Osteolytic bone diseases: physiological analogues of bone resorption effectors as alternative therapeutic tools

Zoledronic acid enhances tumor growth and metastatic spread in a mouse model of jaw osteosarcoma

OBJECTIVES

Investigation of the therapeutic effect of zoledronic acid (ZA) in a preclinical model of jaw osteosarcoma (JO).

MATERIALS AND METHODS

The effect of 100 μg/kg ZA administered twice a week was assessed in a xenogenic mouse model of JO. The clinical (tumor growth, development of lung metastasis), radiological (bone microarchitecture by micro-CT analysis), and molecular and immunohistochemical (TRAP, RANK/RANKL, VEGF, and CD146) parameters were investigated.

RESULTS

Animals receiving ZA exhibited an increased tumor volume compared with nontreated animals (71.3 ± 14.3 mm3 vs. 51.9 ± 19.9 mm3 at D14, respectively; p = 0.06) as well as increased numbers of lung metastases (mean 4.88 ± 4.45 vs. 0.50 ± 1.07 metastases, respectively; p = 0.02). ZA protected mandibular bone against tumor osteolysis (mean bone volume of 12.81 ± 0.53 mm3 in the ZA group vs. 11.55 ± 1.18 mm3 in the control group; p = 0.01). ZA induced a nonsignificant decrease in mRNA expression of the osteoclastic marker TRAP and an increase in RANK/RANKL bone remodeling markers.

CONCLUSION

The use of bisphosphonates in the therapeutic strategy for JO should be further explored, as should the role of bone resorption in the pathophysiology of the disease.

Boric Acid Inhibits RANKL-Stimulated Osteoclastogenesis In Vitro and Attenuates LPS-Induced Bone Loss In Vivo

Boron and boric acid (BA) can promote osteogenic differentiation and reduce bone resorption, which controls bone growth and maintenance of bone tissue. It has been reported that BA activates PERK-eIF2α signaling to induce cytoplasmic stress granules and cell senescence in human prostate DU-145 cells. However, whether BA can affect osteoclasts formation and LPS-induced inflammatory bone loss, and the role of the PERK-eIF2α pathway in the process, remains unknown. In vitro, RAW264.7 cells were pre-treated with boric acid (BA, 1, 10, 100 μmol/L) for 4 h, and then incubated with receptor activator of nuclear factor-kappaB ligand (RANKL, 50 ng/mL) in the presence or absence of BA for 5 days. CCK-8 and tartrate-resistant acid phosphatase (TRAP) were used to examine cell viability, osteoclastogenesis, and bone resorption; quantitative real-time PCR was performed to examine mRNA levels of c-Fos, nuclear factor of activated T cells, cytoplasmic 1 (NFATc1), TRAP, and cathepsin K; western blotting was used to examine protein expressions of glucose-regulated protein 78 (GRP78), protein kinase R (PKR)-like endoplasmic reticulum kinase (PERK), phosphorylated PERK (p-PERK), eukaryotic initiation factor 2α (eIF2α), and phosphorylated eIF2α (p-eIF2α). In vivo, lipopolysaccharide (LPS)-induced bone loss model in mice was established, and micro-computed tomography (micro-CT) scanning, bone biochemical analysis, and osteoclastogenic cytokines were detected to evaluate the effect of BA on LPS-induced bone loss. In our vitro results showed that BA treatment for 5 days inhibited osteoclasts formation as well as osteoclastic bone resorption in a dose-dependent manner. The expression of osteoclasts marker genes c-Fos, NFATc1, TRAP, and cathepsin K were attenuated by BA. Immunoblotting analysis demonstrated that BA attenuated RANKL-induced PERK-eIF2α pathway activation. The in vivo data indicated that BA significantly prevented lipopolysaccharide (LPS)-induced bone loss. Our findings strongly suggest that BA may be a promising agent for the treatment of bone destructive diseases caused by excessive osteoclastogenesis.

Astragalus polysaccharide attenuates LPS-related inflammatory osteolysis by suppressing osteoclastogenesis by reducing the MAPK signalling pathway

Bacterial products can stimulate inflammatory reaction and activate immune cells to enhance the production of inflammatory cytokines, and finally promote osteoclasts recruitment and activity, leading to bone destruction. Unfortunately, effective preventive and treatment measures for inflammatory osteolysis are limited and usually confuse the orthopedist. Astragalus polysaccharide (APS), the main extractive of Astragali Radix, has been widely used for treating inflammatory diseases. In the current study, in vitro and in vivo experimental results demonstrated that APS notably inhibited osteoclast formation and differentiation dose-dependently. Moreover, we found that APS down-regulated RANKL-related osteoclastogenesis and levels of osteoclast marker genes, such as NFATC1, TRAP, c-FOS and cathepsin K. Further underlying mechanism investigation revealed that APS attenuated activity of MAPK signalling pathways (eg ERK, JNK and p38) and ROS production induced by RANKL. Additionally, APS was also found to suppress LPS-related inflammatory osteolysis by decreasing inflammatory factors' production in vivo. Overall, our findings demonstrate that APS effectively down-regulates inflammatory osteolysis due to osteoclast differentiation and has the potential to become an effective treatment of the disorders associated with osteoclast.

Bisphosphonates in common pediatric and adult bone sarcomas

The therapeutic strategies proposed currently for bone sarcomas are based on neo-adjuvant chemotherapy, delayed en-bloc wide resection, and adjuvant chemotherapy. Unfortunately, bone sarcomas are characterized by high rates of poor drug response, with a high risk of drug resistance, local recurrence and/or a high propensity for induced metastases. The pathogenesis of bone sarcomas is strongly associated with dysregulation of local bone remodeling and increased osteolysis that plays a part in tumor development. In this context, bisphosphonates (BPs) have been proposed as a single agent or in combination with conventional drugs to block bone resorption and the vicious cycle established between bone and sarcoma cells. Pre-clinical in vitro studies revealed the potential "anti-tumor" activities of nitrogen-bisphosphonates (N-BPs). In pre-clinical models, N-BPs reduced significantly primary tumor growth in osteosarcoma and Ewing sarcoma, and the installation of lung metastases. In chondrosarcoma, N-BPs reduced the recurrence of local tumors after intralesional curettage, and increased overall survival. In pediatric and adult osteosarcoma patients, N-BPs have been assessed in combination with conventional chemotherapy and surgery in randomized phase 3 studies with no improvement in clinical outcome. The lack of benefit may potentially be explained by the biological impact of N-BPs on macrophage differentiation/recruitment which may alter CD8⁺-T lymphocyte infiltration. Thanks to their considerable affinity for the mineralized extracellular matrix, BPs are an excellent platform for drug delivery in malignant bone sites with reduced systemic toxicity, which opens up new opportunities for their future use.

The protective effect of WKYMVm peptide on inflammatory osteolysis through regulating NF-κB and CD9/gp130/STAT3 signalling pathway

The balance between bone formation and bone resorption is closely related to bone homeostasis. Osteoclasts, originating from the monocyte/macrophage lineage, are the only cell type possessing bone resorption ability. Osteoclast overactivity is thought to be the major reason underlying osteoclast‐related osteolytic problems, such as Paget's disease, aseptic loosening of prostheses and inflammatory osteolysis; therefore, disruption of osteoclastogenesis is considered a crucial treatment option for these issues. WKYMVm, a synthetic peptide, which is a potent FPR2 agonist, exerts an immunoregulatory effect. This peptide inhibits the production of inflammatory cytokines, such as (IL)‐1β and TNF‐α, thus regulating inflammation. However, there are only few reports on the role of WKYMVm and FPR2 in osteoclast cytology. In the current study, we found that WKYMVm negatively regulates RANKL‐ and lipopolysaccharide (LPS)‐induced osteoclast differentiation and maturation in vitro and alleviates LPS‐induced osteolysis in animal models. WKYMVm down‐regulated the expression of osteoclast marker genes and resorption activity. Furthermore, WKYMVm inhibited osteoclastogenesis directly through reducing the phosphorylation of STAT3 and NF‐kB and indirectly through the CD9/gp130/STAT3 pathway. In conclusion, our findings demonstrated the potential medicinal value of WKYMVm for the treatment of inflammatory osteolysis.

Catalpol suppresses osteoclastogenesis and attenuates osteoclast-derived bone resorption by modulating PTEN activity

Excessive activation of osteoclast activity is responsible for many bone diseases, such as osteoporosis, rheumatoid arthritis, periprosthetic osteolysis, and periodontitis. Natural compounds that inhibit osteoclast formation and/or function have therapeutic potential for treating these diseases. Catalpol, a bioactive iridoid extracted from a traditional herbal medicine Rehmannia glutinosa, exhibits various pharmacological properties, including anti-inflammatory, antioxidant, antidiabetic, and antitumor effects. However, its effects on osteoclast formation and function remain unknown. In the present study, we showed that catalpol inhibited receptor activator of nuclear factor-κB (NF-κB) ligand (RANKL)-induced osteoclast formation and bone resorption, as well as the expression of osteoclast-related marker genes. The investigation of molecular mechanisms showed that catalpol upregulated phosphatase and tensin homolog (PTEN) activity by reducing its ubiquitination and degradation, subsequently suppressing RANKL-induced NF-κB and AKT signaling pathways, leading to an inhibition on NFATc1 induction. Furthermore, catalpol protected mice against inflammation- and ovariectomy-induced bone loss by inhibiting osteoclast activity in vivo. These results suggest that catalpol might be developed as a promising candidate for treating osteoclast-related bone diseases.

Diallyl disulfide alleviates inflammatory osteolysis by suppressing osteoclastogenesis via NF-κB-NFATc1 signal pathway

Skeletal homeostasis is closely effectuated by the regulation of bone formation and bone resorption. Osteoclasts are multinuclear giant cells responsible for bone resorption. Overactivated osteoclasts and excessive bone resorption result in various lytic bone diseases, such as osteoporosis, osteoarthritis, periprosthetic infection, and inflammatory aseptic loosening of orthopedic implants. In consideration of the severe side effects caused by the currently available drugs, exploitation of novel drugs has gradually attracted attention. Because of its anti-inflammatory, antioxidant, and antitumor capacities, diallyl disulfide (DADS), a major oil-soluble organosulfur ingredient compound derived from garlic, has been widely researched. However, the effects of DADS on osteoclasts and lytic bone diseases are still unknown. In this study, we investigated the effects of DADS on receptor activator of NF-κB ligand (RANKL)- and LPS-mediated osteoclastogenesis, LPS-stimulated proinflammatory cytokines related to osteoclasts, and LPS-induced inflammatory osteolysis. The results showed that DADS significantly inhibited RANKL-mediated osteoclast formation, fusion, and bone resorption in a dose-dependent manner via inhibiting the NF-κB and signal transducer and activator of transcription 3 signaling and restraining the interaction of NF-κB p65 with nuclear factor of activated T cells cytoplasmic 1. Furthermore, DADS also markedly suppressed LPS-induced osteoclastogenesis and reduced the production of proinflammatory cytokines with LPS stimulation to indirectly mediate osteoclast formation. Consistent with the in vitro results, DADS prevented the LPS-induced severe bone loss by blocking the osteoclastogenesis. All of the results indicate that DADS may be a potential and exploitable drug used for preventing and impeding osteolytic lesions.-Yang, J., Tang, R., Yi, J., Chen, Y., Li, X., Yu, T., Fei, J. Diallyl disulfide alleviates inflammatory osteolysis by suppressing osteoclastogenesis via NF-κB-NFATc1 signal pathway.

ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation through the JNK signaling pathway

Tumor necrosis factor (TNF)-α, which is a proinflammatory cytokine, inhibits osteoblast differentiation under diverse inflammatory conditions. Activating transcription factor 3 (ATF3), which is a member of the ATF/cAMP response element-binding protein family of transcription factors, has been implicated in the regulation of cell proliferation and differentiation. However, the precise interactions between ATF3 and the TNF-α signaling pathway in the regulation of osteoblast differentiation remain unclear. In this study, we examined the role of ATF3 in the TNF-α-mediated inhibition of osteoblast differentiation and investigated the signaling pathways involved. The treatment of cells with TNF-α downregulated osteogenic markers, but significantly upregulated the expression of Atf3. The inhibition of Atf3 by small interfering RNAs rescued osteogenesis, which was inhibited by TNF-α. Conversely, the enforced expression of Atf3 enhanced the TNF-α-mediated inhibition of osteoblast differentiation, as revealed by the measurement of osteogenic markers and alkaline phosphatase staining. Mechanistically, TNF-α-induced Atf3 expression was significantly suppressed by the inhibition of the c-Jun N-terminal kinase (JNK) pathway. Furthermore, the overexpression of Atf3 did not affect the rescue effect that inhibiting TNF-α expression using a JNK inhibitor had on alkaline phosphatase activity and mineralization. Taken together, these results indicate that ATF3 mediates the inhibitory action of TNF-α on osteoblast differentiation and that the TNF-α-activated JNK pathway is responsible for the induction of Atf3 expression.

Novel RANK antagonists for the treatment of bone-resorptive disease: theoretical predictions and experimental validation

Receptor activator of nuclear factor-κB (RANK) and RANK ligand (RANKL) play a pivotal role in bone metabolism, and selective targeting of RANK signaling has become a promising therapeutic strategy in the management of resorptive bone diseases. Existing antibody-based therapies and novel inhibitors currently in development were designed to target the ligand, rather than the membrane receptor expressed on osteoclast precursors. We describe here an alternative approach to designing small peptides able to specifically bind to the hinge region of membrane RANK responsible for the conformational change upon RANKL association. A nonapeptide generated by this method was validated for its biological activity in vitro and in vivo and served as a lead compound for the generation of a series of peptide RANK antagonists derived from the original sequence. Our study presents a structure- and knowledge-based strategy for the design of novel effective and affordable small peptide inhibitors specifically targeting the receptor RANK and opens a new therapeutic opportunity for the treatment of resorptive bone disease.

Key roles of the OPG–RANK–RANKL system in bone oncology

Osteoprotegerin (OPG)-receptor activator of nuclear factor-kappaB (RANK) and RANK ligand (RANKL) have been identified as members of a ligand-receptor system that directly regulates osteoclast differentiation and osteolysis. RANKL may be a powerful inducer of bone resorption through its interaction with RANK, and OPG is a soluble decoy receptor that acts as a strong inhibitor of osteoclastic differentiation. Any dysregulation of their respective expression leads to pathological conditions. Furthermore, recent data demonstrate that the OPG-RANK-RANKL system modulates cancer cell migration, thus controlling the development of bone metastases. This review describes the most recent knowledge on the OPG-RANK-RANKL system, its involvement in bone oncology and the new therapeutic approaches based on this molecular triad.

Anti-RANKL therapy for bone tumours: Basic, pre-clinical and clinical evidences

Bone remodelling is related to coordinated phases of bone resorption and bone apposition allowing the maintenance of bone integrity, the phosphocalcic homoeostasis all along the life and consequently the bone adaptation to mechanical constraints or/and to endocrine fluctuations. Unfortunately, bone is a frequent site of tumour development originated from bone cell lineages (primary bone tumours: bone sarcomas) or from nonosseous origins (bone metastases: carcinomas). These tumour cells disrupt the balance between osteoblast and osteoclast activities resulting in a disturbed bone remodelling weakening the bone tissue, in a strongly altered bone microenvironment and consequently facilitating the tumour growth. At the early stage of tumour development, osteoclast differentiation and recruitment of mature osteoclasts are strongly activated resulting in a strong bone matrix degradation and release of numerous growth factors initially stored into this organic/calcified matrix. In turn these soluble factors stimulate the proliferation of tumour cells and exacerbate their migration and their ability to initiate metastases. Because Receptor Activator of NFκB Ligand (RANKL) is absolutely required for in vivo osteoclastogenesis, its role in the bone tumour growth has been immediately pointed out and has consequently allowed the development of new targeted therapies of these malignant diseases. The present review summarises the role of RANKL in the bone tumour microenvironment, the most recent pre-clinical and clinical evidences of its targeting in bone metastases and bone sarcomas. The following sections position RANKL targeted therapy among the other anti-resorptive therapies available and underline the future directions which are currently under investigations.

Alendronate induces anti-migratory effects and inhibition of neutral phosphatases in UMR106 osteosarcoma cells

Bisphosphonates are nonhydrolysable pyrophosphate analogues that prevent bone loss in several types of cancer. However, the mechanisms of anticancer action of bisphosphonates are not completely known. We have previously shown that nitrogen-containing bisphosphonates directly inhibit alkaline phosphatase of UMR106 rat osteosarcoma cells. In this study, we evaluated the effects of alendronate on the migration of UMR106 osteosarcoma using a model of multicellular cell spheroids, as well as the alendronate effect on neutral phosphatases. Alendronate significantly inhibited the migration of osteoblasts in a dose-dependent manner (10(-6)-10(-4) M). This effect was also dependent on calcium availability. The spheroid morphology and distribution of actin fibers were also affected by alendronate treatment. Alendronate dose-dependently inhibited neutral phosphatase activity in cell-free osteoblastic extracts as well as in osteoblasts in culture. Our results show that alendronate inhibits cell migration through mechanisms dependent on calcium, and that seem to involve inhibition of phosphotyrosine-neutral-phosphatases and disassembly of actin stress fibers.

TRAIL inhibits osteoclastic differentiation by counteracting RANKL-dependent p27Kip1 accumulation in pre-osteoclast precursors

Experimental evidences indicate that the TNF family member TNF-related apoptosis inducing ligand (TRAIL) might be involved in modulating osteoclastic differentiation. The ability of recombinant soluble TRAIL to affect bone density in vivo was evaluated by using 4-week-old mice subcutaneously (s.c.) injected with TRAIL for 8 days. TRAIL injection induced a significant increase of tibia trabecular thickness and total bone mass in 4-week-old mice, accompanied by a significant decrease of TRAP serum levels, without modulation of osteocalcin and osteoprotegerin (OPG). Parallel experiments performed in vitro showed that inhibition of osteoclastic differentiation, induced by treatment of human peripheral blood osteoclast precursors with TRAIL, was associated to inhibition of receptor activator of nuclear factor kappa B ligand (RANKL)-induced accumulation of p27(Kip1). The potential role of p27(Kip1) pathway in mediating the anti-osteoclastic activity of TRAIL was further suggested by in vitro gene knock-down experiments performed in osteoclast precursor cultures. Taken together, our data strongly suggest that recombinant TRAIL inhibits osteoclastogenesis by inducing the ubiquitin-mediated degradation of p27(Kip1).

OPG/membranous--RANKL complex is internalized via the clathrin pathway before a lysosomal and a proteasomal degradation

The members of the OPG/RANK/RANKL (osteoprotegerin/receptor activator of nuclear factor kappaB/RANK ligand) triad are involved in various osteolytic pathologies such as bone tumors. Although many studies described the use of OPG during the treatment of bone diseases, its bioavailability and the mechanism by which the cells control the extracellular OPG remains blurred. The present work uses a strongly RANKL expressing cellular model to assess the becoming and the bioavailability of exogenous OPG in the context of its interactions with RANKL. The human kidney cell line 293, which initially expresses neither OPG nor RANKL, was stably transfected by the full length of mouse transmembranous form of RANKL (293RL). When OPG is incubated with 293RL cells, the extracellular concentration of OPG was strongly decreased in a time-dependent manner. The OPG disappearance was not inhibited by the addition of several proteases inhibitors, thus excluding any extracellular protease degradation. Contrary to previous results obtained on myeloma cells, which strongly express syndecan-1, the OPG disappearance was unaffected by the use of an antibody against syndecan-1. However, this event was abolished by an antibody against RANKL. These results, not necessarily conflicting, could be in relation with the expression level of the receptors in the two cellular models. In this context, an internalization process was put forward. Confocal microscopy demonstrated via the clathrin pathway an internalization of OPG mediated by RANKL. After being internalized, OPG was then degraded by the proteasome and the lysosome. A similar internalization phenomenon was also observed in osteoblast cells expressing physiologically RANKL, thus validating our data observed on 293RL cells. Western blotting analysis revealed that the half-life of RANKL was greatly reduced in the presence of OPG, pointing out that OPG binding to RANKL induces an enhancement of the ligand internalization. By the light of these results, the inhibitory effect of OPG on bone resorption can be explained not only by a decoy receptor function, competitor inhibitor of the RANK/RANKL binding, but also by the modulation of the RANKL half-life induced by OPG. Reciprocally, this modulation contributes to reduce the bioavailability of OPG.

RANKL stimulates inducible nitric-oxide synthase expression and nitric oxide production in developing osteoclasts. An autocrine negative feedback mechanism triggered by RANKL-induced interferon-beta via NF-kappaB that restrains osteoclastogenesis and bone resorption

Nitric oxide (NO) is a multifunctional signaling molecule and a key vasculoprotective and potential osteoprotective factor. NO regulates normal bone remodeling and pathological bone loss in part through affecting the recruitment, formation, and activity of bone-resorbing osteoclasts. Using murine RAW 264.7 and primary bone marrow cells or osteoclasts formed from them by receptor activator of NF-kappaB ligand (RANKL) differentiation, we found that inducible nitric-oxide synthase (iNOS) expression and NO generation were stimulated by interferon (IFN)-gamma or lipopolysaccharide, but not by interleukin-1 or tumor necrosis factor-alpha. Surprisingly, iNOS expression and NO release were also triggered by RANKL. This response was time- and dose-dependent, required NF-kappaB activation and new protein synthesis, and was specifically blocked by the RANKL decoy receptor osteoprotegerin. Preventing RANKL-induced NO (via iNOS-selective inhibition or use of marrow cells from iNOS-/- mice) increased osteoclast formation and bone pit resorption, indicating that such NO normally restrains RANKL-mediated osteoclastogenesis. Additional studies suggested that RANKL-induced NO inhibition of osteoclast formation does not occur via NO activation of a cGMP pathway. Because IFN-beta is also a RANKL-induced autocrine negative feedback inhibitor that limits osteoclastogenesis, we investigated whether IFN-beta is involved in this novel RANKL/iNOS/NO autoregulatory pathway. IFN-beta was induced by RANKL and stimulated iNOS expression and NO release, and a neutralizing antibody to IFN-beta inhibited iNOS/NO elevation in response to RANKL, thereby enhancing osteoclast formation. Thus, RANKL-induced IFN-beta triggers iNOS/NO as an important negative feedback signal during osteoclastogenesis. Specifically targeting this novel autoregulatory pathway may provide new therapeutic approaches to combat various osteolytic bone diseases.

Ibandronate: efficacy in the treatment of metastatic bone disease

Ibandronate is a bisphosphonate treatment for metastatic bone disease. In Phase III trials in breast cancer patients, intravenous and oral formulations of ibandronate lowered the incidence of skeletal-related events, reduced metastatic bone pain scores throughout 2 years of treatment, and had significant positive effects on patient quality of life, demonstrating its efficacy in this condition. Recent pilot studies in other primary cancers suggest that a loading dose of ibandronate may relieve severe or opioid-resistant metastatic bone pain. In safety analyses, ibandronate was well tolerated with a safety profile comparable to placebo. Ibandronate therefore represents a treatment choice with documented efficacy and safety in metastatic bone disease from breast cancer.