, and femoral neck, whereas it decreases the concentration of serum C-telopeptides of type I collagen (sCTx) and urinary N-telopeptide/creatinine ratio (uNTx/Cr). We found no significant differences in total, drug-related, serious, or skin AEs between the ODN and control groups. However, significant differences in fracture and stroke AEs were found between the ODN and control groups.

CONCLUSION

ODN is an appealing long-term osteoporosis treatment method; however, further research should focus on the potential increased risk of fracture and stroke.

Cathepsin K: A Versatile Potential Biomarker and Therapeutic Target for Various Cancers

Cancer, a common malignant disease, is one of the predominant causes of diseases that lead to death. Additionally, cancer is often detected in advanced stages and cannot be radically cured. Consequently, there is an urgent need for reliable and easily detectable markers to identify and monitor cancer onset and progression as early as possible. Our aim was to systematically review the relevant roles of cathepsin K (CTSK) in various possible cancers in existing studies. CTSK, a well-known key enzyme in the bone resorption process and most studied for its roles in the effective degradation of the bone extracellular matrix, is expressed in various organs. Nowadays, CTSK has been involved in various cancers such as prostate cancer, breast cancer, bone cancer, renal carcinoma, lung cancer and other cancers. In addition, CTSK can promote tumor cells proliferation, invasion and migration, and its mechanism may be related to RANK/RANKL, TGF-β, mTOR and the Wnt/β-catenin signaling pathway. Clinically, some progress has been made with the use of cathepsin K inhibitors in the treatment of certain cancers. This paper reviewed our current understanding of the possible roles of CTSK in various cancers and discussed its potential as a biomarker and/or novel molecular target for various cancers.

Cathepsin K+ Non-Osteoclast Cells in the Skeletal System: Function, Models, Identity, and Therapeutic Implications

Cathepsin K (Ctsk) is a cysteine protease of the papain superfamily initially identified in differentiated osteoclasts; it plays a critical role in degrading the bone matrix. However, subsequent in vivo and in vitro studies based on animal models elucidate novel subpopulations of Ctsk-expressing cells, which display markers and properties of mesenchymal stem/progenitor cells. This review introduces the function, identity, and role of Ctsk⁺ cells and their therapeutic implications in related preclinical osseous disorder models. It also summarizes the available in vivo models for studying Ctsk⁺ cells and their progeny. Further investigations of detailed properties and mechanisms of Ctsk⁺ cells in transgenic models are required to guide potential therapeutic targets in multiple diseases in the future.

Bisphosphonates and the risk of atypical femur fractures

Bisphosphonates are effective in reducing hip and other fractures. However, concerns about atypical femur fractures (AFFs) have contributed to substantially decreased bisphosphonate use, and hip fracture rates may be increasing. Despite this impact, important uncertainties remain regarding AFF risks including the association between bisphosphonate use and other risk factors such as BMD, age, weight, and race. To address this evidence gap, a cohort study of 196,129 women ≥50 years of age in the Southern California Kaiser Permanente HMO women (with ≥1 bisphosphonate prescription) were studied; the primary outcome was radiographically-adjudicated AFF between 2007 and 2017. Risk factors including bisphosphonate use and race were obtained from electronic health records. Multivariable Cox models were used for analysis. Benefit-risk was modeled for 1-10 years of bisphosphonates to compare fractures prevented vs. AFFs associated. Among 196,129 women, 277 (0.1%) sustained AFFs. After multivariable adjustment, AFF risk increased with longer bisphosphonate duration: hazard ratio (HR) increased from HR = 8.9 (95%CI: 2.8,28) for 3-5 years to HR = 43.5 (13.7138.1) for >8 years. Hip BMD, surprisingly, was not associated with AFF risk. Other risk factors included Asian ancestry (HR = 4.8 (3.6, 6.6)), short stature, overweight, and glucocorticoid use. Bisphosphonate discontinuation was associated with rapid decrease in AFF risk. Decreases in osteoporotic and hip fractures risk during 1-10 years of bisphosphonates far outweighed the increase AFF risk in Caucasians, but less so in Asians. In Caucasians, after 3 years 149 hip fractures were prevented with 2 AFFs associated compared to 91 and 8 in Asians. The evidence for several potential mechanisms is summarized with femoral geometry being the most likely to explain AFF risk differences between Asians and Caucasians. The results from this new study add to the evidence base for AFF risk factors and will help inform clinical decision-making for individual patients about initiation and duration of bisphosphonate therapy and drug holidays.

A patent review on cathepsin K inhibitors to treat osteoporosis (2011 - 2021)

INTRODUCTION

Cathepsin K (CatK) is a lysosomal cysteine protease and the predominant cathepsin expressed in osteoclasts, where it degrades the bone matrix. Hence, CatK is an attractive therapeutic target related to diseases characterized by bone resorption, like osteoporosis.

AREAS COVERED

This review summarizes the patent literature from 2011 to 2021 on CatK inhibitors and their potential use as new treatments for osteoporosis. The inhibitors were classified by their warheads, with the most explored nitrile-based inhibitors. Promising in vivo results have also been disclosed.

EXPERT OPINION

As one of the most potent lysosomal proteins whose primary function is to mediate bone resorption, cathepsin K remains an excellent target for therapeutic intervention. Nevertheless, there is no record of any approved drug that targets CatK. The most notable cases of drug candidates targeting CatK were balicatib and odanacatib, which reached Phase II and III clinical trials, respectively, but did not enter the market. Further developments include exploring new chemical entities beyond the nitrile-based chemical space, with improved ADME and safety profiles. In addition, CatK's role in cancer immunoexpression and its involvement in the pathophysiology of osteo- and rheumatoid arthritis have raised the race to develop activity-based probes with excellent potency and selectivity.

Early changes in bone turnover and bone mineral density after discontinuation of long-term oral bisphosphonates: a post hoc analysis

This post hoc analysis of a randomized, double-blind study of postmenopausal women with osteoporosis found that there were early increases in bone turnover markers and decreases in bone mineral density after discontinuation of long-term alendronate. These findings might help guide treatment decisions, including monitoring after alendronate withdrawal.

INTRODUCTION

The short-term effects of discontinuing long-term bisphosphonates are poorly characterized. This post hoc analysis investigated 1-12-month changes in bone mineral density (BMD) and bone turnover markers (BTM) after alendronate (ALN) discontinuation.

METHODS

Data were from a randomized, double-blind trial of MK-5442 (calcium-sensing receptor antagonist) following oral bisphosphonates, with placebo and continued ALN controls ( ClinicalTrials.gov NCT00996801). Postmenopausal women with osteoporosis had received oral bisphosphonate (≥ 3-4 preceding years; ALN for the 12 months pre-screening), continuing on ALN 70 mg/week (n = 87) or placebo (n = 88).

RESULTS

At 12 months, least-squares mean percent changes from baseline BMD (placebo vs. ALN) were lumbar spine (LS): - 0.36 vs. 1.29, total hip: - 1.44 vs. 0.46, and femoral neck (FN): - 1.26 vs. - 0.08 (all P < 0.05). BTM levels increased by 1-3 months, to 12 months, with placebo vs. ALN (P < 0.001). FN BMD decline was greater in the placebo subgroup with higher urinary N-terminal cross-linked telopeptides of type I collagen/creatinine [uNTx/Cr] (P < 0.01), and higher serum N-terminal pro-peptide of type 1 collagen [P1NP] levels (P < 0.05), at baseline. There was a trend toward greater FN BMD loss with higher BTM levels at 3 and/or 6 months. Younger age and higher LS BMD at baseline were associated with greater LS BMD loss at 12 months (P = 0.04 and < 0.01, respectively); higher baseline FN BMD predicted greater FN BMD loss (P = 0.04).

CONCLUSION

Early changes in BTM levels and BMD were observed after discontinuation of long-term ALN. Further characterization of factors associated with patients' risk of bone loss upon bisphosphonate discontinuation is warranted.

Preclinical evaluation of [11 C]L-235 as a radioligand for Positron Emission Tomography cathepsin K imaging in bone

The cathepsin K (CatK) enzyme is abundantly expressed in osteoclasts, and CatK inhibitors have been developed for the treatment of osteoporosis. In our effort to support discovery and clinical evaluations of a CatK inhibitor, we sought to discover a radioligand to determine target engagement of the enzyme by therapeutic candidates using positron emission tomography (PET). L-235, a potent and selective CatK inhibitor, was labeled with carbon-11. PET imaging studies recording baseline distribution of [¹¹ C]L-235, and chase and blocking studies using the selective CatK inhibitor MK-0674 were performed in juvenile and adult nonhuman primates (NHP) and ovariectomized rabbits. Retention of the PET tracer in regions expected to be osteoclast-rich compared with osteoclast-poor regions was examined. Increased retention of the radioligand was observed in osteoclast-rich regions of juvenile rabbits and NHP but not in the adult monkey or adult ovariectomized rabbit. Target engagement of CatK was observed in blocking studies with MK-0674, and the radioligand retention was shown to be sensitive to the level of MK-0674 exposure. [¹¹ C]L-235 can assess target engagement of CatK in bone only in juvenile animals. [¹¹ C]L-235 may be a useful tool for guiding the discovery of CatK inhibitors.

Risk of falls in patients with low bone mineral density : Analysis of placebo arms from clinical trials

BACKGROUND

Falls are a major risk factor for osteoporotic fractures. Therefore, the aim of this study was to analyze the risk of falls in patients with low bone mineral density (BMD) and osteoporosis.

METHODS

The risk of falls in patients with low BMD and/or osteoporosis was analyzed using data from placebo arms of clinical trials, indexed on clinicaltrials.gov. The risk was estimated using a single arm meta-analysis method and by applying a binary random effects model. In addition, meta-regression analyses were performed to identify associations between risk of falls and age, body mass index (BMI) and BMD.

RESULTS

A total of 8762 patients from placebo arms of clinical trials were included into the analysis. Risk of falls was 5.2% (0.052, 95% confidence interval [95% CI] 0.022-0.082; n = 8714; I² = 97.3%, p ≤ 0.001) in patients with low BMD and/or osteoporosis and 5.9% (0.059, 95% CI 0.036-0.083; n = 7819; I² = 87.8%, p ≤ 0.001) in patients with osteoporosis. A significant association with risk of falls was identified for age in patients with low BMD and/or osteoporosis. BMD at total hip (TH; coefficient -0.077, 95% CI: -0.113--0.040, p ≤ 0.001; n = 7715) and femoral neck (FN; coefficient -0.044, 95% CI -0.065--0.023, p ≤ 0.001; n = 7662) were significantly associated with risk of falls in patients with osteoporosis.

CONCLUSION

This analysis identified the risk of falls in patients with low BMD and osteoporosis and an association of falls with age and BMD. Therefore, patients with osteoporosis need to receive mandatory fall risk mitigation measures, and the BMD at total hip or femoral neck could function as an indicator for the risk of falling.

Effects of Odanacatib on Bone Structure and Quality in Postmenopausal Women With Osteoporosis: 5-Year Data From the Phase 3 Long-Term Odanacatib Fracture Trial (LOFT) and its Extension

Odanacatib (ODN), a selective oral inhibitor of cathepsin K, was an investigational agent previously in development for the treatment of osteoporosis. In this analysis, the effects of ODN on bone remodeling/modeling and structure were examined in the randomized, double-blind, placebo-controlled, event-driven, Phase 3, Long-term Odanacatib Fracture Trial (LOFT; NCT00529373) and planned double-blind extension in postmenopausal women with osteoporosis. A total of 386 transilial bone biopsies, obtained from consenting patients at baseline (ODN n = 17, placebo n = 23), month 24 (ODN n = 112, placebo n = 104), month 36 (ODN n = 42, placebo n = 41), and month 60 (ODN n = 27, placebo n = 20) were assessed by dynamic and static bone histomorphometry. Patient characteristics at baseline and BMD changes over 5 years for this subset were comparable to the overall LOFT population. Qualitative assessment of biopsies revealed no abnormalities. Consistent with the mechanism of ODN, osteoclast number was higher with ODN versus placebo over time. Regarding bone remodeling, dynamic bone formation indices in trabecular, intracortical, and endocortical surfaces were generally similar in ODN-treated versus placebo-treated patients after 2 years of treatment. Regarding periosteal modeling, the proportion of patients with periosteal double labels and the bone formation indices increased over time in the ODN-treated patients compared with placebo. This finding supported the observed numerical increase in cortical thickness at month 60 versus placebo. In conclusion, ODN treatment for 5 years did not reduce bone remodeling and increased the proportion of patients with periosteal bone formation. These results are consistent with the mechanism of action of ODN, and are associated with continued BMD increases and reduced risk of fractures compared with placebo in the LOFT Phase 3 fracture trial. © 2020 American Society for Bone and Mineral Research.

Biomechanical Computed Tomography analysis (BCT) for clinical assessment of osteoporosis

The surgeon general of the USA defines osteoporosis as "a skeletal disorder characterized by compromised bone strength, predisposing to an increased risk of fracture." Measuring bone strength, Biomechanical Computed Tomography analysis (BCT), namely, finite element analysis of a patient's clinical-resolution computed tomography (CT) scan, is now available in the USA as a Medicare screening benefit for osteoporosis diagnostic testing. Helping to address under-diagnosis of osteoporosis, BCT can be applied "opportunistically" to most existing CT scans that include the spine or hip regions and were previously obtained for an unrelated medical indication. For the BCT test, no modifications are required to standard clinical CT imaging protocols. The analysis provides measurements of bone strength as well as a dual-energy X-ray absorptiometry (DXA)-equivalent bone mineral density (BMD) T-score at the hip and a volumetric BMD of trabecular bone at the spine. Based on both the bone strength and BMD measurements, a physician can identify osteoporosis and assess fracture risk (high, increased, not increased), without needing confirmation by DXA. To help introduce BCT to clinicians and health care professionals, we describe in this review the currently available clinical implementation of the test (VirtuOst), its application for managing patients, and the underlying supporting evidence; we also discuss its main limitations and how its results can be interpreted clinically. Together, this body of evidence supports BCT as an accurate and convenient diagnostic test for osteoporosis in both sexes, particularly when used opportunistically for patients already with CT. Biomechanical Computed Tomography analysis (BCT) uses a patient's CT scan to measure both bone strength and bone mineral density at the hip or spine. Performing at least as well as DXA for both diagnosing osteoporosis and assessing fracture risk, BCT is particularly well-suited to "opportunistic" use for the patient without a recent DXA who is undergoing or has previously undergone CT testing (including hip or spine regions) for an unrelated medical condition.

Perspectives on the non-invasive evaluation of femoral strength in the assessment of hip fracture risk

We reviewed the experimental and clinical evidence that hip bone strength estimated by BMD and/or finite element analysis (FEA) reflects the actual strength of the proximal femur and is associated with hip fracture risk and its changes upon treatment.

INTRODUCTION

The risk of hip fractures increases exponentially with age due to a progressive loss of bone mass, deterioration of bone structure, and increased incidence of falls. Areal bone mineral density (aBMD), measured by dual-energy X-ray absorptiometry (DXA), is the most used surrogate marker of bone strength. However, age-related declines in bone strength exceed those of aBMD, and the majority of fractures occur in those who are not identified as osteoporotic by BMD testing. With hip fracture incidence increasing worldwide, the development of accurate methods to estimate bone strength in vivo would be very useful to predict the risk of hip fracture and to monitor the effects of osteoporosis therapies.

METHODS

We reviewed experimental and clinical evidence regarding the association between aBMD and/orCT-finite element analysis (FEA) estimated femoral strength and hip fracture risk as well as their changes with treatment.

RESULTS

Femoral aBMD and bone strength estimates by CT-FEA explain a large proportion of femoral strength ex vivo and predict hip fracture risk in vivo. Changes in femoral aBMD are strongly associated with anti-fracture efficacy of osteoporosis treatments, though comparable data for FEA are currently not available.

CONCLUSIONS

Hip aBMD and estimated femoral strength are good predictors of fracture risk and could potentially be used as surrogate endpoints for fracture in clinical trials. Further improvements of FEA may be achieved by incorporating trabecular orientations, enhanced cortical modeling, effects of aging on bone tissue ductility, and multiple sideway fall loading conditions.

Pushing the boundaries of C–H bond functionalization chemistry using flow technology

C–H functionalization chemistry is one of the most vibrant research areas within synthetic organic chemistry. While most researchers focus on the development of small-scale batch-type transformations, more recently such transformations have been carried out in flow reactors to explore new chemical space, to boost reactivity or to enable scalability of this important reaction class. Herein, an up-to-date overview of C–H bond functionalization reactions carried out in continuous-flow microreactors is presented. A comprehensive overview of reactions which establish the formal conversion of a C–H bond into carbon–carbon or carbon–heteroatom bonds is provided; this includes metal-assisted C–H bond cleavages, hydrogen atom transfer reactions and C–H bond functionalizations which involve an SE-type process to aromatic or olefinic systems. Particular focus is devoted to showcase the advantages of flow processing to enhance C–H bond functionalization chemistry. Consequently, it is our hope that this review will serve as a guide to inspire researchers to push the boundaries of C–H functionalization chemistry using flow technology.

Effects of Long-Duration Spaceflight on Vertebral Strength and Risk of Spine Fracture

Although the negative impact of long-duration spaceflight on spine BMD has been reported, its impact on vertebral strength and risk of vertebral fracture remains unknown. This study examined 17 crewmembers with long-duration service on the International Space Station in whom computed tomography (CT) scans of the lumbar spine (L₁ and L₂ ) were collected preflight, immediately postflight and 1 to 4 years after return to Earth. We assessed vertebral strength via CT-based finite element analysis (CT-FEA) and spinal loading during different activities via subject-specific musculoskeletal models. Six months of spaceflight reduced vertebral strength by 6.1% (-2.3%, -8.7%) (median [interquartile range]) compared to preflight (p < 0.05), with 65% of subjects experiencing deficits of greater than 5%, and strengths were not recovered up to 4 years after the mission. This decline in vertebral strength exceeded (p < 0.05) the 2.2% (-1.3%, -6.0%) decline in lumbar spine DXA-BMD. Further, the subject-specific changes in vertebral strength were not correlated with the changes in DXA-BMD. Although spinal loading increased slightly postflight, the ratio of vertebral compressive load to vertebral strength for typical daily activities remained well below a value of 1.0, indicating a low risk of vertebral fracture despite the loss in vertebral strength. However, for more strenuous activity, the postflight load-to-strength ratios ranged from 0.3 to 0.7, indicating a moderate risk of vertebral fracture in some individuals. Our findings suggest persistent deficits in vertebral strength following long-duration spaceflight, and although risk of vertebral fracture remains low for typical activities, the risk of vertebral fracture is notable in some crewmembers for strenuous exercise requiring maximal effort. © 2019 American Society for Bone and Mineral Research.

Odanacatib for the treatment of postmenopausal osteoporosis: results of the LOFT multicentre, randomised, double-blind, placebo-controlled trial and LOFT Extension study

BACKGROUND

Odanacatib, a cathepsin K inhibitor, reduces bone resorption while maintaining bone formation. Previous work has shown that odanacatib increases bone mineral density in postmenopausal women with low bone mass. We aimed to investigate the efficacy and safety of odanacatib to reduce fracture risk in postmenopausal women with osteoporosis.

METHODS

The Long-term Odanacatib Fracture Trial (LOFT) was a multicentre, randomised, double-blind, placebo-controlled, event-driven study at 388 outpatient clinics in 40 countries. Eligible participants were women aged at least 65 years who were postmenopausal for 5 years or more, with a femoral neck or total hip bone mineral density T-score between -2·5 and -4·0 if no previous radiographic vertebral fracture, or between -1·5 and -4·0 with a previous vertebral fracture. Women with a previous hip fracture, more than one vertebral fracture, or a T-score of less than -4·0 at the total hip or femoral neck were not eligible unless they were unable or unwilling to use approved osteoporosis treatment. Participants were randomly assigned (1:1) to either oral odanacatib (50 mg once per week) or matching placebo. Randomisation was done using an interactive voice recognition system after stratification for previous radiographic vertebral fracture, and treatment was masked to study participants, investigators and their staff, and sponsor personnel. If the study completed before 5 years of double-blind treatment, consenting participants could enrol in a double-blind extension study (LOFT Extension), continuing their original treatment assignment for up to 5 years from randomisation. Primary endpoints were incidence of vertebral fractures as assessed using radiographs collected at baseline, 6 and 12 months, yearly, and at final study visit in participants for whom evaluable radiograph images were available at baseline and at least one other timepoint, and hip and non-vertebral fractures adjudicated as being a result of osteoporosis as assessed by clinical history and radiograph. Safety was assessed in participants who received at least one dose of study drug. The adjudicated cardiovascular safety endpoints were a composite of cardiovascular death, myocardial infarction, or stroke, and new-onset atrial fibrillation or flutter. Individual cardiovascular endpoints and death were also assessed. LOFT and LOFT Extension are registered with ClinicalTrials.gov (number NCT00529373) and the European Clinical Trials Database (EudraCT number 2007-002693-66).

FINDINGS

Between Sept 14, 2007, and Nov 17, 2009, we randomly assigned 16 071 evaluable patients to treatment: 8043 to odanacatib and 8028 to placebo. After a median follow-up of 36·5 months (IQR 34·43-40·15) 4297 women assigned to odanacatib and 3960 assigned to placebo enrolled in LOFT Extension (total median follow-up 47·6 months, IQR 35·45-60·06). In LOFT, cumulative incidence of primary outcomes for odanacatib versus placebo were: radiographic vertebral fractures 3·7% (251/6770) versus 7·8% (542/6910), hazard ratio (HR) 0·46, 95% CI 0·40-0·53; hip fractures 0·8% (65/8043) versus 1·6% (125/8028), 0·53, 0·39-0·71; non-vertebral fractures 5·1% (412/8043) versus 6·7% (541/8028), 0·77, 0·68-0·87; all p<0·0001. Combined results from LOFT plus LOFT Extension for cumulative incidence of primary outcomes for odanacatib versus placebo were: radiographic vertebral fractures 4·9% (341/6909) versus 9·6% (675/7011), HR 0·48, 95% CI 0·42-0·55; hip fractures 1·1% (86/8043) versus 2·0% (162/8028), 0·52, 0·40-0·67; non-vertebral fractures 6·4% (512/8043) versus 8·4% (675/8028), 0·74, 0·66-0·83; all p<0·0001. In LOFT, the composite cardiovascular endpoint of cardiovascular death, myocardial infarction, or stroke occurred in 273 (3·4%) of 8043 patients in the odanacatib group versus 245 (3·1%) of 8028 in the placebo group (HR 1·12, 95% CI 0·95-1·34; p=0·18). New-onset atrial fibrillation or flutter occurred in 112 (1·4%) of 8043 patients in the odanacatib group versus 96 (1·2%) of 8028 in the placebo group (HR 1·18, 0·90-1·55; p=0·24). Odanacatib was associated with an increased risk of stroke (1·7% [136/8043] vs 1·3% [104/8028], HR 1·32, 1·02-1·70; p=0·034), but not myocardial infarction (0·7% [60/8043] vs 0·9% [74/8028], HR 0·82, 0·58-1·15; p=0·26). The HR for all-cause mortality was 1·13 (5·0% [401/8043] vs 4·4% [356/8028], 0·98-1·30; p=0·10). When data from LOFT Extension were included, the composite of cardiovascular death, myocardial infarction, or stroke occurred in significantly more patients in the odanacatib group than in the placebo group (401 [5·0%] of 8043 vs 343 [4·3%] of 8028, HR 1·17, 1·02-1·36; p=0·029, as did stroke (2·3% [187/8043] vs 1·7% [137/8028], HR 1·37, 1·10-1·71; p=0·0051).

INTERPRETATION

Odanacatib reduced the risk of fracture, but was associated with an increased risk of cardiovascular events, specifically stroke, in postmenopausal women with osteoporosis. Based on the overall balance between benefit and risk, the study's sponsor decided that they would no longer pursue development of odanacatib for treatment of osteoporosis.

FUNDING

Merck Sharp & Dohme Corp, a subsidiary of Merck & Co, Inc, Kenilworth, NJ, USA.

Clinical and translational pharmacology of the cathepsin K inhibitor odanacatib studied for osteoporosis

Cathepsin K (CatK) is a cysteine protease abundantly expressed by osteoclasts and localized in the lysosomes and resorption lacunae of these cells. CatK is the principal enzyme responsible for the degradation of bone collagen. Odanacatib is a selective, reversible inhibitor of CatK at subnanomolar potency. The pharmacokinetics of odanacatib have been extensively studied and are similar in young healthy men, postmenopausal women and elderly men, and were qualitatively similar throughout Phase 1 development and in-patient studies. Following 3 weeks of 50 mg once weekly dosing the geometric mean area under the curve from 0 to 168 hours was 41.1 μM h, the concentration at 168 hours was 126 nM and the harmonic mean apparent terminal half-life was 84.8 hr. Odanacatib exposure increased in a less than dose proportional manner due to solubility limited absorption. It is estimated that approximately 70% of the absorbed dose of odanacatib is eliminated via metabolism, 20% is excreted as unchanged drug in the bile or faeces, and 10% is excreted as unchanged drug in the urine. The systemic clearance was low (approximately 13 mL/min). Odanacatib decreases the degradation of bone matrix proteins and reduces the efficiency of bone resorption with target engagement confirmed by a robust decrease in serum C-telopeptides of type 1 collagen (approximately 60%), urinary aminoterminal crosslinked telopeptides of type 1 collagen to creatinine ratio (approximately 50%) and total urine deoxypyridinoline/Cr (approximately 30%), with an increase in serum cross-linked carboxy-terminal telopeptide of type 1 collagen (approximately 55%). The 50-mg weekly dosing regimen evaluated in Phase 3 achieved near maximal reduction in bone resorption throughout the treatment period. The extensive clinical programme for odanacatib, together with more limited clinical experience with other CatK inhibitors (balicatib and ONO-5334), provides important insights into the clinical pharmacology of CatK inhibition and the potential role of CatK in bone turnover and mineral homeostasis. Key findings include the ability of this mechanism to: (i) provide sustained reductions in resorption markers, increases in bone mineral density, and demonstrated fracture risk reduction; (ii) be associated with relative formation-sparing effects such that sustained resorption reduction is achieved without accompanying meaningful reductions in bone formation; and (iii) lead to increases in osteoclast number as well as other osteoclast activity (including build-up of CatK enzyme), which may yield transient increases in resorption following treatment discontinuation and the potential for nonmonotonic responses at subtherapeutic doses.

Assessment of finite element models for prediction of osteoporotic fracture

With increasing life expectancy and mortality rates, the burden of osteoporotic hip fractures is continually on an upward trend. In terms of prevention, there are several osteoporosis treatment strategies such as anti-resorptive drug treatments, which attempt to retard the rate of bone resorption, while promoting the rate of formation. With respect to prediction, several studies have provided insights into obtaining bone strength by non-invasive means through the application of FE analysis. However, what valuable information can we obtain from FE studies that have focused on osteoporosis research, with respect to the prediction of osteoporotic fractures? This paper aims to fine studies that have used FE analysis to predict fractures in the proximal femur through a systematic search of literature using PUBMED, with the main objective of supporting the diagnosis of osteoporosis. The focus of these FE studies is first discussed, and the methodological aspects are summarized, by mainly comparing and contrasting their meshing properties, material properties, and boundary conditions. The implications of these methodological differences in FE modelling processes and propositions with the aim of consolidating or minimalizing these differences are further discussed. We proved that studies need to start converging in terms of their input parameters to make the FE method applicable to clinical settings. This, in turn, will decrease the time needed for in vitro tests. Current advancements in FE analysis need to be consolidated before any further steps can be taken to implement engineering analysis into the clinical scenario.

A novel technique with reduced computed tomography exposure to predict vertebral compression fracture: a finite element study based on rat vertebrae

Vertebral compression fractures are a significant clinical issue with an annual incidence of approximately 750,000 cases in the USA alone. Mechanical properties of vertebrae are successfully evaluated through finite element (FE) models based on vertebrae CT. However, clinical drawbacks associated to radiation transmission encouraged to explore the possibility to use selected or reduced portions of the vertebra. The objective of our study was to develop a new procedure to predict vertebral compression fracture from sub-volumes. We reconstructed rat vertebras from micro-CT of thoracic and lumbar groups. Each vertebra was partitioned into three sub-volumes of different axial thickness. FE simulating compression tests were performed on each model to evaluate their failure load and stiffness. Using a power function, a high correlation was found for stiffness and strength. The sub-volume with three fifths thickness had a failure load of 180.7 ± 19.2 N for thoracic and of 209.5 ± 27.4 N for the lumbar vertebra. These values were not significantly different from the values found for the entire vertebra (p > 0.05). Based on our findings, failure loads and stiffnesses obtained with reduced CT scans can be successfully used to predict full vertebral failure. This sub-region analysis and power relationship suggests that one can limit radiation exposure to patients when bone characterization is needed. Graphical abstract Estimated mechanical properties in relation to the extent of the computed tomography reconstruction.

Chitosan-gold nanoparticles mediated gene delivery of c-myb facilitates osseointegration of dental implants in ovariectomized rat

Osseointegration of dental implants is affected by osteoporosis. The purpose of this study was overcome the implant failure and facilitate the osseointegration of dental implants by c-myb in ovariectomized (OVX)-induced osteoporosis. c-myb is a transcription factor and supports bone formation. Plasmid DNA/c-myb conjugated with chitosan-gold nanoparticles (Ch-GNPs/c-myb) promoted osteogenesis and inhibited osteoclastogenesis in MC-3T3 E1 cells. Ch-GNPs/c-myb involved the reduction of the nuclear factor of activated T-cells 1, c-Fos, and tartrate-resistant acid phosphatase-positive multinucleated osteoclasts in receptor activator of nuclear factor-κB ligand (RANKL) stimulated bone marrow macrophages. In vivo results of rat mandibles demonstrated Ch-GNP/c-myb-coated titanium (Ti) implants increased the volume and density of newly formed bone and the osseointegration of dental implant with bone by micro computed tomography examination after OVX-induced osteoporosis. Immunohistochemical analysis showed increased c-myb expression and upregulation of bone morphogenic proteins, osteoprotegerin and EphB4, as well as the downregulation of RANKL by Ch-GNP/c-myb-coated Ti implants. Hematoxylin and Eosin staining expressed new bone formation by Ch-GNP/c-myb-coated Ti implants. Our findings indicated that c-myb delivered by Ch-GNPs supports osseointegration of dental implant even in osteoporotic condition. c-myb may be applicable to support dental implant integration and treatment in age-dependent bone destruction disease.

The effect of ovariectomy and 2 antiresorptive therapeutic agents on bone response in rats: A 3-dimensional imaging analysis

OBJECTIVE

The aim of this study was to evaluate bone mineral density (BMD) and microarchitecture in femurs and maxillary bones of ovariectomized (OVX) rats treated or not treated with alendronate (ALD) or odanacatib (ODN).

STUDY DESIGN

Twenty rats were divided into groups: SHAM, OVX, OVX/ALD, and OVX/ODN. After 12 weeks, the femurs and maxillae were removed and subjected to 3-dimensional analysis by micro-computed tomography. Results were analyzed with 1-way analysis of variance and Tukey's post hoc test (α = 0.05).

RESULTS

OVX decreased maxillary and femoral BMD and altered femoral microarchitecture (P < .05). The drugs increased BMD of both types of bones, but only ALD maintained the phenotype similar to the SHAM group. The action of ALD was limited to the femoral trabecular separation (Tb.Sp). OVX and the drugs had no effect on the microarchitecture of the maxilla (P > .05).

CONCLUSIONS

ALD and ODN therapy increased BMD in both bones after ovariectomy. ALD was more successful than ODN in preserving the morphology of bone similar to the SHAM group. ALD maintained the phenotype for Tb.Sp in the femur, but ODN did not. In the maxillae, neither ovariectomy nor the 2 antiresorptive drugs had significant effects on microarchitecture.

MicroRNA‑148a inhibition protects against ovariectomy‑induced osteoporosis through PI3K/AKT signaling by estrogen receptor α

The present study aimed to investigate the effect of microRNA‑148a downregulation on osteoporosis by using an ovariectomized rat model. Reverse transcription‑quantitative polymerase chain reaction was used to analyze microRNA‑148a expression levels, MTT and flow cytometry assays were used to examine cytotoxicity and apoptosis, respectively. The gap‑associated proteins were quantified using western blotting. The expression of microRNA‑148a was significantly increased in osteoporosis rat following ovariectomy. Overexpression of microRNA‑148a significantly promoted apoptosis and inhibited cell growth, whereas downregulation of microRNA‑148a significantly reduced apoptosis and increased cell growth. Overexpression of microRNA‑148a significantly reduced estrogen receptor a (ERα) protein expression and suppressed phosphoinositide‑3‑kinase regulatory subunit 1 (PI3K) and phosphorylated‑protein kinase B (AKT) protein expression in osteoblasts in vitro. The inhibition of ERα increased the microRNA‑148a effect on apoptosis in osteoblasts in vitro. Subsequently, LY294002, an PI3K inhibitor, significantly increased the effect of microRNA‑148a on apoptosis in osteoblasts in vitro. The findings of the present study revealed that anti‑microRNA‑148a protected cells against ovariectomy‑induced osteoporosis through ERα by PI3K/AKT signaling.

A novel role for cathepsin K in periosteal osteoclast precursors during fracture repair

Osteoporosis management is currently centered around bisphosphonates, which inhibit osteoclast (OC) bone resorption but do not affect bone formation. This reduces fracture risk, but fails to restore healthy bone remodeling. Studies in animal models showed that cathepsin K (CatK) inhibition by genetic deletion or chemical inhibitors maintained bone formation while abrogating resorption during bone remodeling and stimulated periosteal bone modeling. Recently, periosteal mononuclear tartrate-resistant acid phosphatase-positive (TRAP⁺ ) osteoclast precursors (OCPs) were shown to augment angiogenesis-coupled osteogenesis. CatK gene deletion increased osteoblast differentiation via enhanced OCP and OC secretion of platelet-derived growth factor (PDGF)-BB and sphingosine 1 phosphate. The effects of periosteum-derived OCPs on bone remodeling are unknown, particularly with regard to fracture repair. We hypothesized that periosteal OCPs derived from CatK-null (Ctsk^-/- ) mice may enhance periosteal bone formation during fracture repair. We found fewer periosteal OCPs in Ctsk^-/- mice under homeostatic conditions; however, after fracture, this population increased in number relative to that seen in wild-type (WT) mice. Enhanced TRAP staining and greater expression of PDGF-BB were observed in fractured Ctsk^-/- femurs relative to WT femurs. This early pattern of augmented PDGF-BB expression in Ctsk^-/- mice may contribute to improved fracture healing by enhancing callus mineralization in Ctsk^-/- mice.

Odanacatib Pharmacokinetics Comparison Between Chinese and Non-Chinese Postmenopausal Women

Odanacatib (ODN), an oral selective inhibitor of cathepsin K, was an investigational agent previously in development for the treatment of osteoporosis. In this phase 1 open-label study, 12 healthy Chinese postmenopausal women received single-dose ODN 50 mg on day 1 and multiple-dose ODN 50 mg once weekly on days 15, 22, 29, and 36 under fasted conditions. Pharmacokinetic (PK) parameters were evaluated on days 1 and 36. Multiple-dose area under the concentration-time profile (AUC_0-168h ) and maximum plasma concentration (C_max ) were compared with historical data from 9 non-Chinese postmenopausal women who also received ODN 50 mg once weekly for 4 weeks. Median time to C_max (t_max ) was 3 and 4 hours following single- and multiple-dose administration, respectively. The arithmetic mean ± SD terminal half-life was 81.0 ± 14.0 and 106.7 ± 14.4 hours following single- and multiple-dose administration, respectively. Comparison of multiple-dose PK parameters showed that the geometric mean ratios (Chinese/non-Chinese) and 95%CIs for AUC_0-168h and C_max were 0.81 (0.55-1.19) and 0.87 (0.69-1.11), respectively. All adverse events were mild, none were serious, and none led to discontinuation. Single- and multiple-dose PKs of ODN 50 mg in Chinese postmenopausal women were generally similar to those previously reported in non-Chinese postmenopausal women.

Icariin ameliorates dexamethasone‑induced bone deterioration in an experimental mouse model via activation of microRNA‑186 inhibition of cathepsin K

The present study aimed to investigate bone deterioration in glucocorticoid‑induced osteoporosis (GIOP) mice, and the anti‑osteoporosis effect and underlying molecular mechanism of icariin. Dexamethasone (DSM) treatment was demonstrated to facilitate the induction of hypercalciuria in GIOP mice. Icariin treatment reversed the dexamethasone (DXM)‑induced disequilibrium of calcium homeostasis and bone resorption, and increased serum alkaline phosphatase, tartrate resistant acid phosphatase, osteocalcin and deoxypyridinoline. Haematoxylin and eosin staining revealed an increase in disconnections and separation in the trabecular bone network of the tibial proximal metaphysis, in the GIOP group. Icariin treatment reversed the DXM‑induced trabecular deleterious effects, and stimulated bone remodeling in GIOP mice. Furthermore, the results demonstrated that the mRNA and protein expression of cathepsin K were significantly increased in GIOP mice, compared with the control group. Icariin treatment may suppress the expression of cathepsin K in the tibia of GIOP mice. The levels of microRNA (miR)‑186 were markedly reduced in the tibia of GIOP mice compared with control group; however, this was inhibited by icariin treatment. Bioinformatics analysis demonstrated that miR‑186 regulates cathepsin K via binding to the upstream 3'‑untranslated region. Furthermore, transfection with miR‑186 mimics resulted in inhibition of cathepsin K expression, whereas miR‑186 inhibitors facilitated cathepsin K expression in osteoclasts. In conclusion, the present study demonstrated the protective effects of icariin against bone deteriorations in the experimental GIOP mice, and the underlying mechanism was mediated, at least partially, via activation of miR‑186‑mediated suppression of cathepsin K. These results provide evidence to support the use of icariin as a therapeutic approach in the management of glucocorticoid‑induced bone loss, and the disequilibrium of calcium homeostasis.

Cathepsin K Inhibitors for Osteoporosis: Biology, Potential Clinical Utility, and Lessons Learned

Cathepsin K is a cysteine protease member of the cathepsin lysosomal protease family. Although cathepsin K is highly expressed in osteoclasts, lower levels of cathepsin K are also found in a variety of other tissues. Secretion of cathepsin K from the osteoclast into the sealed osteoclast-bone cell interface results in efficient degradation of type I collagen. The absence of cathepsin K activity in humans results in pycnodysostosis, characterized by increased bone mineral density and fractures. Pharmacologic cathepsin K inhibition leads to continuous increases in bone mineral density for ≤5 years of treatment and improves bone strength at the spine and hip. Compared with other antiresorptive agents, cathepsin K inhibition is nearly equally efficacious for reducing biochemical markers of bone resorption but comparatively less active for reducing bone formation markers. Despite multiple efforts to develop cathepsin K inhibitors, potential concerns related to off-target effects of the inhibitors against other cathepsins and cathepsin K inhibition at nonbone sites, including skin and perhaps cardiovascular and cerebrovascular sites, prolonged the regulatory approval process. A large multinational randomized, double-blind phase III study of odanacatib in postmenopausal women with osteoporosis was recently completed. Although that study demonstrated clinically relevant reductions in fractures at multiple sites, odanacatib was ultimately withdrawn from the regulatory approval process after it was found to be associated with an increased risk of cerebrovascular accidents. Nonetheless, the underlying biology and clinical effects of cathepsin K inhibition remain of considerable interest and could guide future therapeutic approaches for osteoporosis.

Effect of Testosterone Treatment on Volumetric Bone Density and Strength in Older Men With Low Testosterone: A Controlled Clinical Trial

IMPORTANCE

As men age, they experience decreased serum testosterone concentrations, decreased bone mineral density (BMD), and increased risk of fracture.

OBJECTIVE

To determine whether testosterone treatment of older men with low testosterone increases volumetric BMD (vBMD) and estimated bone strength.

DESIGN, SETTING, AND PARTICIPANTS

Placebo-controlled, double-blind trial with treatment allocation by minimization at 9 US academic medical centers of men 65 years or older with 2 testosterone concentrations averaging less than 275 ng/L participating in the Testosterone Trials from December 2011 to June 2014. The analysis was a modified intent-to-treat comparison of treatment groups by multivariable linear regression adjusted for balancing factors as required by minimization.

INTERVENTIONS

Testosterone gel, adjusted to maintain the testosterone level within the normal range for young men, or placebo gel for 1 year.

MAIN OUTCOMES AND MEASURES

Spine and hip vBMD was determined by quantitative computed tomography at baseline and 12 months. Bone strength was estimated by finite element analysis of quantitative computed tomography data. Areal BMD was assessed by dual energy x-ray absorptiometry at baseline and 12 months.

RESULTS

There were 211 participants (mean [SD] age, 72.3 [5.9] years; 86% white; mean [SD] body mass index, 31.2 [3.4]). Testosterone treatment was associated with significantly greater increases than placebo in mean spine trabecular vBMD (7.5%; 95% CI, 4.8% to 10.3% vs 0.8%; 95% CI, -1.9% to 3.4%; treatment effect, 6.8%; 95% CI, 4.8%-8.7%; P < .001), spine peripheral vBMD, hip trabecular and peripheral vBMD, and mean estimated strength of spine trabecular bone (10.8%; 95% CI, 7.4% to 14.3% vs 2.4%; 95% CI, -1.0% to 5.7%; treatment effect, 8.5%; 95% CI, 6.0%-10.9%; P < .001), spine peripheral bone, and hip trabecular and peripheral bone. The estimated strength increases were greater in trabecular than peripheral bone and greater in the spine than hip. Testosterone treatment increased spine areal BMD but less than vBMD.

CONCLUSIONS AND RELEVANCE

Testosterone treatment for 1 year of older men with low testosterone significantly increased vBMD and estimated bone strength, more in trabecular than peripheral bone and more in the spine than hip. A larger, longer trial could determine whether this treatment also reduces fracture risk.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00799617.

Inhibition of cathepsin K promotes osseointegration of titanium implants in ovariectomised rats

The bone mineral deficiency in osteoporosis poses a threat to the long-term outcomes of endosseous implants. The inhibitors of cathepsin K (CatK) significantly affect bone turnover, bone mineral density (BMD) and bone strength in the patients with osteoporosis. Therefore, we hypothesised that the application of a CatK inhibitor (CatKI) could increase the osseointegration of endosseous implants under osteoporotic conditions. Odanacatib (ODN), a highly selective CatKI, was chosen as the experimental drug. Sixteen rats were randomised into 4 groups: sham, ovariectomy (OVX) with vehicle, OVX with low-dose ODN (5 mg/kg) and OVX with high-dose ODN (30 mg/kg). Titanium implants were placed into the distal metaphysis of bilateral femurs of each OVX rat. After 8 weeks of gavaging, CatKI treatment increased the removal torque, BMD and bone-to-implant contact (BIC). Moreover, high-dose CatKI exerted a better influence than low-dose CatKI. Furthermore, CatKI treatment not only robustly suppressed CatK gene (CTSK) expression, but also moderately reduced expression of the osteoblast-related genes Runx2, Collagen-1, BSP, Osterix, OPN, SPP1 and ALP. Thus, CatKI could affect the osteoblast-related genes, although the balance of bone turnover was achieved mainly by CatK inhibition. In conclusion, CatKI prevented bone loss and aided endosseous implantation in osteoporotic conditions.

Novel Therapies for Postmenopausal Osteoporosis

Recently discovered mechanisms have assisted in developing new therapies for osteoporosis. New classes of drugs have been developed for the treatment of postmenopausal osteoporosis. Although there have been numerous advances over the past 2 decades, the search for newer therapies continues.

Osteoporosis treatment: bisphosphonates reign to continue for a few more years, at least?

The findings of the Women's Health Initiative study in 2002 marginalized the use of hormone replacement therapy and established bisphosphonates as the first line of treatment for osteoporosis.  Denosumab could be used in selected patients. Although bisphosphonates only maintain the structure of bone complete with any accumulated structural or material faults, their bone selectivity and effectiveness in reducing the risk of fractures, together with their low cost, have left little room for improvement for new antiresorptives. The osteoanabolic teriparatide increases new bone formation, but it is administered for up to 2 years only and the cost remains a consideration. Similar restrictions are expected to apply to an anti-sclerostin antibody, which could be evaluated by the U.S. Food and Drug Administration in the near future. Cathepsin K-inhibiting antibody could be an alternative if approved; although an antiresorptive, it maintains bone formation, in contrast with bisphosphonates, and can be probably used for long-term treatment.  Rare adverse effects of bisphosphonates, namely osteonecrosis of the jaws and atypical femoral fractures, have been disproportionally emphasized relative to their benefits/harm ratio. Treatment of osteoporosis is a long process, and many patients will require treatment with more than one type of drug over their lifetime.

Finite Element Analysis of Denosumab Treatment Effects on Vertebral Strength in Ovariectomized Cynomolgus Monkeys

Finite element analysis has not yet been validated for measuring changes in whole-bone strength at the hip or spine in people after treatment with an osteoporosis agent. Toward that end, we assessed the ability of a clinically approved implementation of finite element analysis to correctly quantify treatment effects on vertebral strength, comparing against direct mechanical testing, in cynomolgus monkeys randomly assigned to one of three 16-month-long treatments: sham surgery with vehicle (Sham-Vehicle), ovariectomy with vehicle (OVX-Vehicle), or ovariectomy with denosumab (OVX-DMAb). After treatment, T12 vertebrae were retrieved, scanned with micro-CT, and mechanically tested to measure compressive strength. Blinded to the strength data and treatment codes, the micro-CT images were coarsened and homogenized to create continuum-type finite element models, without explicit porosity. With clinical translation in mind, these models were then analyzed for strength using the U.S. Food and Drug Administration (FDA)-cleared VirtuOst software application (O.N. Diagnostics, Berkeley, CA, USA), developed for analysis of human bones. We found that vertebral strength by finite element analysis was highly correlated (R(2)  = 0.97; n = 52) with mechanical testing, independent of treatment (p = 0.12). Further, the size of the treatment effect on strength (ratio of mean OVX-DMAb to mean OVX-Vehicle, as a percentage) was large and did not differ (p = 0.79) between mechanical testing (+57%; 95% CI [26%, 95%]) and finite element analysis (+51% [20%, 88%]). The micro-CT analysis revealed increases in cortical thickness (+45% [19%, 73%]) and trabecular bone volume fraction (+24% [8%, 42%]). These results show that a preestablished clinical finite element analysis implementation-developed for human bone and clinically validated in fracture-outcome studies-correctly quantified the observed treatment effects of denosumab on vertebral strength in cynomolgus monkeys. One implication is that the treatment effects in this study are well explained by the features contained within these finite element models, namely, the bone geometry and mass and the spatial distribution of bone mass. © 2016 American Society for Bone and Mineral Research.

Continuous treatment with odanacatib for up to 8 years in postmenopausal women with low bone mineral density: a phase 2 study

The efficacy and safety of weekly oral odanacatib (ODN) 50 mg for up to 8 years were assessed in postmenopausal women with low bone mineral density (BMD). Treatment with ODN for up to 8 years resulted in continued or maintained increases in BMD at multiple sites and was well tolerated.

INTRODUCTION

ODN is a selective inhibitor of cathepsin K. In a 2-year phase 2b study (3/10/25/50 mg ODN once weekly [QW] or placebo) and extensions (50 mg ODN QW or placebo), ODN treatment for 5 years progressively increased BMD and decreased bone resorption markers in postmenopausal women with low BMD ( ClinicalTrials.gov NCT00112437).

METHODS

In this prespecified interim analysis at year 8 of an additional 5-year extension (years 6 to 10), patients (n = 117) received open-label ODN 50 mg QW plus weekly vitamin D3 (5600 IU) and calcium supplementation as needed. Primary end points were lumbar spine BMD and safety. Patients were grouped by ODN exposure duration.

RESULTS

Mean (95 % confidence interval [CI]) lumbar spine BMD changes from baseline were 4.6 % (2.4, 6.7; 3-year continuous ODN exposure), 12.9 % (8.1, 17.7; 5 years), 12.8 % (10.0, 15.7; 6 years), and 14.8 % (11.0, 18.6; 8 years). Similar patterns of results were observed for BMD of trochanter, femoral neck, and total hip versus baseline. Geometric mean changes from baseline to year 8 for bone resorption markers were approximately -50 % (uNTx/Cr) and -45 % (sCTx), respectively (all groups); bone formation markers remained near baseline levels. No osteonecrosis of the jaw, delayed fracture union, or morphea-like skin reactions were reported.

CONCLUSIONS

Treatment with ODN for up to 8 years resulted in gains in BMD at multiple sites. Bone resorption markers remained reduced, with no significant change observed in bone formation markers. Treatment with ODN for up to 8 years was well tolerated.

From disease to treatment: from rare skeletal disorders to treatments for osteoporosis

During the past 15 years there has been an expansion of our knowledge of the cellular and molecular mechanisms regulating bone remodeling that identified new signaling pathways fundamental for bone renewal as well as previously unknown interactions between bone cells. Central for these developments have been studies of rare bone disorders. These findings, in turn, have led to new treatment paradigms for osteoporosis some of which are at late stages of clinical development. In this article, we review three rare skeletal disorders with case descriptions, pycnodysostosis and the craniotubular hyperostoses sclerosteosis and van Buchem disease that led to the development of cathepsin K and sclerostin inhibitors, respectively, for the treatment of osteoporosis.

Cathepsin K Inhibition: A New Mechanism for the Treatment of Osteoporosis

Cathepsin K (CatK), a cysteine protease, is highly expressed by osteoclasts and very efficiently degrades type I collagen, the major component of the organic bone matrix. Robust genetic and pharmacological preclinical studies consistently demonstrate that CatK inhibition increases bone mass, improves bone microarchitecture and strength. Recent advances in the understanding of the molecular and cellular mechanisms involved in bone modeling and remodeling suggest that inhibition of CatK decreases bone resorption, but increases the number of cells of osteoclast lineage. This in turn maintains the signals for bone formation, and perhaps may even increase bone formation on some cortical surfaces. Several CatK inhibitors, including relacatib, balicatib, odanacatib and ONO-5334 had entered clinical development for metabolic bone disorders with increased bone resorption, such as postmenopausal osteoporosis. However, odanacatib (ODN) is the only candidate continuing in development. ODN is a highly selective oral CatK inhibitor dosed once-weekly in humans. In a Phase 2 clinical trial, postmenopausal women treated with ODN had sustained reductions of bone resorption markers, while bone formation markers returned to normal after an initial decline within the first 2 years on treatment. In turn areal bone mineral density increased continuously at both spine and hip for up to 5 years. ODN has also been demonstrated to improve bone mass in women with postmenopausal osteoporosis previously treated with alendronate and in men with osteoporosis. ODN is currently in a worldwide Phase 3 fracture outcome trial for the treatment of postmenopausal osteoporosis with interim results supporting its anti-fracture efficacy at the spine, hip and non-vertebral sites.

Effects of odanacatib on bone matrix mineralization in rhesus monkeys are similar to those of alendronate

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K which is an important enzyme for the degradation of collagen I. Aim of the present work was the head-to-head comparison between the effects of ODN and alendronate (ALN) on bone mineralization density distribution (BMDD), based on quantitative backscattered electron imaging in relation to changes in histomorphometric mineralizing surface per bone surface (MS/BS) in 12–22 years old ovariectomized rhesus monkeys. Trabecular and cortical BMDD derived parameters from vertebrae and proximal tibiae were compared among vehicle (VEH, n = 8), odanacatib low dose (ODN-L, n = 8), odanacatib high dose (ODN-H, n = 8), and alendronate (ALN, n = 6) treated animals. Additionally, data from an intact, non-treated group of animals are shown (INT, n = 8). In trabecular bone from the vertebra and metaphyseal tibia, the BMDD of the ODN and ALN treatment groups was shifted toward higher mineralization densities (p < 0.001) consistent with the significant reduction of MS/BS (p < 0.05 in ODN-H and ALN) compared to VEH. Vertebral trabecular CaMean (average degree of mineralization) was significantly higher in ODN-L (+ 6.5%), ODN-H (+ 6.1%), and ALN (+ 6.7%, all p < 0.001). Tibial osteonal cortical bone revealed also significantly increased CaMean for ODN-L (+ 1.4%, p < 0.05), ODN-H (+ 2.2%, p < 0.05), and ALN (+ 3.4%, p < 0.001) versus VEH, while primary cortical bone (devoid of secondary osteons) did not show any significant differences between the study groups. The percentage of primary bone area in the tibial cross-sections (on average 45 ± 12%) was also not significantly different between the study groups (p = 0.232). No significant differences in any BMDD parameters of all studied skeletal sites between ODN and ALN treatment were found. Correlation analysis revealed that MS/BS was highly predictive for trabecular BMDD in vertebral bone. The higher MS/BS, the lower was CaMean. Our findings are consistent with the inhibition of bone resorption of ODN and ALN in trabecular and osteonal compartments.

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In line with its anti-resorptive action ODN increased trabecular and osteonal bone mineralization in treated rhesus monkeys.

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Both lower and higher dosages of ODN were similarly efficient with respect to bone matrix mineralization outcomes.

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ODN treatment affected bone matrix mineralization in a similar manner compared to ALN.

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ODN treatment did not significantly change the percentage of primary bone area in tibial cross-sections.

Odanacatib: An Emerging Novel Treatment Alternative for Postmenopausal Osteoporosis

Odanacatib represents a novel treatment option in the approach of postmenopausal women. Postmenopausal women with osteoporosis experience a disturbance in bone remodeling wherein bone resorption exceeds bone formation. Cathepsin K is a lysosomal cysteine protease found primarily in osteoclasts that plays a major role in the breakdown of bone via its collagenase properties. Targeting a new area of pathophysiology, odanacatib inhibits cathepsin K to reduce bone resorption while preserving bone formation. Phase II and III trials have shown efficacy in increasing bone mineral density in the target treatment group. Overall, safety studies have found odanacatib to be well-tolerated and comparable to placebo; however, some imbalances in adverse events have been observed in the Phase III trials. Current and future studies will analyze the long-term ability of odanacatib in preventing bone fracture.

Emerging therapeutic concepts for muscle and bone preservation/building

Loss of muscle or bone mass occurs with ageing, immobility and in association with a variety of systemic diseases. The interaction of these two processes is most evident in the major contribution of falls to the risk of fractures in the elderly population. Exercise and nutrition are key common physiological variables that allow for preservation or formation of greater muscle or bone mass. However, although several pharmacological approaches have the potential to benefit both muscle and bone health, for example vitamin D, selective androgen receptor modulators and ghrelin mimetics, clinical trials with appropriate primary outcomes are lacking. Conventional approaches to address muscle loss are being extended to include stem cell biology and conserved molecular mechanisms of atrophy/hypertrophy. Pharmacological interventions to reduce fracture risk are exploring new mechanisms of action, in particular the uncoupling of bone resorption and formation. Emerging key issues for clinical trial design include adequate phenotyping of patients (personalised medicine), optimisation of the physiological background (multimodal approach) and the use of meaningful and robust outcomes relevant to daily clinical practice. At present, effective treatments that combine beneficial effects on both muscle and bone are lacking, although this is an important target for the future. This review therefore considers current and developing strategies to improve muscle function and bone strength in separate sections.

Bone Tissue Properties Measurement by Reference Point Indentation in Glucocorticoid-Induced Osteoporosis

Glucocorticoids, widely used in inflammatory disorders, rapidly increase bone fragility and, therefore, fracture risk. However, common bone densitometry measurements are not sensitive enough to detect these changes. Moreover, densitometry only partially recognizes treatment-induced fracture reductions in osteoporosis. Here, we tested whether the reference point indentation technique could detect bone tissue property changes early after glucocorticoid treatment initiation. After initial laboratory and bone density measurements, patients were allocated into groups receiving calcium + vitamin D (Ca+D) supplements or anti-osteoporotic drugs (risedronate, denosumab, teriparatide). Reference point indentation was performed on the cortical bone layer of the tibia by a handheld device measuring bone material strength index (BMSi). Bone mineral density was measured by dual-energy X-ray absorptiometry (DXA). Although Ca+D-treated patients exhibited substantial and significant deterioration, risedronate-treated patients exhibited no significant change, and both denosumab- and teriparatide-treated participants exhibited significantly improved BMSi 7 weeks after initial treatment compared with baseline; these trends remained stable for 20 weeks. In contrast, no densitometry changes were observed during this study period. In conclusion, our study is the first to our knowledge to demonstrate that reference point indentation is sensitive enough to reflect changes in cortical bone indentation after treatment with osteoporosis therapies in patients newly exposed to glucocorticoids.

Development of N-(Functionalized benzoyl)-homocycloleucyl-glycinonitriles as Potent Cathepsin K Inhibitors

Cathepsin K is a major drug target for osteoporosis and related-bone disorders. Using a combination of virtual combinatorial chemistry, QSAR modeling, and molecular docking studies, a series of cathepsin K inhibitors based on N-(functionalized benzoyl)-homocycloleucyl-glycinonitrile scaffold was developed. In order to avoid previous problems of cathepsin K inhibitors associated with lysosomotropism of compounds with basic character that resulted in off-target effects, a weakly- to nonbasic moiety was incorporated into the P3 position. Compounds 5, 6, and 9 were highly selective for cathepsin K when compared with cathepsins L and S, with the Ki values in the 10-30 nM range. The kinetic studies revealed that the new compounds exhibited reversible tight binding to cathepsin K, while the X-ray structural studies showed covalent and noncovalent binding between the nitrile group and the catalytic cysteine (Cys25) site.

New Frontiers in Druggability

A powerful early approach to evaluating the druggability of proteins involved determining the hit rate in NMR-based screening of a library of small compounds. Here, we show that a computational analog of this method, based on mapping proteins using small molecules as probes, can reliably reproduce druggability results from NMR-based screening and can provide a more meaningful assessment in cases where the two approaches disagree. We apply the method to a large set of proteins. The results show that, because the method is based on the biophysics of binding rather than on empirical parametrization, meaningful information can be gained about classes of proteins and classes of compounds beyond those resembling validated targets and conventionally druglike ligands. In particular, the method identifies targets that, while not druggable by druglike compounds, may become druggable using compound classes such as macrocycles or other large molecules beyond the rule-of-five limit.

Molecular Design, Synthesis and Trypanocidal Activity of Dipeptidyl Nitriles as Cruzain Inhibitors

A series of compounds based on the dipeptidyl nitrile scaffold were synthesized and assayed for their inhibitory activity against the T. cruzi cysteine protease cruzain. Structure activity relationships (SARs) were established using three, eleven and twelve variations respectively at the P1, P2 and P3 positions. A K_i value of 16 nM was observed for the most potent of these inhibitors which reflects a degree of non-additivity in the SAR. An X-ray crystal structure was determined for the ligand-protein complex for the structural prototype for the series. Twenty three inhibitors were also evaluated for their anti-trypanosomal effects and an EC₅₀ value of 28 μM was observed for the most potent of these. Although there remains scope for further optimization, the knowledge gained from this study is also transferable to the design of cruzain inhibitors based on warheads other than nitrile as well as alternative scaffolds.

Chagas disease is a parasitic infection with high morbidity and mortality that is endemic in much of Latin America where it remains a serious public health problem. With increased migration, Chagas disease represents an emerging worldwide challenge and there is an urgent, unmet need for safe and effective medication. The available drugs to treat Chagas disease may be effective in the acute phase of the disease, but efficacy in the chronic phase remains controversial. They can cause serious side effects that lead sufferers to abandon treatment. Using a hypothesis-driven approach to molecular design and drawing on cysteine protease cruzain structural information, we have mapped structure-activity relationships for a dipeptidyl nitrile scaffold and demonstrated that compounds are competitive inhibitors, bind reversibly and bear trypanocidal activity. The binding mode revealed by the crystal structure of the protein-ligand complex for one of the inhibitors shows that binding involves the formation of a covalent bond between the catalytic cysteine and the nitrile carbon. As such, we believe that our study represents a valuable step in the search for new drugs for the treatment of a neglected disease that continues to affect the lives of millions of people.

Odanacatib for the treatment of osteoporosis

INTRODUCTION

Osteoporosis and fragility fractures are important public health concerns. Cathepsin K inhibitors, including odanacatib , are a novel class of medications for osteoporosis whose mechanism of action is to directly inhibit bone resorption without killing osteoclasts, thereby permitting the complex coupling between bone resorption and formation to continue.

AREAS COVERED

The physiological basis for the mechanism of action of cathepsin K inhibitors is covered in addition to a review of the preclinical, Phase I, Phase II and preliminary Phase III trial data of odanacatib.

EXPERT OPINION

Evidence suggests that odanacatib has similar efficacy to bisphosphonates at increasing bone mineral density and decreasing risk of fragility fractures. Although odanacatib may preferentially inhibit bone resorption more than formation, the clinical significance of this difference in mechanism of action is not yet known. A careful analysis of the Phase III trial data is needed with specific attention to adverse events.