Denosumab - a new option in the treatment of osteoporosis

Denosumab is the international name of a human, monoclonal antibody approved for the treatment of osteoporosis. This antibody is associated with RANK ligand (RANKL), inactivating it. In consequence, the formation and survival of osteoclasts are suppressed, leading to their apoptosis. All this results in lower bone resorption, while bone mineral density (BMD) increases. Denosumab also reduces the risk of vertebral and non-vertebral fractures. This agent is similarly effective in various stages of renal function impairment; it does not impair fracture healing processes nor contribute to atherosclerosis progression in patients with high cardiovascular risks. Following an analysis of adverse effects, performed in the FREEDOM study (in which it was demonstrated that the incidence of the majority of adverse effects observed in the course of denosumab use was similar to that in the placebo group), its safety for patients can definitely be confirmed.     

Denosumab--a new option in the treatment of osteoporosis

Denosumab is the international name of a human, monoclonal antibody approved for the treatment of osteoporosis. This antibody is associated with RANK ligand (RANKL), inactivating it. In consequence, the formation and survival of osteoclasts are suppressed, leading to their apoptosis. All this results in lower bone resorption, while bone mineral density (BMD) increases. Denosumab also reduces the risk of vertebral and non-vertebral fractures. This agent is similarly effective in various stages of renal function impairment; it does not impair fracture healing processes nor contribute to atherosclerosis progression in patients with high cardiovascular risks. Following an analysis of adverse effects, performed in the FREEDOM study (in which it was demonstrated that the incidence of the majority of adverse effects observed in the course of denosumab use was similar to that in the placebo group), its safety for patients can definitely be confirmed.     

The development of denosumab for the treatment of diseases of bone loss and cancer-induced bone destruction

Denosumab is a fully human monoclonal antibody against RANK ligand (RANKL), an essential cytokine for the formation, function, and survival of osteoclasts. The role of excessive RANKL as a contributor to conditions characterized by bone loss or bone destruction has been well studied. With its novel mechanism of action, denosumab offers a significant advance in the treatment of postmenopausal osteoporosis; bone loss associated with hormone ablation therapy in women with breast cancer and men with prostate cancer; and the prevention of skeletal-related events in patients with bone metastases from solid tumors by offering clinical benefit to these patients in need.     

In vitro stoichiometry of complexes between the soluble RANK ligand and the monoclonal antibody denosumab

The in vitro binding stoichiometry of denosumab, an IgG2 fully human monoclonal therapeutic antibody, to RANK ligand was determined by multiple complementary size separation techniques with mass measuring detectors, including two solution-based techniques (size-exclusion chromatography with static light scattering detection and sedimentation velocity analytical ultracentrifugation) and a gas-phase analysis by electrospray ionization time-of-flight mass spectrometry from aqueous nondenaturing solutions. The stoichiometry was determined under defined conditions ranging from small excess RANK ligand to large excess denosumab (up to 40:1). High concentrations of denosumab relative to RANK ligand were studied because of their physiological relevance; a large excess of denosumab is anticipated in circulation for extended periods relative to much lower concentrations of free soluble RANKL. The studies revealed that an assembly including 3 denosumab antibody molecules bound to 2 RANKL trimers (3D2R) is the most stable complex in DPBS at 37 °C. This differs from the 1:1 binding stoichiometry reported for RANKL and osteoprotegerin (OPG), a soluble homodimeric decoy receptor which binds RANKL with high affinity. Denosumab and RANKL also formed smaller assemblies including 1 denosumab and 2 RANKL trimer molecules (1D2R) under conditions of excess RANKL, 3 denosumab molecules and 1 RANKL trimer (3D1R) under conditions of excess denosumab, and larger assemblies, but these intermediate species were only present at lower temperatures (4 °C), shortly after mixing denosumab and RANKL, and converted over time to the more stable 3D2R assembly.     

Role of RANKL inhibition in osteoporosis

When the rate of bone resorption exceeds that of bone formation, destruction of bone tissue occurs, resulting in a fragile skeleton. The clinical consequences, namely osteoporosis and fragility fractures, are common and costly problems. Treatments that normalize the balance of bone turnover by inhibiting bone resorption preserve bone mass and reduce fracture risk. The discovery of receptor activator of nuclear factor-kappaB ligand (RANKL) as a pivotal regulator of osteoclast activity provides a new therapeutic target. Early studies have demonstrated that denosumab, an investigational, highly specific anti-RANKL antibody, rapidly and substantially reduces bone resorption. Pharmacokinetics of the antibody allow dosing by subcutaneous injection at an interval of 6 months. Inhibiting RANKL appears to be a promising new treatment for osteoporosis and related disorders. More information about the effectiveness of denosumab in reducing fracture risk, its tolerability and safety, and the response to discontinuing therapy will be provided by ongoing clinical studies.     

Denosumab

Denosumab is an anti-receptor activator of nuclear factor (NF)-kappaB (RANK) ligand human monoclonal antibody studied as a treatment for postmenopausal osteoporosis (PMO) and bone destruction due to rheumatoid arthritis (RA) or metastatic cancers. As of February 2009, the candidate was undergoing US Food and Drug Administration review, and might be approved by October 2009. Late phase clinical trials demonstrated that denosumab possesses a similar safety profile to bisphosphonates and that it can be either equally or more effective than bisphosphonates at preventing bone loss due to PMO, RA or cancer treatment and metastases.Key Words: monoclonal antibody, RANKL, bone loss, osteoporosis, breast cancer, rheumatoid arthritis     

OPG/RANKL: role and therapeutic target in osteoporosis

Given the increasing risk of fractures with aging in western countries, there is a need for the development of safe and efficient anti-osteoporotic drugs for the prevention and treatment of osteoporosis. Recent studies have provided evidence for an essential role of RANKL (Receptor Activator of Nuclear Factor-kappa B Ligand) and its decoy receptor osteoprotegerin in the control of osteoclast differentiation and survival. Post-menopausal osteoporosis results from an imbalance between resorption and formation associated with decreased OPG/RANKL. Targeting the OPG/RANKL system may therefore have a beneficial impact in osteoporosis. Accordingly, the development of novel strategies targeting OPG/RANKL using anti-RANKL or therapeutic intervention proved to be efficient to reduce bone resorption and to prevent bone loss in postmenopausal osteoporosis. This opens the way for novel therapeutic strategies for correcting bone metabolism in various pathologic disorders characterized by increased bone remodelling and bone loss.     

Expression of RANKL/OPG during bone remodeling in vivo

The interaction between receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG) plays a dominant role in osteoclastogenesis. As both proteins are produced by osteoblast lineage cells, they are considered to represent a key link between bone formation and resorption. In this study, we investigated the expression of RANKL and OPG during bone remodeling in vivo to determine the relationship between osteoclastogenic stimulation and osteoblastic differentiation.Total RNA was prepared from rat femurs after marrow ablation on days 0, 3, 6, and 9. The temporal activation patterns of osteoblast-related genes (procollagen α1 (I), alkaline phosphatase, osteopontin, and osteocalcin) were examined by Northern blot analysis. An appreciable increase in the expression of these osteoblast markers was observed on day 3. The peak increase in gene expression was observed on day 6 followed by a slight reduction by day 9. Real-time PCR analysis showed that the OPG mRNA expression was markedly upregulated on day 6 and slightly decreased on day 9. In contrast, RANKL mRNA expression was increased by more than 20-fold on day 9. The RANKL/OPG ratio, an index of osteoclastogenic stimulation, peaked on day 9. Histological analysis showed that RANKL and OPG immunoreactivity were predominantly associated with bone marrow cells. The expression of bone formation markers was activated in the bone formation phase, followed by the stimulation of RANKL/OPG expression in the bone resorption phase, which confirmed that these molecules are key factors linking bone formation to resorption during bone remodeling.     

Depth and volume of resorption induced by osteoclasts generated in the presence of RANKL, TNF-alpha/IL-1 or LIGHT

Rheumatoid arthritis (RA) is associated with pathological bone destruction mediated by osteoclasts. Although RANKL has been reported as a crucial factor for osteoclastogenesis, several other factors increased in RA support osteoclast formation and resorption in the absence of RANKL such as TNF-alpha and LIGHT. To date, in vitro bone resorption experiments are reported as the mean area of bone resorption per cortical or dentine slices and do not provide any information about depth and volume of resorption. The aims of this study were to assess these parameters by light microscopy and vertical scanning profilometry (VSP). Peripheral blood mononuclear cells were used as a source of osteoclast precursors and were cultured for up to 21 days in the presence of RANKL, TNF-alpha/IL-1 or LIGHT. Mean area, depth and volume of resorption were assessed by light microscopy and vertical scanning profilometry. As expected, RANKL induced large resorption pits (10,876 ± 2190μm(2)) whereas TNF-alpha/IL-1 and LIGHT generated smaller pits (respectively 1328 ± 210 and 1267 ± 173μm(2)) with no noticeable differences between these two cytokines. Depth and volume of resorption measured by VSP showed that RANKL promoted deep resorption pits resulting in large volume of resorption. Interestingly, although mean area of resorption was similar between TNF-alpha/IL-1 and LIGHT, the depth and volume of resorption of these lacunae were significantly increased by 2-fold with TNF-alpha/IL-1. These results provide evidence that although LIGHT appeared elevated in the synovial fluid of RA patients, its role in bone resorption is less than TNF-alpha/IL-1 or RANKL.     

Clinical development of anti-RANKL therapy

The receptor activator of nuclear factor-kappaB ligand (RANKL), its cognate receptor RANK, and its natural decoy receptor osteoprotegerin have been identified as the final effector molecules of osteoclastic bone resorption. This has provided an ideal target for therapeutic interventions in metabolic bone disease. As described in previous reviews in this supplement, RANKL signaling is required for osteoclast differentiation, activation, and survival. Furthermore, in vivo inhibition of RANKL leads to immediate osteoclast apoptosis, and there are no in vivo models of bone resorption that are refractory to RANKL inhibition. Thus, the only step remaining in the development of a clinical intervention is the generation of a safe, effective, and specific drug that can inhibit RANKL in humans. Here we review the clinical development of denosumab (formerly known as AMG 162), which is a fully human mAb directed against RANKL. This discussion includes the breadth of 21 human studies that have led to the current phase 3 clinical trials seeking approval for use of this agent to treat postmenopausal women with low bone mineral density (osteoporosis) and patients with metastatic lytic bone lesions (multiple myeloma, and prostate and breast cancer).     

Denosumab Use in Adults With Fibrous Dysplasia: Case Reports and Review of the Literature

ObjectiveIn fibrous dysplasia (FD) of the bone, a gain-of-function mutation in the G-nucleotide binding protein alpha subunit results in constitutively active cyclic adenosine monophosphate. Downstream effects include formation of disorganized cortex and bone marrow fibrosis. Patients with FD experience bone pain and are at risk of fracture. Bisphosphonates are traditionally used to manage pain with mixed results. We sought to report denosumab use in patients with FD at our institution and summarized the existing literature on denosumab use in FD.MethodsWe retrospectively identified patients with FD who were treated with denosumab at our institution, describing patient characteristics and outcomes. We reviewed the existing literature on denosumab use in patients with FD.ResultsPatient 1 was diagnosed with FD at the age of 17 years and took bisphosphonates with initial improvement in pain. Pain eventually worsened; therefore, she received 4 doses of denosumab. Patient 2 was diagnosed with FD after a fall and was treated with bisphosphonates, reporting some initial improvement in bone pain. A few years later, the pain recurred, and he received 3 doses of denosumab. Both patients tolerated denosumab well but experienced no improvement in pain. On literature review, although some serious side effects were noted, patients experienced a decline in bone turnover markers, and most reported improvement in bone pain with denosumab.ConclusionDenosumab is a promising therapy for managing symptoms of FD. Further studies are needed to determine the optimal dose and duration of treatment. Its long-term effect on FD lesions remains unclear.     

Lyn inhibits osteoclast differentiation by interfering with PLCγ1-mediated Ca signaling

Osteoclasts differentiate from macrophage-lineage cells to become specialized for bone resorption function. By a proteomics approach, we found that Lyn was down-regulated by the osteoclast differentiation factor, receptor activator of NF-κB ligand (RANKL). The forced reduction of Lyn caused a striking increase in the RANKL-induced PLCγ1, Ca²⁺, and NFATc1 responses during differentiation. These data suggest that Lyn plays a negative role in osteoclastogenesis by interfering with the PLCγ1-mediated Ca²⁺ signaling that leads to NFATc1 activation. Consistent with the in vitro results, in vivo injection of Lyn specific siRNA into mice calvariae provoked a fulminant bone resorption. Our study provides the first evidence of the involvement of Lyn in the negative regulation of osteoclastogenesis by RANKL.     

Protein Expression Profiling of Giant Cell Tumors of Bone Treated with Denosumab

Giant cell tumors of bone (GCTB) are locally aggressive osteolytic bone tumors. Recently, some clinical trials have shown that denosumab is a novel and effective therapeutic option for aggressive and recurrent GCTB. This study was performed to investigate the molecular mechanism underlying the therapeutic effect of denosumab. Comparative proteomic analyses were performed using GCTB samples which were taken before and after denosumab treatment. Each expression profile was analyzed using the software program to further understand the affected biological network. One of identified proteins was further evaluated by gelatin zymography and an immunohistochemical analysis. We identified 13 consistently upregulated proteins and 19 consistently downregulated proteins in the pre- and post-denosumab samples. Using these profiles, the software program identified molecular interactions between the differentially expressed proteins that were indirectly involved in the RANK/RANKL pathway and in several non-canonical subpathways including the Matrix metalloproteinase pathway. The data analysis also suggested that the identified proteins play a critical functional role in the osteolytic process of GCTB. Among the most downregulated proteins, the activity of MMP-9 was significantly decreased in the denosumab-treated samples, although the residual stromal cells were found to express MMP-9 by an immunohistochemical analysis. The expression level of MMP-9 in the primary GCTB samples was not correlated with any clinicopathological factors, including patient outcomes. Although the replacement of tumors by fibro-osseous tissue or the diminishment of osteoclast-like giant cells have been shown as therapeutic effects of denosumab, the residual tumor after denosumab treatment, which is composed of only stromal cells, might be capable of causing bone destruction; thus the therapeutic application of denosumab would be still necessary for these lesions. We believe that the protein expression patterns and the results of the network analysis will provide a better understanding of the effects of denosumab administration in patients with GCTB.     

淫羊藿苷对大鼠正畸牙齿压力区牙周组织RANKL和Wnt3a表达的影响

目的:观察不同剂量的淫羊藿苷对大鼠正畸牙齿移动时压力区牙周组织中RANKL和Wnt3a表达的影响。方法:将24只健康雄性SD大鼠随机分为4组,根据淫羊藿苷灌胃的剂量分为生理盐水组(对照组)、1 mg/kg淫羊藿苷组、3 mg/kg淫羊藿苷组、5mg/kg淫羊藿苷组(实验组),使用50 g力近中移动左侧上颌第一磨牙。通过免疫组化方法检测压力区牙周组织中RANKL和Wnt3a蛋白的表达。结果:生理盐水组上颌第一磨牙压力区牙根和牙槽骨表面粗糙,牙周膜间隙变窄,可见骨吸收陷窝和破骨细胞,不同剂量淫羊藿苷组牙周膜间隙趋于恢复正常,骨吸收陷窝出现明显减少。RANKL和Wnt3a在生理盐水组和淫羊藿苷组的压力区牙周组织中都有表达。与生理盐水组比较,不同剂量淫羊藿苷组压力区牙周组织中RANKL的表达均显著降低,Wnt3a的表达均明显增加,且RANKL的表达随淫羊藿苷剂量的增加而逐渐减少(P0.05),Wnt3a的表达随淫羊藿苷剂量的增加明显增加(P0.05)。结论:不同剂量淫羊藿苷能减少正畸时牙齿移动过程中压力区牙周组织中RANKL的表达,增加Wnt3a的表达,且作用与其剂量具有一定的相关性。     

Erosive arthritis

Inflammation and degradation of bone are two closely linked processes. Chronic inflammatory arthritis not only leads to inflammatory bone loss but it also involves local erosion of articular bone. This osteo-destructive feature of chronic inflammatory arthritis is a major cause of disability in patients with rheumatoid arthritis. Osteoclasts are essential for the resorption of mineralized cartilage and subchondral bone in chronic arthritis. The observed up-regulation of osteoclast differentiation factors (receptor activator of nuclear factor-kappaB ligand [RANKL]) in the synovial membrane of chronically inflamed joints indicates that osteoclasts are abundant in this setting, leading to rapid degradation of mineralized tissue. Blockade of osteoclast formation is thus a key strategy in preventing structural damage in arthritis. Denosumab, a humanized antibody that neutralizes RANKL, is an attractive candidate agent to inhibit inflammatory bone loss.     

MCP-1-induced human osteoclast-like cells are tartrate-resistant acid phosphatase, NFATc1, and calcitonin receptor-positive but require receptor activator of NFkappaB ligand for bone resorption

MCP-1 (monocyte chemotactic protein-1) is a CC chemokine that is induced by receptor activator of NFkappaB ligand (RANKL) in human osteoclasts. In the absence of RANKL, treatment of human peripheral blood mononuclear cells with macrophage colony-stimulating factor and MCP-1 resulted in tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cells that are positive for calcitonin receptor (CTR) and a number of other osteoclast markers, including nuclear factor of activated t cells, cytoplasmic, calcineurin-dependent 1 (NFATc1). Although NFATc1 was strongly induced by MCP-1 and was observed in the nucleus, MCP-1 did not permit the formation of bone-resorbing osteoclasts, although these cells had the typical TRAP(+)/CTR(+) multinuclear phenotype of osteoclasts. Despite a similar appearance to osteoclasts, RANKL treatment was required in order for TRAP(+)/CTR(+) multinuclear cells to develop bone resorption activity. The lack of bone resorption was correlated with a deficiency in expression of certain genes related to bone resorption, such as cathepsin K and MMP9. Furthermore, calcitonin blocked the MCP-1-induced formation of TRAP(+)/CTR(+) multinuclear cells as well as blocking osteoclast bone resorption activity, indicating that calcitonin acts at two stages of osteoclast differentiation. Ablation of NFATc1 in mature osteoclasts did not prevent bone resorption activity, suggesting NFATc1 is involved in cell fusion events and not bone resorption. We propose that the MCP-1-induced TRAP(+)/CTR(+) multinuclear cells represent an arrested stage in osteoclast differentiation, after NFATc1 induction and cellular fusion but prior to the development of bone resorption activity.     

Multiple roles of M-CSF in human osteoclastogenesis

Although the critical role of M-CSF in osteoclastogenesis is well documented, there has been no detailed analysis of how it regulates human osteoclast formation and function in vitro. We used a human osteoclastogenesis model employing CFU-GM osteoclast precursors cultured for 14 days on dentine with RANKL, with varying exposure to exogenous human M-CSF. Short-term treatment of precursors with M-CSF (10-100 ng/mL) resulted in increased proliferation with or without RANKL. Treatment with M-CSF (1-100 ng/mL) for 14 days caused a biphasic concentration-dependent stimulation of formation, fusion, and resorption peaking at 10-50 ng/mL and almost complete abolition of resorption at 100 ng/mL. Time-course studies using M-CSF (25 ng/mL) showed that osteoclast size, nuclei/cell, and resorption increased with longer duration of M-CSF treatment. When treatment was restricted to the first 4 days, M-CSF (25-100 ng/mL) stimulated formation of normal numbers of osteoclasts that resorbed less. Blockade of endogenous M-CSF signaling with neutralizing M-CSF antibody during the first week of culture extensively inhibited osteoclastogenesis, whereas blockade during the second week produced only a small reduction in resorption. Treatment with M-CSF during the second week of culture caused a small increase in osteoclast number and a concentration-dependent increase in cytoplasmic spreading with inhibition of resorption. We have shown that M-CSF modulates multiple steps of human osteoclastogenesis, including proliferation, differentiation and fusion of precursors. In the later stages of osteoclastogenesis, M-CSF modulates osteoclast-resorbing activity, but is not required for survival. Modulation of M-CSF signaling is a potential therapeutic target for conditions associated with excess bone resorption.     

Mechanical strain differentially regulates endothelial nitric-oxide synthase and receptor activator of nuclear kappa B ligand expression via ERK1/2 MAPK

Exercise promotes positive bone remodeling through controlling cellular processes in bone. Nitric oxide (NO), generated from endothelial nitric-oxide synthase (eNOS), prevents resorption, whereas receptor activator of nuclear kappa B ligand (RANKL) promotes resorption through regulating osteoclast activity. Here we show that mechanical strain differentially regulates eNOS and RANKL expression from osteoprogenitor stromal cells in a magnitude-dependent fashion. Strain (0.25-2%) induction of eNOS expression was magnitude-dependent, reaching a plateau at 218 +/- 36% of control eNOS. This was accompanied by increases in eNOS protein and a doubling of NO production. Concurrently, 0.25% strain inhibited RANKL expression with increasing response up to 1% strain (44 +/- 3% of control RANKL). These differential responses to mechanical input were blocked when an ERK1/2 inhibitor was present during strain application. Inhibition of NO generation did not prevent strain-activated ERK1/2. To confirm the role of ERK1/2, cells were treated with an adenovirus encoding a constitutively activated MEK; Ad.caMEK significantly increased eNOS expression and NO production by more than 4-fold and decreased RANKL expression by half. In contrast, inhibition of strain-activated c-Jun kinase failed to prevent strain effects on either eNOS or RANKL. Our data suggest that physiologic levels of mechanical strain utilize ERK1/2 kinase to coordinately regulate eNOS and RANKL in a manner leading to positive bone remodeling.     

Osteoprotegerin inhibit osteoclast differentiation and bone resorption by enhancing autophagy via AMPK/mTOR/p70S6K signaling pathway in vitro

Osteoclasts are highly differentiated terminal cells formed by fusion of hematopoietic stem cells. Previously, osteoprotegerin (OPG) inhibit osteoclast differentiation and bone resorption by blocking receptor activator of nuclear factor-κB ligand (RANKL) binding to RANK indirect mechanism. Furthermore, autophagy plays an important role during osteoclast differentiation and function. However, whether autophagy is involved in OPG-inhibited osteoclast formation and bone resorption is not known. To elucidate the role of autophagy in OPG-inhibited osteoclast differentiation and bone resorption, we used primary osteoclast derived from mice bone marrow monocytes/macrophages (BMM) by induced M-CSF and RANKL. The results showed that autophagy-related proteins expression were upregulated; tartrate-resistant acid phosphatase-positive osteoclast number and bone resorption activity were decreased; LC3 puncta and autophagosomes number were increased and activated AMPK/mTOR/p70S6K signaling pathway. In addition, chloroquine (as the autophagy/lysosome inhibitor, CQ) or rapamycin (as the autophagy/lysosome inhibitor, Rap) attenuated osteoclast differentiation and bone resorption activity by OPG treatment via AMPK/mTOR/p70S6K signaling pathway. Our data demonstrated that autophagy plays a critical role in OPG inhibiting osteoclast differentiation and bone resorption via AMPK/mTOR/p70S6K signaling pathway in vitro.