Denosumab and bisphosphonates: different mechanisms of action and effects

Nuclear lamin functions and disease

Recent studies have shown that premature cellular senescence and normal organ development and function depend on the type V intermediate filament proteins, the lamins, which are major structural proteins of the nucleus. This review presents an up-to-date summary of the literature describing new findings on lamin functions in various cellular processes and emphasizes the relationship between the lamins and devastating diseases ranging from premature aging to cancer. Recent insights into the structure and function of the A- and B- type lamins in normal cells and their dysfunctions in diseased cells are providing novel targets for the development of new diagnostic procedures and disease intervention. We summarize these recent findings, focusing on data from mice and humans, and highlight the expanding knowledge of these proteins in both healthy and diseased cells.

Potential role of odanacatib in the treatment of osteoporosis

Cathepsin K is a key enzyme involved in the degradation of organic bone matrix by osteoclasts. Inhibition of bone resorption observed in human and animal models deficient for cathepsin K has identified this enzyme as a suitable target for intervention by small molecules with the potential to be used as therapeutic agents in the treatment of osteoporosis. Odanacatib (ODN) is a nonbasic selective cathepsin K inhibitor with good pharmacokinetic parameters such as minimal in vitro metabolism, long half-life, and oral bioavailability. In preclinical studies, ovariectomized monkeys and rabbits treated with ODN showed substantial inhibition of bone resorption markers along with increases in bone mineral density (BMD). Significant differences were observed in the effects of ODN treatment compared with those of other antiresorptive agents such as bisphosphonates and denosumab. ODN displayed compartment-specific effects on trabecular versus cortical bone formation, with treatment resulting in marked increases in periosteal bone formation and cortical thickness in ovariectomized monkeys whereas trabecular bone formation was reduced. Furthermore, osteoclasts remained viable. Phase I and II studies conducted in postmenopausal women showed ODN to be safe and well tolerated. After 5 years, women who received ODN 50 mg weekly continuously from year 1 (n = 13), showed BMD increases from baseline of 11.9% at the lumbar spine, 9.8% at the femoral neck, 10.9% at the hip trochanter, and 8.5% at the total hip. Additionally, these subjects maintained a low level of the urine bone resorption marker N-terminal telopeptide/creatinine (−67.4% from baseline) through 5 years of treatment, while levels of serum bone-specific alkaline phosphatase remained only slightly reduced relative to baseline (−15.3%). In women who were switched from ODN to placebo after 2 years, bone turnover markers were transiently increased and BMD gains reversed after 12 months off medication. Adverse experiences in the ODN-treated group were not significantly different from the placebo group. In conclusion, available data suggests that cathepsin K inhibition could be a promising intervention with which to treat osteoporosis. Ongoing studies are expected to provide information on the long-term efficacy in fracture reduction and safety of prolonged treatment with ODN.

Conditional inactivation of Blimp1 in adult mice promotes increased bone mass

Bone resorption, which is regulated by osteoclasts, is excessively activated in bone destructive diseases such as osteoporosis. Thus, controlling osteoclasts would be an effective strategy to prevent pathological bone loss. Although several transcription factors that regulate osteoclast differentiation and function could serve as molecular targets to inhibit osteoclast formation, those factors have not yet been characterized using a loss of function approach in adults. Here we report such a study showing that inactivation of B-lymphocyte induced maturation protein 1 (Blimp1) in adult mice increases bone mass by suppressing osteoclast formation. Using an ex vivo assay, we show that osteoclast differentiation is significantly inhibited by Blimp1 inactivation at an early stage of osteoclastogenesis. Conditional inactivation of Blimp1 inhibited osteoclast formation and increased bone mass in both male and female adult mice. Bone resorption parameters were significantly reduced by Blimp1 inactivation in vivo. Blimp1 reportedly regulates immune cell differentiation and function, but we detected no immune cell failure following Blimp1 inactivation. These data suggest that Blimp1 is a potential target to promote increased bone mass and prevent osteoclastogenesis.

Significant addition to treatment options for bone metastasis in prostate cancer

Pathologic fractures, spinal compression, and pain take a great toll on the healthcare costs and well-being of men with prostate cancer metastatic to the bone. For almost 10 years, the only drug proven to prevent these skeletal-related adverse events was the bisphosphonate zoledronic acid. In a study published by Fizazi et al. in The Lancet, the monoclonal antibody to RANKL, denosumab, is shown to be superior to zoledronic acid in the prevention of these events. The only notable adverse event more frequent in either arm was increased hypocalcemia in the denosumab arm. There was a greater frequency of osteonecrosis of the jaw in the denosumab treatment group that did not reach statistical significance, but is of great concern. While further analysis is needed to determine the value of denosumab in preventing adverse events and improving quality of life, this new therapy is a significant addition to the treatment of men living with metastatic prostate cancer.

Update on denosumab in postmenopausal osteoporosis--recent clinical data

Denosumab, a fully human monoclonal antibody against the key osteoclastogenic factor RANK ligand, is currently approved for the treatment of postmenopausal osteoporosis. Denosumab differs from bisphosphonates in many aspects, for example, its ability to act in the extracellular compartment and its likelihood to be distributed throughout the skeleton. In contrast, bisphosphonates have to be internalized by osteoclasts and are mainly located across bone surfaces. This could explain why patients with osteoporosis, who are already treated with bisphosphonates, might experience further benefit when switching to denosumab. Head-to-head studies revealed that transition to denosumab resulted in a greater increase of bone mineral density (BMD) and a greater reduction of bone turnover than did continued alendronate. Additional analyses of the phase 3 FREEDOM trial demonstrated that fracture reduction was particularly high in cortical bone, such as the wrist. In addition, denosumab treatment for a 5- and 8-year period showed sustained reduction in fracture risk, increase in BMD and continued to be well tolerated. The 7-year extension study of FREEDOM and a phase 3 trial evaluating denosumab for the treatment of male osteoporosis are still ongoing and will provide supportive data in the near future.

Denosumab--a powerful RANKL inhibitor to stop lytic metastases and other bone loss actions by osteoclasts

Denosumab is a perfect example on the targeted anticancer therapy. The inhibition of RANKL activity suppressed the osteoclasts' resorptive function and so prevented skeletal related events. This effect is useful not only against bone metastases, but also in the treatment of other diseases caused by bone loss. In different solid tumors with bone metastasis the quality of life also improved, although the overall survival usually showed no change. On the market the main competitors for denosumab are still the bisphosphonates (questions of costs and reimbursement are not discussed) and some potential new agents e.g. Src kinases (as dasatinib, saracatinib, bosutinib), cathepsin K inhibitors, (e.g. odanacatib), and new selective estrogen receptor modulators (e.g. bazedoxifene, lasofoxifene). Nevertheless, today denosumab is one of the most powerful agents in bone-saving area.

Therapeutic inhibition of cathepsin K-reducing bone resorption while maintaining bone formation

Osteoporosis is a disease of high bone remodeling with an imbalance of bone resorption over bone formation, resulting in decreased bone mineral density and deterioration of bone microarchitecture. From the emerging understandings of the molecular and cellular regulators of bone remodeling, potential new targets for therapeutic intervention for this disease have been identified. Cathepsin K (CatK), a cysteine protease produced by osteoclasts, is the primary enzyme mediating the degradation of the demineralized bone matrix. Current genetic and pharmacological evidence from studies in multiple preclinical species have consistently demonstrated that inhibition of CatK results in the reduction of bone resorption while allowing bone formation to continue. Early results from clinical studies with several investigational CatK inhibitors indicate that the impact of CatK inhibition on bone formation is distinct from that of either the bisphosphonates or the anti-receptor activator of nuclear factor-κB ligand antibody, denosumab. Odanacatib, a highly selective, reversible and potent inhibitor of CatK, is currently in phase III clinical trials for the treatment of postmenopausal osteoporosis.

Postmenopausal osteoporosis treatment with antiresorptives: effects of discontinuation or long-term continuation on bone turnover and fracture risk--a perspective

Osteoporosis may be a lifelong condition. Robust data regarding the efficacy and safety of both long-term osteoporosis therapy and therapy discontinuation are therefore important. A paucity of clinical trial data regarding the long-term antifracture efficacy of osteoporosis therapies necessitates the use of surrogate endpoints in discussions surrounding long-term use and/or discontinuation. Long-term treatment (beyond 3-4 years) may produce further increases in bone mineral density (BMD) or BMD stability, depending on the specific treatment and the skeletal site. Bisphosphonates, when discontinued, are associated with a prolonged reduction in bone turnover markers (BTMs), with a very gradual increase to pretreatment levels within 3 to 60 months of treatment cessation, depending on the bisphosphonate used and the prior duration of therapy. In contrast, with nonbisphosphonate antiresorptive agents, such as estrogen and denosumab, BTMs rebound to above pretreatment values within months of discontinuation. The pattern of BTM change is generally mirrored by a more or less rapid decrease in BMD. Although the prolonged effect of some bisphosphonates on BTMs and BMD may contribute to residual benefit on bone strength, it may also raise safety concerns. Adequately powered postdiscontinuation fracture studies and conclusive evidence on maintenance or loss of fracture benefit is lacking for bisphosphonates. Similarly, the effects of rapid reversal of bone turnover upon discontinuation of denosumab on fracture risk remain unknown. Ideally, studies evaluating the effects of long-term treatment and treatment discontinuation should be designed to provide head-to-head "offset" data between bisphosphonates and nonbisphosphonate antiresorptive agents. In the absence of this, a clinical recommendation for physicians may be to periodically assess the benefits/risks of continuation versus discontinuation versus alternative management strategies.

Comparison of clinical efficacy and safety between denosumab and alendronate in postmenopausal women with osteoporosis: a meta-analysis

The aim of this study was to perform a head-to-head comparison of efficacy and safety profile between 60 mg denosumab (Den) subcutaneously (SC) per 6 months (Q6M) and 70 mg alendronate (Aln) orally per week (QW) for postmenopausal women with low bone mineral density. We searched electronic databases comparing efficacy and safety of Den SC Q6M and Aln QW in postmenopausal women. The primary outcomes of efficacy evaluation in included trials were incidence of clinical fracture in both groups and bone mineral density (BMD) at different skeletal sites. And adverse events (AEs), including incidence of neoplasms and infections, were considered as secondary outcomes. Following the instructions of 'Cochrane Handbook for systematic Reviews of Interventions 5.0.2', we identified eligible studies, evaluated the methodological quality and abstracted relevant data. Four heterogeneous randomised controlled trials (RCTs) involving 1942 women were identified. The results of review showed low evidence quality that supported the hypothesis the denosumab vs. alendronate could reduce risk of fracture [OR (95% CI) 1.42 (0.84 to 2.40), 11 more women per 1000 (from 4 fewer to 36 more), p = 0.19] but the moderate to high quality evidence suggesting treatment with 60 mg Den SC Q6M was more effective for postmenopausal women in increasing BMD [at distal radius (DR), total hip (TH), lumbar spine (LS), and femoral neck (FN)]. Hazards of neoplasms [OR (95% CI) 1.10 (0.65 to 1.86), 3 more per 1000 (from 10 fewer to 24 more), p = 0.62] or infections [OR (95% CI) 0.95 (0.79 to 1.15), 12 fewer per 1000 (from 53 fewer to 33 more,), p = 0.62] were appeared to be similar.Our review suggested within 1 year 60 mg Den SC Q6M treatment was more effective in increasing bone mass but could not reduce the fracture risk to a greater extent than 70 mg Aln QW therapy. Also the Den SC Q6M therapy did not increase the risks of neoplasms and infections compared with Aln QW.

Denosumab dose selection for patients with bone metastases from solid tumors

PURPOSE

To quantitatively characterize the longitudinal dose exposure-response [urinary N-telopeptide normalized to urinary creatinine (uNTx/Cr) suppression] relationship for denosumab in patients with bone metastases from solid tumors.

EXPERIMENTAL DESIGN

Data from 373 patients who received denosumab as single or multiple subcutaneous doses ranging from 30 to 180 mg (or 0.01 to 3 mg/kg) administered every 4 or 12 weeks for up to 3 years were used in this analysis. An inhibitory sigmoid I(Max) model was used to characterize the time course of uNTx/Cr as a function of serum denosumab concentrations and the M3 method was used to analyze the 52% of uNTx/Cr values below the limit of quantification in the context of a mixed-effects model. Age, weight, sex, race, and cancer type were evaluated as potential covariates for model parameters. Model-based simulations were undertaken to explore and predict the role of denosumab dose and dosing intervals on uNTx/Cr suppression.

RESULTS

The typical value (between-subject variability; %) for uNTx/Cr at baseline was 49.2 nmol/L/mmol/L (76.8%), denosumab maximal uNTx/Cr suppression (efficacy) was 93.7% (127%), and the denosumab concentration providing half-maximal uNTx/Cr suppression (potency) was 31.8 ng/mL (287%). No effect of covariates on denosumab efficacy and potency was identified. Simulations indicated that a s.c. denosumab dose of 120 mg administered every 4 weeks provides more than 90% suppression of uNTx/Cr in the maximum proportion of patients relative to other every 4- and 12-week doses evaluated.

CONCLUSIONS

Over the wide range of dosing regimens examined, a s.c. denosumab dose of 120 mg administered every 4 weeks is the optimal dosing regimen to suppress uNTx/Cr in patients with bone metastases from solid tumors. Clin Cancer Res; 18(9); 2648-57. ©2012 AACR.

Relationship between bone mineral density changes with denosumab treatment and risk reduction for vertebral and nonvertebral fractures

Dual-energy X-ray absorptiometric bone mineral density (DXA BMD) is a strong predictor of fracture risk in untreated patients. However, previous patient-level studies suggest that BMD changes explain little of the fracture risk reduction observed with osteoporosis treatment. We investigated the relevance of DXA BMD changes as a predictor for fracture risk reduction using data from the FREEDOM trial, which randomly assigned placebo or denosumab 60 mg every 6 months to 7808 women aged 60 to 90 years with a spine or total hip BMD T-score < -2.5 and not < -4.0. We took a standard approach to estimate the percent of treatment effect explained using percent changes in BMD at a single visit (months 12, 24, or 36). We also applied a novel approach using estimated percent changes in BMD from baseline at the time of fracture occurrence (time-dependent models). Denosumab significantly increased total hip BMD by 3.2%, 4.4%, and 5.0% at 12, 24, and 36 months, respectively. Denosumab decreased the risk of new vertebral fractures by 68% (p < 0.0001) and nonvertebral fracture by 20% (p = 0.01) over 36 months. Regardless of the method used, the change in total hip BMD explained a considerable proportion of the effect of denosumab in reducing new or worsening vertebral fracture risk (35% [95% confidence interval (CI): 20%-61%] and 51% [95% CI: 39%-66%] accounted for by percent change at month 36 and change in time-dependent BMD, respectively) and explained a considerable amount of the reduction in nonvertebral fracture risk (87% [95% CI: 35% - >100%] and 72% [95% CI: 24% - >100%], respectively). Previous patient-level studies may have underestimated the strength of the relationship between BMD change and the effect of treatment on fracture risk or this relationship may be unique to denosumab.

Odanacatib treatment increases hip bone mass and cortical thickness by preserving endocortical bone formation and stimulating periosteal bone formation in the ovariectomized adult rhesus monkey

Odanacatib (ODN) is a selective and reversible inhibitor of cathepsin K (CatK). Previously, ODN was shown to increase bone mineral density (BMD) and maintained normal bone strength at the spine in ovariectomized (OVX) rhesus monkeys. Here, we further characterize the effects of ODN on BMD, bone strength, and dynamic histomorphometric analyses of the hip from the same monkeys. Animals were treated for 21 months with vehicle, 6 or 30 mg/kg ODN (p.o., q.d.). ODN increased femoral neck (FN) BMD by 11% and 15% (p < 0.07) and ultimate load by 25% (p < 0.05) and 30% (p < 0.01) versus vehicle. Treatment-related increases in ultimate load positively correlated with the increased FN BMD, bone mineral content (BMC), and cortical thickness. Histomorphometry of FN and proximal femur (PF) revealed that ODN reduced trabecular and intracortical bone formation rate (BFR) but did not affect long-term endocortical BFR. Moreover, ODN stimulated long-term FN and PF periosteal BFR by 3.5-fold and 6-fold with the 30 mg/kg dose versus vehicle, respectively. Osteoclast surfaces were either unaffected or trended higher (~twofold) in endocortical and trabecular surfaces in the ODN group. Lastly, ODN increased cortical thickness of FN by 21% (p = 0.08) and PF by 19% (p < 0.05) versus vehicle after 21 months of treatment. Together, both doses of ODN increased bone mass and improved bone strength at the hip. Unlike conventional antiresorptives, ODN displayed site-specific effects on trabecular versus cortical bone formation. The drug provided marked increases in periosteal bone formation and cortical thickness in OVX monkeys, suggesting that CatK inhibition may represent a novel therapeutic approach for the treatment of osteoporosis.

Denosumab for the prevention of skeletal-related events in patients with bone metastasis from solid tumor

Most patients with advanced malignancy develop bone metastases during the course of their disease. For the remainder of the patient's life, these bone metastases lead to skeletal-related events such as pathologic fractures and spinal cord compression, as well as bone pain or lesions requiring palliative radiation therapy or surgery to prevent or treat fractures. Skeletal-related events result in increased morbidity, mortality and health care costs. For the past decade, intravenous bisphosphonates (zoledronic acid, pamidronate) have been recognized as the primary pharmacologic options in the prevention or treatment of skeletal-related events in patients with bone metastasis. Recently, the United States Food and Drug Administration approved denosumab, a fully human monoclonal antibody, for the prevention of skeletal-related events in patients with bone metastases from solid tumors. Three prominent clinical trials were conducted to establish the efficacy of denosumab. In two of three trials, denosumab was found to delay the time to first skeletal-related event significantly more than zoledronic acid in patients with breast or castration-resistant prostate cancer with bone metastasis. The third trial found denosumab to be noninferior to zoledronic acid in patients with metastases from solid tumors, excluding breast and prostate solid tumors. Overall survival and progression-free survival were similar between zoledronic acid and denosumab. Thus, evidence is insufficient to prove a greater efficacy of one agent over the other. According to the American Society of Clinical Oncology and the National Comprehensive Cancer Network, patients with bone metastasis should have zoledronic acid, pamidronate, or denosumab (with calcium and vitamin D supplementation) added to their chemotherapy regimen if they have an expected survival of 3 months or longer and have adequate renal function.

Denosumab for the management of bone disease in patients with solid tumors

Many patients with advanced cancer develop bone metastases, which reduces their quality of life. Bone metastases are associated with an increased risk of skeletal-related events, which can lead to increased morbidity and mortality. In patients with bone metastases, tumor cells disrupt the normal process of bone remodeling, leading to increased bone destruction. Denosumab is a fully human monoclonal antibody against receptor activator of NF-κB ligand (RANKL), a key regulatory factor in bone remodeling. By binding to RANKL, denosumab disrupts the cycle of bone destruction. In clinical studies in patients with prostate or breast cancer and bone metastases, denosumab was superior to the current standard of care, zoledronic acid, for delaying skeletal-related events, while in patients with other solid tumors or multiple myeloma, denosumab was noninferior to zoledronic acid. This article examines the pharmacokinetics, efficacy, and safety and tolerability of denosumab for the management of bone events in patients with cancer.

[Denosumab for treatment of postmenopausal osteoporosis]

BACKGROUND

Treatment with bisphosphonates reduces the risk of new fractures and is the treatment of choice for osteoporosis. Denosumab inhibits bone resorption via a different mechanism than bisphosphonates, and is a new option in the treatment of osteoporosis. In this paper we give an overview of the mode of action and clinical effects.

MATERIAL AND METHODS

The paper is based on a non-systematic literature search in Pubmed/Medline.

RESULTS

Denosumab is a human monoclonal antibody to receptor-activated nuclear factor kappa B (RANKL), a member of the TNF family that is formed in the osteoblast. Binding to RANKL results in reduced recruitment and activity of osteoclasts. Denosumab 60 mg given subcutaneously every six months is shown to inhibit bone resorption to a greater degree than bisphosphonates. In a three-year study of 7,868 women with postmenopausal osteoporosis, a reduction in the relative risk of vertebral, non-vertebral and hip fractures compared to placebo was found (68. 20 and 40 %, correspondingly). In the clinical trials with denosumab, the safety profile was similar to placebo, except for a slightly higher incidence of cellulitis and exanthema. Denosumab has also shown promising skeletal effects in the treatment of cancer and rheumatoid arthritis.

INTERPRETATION

Treatment with denosumab has an effect on postmenopausal osteoporosis and may be an alternative to treatment with bisphosphonates. There are few adverse effects and it is simple to administer.

Transgenic over-expression of interleukin-33 in osteoblasts results in decreased osteoclastogenesis

Interleukin-33 (IL-33) is the most recently identified member of the IL-1 family of cytokines, which is primarily known for its proinflammatory functions. We have previously reported that IL-33 is expressed by bone-forming osteoblasts, and that administration of recombinant IL-33 to bone marrow cultures inhibits their differentiation into bone-resorbing osteoclasts. Likewise, while the inhibitory effect of IL-33 on osteoclast differentiation was fully abolished in cultures lacking the IL-33 receptor ST2, mice lacking ST2 displayed low bone mass caused by increased osteoclastogenesis. Although these data suggested a physiological role of IL-33 as an inhibitor of bone resorption, direct in vivo evidence supporting such a function was still missing. Here we describe the generation and bone histomorphometric analysis of a transgenic mouse model (Col1a1-Il33) over-expressing IL-33 specifically in osteoblasts. While we did not observe differences in osteoblast number and bone formation between wildtype and Col1a1-Il33 mice, the number of osteoclasts was significantly reduced compared to wildtype littermates in two independent transgenic lines. Since we did not observe quantitative differences in the populations of eosinophils, neutrophils, basophils or M2-macrophages from the bone marrow of wildtype and Col1a1-Il33 mice, our data demonstrate that an inhibition of osteoclastogenesis is one of the major physiological functions of IL-33, at least in mice.

Denosumab for the treatment of bone metastases in breast cancer: evidence and opinion

INTRODUCTION

Denosumab, a fully human monoclonal antibody, targets the receptor activator of nuclear factor-kappaB (RANK) ligand, a protein essential for osteoclast differentiation, activity and survival. Loss of osteoclasts from the bone surface reduces bone turnover and bone loss in malignant and benign diseases. In breast cancer, bone metastases are frequently observed; cancer treatment-induced bone loss (CTIBL) may result as a consequence of endocrine treatment or chemotherapy. Furthermore, preclinical studies suggest a direct role of the RANK/RANK-ligand pathway in breast tumorigenesis. This paper reviews preclinical and clinical data on denosumab in breast cancer.

MATERIALS AND METHODS

Studies were identified through the Medline database. Key search terms included: AMG-162, bisphosphonates, denosumab, RANK-ligand and zoledronic acid. Information available in abstract form only was retrieved from major oncology meetings, such as the American Society of Clinical Oncology (ASCO) annual meeting, ASCO breast meeting, European Cancer Organization, European Society of Medical Oncology and the San Antonio Breast Cancer Symposium.

RESULTS

Denosumab was consistently well tolerated throughout clinical trials, although the observed incidence of osteonecrosis of the jaw was comparable to that with bisphosphonates. Efficacy as determined by a reduction of skeletal-related events was at least equal to zoledronic acid, and superior in one phase III study conducted in patients with metastatic breast cancer. Clinical trials investigating the role of denosumab for the prevention of CTIBL and breast cancer recurrences are currently ongoing.

CONCLUSION

In conclusion, denosumab appears to be an effective and safe treatment option in patients with bone metastases from breast cancer with the potential of also preventing CTIBL.

Molecular pathways: osteoclast-dependent and osteoclast-independent roles of the RANKL/RANK/OPG pathway in tumorigenesis and metastasis

Receptor activator of nuclear factor-kappa B ligand (RANKL) is a TNF ligand superfamily member that is essential for the formation, activation, and function of osteoclasts. RANKL functions via its cognate receptor RANK, and it is inhibited by the soluble decoy receptor osteoprotegerin (OPG). In skeletal metastases, the ratio of RANKL to OPG is upregulated, which leads to increased osteoclast-mediated bone destruction. These changes in the bone microenvironment not only compromise the structural integrity of bone, leading to severe clinical morbidities, but have also been implicated in establishment of de novo bone metastasis and the progression of existing skeletal tumors. Evaluation of RANKL inhibitors, including the fully human anti-RANKL antibody denosumab, in patients with cancer has shown reductions in tumor-induced bone resorption activity and successful management of skeletal complications of bone metastases. RANKL also functions as a major paracrine effector of the mitogenic action of progesterone in mouse mammary epithelium, and it has a role in ovarian hormone-dependent expansion and regenerative potential of mammary stem cells. RANKL inhibition attenuates mammary tumorigenesis and pulmonary metastases in mouse models. These data suggest that the contribution of progesterone to increased mammary cancer incidence is mediated, at least in part, by RANKL-dependent changes in the mammary epithelium; RANKL also directly promotes distant metastases. In summary, the antitumor and antimetastatic effects of RANKL inhibition can occur by at least 2 distinct mechanisms, one in the bone via osteoclast-dependent effects, and the second via direct effects on the tumor cells of various origins and/or mammary epithelium.

Choosing a treatment for patients at the time a fracture is presented

The occurrence of a fragility fracture is an opportunity to recognize osteoporosis and begin treatment to reduce the risk of another fracture. However, selecting the treatment may have an impact on the incident fracture and this requires careful consideration of the patient and the treatment choices. There is no consensus regarding the management of osteoporosis at the time of an incident fracture. This review will consider the treatment options after a fragility fracture.

Sost down-regulation by mechanical strain in human osteoblastic cells involves PGE2 signaling via EP4

Sclerostin is a potent inhibitor of bone formation which is down-regulated by mechanical loading. To investigate the mechanisms involved we subjected Saos2 human osteoblastic cells to short periods of dynamic strain and used quantitative reverse transcriptase polymerase chain reaction to compare their responses to unstrained controls. Strain-induced Sost down-regulation was recapitulated by cyclo-oxygenase-2-mediated PGE2, acting through the EP4 receptor, whereas strain-related up-regulation of osteocalcin was mediated by the EP2 receptor. Strain-related Sost regulation required extracellular signal-regulated kinase signaling, whereas osteocalcin required protein kinase C. These findings indicate early divergence in the signaling pathways stimulated by strain and establish PGE2/EP4 as the pathway used by strain to regulate Sost expression.

Risedronate does not reduce mechanical loading-related increases in cortical and trabecular bone mass in mice

To establish whether the combination of anti-resorptive therapy with mechanical loading has a negative, additive or synergistic effect on bone structure, we assessed the separate and combined effects of risedronate and non-invasive dynamic loading on trabecular and cortical bone. Seventeen-week-old female C57BL/6 mice were given daily subcutaneous injections of vehicle (n=20) or risedronate at a dose of 0.15, 1.5, 15 or 150 μg/kg/day (n=10 in each) for 17 days. From the fourth day of treatment, the right tibiae were subjected to a single period of axial loading (40 cycles/day) for three alternate days per week for two weeks. The left tibiae were used as internal controls. Trabecular and cortical sites in the tibiae were analyzed by high-resolution micro-computed tomography and imaging of fluorochrome labels. In the non-loaded tibiae, treatment with the higher doses of risedronate at 15 or 150 μg/kg/day resulted in higher trabecular bone volume and trabecular number than in vehicle-treated controls, whereas such treatment was associated with no differences in cortical bone volume at any dose. In the loaded tibiae, loading induced increases in trabecular and cortical bone volume compared with contra-lateral controls primarily through increased trabecular thickness and periosteal expansion, respectively, independently of risedronate treatment. In conclusion, the response to mechanical loading in both trabecular and cortical bone in mice is therefore not impaired by short-term treatment with risedronate, even over a 1000-fold dose range. In considering the optimization of treatments for osteoporosis, it is reassuring that anti-resorptive therapy and mechanical loading can exert independent beneficial effects.

Bisphosphonates: the first 40 years

The first full publications on the biological effects of the diphosphonates, later renamed bisphosphonates, appeared in 1969, so it is timely after 40years to review the history of their development and their impact on clinical medicine. This special issue of BONE contains a series of review articles covering the basic science and clinical aspects of these drugs, written by some of many scientists who have participated in the advances made in this field. The discovery and development of the bisphosphonates (BPs) as a major class of drugs for the treatment of bone diseases has been a fascinating story, and is a paradigm of a successful journey from 'bench to bedside'. Bisphosphonates are chemically stable analogues of inorganic pyrophosphate (PPi), and it was studies on the role of PPi as the body's natural 'water softener' in the control of soft tissue and skeletal mineralisation that led to the need to find inhibitors of calcification that would resist hydrolysis by alkaline phosphatase. The observation that PPi and BPs could not only retard the growth but also the dissolution of hydroxyapatite crystals prompted studies on their ability to inhibit bone resorption. Although PPi was unable to do this, BPs turned out to be remarkably effective inhibitors of bone resorption, both in vitro and in vivo experimental systems, and eventually in humans. As ever more potent BPs were synthesised and studied, it became apparent that physico-chemical effects were insufficient to explain their biological effects, and that cellular actions must be involved. Despite many attempts, it was not until the 1990s that their biochemical actions were elucidated. It is now clear that bisphosphonates inhibit bone resorption by being selectively taken up and adsorbed to mineral surfaces in bone, where they interfere with the action of the bone-resorbing osteoclasts. Bisphosphonates are internalised by osteoclasts and interfere with specific biochemical processes. Bisphosphonates can be classified into at least two groups with different molecular modes of action. The simpler non-nitrogen containing bisphosphonates (such as etidronate and clodronate) can be metabolically incorporated into non-hydrolysable analogues of ATP, which interfere with ATP-dependent intracellular pathways. The more potent, nitrogen-containing bisphosphonates (including pamidronate, alendronate, risedronate, ibandronate and zoledronate) are not metabolised in this way but inhibit key enzymes of the mevalonate/cholesterol biosynthetic pathway. The major enzyme target for bisphosphonates is farnesyl pyrophosphate synthase (FPPS), and the crystal structure elucidated for this enzyme reveals how BPs bind to and inhibit at the active site via their critical N atoms. Inhibition of FPPS prevents the biosynthesis of isoprenoid compounds (notably farnesol and geranylgeraniol) that are required for the post-translational prenylation of small GTP-binding proteins (which are also GTPases) such as rab, rho and rac, which are essential for intracellular signalling events within osteoclasts. The accumulation of the upstream metabolite, isopentenyl pyrophosphate (IPP), as a result of inhibition of FPPS may be responsible for immunomodulatory effects on gamma delta (γδ) T cells, and can also lead to production of another ATP metabolite called ApppI, which has intracellular actions. Effects on other cellular targets, such as osteocytes, may also be important. Over the years many hundreds of BPs have been made, and more than a dozen have been studied in man. As reviewed elsewhere in this issue, bisphosphonates are established as the treatments of choice for various diseases of excessive bone resorption, including Paget's disease of bone, the skeletal complications of malignancy, and osteoporosis. Several of the leading BPs have achieved 'block-buster' status with annual sales in excess of a billion dollars. As a class, BPs share properties in common. However, as with other classes of drugs, there are obvious chemical, biochemical, and pharmacological differences among the various BPs. Each BP has a unique profile in terms of mineral binding and cellular effects that may help to explain potential clinical differences among the BPs. Even though many of the well-established BPs have come or are coming to the end of their patent life, their use as cheaper generic drugs is likely to continue for many years to come. Furthermore in many areas, e.g. in cancer therapy, the way they are used is not yet optimised. New 'designer' BPs continue to be made, and there are several interesting potential applications in other areas of medicine, with unmet medical needs still to be fulfilled. The adventure that began in Davos more than 40 years ago is not yet over.

Clinical utility of denosumab for treatment of bone loss in men and women

While most older patients with osteoporosis are treated with antiresorptive bisphosphonates such as alendronate, risedronate, ibandronate, and zoledronic acid, such drugs have side effects, remain in bone for extended periods, and lead to poor adherence to chronic treatment. Denosumab is a humanized monoclonal antibody and antiresorptive agent that works by decreasing the activity of the receptor activator of nuclear factor kappa B ligand. In major trials in postmenopausal women, denosumab increased bone mineral density by dual energy x-ray absorptiometry in the spine, hip, and distal third of the radius and decreased vertebral, nonvertebral, and hip fractures. Denosumab is administered by subcutaneous injection every six months, suggesting that adherence may be improved with such therapy. In addition, pharmacokinetic studies measuring bone turnover markers imply that the antiresorptive effect diminishes more quickly over time. Whether these properties will lead to fewer long-term side effects needs to be proven. Denosumab has also been studied in men with prostate cancer treated with androgen deprivation therapy. These men, at high risk for fracture, also have increases in spine, hip, and forearm dual energy x-ray absorptiometry, as well as fewer morphologic vertebral fractures on x-ray. Denosumab is approved for postmenopausal women with osteoporosis in the US and Europe and for men on androgen deprivation therapy in Europe.