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

Modulating Bone Resorption and Bone Formation in Opposite Directions in the Treatment of Postmenopausal Osteoporosis

Bone remodeling, the fundamental process for bone renewal, is targeted by treatments of osteoporosis to correct the imbalance between bone resorption and bone formation and reduce the risk of fractures and associated clinical consequences. Currently available therapeutics affect bone resorption and bone formation in the same direction and either decrease (inhibitors of bone resorption) or increase (parathyroid hormone [PTH] peptides) bone remodeling. Studies of patients with rare bone diseases and genetically modified animal models demonstrated that bone resorption and bone formation may not necessarily be coupled, leading to identification of molecular targets in bone cells for the development of novel agents for the treatment of osteoporosis. Application of such agents to the treatment of women with low bone mass confirmed that bone resorption and bone formation can be modulated in different directions and so far two new classes of therapeutics for osteoporosis have been defined with distinct mechanisms of action. Such treatments, if combined with a favorable safety profile, will offer new therapeutic options and will improve the management of patients with osteoporosis.

Efficacy and safety of odanacatib treatment for patients with osteoporosis: a meta-analysis

The aim of this study was to evaluate the efficacy and safety of odanacatib (ODN) for the treatment of osteoporosis, using data in studies reported in the literature. We performed a literature search to compare the outcomes of applications of once-weekly ODN 50 mg and control. The outcomes of osteoporosis evaluated include primary outcome as bone mineral density (BMD) at different skeletal sites, and secondary outcomes, including adverse events (AEs), such as incidence of skin AEs, fracture, and serious adverse events (SAEs). Four trials were included. Mean difference (95% CI) of lumbar spine BMD was 3.41 (1.57-5.24) at 12 months and 4.89 (2.72-7.05) at 24 months; mean difference (95% CI) of femoral neck BMD was 1.90 (0.73-3.08) at 12 months and 3.85 (2.55-5.15) at 24 months; mean difference (95% CI) of total hip BMD was 2.65 (1.20-4.09) at 12 months and 3.70 (1.76-5.64) at 24 months; risk ratio (95% CI) of AEs was 0.98 (0.91-1.07); risk ratio (95% CI) of SAEs was 1.11 (0.72-1.72); risk ratio (95% CI) of skin AEs was 0.92 (0.63-1.35); and risk ratio (95% CI) of fracture was 0.34 (0.16-0.70). In this study, application of 50 mg ODN produced significantly greater BMD increases and lower fracture incidence than that of the control. In addition, ODN was generally well tolerated.

Clinical Use of Quantitative Computed Tomography (QCT) of the Hip in the Management of Osteoporosis in Adults: the 2015 ISCD Official Positions-Part I

The International Society for Clinical Densitometry (ISCD) has developed new official positions for the clinical use of quantitative computed tomography of the hip. The ISCD task force for quantitative computed tomography reviewed the evidence for clinical applications and presented a report with recommendations at the 2015 ISCD Position Development Conference. Here, we discuss the agreed on ISCD official positions with supporting medical evidence, rationale, controversy, and suggestions for further study. Parts II and III address the advanced techniques of finite element analysis applied to computed tomography scans and the clinical feasibility of existing techniques for opportunistic screening of osteoporosis using computed tomography scans obtained for other diagnosis such as colonography was addressed.

Clinical Use of Quantitative Computed Tomography-Based Finite Element Analysis of the Hip and Spine in the Management of Osteoporosis in Adults: the 2015 ISCD Official Positions-Part II

The International Society for Clinical Densitometry (ISCD) has developed new official positions for the clinical use of quantitative computed tomography (QCT)-based finite element analysis of the spine and hip. The ISCD task force for QCT reviewed the evidence for clinical applications and presented a report with recommendations at the 2015 ISCD Position Development Conference. Here we discuss the agreed upon ISCD official positions with supporting medical evidence, rationale, controversy, and suggestions for further study. Parts I and III address the clinical use of QCT of the hip, and the clinical feasibility of existing techniques for opportunistic screening of osteoporosis using CT scans obtained for other diagnosis such as colonography was addressed.

Odanacatib: a review of its potential in the management of osteoporosis in postmenopausal women

Odanacatib is a cathepsin K inhibitor developed for the treatment of postmenopausal osteoporosis. It is a bone resorption inhibitor, but which preserves bone formation to some extent. It can be administered once a week, in tablets also containing vitamin D. In a large clinical development program, it has been shown that odanacatib reduces bone resorption, with a reduction of about 60-70% in biochemical markers of resorption, while bone formation decreases to a lesser magnitude. Odanacatib continuously increases bone mineral density (BMD) at the hip and lumbar spine over 5 years. Once it is stopped, a complete resolution of effect is observed, with declining BMD and increased bone turnover. Bone microarchitecture and bone strength have also been improved in clinical trials using quantitative computed tomography (QCT) at the lumbar spine and hip, and high resolution peripheral QCT at the distal radius and tibia. In a phase III trial involving 16,713 postmenopausal women ⩾65 years of age with low BMD, the risk of fragility fracture was significantly reduced at the spine, hip and other nonvertebral sites compared with the placebo group. Odanacatib has been generally well tolerated, with no observation of osteonecrosis of the jaw so far, but with exceptional observations of subtrochanteric atypical fracture and morphea-like lesions. Odanacatib appears a useful new option in the treatment of postmenopausal osteoporosis.

Predicting mouse vertebra strength with micro-computed tomography-derived finite element analysis

As in clinical studies, finite element analysis (FEA) developed from computed tomography (CT) images of bones are useful in pre-clinical rodent studies assessing treatment effects on vertebral body (VB) strength. Since strength predictions from microCT-derived FEAs (μFEA) have not been validated against experimental measurements of mouse VB strength, a parametric analysis exploring material and failure definitions was performed to determine whether elastic μFEAs with linear failure criteria could reasonably assess VB strength in two studies, treatment and genetic, with differences in bone volume fraction between the control and the experimental groups. VBs were scanned with a 12-μm voxel size, and voxels were directly converted to 8-node, hexahedral elements. The coefficient of determination or R (2) between predicted VB strength and experimental VB strength, as determined from compression tests, was 62.3% for the treatment study and 85.3% for the genetic study when using a homogenous tissue modulus (E t) of 18 GPa for all elements, a failure volume of 2%, and an equivalent failure strain of 0.007. The difference between prediction and measurement (that is, error) increased when lowering the failure volume to 0.1% or increasing it to 4%. Using inhomogeneous tissue density-specific moduli improved the R (2) between predicted and experimental strength when compared with uniform E t=18 GPa. Also, the optimum failure volume is higher for the inhomogeneous than for the homogeneous material definition. Regardless of model assumptions, μFEA can assess differences in murine VB strength between experimental groups when the expected difference in strength is at least 20%.

Perspectives on osteoporosis therapies

Osteoporosis is a skeletal disease which predisposes to fragility fractures with high morbidity and economic impact, and, therefore, the goal of any osteoporosis treatment is to reduce the fracture risk. In the various forms of osteoporosis an imbalance between bone resorption and apposition is present, that generally leads to a reduction of bone mineral density and bone quality, and finally to the increased fracture risk. Nowadays, several drugs are available with a demonstrated anti-fracturative effect obtained by inhibiting bone resorption or stimulating bone formation. However, their use is not free from limitations and side effects. Importantly, to date, the available antiresorptive drugs have also an inhibiting, though to a lesser extent, effect on bone apposition and, similarly, the anabolic drugs lead to an increase also of bone resorption. Advances in our knowledge about bone biology, with molecular insights into mechanisms underlying osteoblast, osteoclast, and osteocyte activity, have led to the recognition of new potential targets and consequently to the formulation of new therapeutic agents to treat osteoporosis. New potential developments among the antiresorptive drugs include cathepsin K inhibitors and among the osteoanabolic drugs those activating the Wnt signaling pathway, such as the monoclonal antibodies against sclerostin. The novelty of these compounds is that their mechanism of action gives the exciting possibility to uncouple bone resorption and bone formation, and data available so far appear to be promising. Finally, several new therapeutic targets are under investigation in preclinical studies which could open further approaches to treat osteoporosis in the future.

Long-term safety of antiresorptive treatment: bone material, matrix and mineralization aspects

It is well established that long-term antiresorptive use is effective in the reduction of fracture risk in high bone turnover osteoporosis. Nevertheless, during recent years, concerns emerged that longer bone turnover reduction might favor the occurrence of fatigue fractures. However, the underlying mechanisms for both beneficial and suspected adverse effects are not fully understood yet. There is some evidence that their effects on the bone material characteristics have an important role. In principle, the composition and nanostructure of bone material, for example, collagen cross-links and mineral content and crystallinity, is highly dependent on tissue age. Bone turnover determines the age distribution of the bone structural units (BSUs) present in bone, which in turn is decisive for its intrinsic material properties. It is noteworthy that the effects of bone turnover reduction on bone material were observed to be dependent on the duration of the antiresorptive therapy. During the first 2-3 years, significant decreases in the heterogeneity of material properties such as mineralization of the BSUs have been observed. In the long term (5-10 years), the mineralization pattern reverts towards normal heterogeneity and degree of mineralization, with no signs of hypermineralization in the bone matrix. Nevertheless, it has been hypothesized that the occurrence of fatigue fractures (such as atypical femoral fractures) might be linked to a reduced ability of microdamage repair under antiresorptive therapy. The present article examines results from clinical studies after antiresorptive, in particular long-term, therapy with the aforementioned potentially positive or negative effects on bone material.

Antiresorptive drugs beyond bisphosphonates and selective oestrogen receptor modulators for the management of postmenopausal osteoporosis

Osteoporotic fractures are a major cause of morbidity in the elderly population. Since postmenopausal osteoporosis is related to an increase in osteoclastic activity at the time of menopause, inhibitors of bone resorption have genuinely been considered an adequate strategy for prevention and treatment of osteoporosis. Bisphosphonates and selective oestrogen receptor modulators are widely prescribed to treat osteoporosis. However, other antiresorptive drugs have been developed for the management of osteoporosis, with the objective of providing a substantial reduction in osteoporotic fractures at all skeletal sites, combined with an acceptable long-term skeletal and systemic safety profile. Denosumab, a human monoclonal antibody to receptor activator for nuclear factor kappa B ligand, has shown efficacy against vertebral, nonvertebral and hip fractures. Its administration every 6 months as a subcutaneous formulation might significantly influence compliance and persistence to therapy. Additional results regarding long-term skeletal safety (i.e. osteonecrosis of the jaw and atypical diaphyseal femoral fracture) are needed. Odanacatib, a selective cathepsin K inhibitor, is a promising new approach to the inhibition of osteoclastic resorption, with the potential to uncouple bone formation from bone resorption. Results regarding its anti-fracture efficacy are expected in the coming months.

Odanacatib treatment affects trabecular and cortical bone in the femur of postmenopausal women: results of a two-year placebo-controlled trial

Odanacatib, a selective cathepsin K inhibitor, increases areal bone mineral density (aBMD) at the spine and hip of postmenopausal women. To gain additional insight into the effects on trabecular and cortical bone, we analyzed quantitative computed tomography (QCT) data of postmenopausal women treated with odanacatib using Medical Image Analysis Framework (MIAF; Institute of Medical Physics, University of Erlangen, Erlangen, Germany). This international, randomized, double-blind, placebo-controlled, 2-year, phase 3 trial enrolled 214 postmenopausal women (mean age 64 years) with low aBMD. Subjects were randomized to odanacatib 50 mg weekly (ODN) or placebo (PBO); all participants received calcium and vitamin D. Hip QCT scans at 24 months were available for 158 women (ODN: n = 78 women; PBO: n = 80 women). There were consistent and significant differential treatment effects (ODN-PBO) for total hip integral (5.4%), trabecular volumetric BMD (vBMD) (12.2%), and cortical vBMD (2.5%) at 24 months. There was no significant differential treatment effect on integral bone volume. Results for bone mineral content (BMC) closely matched those for vBMD for integral and trabecular compartments. However, with small but mostly significant differential increases in cortical volume (1.0% to 1.3%) and thickness (1.4% to 1.9%), the percentage cortical BMC increases were numerically larger than those of vBMD. With a total hip BMC differential treatment effect (ODN-PBO) of nearly 1000 mg, the proportions of BMC attributed to cortical gain were 45%, 44%, 52%, and 40% for the total, neck, trochanter, and intertrochanter subregions, respectively. In postmenopausal women treated for 2 years, odanacatib improved integral, trabecular, and cortical vBMD and BMC at all femur regions relative to placebo when assessed by MIAF. Cortical volume and thickness increased significantly in all regions except the femoral neck. The increase in cortical volume and BMC paralleled the increase in cortical vBMD, demonstrating a consistent effect of ODN on cortical bone. Approximately one-half of the absolute BMC gain occurred in cortical bone.

Established and forthcoming drugs for the treatment of osteoporosis

PURPOSE OF REVIEW

The aim of treatment in patients at high risk for fractures is to reduce the risk of a first or a subsequent fracture. New data are available on the antifracture effects and side-effects of antiresorptive and osteoanabolic drugs, and new emerging therapies with new modes of action are on the horizon.

RECENT FINDINGS

Calcium and vitamin D intake should be sufficient, but not too high. Vertebral, nonvertebral (including hip fracture) prevention with antiresorptive drugs such as bisphosphonates (alendronate, risedronate and zoledronic acid) and denosumab exceeds the risk of rare side-effects such as atypical femur fracture and osteonecrosis of the jaw. Teriparatide is an osteoanabolic drug that improves quality of life in severe osteoporosis. Strontium ranelate decreases dynamic parameters of bone formation during the first year of treatment, and could increase the risk of cardiovascular events in high-risk patients. Initiation of and adherence to fracture prevention drugs are still low. New potential developments in antiresorptive drugs include odanacatib, a selective inhibitor of cathepsin K, and, in osteoanabolic drugs, monoclonal antibodies against sclerostin.

SUMMARY

These recent data indicate that fracture prevention with antiresorptives and teriparatide is effective with a reasonable safety profile. Odanacatib and antisclerostin are promising new drugs with new mechanisms of action, as they are able to disconnect the normal coupling between bone resorption and bone formation.

Novel approaches to the treatment of osteoporosis

Despite the availability of efficacious treatments for fracture reduction in patients with osteoporosis, there are still unmet needs requiring a broader range of therapeutics. In particular, agents that are capable of replacing already lost bone and that also drastically reduce the risk of non-vertebral fractures are needed. Studies of rare bone diseases in humans and animal genetics have identified targets in bone cells for the development of therapies for osteoporosis with novel mechanisms of action. Here, we review these new developments, with emphasis on inhibitors of cathepsin K in osteoclasts and sclerostin in osteocytes, which are currently studied in phase 3 clinical trials.

Future directions for new medical entities in osteoporosis

Odanacatib, a selective cathepsin K inhibitor, decreases bone resorption, whereas osteoclast number increases and bone formation is maintained, perhaps even increased on some cortical surfaces. In a phase 2 clinical trial, post-menopausal women receiving odanacatib presented a sustained reduction of bone resorption markers, whereas procollagen type 1 N-terminal propeptide returned to normal. In turn areal bone mineral density increased continuously at both spine and hip for up to 5 years. Blosozumab and romosozumab are sclerostin neutralizing antibodies that exert potent anabolic effects on both trabecular and cortical compartments. A phase 2 clinical trial has reported areal bone mineral density gains at spine and hip that were greater with romosozumab compared with placebo, but also with teriparatide. It also showed that antagonizing sclerostin results in a transient stimulation of bone formation but progressive inhibition of bone resorption. Other new medical entities that are promising for the treatment of osteoporosis include abaloparatide, a parathyroid hormone-related analogue with improved bone formation-resorption ratio.

Implementation of quantitative and systems pharmacology in large pharma

Quantitative and systems pharmacology concepts and tools are the foundation of the model-informed drug development paradigm at Merck for integrating knowledge, enabling decisions, and enhancing submissions. Rigorous prioritization of modeling and simulation activities has enabled key drug development decisions and led to a high return on investment through significant cost avoidance. Critical factors for the successful implementation, examples on impact on decision making with associated return of investment, and drivers for continued success are discussed.

PDGF-BB secreted by preosteoclasts induces angiogenesis during coupling with osteogenesis

Osteogenesis during bone modeling and remodeling is coupled with angiogenesis. A recent study shows that the specific vessel subtype, strongly positive for CD31 and Endomucin (CD31^hiEmcn^hi), couples angiogenesis and osteogenesis. We found that preosteoclasts secrete platelet derived growth factor-BB (PDGF-BB), inducing CD31^hiEmcn^hi vessels during bone modeling and remodeling. Mice with depletion of PDGF-BB in tartrate-resistant acid phosphatase positive (TRAP⁺) cell lineage (Pdgfb^–/–) show significantly lower trabecular and cortical bone mass, serum and bone marrow PDGF-BB concentrations, and CD31^hiEmcn^hi vessels compared to wild-type mice. In the ovariectomized (OVX) osteoporotic mouse model, concentrations of serum and bone marrow PDGF-BB and CD31^hiEmcn^hi vessels are significantly decreased. Inhibition of cathepsin K (CTSK) increases preosteoclast numbers, resulting in higher levels of PDGF-BB to stimulate CD31^hiEmcn^hi vessels and bone formation in OVX mice. Thus, pharmacotherapies that increase PDGF-BB secretion from preosteoclasts offer a novel therapeutic target for osteoporosis to promote angiogenesis for bone formation.

Biological agents in management of osteoporosis

Osteoporosis is a skeletal disease associated with an imbalance between formation and resorption, leading to net loss of bone mass, loss of bone microarchitecture, and development of fractures. Bone resorption is primarily due to an activation of osteoclastogenesis and an increase in receptor activator of nuclear factor kappa-B ligand (RANKL) expression, a cytokine involved in the final pathway of the osteoclast cycle.Recent studies of genetic diseases led to the discovery of the wingless-type (Wnt) signaling pathway that plays a major role in bone formation. Further work showed that sclerostin produced by osteocytes and the Dickkopf (DKK1) protein secreted in bone were negative regulators of the Wnt signaling bone formation pathway that act directly by binding to the co-receptors LRP5 and LRP6 of WnT and thereby inhibiting the anabolic Wnt pathway. This understanding of the bone remodeling led to the discovery of new biological drugs that target these pathways and have been evaluated in clinical trials.The current article discusses the role of these newer "biological" agents in management of osteoporosis. Denosumab, a human monoclonal antibody that specifically binds RANKL, blocks the binding of RANK to its ligand markedly reducing bone resorption, increases bone density, and reduces fractures and is approved for osteoporosis. Parathyroid hormone PTH 1-34 (teriparatide) stimulates bone formation through inhibition of sclerostin, DKK1, and frizzled protein; increases BMD; improves microarchitecture; and decreases fractures and is approved for osteoporosis. The anti-sclerostin antibodies (romosozumab, blosozumab) increase bone mass by neutralizing the negative effects of sclerostin on the Wnt signaling pathway. These biologics are being evaluated now in a clinical trial and early data looks promising. Cathepsin K is a proteolytic enzyme that degrades bone matrix and inhibitors such as odanacatib show increasing bone density and perhaps decreased fractures. The potential power of combining these newer antiresorptives with the newer anabolic agents could theoretically increase bone mass rapidly to normal within 1 year and reduce fractures. These newer treatments are revolutionizing the management of osteoporosis.

Effect of odanacatib on BMD and fractures: estimates from Bayesian univariate and bivariate meta-analyses

CONTEXT

Odanacatib (ODN), a selective cathepsin-K inhibitor, was found to increase bone mineral density (BMD); the effect on fractures is based on adverse event reports.

OBJECTIVE

To estimate current effects and predict future effects of ODN on BMD and fractures.

DATA SOURCES

Electronic databases (Medline, EMBASE, Cochrane Library), conference proceedings, and bibliographies.

STUDY SELECTION

Trials that compared ODN 50 mg/wk to placebo for at least 1 year and reported changes in BMD or fractures. Meta-analysis: Two bone outcomes were pooled as independent and as joint outcomes in Bayesian univariate and bivariate random-effects models.

DATA SYNTHESIS

Of 32 potentially eligible articles, six citations describing four trials (993 patients) were included. ODN for 3 years increased mean BMD at the lumbar spine by 5.0% (95% credible interval [CrI], 2.7, 7.5), total hip by 3.6% (95% CrI, 1.6, 5.9), and femoral neck (FN) by 3.6% (95% CrI, 1.6, 5.7). In a future trial of 3-year duration, the predicted mean increase in BMD, adjusted for the effect on fractures, was 4.9% for lumbar spine (95% CrI, 2.5, 7.4), 3.4% for total hip (95% CrI, 1.7, 5.2), and 3.5% for FN (95% CrI, 1.8, 5.3). After accounting for the effect on FN BMD, ODN for 3 years was associated with a population odds ratio of 0.38 (95% CrI, 0.1, 0.8). In a future trial, the odds ratio was 0.41 (95% CrI, 0.1, 1.1). The probability of benefit on fractures was 96-99%. The estimates remained robust in sensitivity analyses.

CONCLUSIONS

Our analyses suggest that ODN will increase BMD and decrease all fractures in the fracture outcome trial; however, direct demonstration of this antifracture efficacy is needed.

Chinese bone turnover marker study: reference ranges for C-terminal telopeptide of type I collagen and procollagen I N-terminal peptide by age and gender

Background

Bone formation marker procollagen I N-terminal peptide (PINP) and resorption marker C-terminal telopeptide of type I collagen (β-CTX) are useful biomarkers for differential diagnosis and therapeutic evaluation of osteoporosis, but reference values are required.

Methods

The multi-center, cross-sectional Chinese Bone Turnover Marker Study included 3800 healthy volunteers in 5 Chinese cities. Serum PINP, β-CTX, parathyroid hormone (PTH) and 25OHD levels were measured by chemiluminescence assay. Lumbar spine and proximal femur BMD were measured by dual-energy X-ray absorptiometry. Serum PINP and β-CTX levels were assessed by age, gender, weight, recruitment latitude, levels of PTH and 25OHD.

Results

Subjects (n = 1436, M∶F, 500∶936; mean age 50.6±19.6 years) exhibited non-normally distributed PINP and β-CTX peaking between 15–19 years, gradually declining throughout adulthood, elevating within 10 years of postmenopause, and then declining by age 70. In women between the age of 30 and menopause, median PINP and β-CTX levels were 40.42 (95% CI: 17.10–102.15) and 0.26 (95% CI: 0.08–0.72) ng/mL, respectively. β-CTX and PINP were positively linearly correlated (r = 0.599, P<0.001). β-CTX correlated positively (r = 0.054 and 0.093) and PINP correlated negatively (r = −0.012 and −0.053) with 25OHD and PTH (P<0.05).

Conclusions

We established Chinese reference ranges for PINP and CTX. Chinese individuals exhibited high serum PINP and β-CTX levels between 15 and 19 years of age and at menopause, which gradually declined after 70 years of age.

Effects of odanacatib on the radius and tibia of postmenopausal women: improvements in bone geometry, microarchitecture, and estimated bone strength

The cathepsin K inhibitor odanacatib (ODN), currently in phase 3 development for postmenopausal osteoporosis, has a novel mechanism of action that reduces bone resorption while maintaining bone formation. In phase 2 studies, odanacatib increased areal bone mineral density (aBMD) at the lumbar spine and total hip progressively over 5 years. To determine the effects of ODN on cortical and trabecular bone and estimate changes in bone strength, we conducted a randomized, double-blind, placebo-controlled trial, using both quantitative computed tomography (QCT) and high-resolution peripheral (HR-p)QCT. In previously published results, odanacatib was superior to placebo with respect to increases in trabecular volumetric BMD (vBMD) and estimated compressive strength at the spine, and integral and trabecular vBMD and estimated strength at the hip. Here, we report the results of HR-pQCT assessment. A total of 214 postmenopausal women (mean age 64.0 ± 6.8 years and baseline lumbar spine T-score -1.81 ± 0.83) were randomized to oral ODN 50 mg or placebo, weekly for 2 years. With ODN, significant increases from baseline in total vBMD occurred at the distal radius and tibia. Treatment differences from placebo were also significant (3.84% and 2.63% for radius and tibia, respectively). At both sites, significant differences from placebo were also found in trabecular vBMD, cortical vBMD, cortical thickness, cortical area, and strength (failure load) estimated using finite element analysis of HR-pQCT scans (treatment differences at radius and tibia = 2.64% and 2.66%). At the distal radius, odanacatib significantly improved trabecular thickness and bone volume/total volume (BV/TV) versus placebo. At a more proximal radial site, odanacatib attenuated the increase in cortical porosity found with placebo (treatment difference = -7.7%, p = 0.066). At the distal tibia, odanacatib significantly improved trabecular number, separation, and BV/TV versus placebo. Safety and tolerability were similar between treatment groups. In conclusion, odanacatib increased cortical and trabecular density, cortical thickness, aspects of trabecular microarchitecture, and estimated strength at the distal radius and distal tibia compared with placebo.

Emerging drugs for osteoporosis

INTRODUCTION

Osteoporotic fracture is a cause of pain, loss of autonomy and excess mortality. Current drugs however, do not allow for a satisfactory non vertebral fracture risk reduction and the compliance is suboptimal.

AREAS COVERED

Current treatments consist of mainly bisphosphonates, denosumabs, selective estrogen receptor modulators and teriparatides. All drugs currently in development will target some aspect of bone remodeling by using the recent advances in our knowledge of bone biology: cathepsin-K inhibitors (odanacatib) are antiresorptive, antisclerostin monoclonal antibodies (romosozumab and blosozumab) are anabolic agents and PTHrp 1-34 (abaloparatide) is an anabolic agent.

EXPERT OPINION

New drugs with better tolerance and ideally with intermittent administration may improve their compliance. New drugs will have to provide higher efficiency levels with regards to reducing the risk of fractures. They may be second-line options, targeted at patients who are poor responders, or those who display contraindications to the older drugs, as a result of cost issues. In addition, some of these new drugs with potent anabolic effect may be confined to niches, for those patients at high risk of refracture after an initial severe fracture such as a hip fracture or a clinical vertebral fracture.

Cortical bone assessed with clinical computed tomography at the proximal femur

Hip fractures are the most serious of all fragility fractures in older people of both sexes. Trips, stumbles, and falls result in fractures of the femoral neck or trochanter, and the incidence of these two common fractures is increasing worldwide as populations age. Although clinical risk factors and chance are important in causation, the ability of a femur to resist fracture also depends on the size and spatial distribution of the bone, its intrinsic material properties, and the loads applied. Over the past two decades, clinical quantitative computed tomography (QCT) studies of living volunteers have provided insight into how the femur changes with advancing age to leave older men and women at increased risk of hip fractures. In this review, we focus on patterns of cortical bone loss associated with hip fracture, age-related changes in cortical bone, and the effects of drugs used to treat osteoporosis. There are several methodologies available to measure cortical bone in vivo using QCT. Most techniques quantify bone density (g/cm(3)), mass (g), and thickness (mm) in selected, predefined or “traditional” regions of interest such as the “femoral neck” or “total hip” region. A recent alternative approach termed “computational anatomy,” uses parametric methods to identify systematic differences, before displaying statistically significant regions as color-scaled maps of density, mass, or thickness on or within a representative femur model. This review will highlight discoveries made using both traditional and computational anatomy methods, focusing on cortical bone of the proximal femur.

New therapeutics for osteoporosis

Two new approaches for the treatment of osteoporosis are summarized, each having arisen out of important new discoveries in bone biology. Odanacatib (ODN) inhibits the enzyme, cathepsin K, that is essential for the resorbing activity of osteoclasts. It is effective in preventing ovariectomy-induced bone loss in preclinical studies, and a phase II clinical study has shown inhibition of resorption sustained over five years. Outcome of a phase III study is awaited. The finding from mouse and human genetics that Wnt signaling is a powerful inducer of bone formation led to developments aimed at enhancing this pathway. Of the several approaches towards this, the most advanced is with a neutralizing antibody against sclerostin, the osteocyte-derived inhibitor of Wnt signaling. Preclinical studies show a powerful bone anabolic effect, and a clinical phase II study shows dose-dependent increases in bone formation and decreases in bone resorption markers.

Cysteine cathepsins and extracellular matrix degradation

BACKGROUND

Cysteine cathepsins are normally found in the lysosomes where they are involved in intracellular protein turnover. Their ability to degrade the components of the extracellular matrix in vitro was first reported more than 25years ago. However, cathepsins were for a long time not considered to be among the major players in ECM degradation in vivo. During the last decade it has, however, become evident that abundant secretion of cysteine cathepsins into extracellular milieu is accompanying numerous physiological and disease conditions, enabling the cathepsins to degrade extracellular proteins.

SCOPE OF VIEW

In this review we will focus on cysteine cathepsins and their extracellular functions linked with ECM degradation, including regulation of their activity, which is often enhanced by acidification of the extracellular microenvironment, such as found in the bone resorption lacunae or tumor microenvironment. We will further discuss the ECM substrates of cathepsins with a focus on collagen and elastin, including the importance of that for pathologies. Finally, we will overview the current status of cathepsin inhibitors in clinical development for treatment of ECM-linked diseases, in particular osteoporosis.

MAJOR CONCLUSIONS

Cysteine cathepsins are among the major proteases involved in ECM remodeling, and their role is not limited to degradation only. Deregulation of their activity is linked with numerous ECM-linked diseases and they are now validated targets in a number of them. Cathepsins S and K are the most attractive targets, especially cathepsin K as a major therapeutic target for osteoporosis with drugs targeting it in advanced clinical trials.

GENERAL SIGNIFICANCE

Due to their major role in ECM remodeling cysteine cathepsins have emerged as an important group of therapeutic targets for a number of ECM-related diseases, including, osteoporosis, cancer and cardiovascular diseases. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Modulation of osteoclast differentiation and bone resorption by Rho GTPases

Bone is a dynamic tissue constantly renewed through a regulated balance between bone formation and resorption. Excessive bone degradation by osteoclasts leads to pathological decreased bone density characteristic of osteolytic diseases such as post-menopausal osteoporosis or bone metastasis. Osteoclasts are multinucleated cells derived from hematopoietic stem cells via a complex differentiation process. Their unique ability to resorb bone is dependent on the formation of the actin-rich sealing zone. Within this adhesion structure, the plasma membrane differentiates into the ruffled border where protons and proteases are secreted to demineralize and degrade bone, respectively. On the bone surface, mature osteoclasts alternate between stationary resorptive and migratory phases. These are associated with profound actin cytoskeleton reorganization, until osteoclasts die of apoptosis. In this review, we highlight the role of Rho GTPases in all the steps of osteoclasts differentiation, function, and death and conclude on their interest as targets for treatment of osteolytic pathologies.

Implications of osteoblast-osteoclast interactions in the management of osteoporosis by antiresorptive agents denosumab and odanacatib

Antiresorptive agents, used in the treatment of osteoporosis, inhibit either osteoclast formation or function. However, with these approaches, osteoblast activity is also reduced because of the loss of osteoclast-derived coupling factors that serve to stimulate bone formation. This review discusses how osteoclast inhibition influences osteoblast function, comparing the actions of an inhibitor of osteoclast formation [anti-RANKL/Denosumab (DMAB)] with that of a specific inhibitor of osteoclastic cathepsin K activity [Odanacatib (ODN)]. Denosumab rapidly and profoundly, but reversibly, reduces bone formation. In contrast, preclinical studies and clinical trials of ODN showed that bone formation at some skeletal sites was preserved although resorption was reduced. This preservation of bone formation appears to be due to effects of coupling factors, secreted by osteoclasts and released from demineralized bone matrix. This indicates that bone resorptive activities of osteoclasts are separable from their coupling activities.

A low-radiation exposure protocol for 3D QCT of the spine

SUMMARY

Cadaver and phantom measurements and simulations confirmed that radiation exposure in 3D QCT of the spine can be reduced if 80 kV instead of 120 kV protocols are used; 120 mAs and slice thicknesses of 1-1.3 mm should be usable but obese patient will require higher milliampere-second settings.

PURPOSE

To develop a low-radiation exposure CT acquisition protocol for 3D QCT of the thoracolumbar spine.

METHODS

Twenty-six cadavers were scanned with a standard protocol of 120 kV, 100 mAs and with a low-dose protocol using 90 kV, 150 mAs. The scan range included the vertebrae T6 to L4. Each vertebra was segmented and the integral volume and BMD of the total vertebral body were determined. Effective dose values were estimated. The impact of milliampere-second reduction on image quality was simulated by adding noise.

RESULTS

One hundred ninety-six vertebrae were analyzed. Integral volume as well as integral BMD correlated significantly (p < 0.001) between standard and low-dose protocols (volume, r (2) = 0.991, residual root mean square (RMS) error, 0.77 cm(3); BMD, r (2) = 0.985, RMS error, 4.21 mg/cm(3)). The slope significantly differed from 1 for integral BMD but not for volume hinting at residual field inhomogeneity differences between the two voltage settings that could be corrected by cross-calibration. Compared to the standard protocol, effective dose was reduced by over 50 % in the low-dose protocol. Adding noise in the 90 kV images to simulate a reduction from 150 to 100 mAs did not affect the results for integral volume or BMD.

CONCLUSIONS

For 3D QCT of the spine, depending on scanner type, 80 or 90 kV instead of 120 kV protocols may be considered as an important option to reduce radiation exposure; 120 mAs and slice thicknesses of 1-1.5 mm are usable if segmentation is robust to noise. In obese patients, higher milliampere-second settings will be required.

The Influence of Bioisosteres in Drug Design: Tactical Applications to Address Developability Problems

The application of bioisosteres in drug discovery is a well-established design concept that has demonstrated utility as an approach to solving a range of problems that affect candidate optimization, progression, and durability. In this chapter, the application of isosteric substitution is explored in a fashion that focuses on the development of practical solutions to problems that are encountered in typical optimization campaigns. The role of bioisosteres to affect intrinsic potency and selectivity, influence conformation, solve problems associated with drug developability, including P-glycoprotein recognition, modulating basicity, solubility, and lipophilicity, and to address issues associated with metabolism and toxicity is used as the underlying theme to capture a spectrum of creative applications of structural emulation in the design of drug candidates.

Review of new guidelines for the management of glucocorticoid induced osteoporosis

The chronic use of glucocorticoids results in osteoporosis. Several sets of guidelines have been published on the management of glucocorticoid induced osteoporosis (GIO). These guidelines vary on their focus and highlight different aspects of the current concepts in the management of GIO. In this current article, we summarize recent guidelines for management of GIO and highlight similarities and differences as well as address some of the controversies generated by these guidelines.

Postmenopausal osteoporosis

PURPOSE OF REVIEW

The aim of this study is to provide a thorough updated review of the diagnosis and treatment of postmenopausal osteoporosis.

RECENT FINDINGS

There have been several important findings in the field of postmenopausal osteoporosis over the past 1-2 years. Fewer morphometric vertebral fractures were found in women treated for 6 years with zoledronic acid compared with those who stopped treatment after 3 years. Longer duration of bisphosphonate therapy is associated with a higher risk of atypical femur fractures. Combination therapy with teriparatide and denosumab appears to increase bone mineral density to a greater extent than either therapy alone in postmenopausal women at high risk for fracture. There are several novel therapies under investigation for the treatment of osteoporosis, which are in various stages of development. Nonadherence to osteoporosis therapies continues to be a major problem in clinical practice.

SUMMARY

There are numerous effective pharmacologic treatment options for postmenopausal osteoporosis. Bisphosphonate drug holidays continue to be an area of significant debate.

New therapeutical horizons in the management of postmenopausal osteoporosis

Osteoporosis is a bone metabolic disease characterized by a compromised skeletal fragility, leading to an increased risk of developing spontaneous and traumatic fractures. This disease is the consequence of an imbalance of the physiological process of bone turnover (or coupling), with the lost of the equilibrium between the activity of osteoblasts and osteoclasts. Therapy has been aimed mainly at the correction of the imbalance between bone resorption and bone formation, to protect skeletal integrity and reduce the risk of fractures. Thus, pharmacological treatments have been aimed at modulating the activity of bone cells.

Advanced CT based in vivo methods for the assessment of bone density, structure, and strength

Based on spiral 3D tomography a large variety of applications have been developed during the last decade to asses bone mineral density, bone macro and micro structure, and bone strength. Quantitative computed tomography (QCT) using clinical whole body scanners provides separate assessment of trabecular, cortical, and subcortical bone mineral density (BMD) and content (BMC) principally in the spine and hip, although the distal forearm can also be assessed. Further bone macrostructure, for example bone geometry or cortical thickness can be quantified. Special high resolution peripheral CT (hr-pQCT) devices have been introduced to measure bone microstructure for example the trabecular architecture or cortical porosity at the distal forearm or tibia. 3D CT is also the basis for finite element analysis (FEA) to determine bone strength. QCT, hr-pQCT, and FEM are increasingly used in research as well as in clinical trials to complement areal BMD measurements obtained by the standard densitometric technique of dual x-ray absorptiometry (DXA). This review explains technical developments and demonstrates how QCT based techniques advanced our understanding of bone biology.

Treating osteoporosis by targeting parathyroid hormone to bone

Osteoporosis is a major public health problem despite widespread use of bisphosphonate therapy. PTH(1-34) is a more effective treatment; but its use has been limited by side effects (hypercalcemia, tumor risk) and inconvenient dosing (daily injection). Long-acting forms of PTH are also effective but cause severe hypercalcemia, presumably from effects in kidney. We hypothesized that targeted delivery of PTH to bone using a collagen binding domain (PTH-CBD) could reduce hypercalcemia. PTH-CBD is cleared from serum within 12hours after subcutaneous administration. In ovariectomized rats, monthly administration of PTH-CBD increased spinal BMD by 14.2% with no associated hypercalcemia. Such bone-targeted anabolic agents may ultimately allow the superior efficacy of anabolic therapy to be obtained with the dosing convenience of bisphosphonates.

Autosomal dominant osteopetrosis revisited: lessons from recent studies

Systematic studies of autosomal dominant osteopetrosis (ADO) were followed by the identification of underlying mutations giving unique possibilities to perform translational studies. What was previously designated ADO1 turned out to be a high bone mass phenotype caused by a missense mutation in the first propeller of LRP5, a region of importance for binding inhibitory proteins. Thereby, ADO1 cannot be regarded as a classical form of osteopetrosis but must now be considered a disease of LRP5 activation. ADO (Albers-Schönberg disease, or previously ADO2) is characterized by increased number of osteoclasts and a defect in the chloride transport system (ClC-7) of importance for acidification of the resorption lacuna (a form of Chloride Channel 7 Deficiency Osteopetrosis). Ex vivo studies of osteoclasts from ADO have shown that cells do form normally but have reduced resorption capacity and an expanded life span. Bone formation seems normal despite decreased osteoclast function. Uncoupling of formation from resorption makes ADO of interest for new strategies for treatment of osteoporosis. Recent studies have integrated bone metabolism in whole-body energy homeostasis. Patients with ADO may have decreased insulin levels indicating importance beyond bone metabolism. There seems to be a paradigm shift in the treatment of osteoporosis. Targeting ClC-7 might introduce a new principle of dual action. Drugs affecting ClC-7 could be antiresorptive, still allowing ongoing bone formation. Inversely, drugs affecting the inhibitory site of LRP5 might stimulate bone formation and inhibit resorption. Thereby, these studies have highlighted several intriguing treatment possibilities, employing novel modes of action, which could provide benefits to the treatment of osteoporosis.