LIGHT (TNFSF14), a novel mediator of bone resorption, is elevated in rheumatoid arthritis.

OBJECTIVE: Human osteoclast formation from mononuclear phagocyte precursors involves interactions between tumor necrosis factor (TNF) ligand superfamily members and their receptors. LIGHT is a transmembrane protein expressed and shed from the surface of activated T cells. Since activated T cells have been implicated in osteoclastogenesis in rheumatoid arthritis (RA), this study sought to determine whether LIGHT can regulate RANKL/cytokine-induced osteoclast formation, to identify the mechanism by which LIGHT influences osteoclastogenesis, and to investigate the presence of LIGHT in the serum of RA patients. METHODS: The effect of LIGHT on human and murine osteoclast formation was assessed in the presence and absence of neutralizing reagents to known osteoclastogenic factors. Serum levels of LIGHT in RA patients were measured by enzyme-linked immunosorbent assay. RESULTS: In the presence and absence of RANKL, LIGHT induced osteoclast formation from both human peripheral blood mononuclear cells and murine macrophage precursors, in a dose-dependent manner, whereas no inhibition was observed by adding osteoprotegerin, RANK:Fc, TNFalpha, or interleukin-8 or by blocking the LIGHT receptors herpesvirus entry mediator or lymphotoxin beta receptor. However, formation of osteoclasts was significantly decreased by the soluble decoy receptor for LIGHT, DcR3, and by blocking antibodies to the p75 component of the TNF receptor. A significant increase in LIGHT levels in the serum of RA patients compared with normal controls was also noted. CONCLUSION: Our results indicate that LIGHT promotes RANKL-mediated osteoclastogenesis and that it can induce osteoclast formation by a mechanism independent of RANKL. The increased concentration of LIGHT in patients with RA raises the possibility that LIGHT may play a role in immunopathogenic conditions that are associated with localized or systemic bone loss.

Osteoprotegerin inhibits the development of osteolytic bone disease in multiple myeloma.

Multiple myeloma is a B-cell malignancy characterized by the accumulation of plasma cells in the bone marrow and the development of osteolytic bone disease. The present study demonstrates that myeloma cells express the critical osteoclastogenic factor RANKL (the ligand for receptor activator of NF-kappa B). Injection of 5T2MM myeloma cells into C57BL/KaLwRij mice resulted in the development of bone disease characterized by a significant decrease in cancellous bone volume in the tibial and femoral metaphyses, an increase in osteoclast formation, and radiologic evidence of osteolytic bone lesions. Dual-energy x-ray absorptiometry demonstrated a decrease in bone mineral density (BMD) at each of these sites. Treatment of mice with established myeloma with recombinant osteoprotegerin (OPG) protein, the soluble decoy receptor for RANKL, prevented the development of lytic bone lesions. OPG treatment was associated with preservation of cancellous bone volume and inhibition of osteoclast formation. OPG also promoted an increase in femoral, tibial, and vertebral BMD. These data suggest that the RANKL/RANK/OPG system may play a critical role in the development of osteolytic bone disease in multiple myeloma and that targeting this system may have therapeutic potential.

The bisphosphonate, zoledronic acid, induces apoptosis of breast cancer cells: evidence for synergy with paclitaxel.

Bisphosphonates are well established in the management of breast-cancer-induced bone disease. Recent studies have suggested that these compounds are effective in preventing the development of bone metastases. However, it is unclear whether this reflects an indirect effect via an inhibition of bone resorption or a direct anti-tumour effect. The breast cancer cell lines, MCF-7 and MDA-MB-231 cells were treated with increasing concentrations of the bisphosphonate, zoledronic acid, for varying time periods, in the presence or absence of paclitaxel. The effects of zoledronic acid were determined by assessing cell number and rate of apoptosis by evaluating changes in nuclear morphology and using a fluorescence nick translation assay. Zoledronic acid caused a dose- and time-dependent decrease in cell number (P< 0.001) and a concomitant increase in tumour cell apoptosis (P< 0.005). Short-term exposure to zoledronic acid was sufficient to cause a significant reduction in cell number and increase in apoptosis (P< 0.05). These effects could be prevented by incubation with geranyl geraniol, suggesting that zoledronic acid-induced apoptosis is mediated by inhibiting the mevalonate pathway. Treatment with zoledronic acid and clinically achievable concentrations of paclitaxel resulted in a 4-5-fold increase in tumour cell apoptosis (P< 0.02). Isobologram analysis revealed synergistic effects on tumour cell number and apoptosis when zoledronic acid and paclitaxel were combined. Short-term treatment with zoledronic acid, which closely resembles the clinical setting, has a clear anti-tumour effect on breast cancer cells. Importantly, the commonly used anti-neoplastic agent, paclitaxel, potentiates the anti-tumour effects of zoledronic acid. These data suggest that, in addition to inhibiting bone resorption, zoledronic acid has a direct anti-tumour activity on breast cancer cells in vitro.

The potent bisphosphonate ibandronate does not induce myeloma cell apoptosis in a murine model of established multiple myeloma.

Bisphosphonates are effective in the management of bone disease in patients with multiple myeloma and recent reports have suggested that they may also have an anti-tumour activity. In support of this, we have previously demonstrated that bisphosphonates can induce myeloma cell apoptosis in vitro; however, it remains unclear whether this occurs in vivo. We have therefore investigated the effect of the potent bisphosphonate ibandronate in the 5T2MM murine model of established multiple myeloma. Short-term treatment with a high dose of ibandronate had no effect on either myeloma cell number or the proportion of myeloma cells undergoing apoptosis. These observations suggest that although bisphosphonates induce apoptosis in myeloma cells in vitro, they may not have the same anti-tumour effects in vivo.

Bisphosphonates--mechanisms of action in multiple myeloma.

Bisphosphonates are a class of anti-resorptive drugs, which are effective in the treatment of osteoclast-mediated bone disease, including the osteolytic bone disease. which is a major clinical feature of patients with multiple myeloma. Recently, increases in survival following treatment with pamidronate have been observed in some patients with multiple myeloma, raising the possibility that bisphosphonates may also have an anti-tumour effect. We have demonstrated that bisphosphonates can have an anti-tumour effect in human myeloma cell in vitro, and that these anti-tumour effects induced by potent nitrogen-containing bisphosphonates are a result of inhibition of enzymes of the mevalonate pathway. However, we and others have been unable to demonstrate an anti-tumour effect of the potent bisphosphonate ibandronate in vivo, using murine models of multiple myeloma. It is therefore likely that only by studying patients receiving bisphosphonates will we be able to determine whether these compounds have a clinically important anti-tumour effect.

The bisphosphonate incadronate (YM175) causes apoptosis of human myeloma cells in vitro by inhibiting the mevalonate pathway.

It has recently been suggested that bisphosphonates may have direct antitumor effects in vivo, in addition to their therapeutic antiresorptive properties. Bisphosphonates can inhibit proliferation and cause apoptosis in human myeloma cells in vitro. In macrophages, bisphosphonate-induced apoptosis was recently found to be a result of inhibition of the mevalonate (MVA) pathway. The aim of this study was to determine whether bisphosphonates also affect human myeloma cells in vitro by inhibiting the MVA pathway. Incadronate and mevastatin (a known inhibitor of the MVA pathway) caused apoptosis in JJN-3 myeloma cells and inhibited cell proliferation. Geranylgeraniol and farnesol prevented incadronate-induced apoptosis and had a partial effect on cell cycle arrest. MVA and geranylgeraniol prevented mevastatin-induced apoptosis and inhibition of proliferation and completely prevented the effect of mevastatin on the cell cycle. These observations demonstrate that incadronate-induced apoptosis in human myeloma cells in vitro is the result of inhibition of the MVA pathway.

Anti-tumour activity of bisphosphonates in human myeloma cells.

Multiple myeloma is a haematological malignancy characterized by an expansion of malignant plasma cells within the bone marrow and is frequently associated with bone disease involving the development of osteolytic bone lesions, pathological fractures, osteoporosis and hypercalcaemia. A class of anti-resorptive drugs known as bisphosphonates have been in use to treat osteoclast-mediated bone diseases for the past 3 decades, and are currently proving effective in the treatment of the bone disease associated with multiple myeloma. Recent studies have suggested that bisphosphonate treatment may also result in an improvement in survival in some patients with multiple myeloma. These effects on survival may reflect an indirect effect of the bisphosphonates on tumour growth, via inhibition of osteoclast activity and hence a reduction in the release of tumour growth factors. However, it is also possible that bisphosphonates may have a direct effect on myeloma cells. In support of this we have demonstrated that bisphosphonates can decrease cell proliferation and induce apoptosis in human myeloma cells in vitro, and this review discusses the possibility that bisphosphonates may have not only an anti-resorptive action, but may also have a direct anti-tumour activity.

Bisphosphonates induce apoptosis in human myeloma cell lines: a novel anti-tumour activity.

Bisphosphonates are in widespread use to prevent bone resorption in a number of metabolic and tumour-induced bone diseases including multiple myeloma. Recent reports suggest that bisphosphonate treatment may be associated with an increase in patient survival, raising the possibility that these compounds may have a direct effect on the tumour cells. We have investigated whether the bisphosphonates clodronate, pamidronate and YM175 can directly affect the human myeloma cell lines U266-B1, JJN-3 and HS-Sultan in vitro. The effect of bisphosphonate treatment on cell number and cell cycle progression was examined using flow cytometry. The ability of bisphosphonates to induce apoptosis in human myeloma cell lines was determined on the basis of changes in nuclear morphology and of DNA fragmentation. Pamidronate and the more potent bisphosphonate. YM175, significantly decreased cell number (P < 0.001) in JJN-3 and HS-Sultan cells. YM175 also caused cells to arrest in the S-phase of the cell cycle in the JJN-3 cell line. Both pamidronate and YM175 also caused an increase in the proportion of cells with altered nuclear morphology (P < 0.05) and fragmented DNA, characteristic of apoptosis, in both JJN-3 and HS-Sultan cells. In contrast, clodronate had little effect on cell number and did not cause apoptosis at the concentrations examined. These data raise the possibility that some bisphosphonates could have direct anti-tumour effects on human myeloma cells in vivo.