Human osteosarcoma-derived cell lines produce soluble factor(s) that induces differentiation of blood monocytes to osteoclast-like cells

Single-Cell Transcriptome Analysis Reveals Paraspeckles Expression in Osteosarcoma Tissues

Nuclear paraspeckles are subnuclear bodies contracted by nuclear-enriched abundant transcript 1 (NEAT1) long non-coding RNA, localised in the interchromatin space of mammalian cell nuclei. Paraspeckles have been critically involved in tumour progression, metastasis and chemoresistance. To this date, there are limited findings to suggest that paraspeckles, NEAT1 and heterogeneous nuclear ribonucleoproteins (hnRNPs) directly or indirectly play roles in osteosarcoma progression. Herein, we analysed NEAT1, paraspeckle proteins (SFPQ, PSPC1 and NONO) and hnRNP members (HNRNPK, HNRNPM, HNRNPR and HNRNPD) gene expression in 6 osteosarcoma tumour tissues using the single-cell RNA-sequencing method. The normalised data highlighted that the paraspeckles transcripts were highly abundant in osteoblastic OS cells, except NEAT1, which was highly expressed in myeloid cell 1 and 2 subpopulations.

Roles of the RANKL-RANK Axis in Immunity-Implications for Pathogenesis and Treatment of Bone Metastasis

A substantial amount patients with cancer will develop bone metastases, with 70% of metastatic prostate and breast cancer patients harboring bone metastasis. Despite advancements in systemic therapies for advanced cancer, survival remains poor for those with bone metastases. The interaction between bone cells and the immune system contributes to a better understanding of the role that the immune system plays in the bone metastasis of cancer. The immune and bone systems share various molecules, including transcription factors, signaling molecules, and membrane receptors, which can stimulate the differentiation and activation of bone-resorbing osteoclasts. The process of cancer metastasis to bone, which deregulates bone turnover and results in bone loss and skeletal-related events (SREs), is also controlled by primary cancer-related factors that modulate the intratumoral microenvironment as well as cellular immune process. The nuclear factor kappa B ligand (RANKL) and the receptor activator of nuclear factor kappa B (RANK) are key regulators of osteoclast development, bone metabolism, lymph node development, and T-cell/dendritic cell communication. RANKL is an osteoclastogenic cytokine that links the bone and the immune system. In this review, we highlight the role of RANKL and RANK in the immune microenvironment and bone metastases and review data on the role of the regulatory mechanism of immunity in bone metastases, which could be verified through clinical efficacy of RANKL inhibitors for cancer patients with bone metastases. With the discovery of the specific role of RANK signaling in osteoclastogenesis, the humanized monoclonal antibody against RANKL, such as denosumab, was available to prevent bone loss, SREs, and bone metastases, providing a unique opportunity to target RANKL/RANK as a future strategy to prevent bone metastases.

Acid Microenvironment in Bone Sarcomas

Simple Summary

Although rare, malignant bone sarcomas have devastating clinical implications for the health and survival of young adults and children. To date, efforts to identify the molecular drivers and targets have focused on cancer cells or on the interplay between cancer cells and stromal cells in the tumour microenvironment. On the contrary, in the current literature, the role of the chemical-physical conditions of the tumour microenvironment that may be implicated in sarcoma aggressiveness and progression are poorly reported and discussed. Among these, extracellular acidosis is a well-recognized hallmark of bone sarcomas and promotes cancer growth and dissemination but data presented on this topic are fragmented. Hence, we intended to provide a general and comprehensive overview of the causes and implications of acidosis in bone sarcoma.

Abstract

In bone sarcomas, extracellular proton accumulation is an intrinsic driver of malignancy. Extracellular acidosis increases stemness, invasion, angiogenesis, metastasis, and resistance to therapy of cancer cells. It reprograms tumour-associated stroma into a protumour phenotype through the release of inflammatory cytokines. It affects bone homeostasis, as extracellular proton accumulation is perceived by acid-sensing ion channels located at the cell membrane of normal bone cells. In bone, acidosis results from the altered glycolytic metabolism of bone cancer cells and the resorption activity of tumour-induced osteoclasts that share the same ecosystem. Proton extrusion activity is mediated by extruders and transporters located at the cell membrane of normal and transformed cells, including vacuolar ATPase and carbonic anhydrase IX, or by the release of highly acidic lysosomes by exocytosis. To date, a number of investigations have focused on the effects of acidosis and its inhibition in bone sarcomas, including studies evaluating the use of photodynamic therapy. In this review, we will discuss the current status of all findings on extracellular acidosis in bone sarcomas, with a specific focus on the characteristics of the bone microenvironment and the acid-targeting therapeutic approaches that are currently being evaluated.

Angiopoietin-like 4 promotes osteosarcoma cell proliferation and migration and stimulates osteoclastogenesis

BACKGROUND

Osteosarcoma is the most common primary bone cancer in children and young adults. It is highly aggressive and patients that present with metastasis have a poor prognosis. Angiopoietin-like 4 (ANGPTL4) drives the progression and metastasis of many solid tumours, but has not been described in osteosarcoma tissue. ANGPTL4 also enhances osteoclast activity, which is required for osteosarcoma growth in bone. We therefore investigated the expression and function of ANGPTL4 in human osteosarcoma tissue and cell lines.

METHODS

Expression of ANGPTL4 in osteosarcoma tissue microarrays was determined by immunohistochemistry. Hypoxic secretion of ANGPTL4 was tested by ELISA and Western blot. Regulation of ANGPTL4 by hypoxia-inducible factor (HIF) was investigated using isoform specific HIF siRNA (HIF-1α, HIF-2α). Effects of ANGPTL4 on cell proliferation, migration (scratch wound assay), colony formation and osteoblastogenesis were assessed using exogenous ANGPTL4 or cells stably transfected with ANGPTL4. Osteoclastogenic differentiation of CD14+ monocytes was assessed by staining for tartrate-resistant acid phosphatase (TRAP), bone resorption was assessed by lacunar resorption of dentine.

RESULTS

ANGPTL4 was immunohistochemically detectable in 76/109 cases. ANGPTL4 was induced by hypoxia in 6 osteosarcoma cell lines, under the control of the HIF-1α transcription factor. MG-63 cells transfected with an ANGPTL4 over-expression plasmid exhibited increased proliferation and migration capacity and promoted osteoclastogenesis and osteoclast-mediated bone resorption. Individually the full-length form of ANGPTL4 could increase MG-63 cell proliferation, whereas N-terminal ANGPTL4 mediated the other pro-tumourigenic phenotypes.

CONCLUSIONS

This study describes a role(s) for ANGPTL4 in osteosarcoma and identifies ANGPTL4 as a treatment target that could potentially reduce tumour progression, inhibit angiogenesis, reduce bone destruction and prevent metastatic events.

Galectin-3 in bone tumor microenvironment: a beacon for individual skeletal metastasis management

The skeleton is frequently a secondary growth site of disseminated cancers, often leading to painful and devastating clinical outcomes. Metastatic cancer distorts bone marrow homeostasis through tumor-derived factors, which shapes different bone tumor microenvironments depending on the tumor cells' origin. Here, we propose a novel insight on tumor-secreted Galectin-3 (Gal-3) that controls the induction of an inflammatory cascade, differentiation of osteoblasts, osteoclasts, and bone marrow cells, resulting in bone destruction and therapeutic failure. In the approaching era of personalized medicine, the current treatment modalities targeting bone metastatic environments are provided to the patient with limited consideration of the cancer cells' origin. Our new outlook suggests delivering individual tumor microenvironment treatments based on the expression level/activity/functionality of tumor-derived factors, rather than utilizing a commonly shared therapeutic umbrella. The notion of "Gal-3-associated bone remodeling" could be the first step toward a specific personalized therapy for each cancer type generating a different bone niche in patients afflicted with non-curable bone metastasis.

Dendritic and mast cell involvement in the inflammatory response to primary malignant bone tumours

Background

A chronic inflammatory cell infiltrate is commonly seen in response to primary malignant tumours of bone. This is known to contain tumour-associated macrophages (TAMs) and lymphocytes; dendritic cells (DCs) and mast cells (MCs) have also been identified but whether these and other inflammatory cells are seen commonly in specific types of bone sarcoma is uncertain.

Methods

In this study we determined the nature of the inflammatory cell infiltrate in 56 primary bone sarcomas. Immunohistochemistry using monoclonal antibodies was employed to assess semiquantitatively CD45+ leukocyte infiltration and the extent of the DC, MC, TAM and T and B lymphocyte infiltrate.

Results

The extent of the inflammatory infiltrate in individual sarcomas was very variable. A moderate or heavy leukocyte infiltrate was more commonly seen in conventional high-grade osteosarcoma, undifferentiated pleomorphic sarcoma and giant cell tumour of bone (GCTB) than in Ewing sarcoma, chordoma and chondrosarcoma. CD14+/CD68+ TAMs and CD3+ T lymphocytes were the major components of the inflammatory cell response but (DC-SIGN/CD11c+) DCs were also commonly noted when there was a significant TAM and T lymphocyte infiltrate. MCs were identified mainly at the periphery of sarcomas, including the osteolytic tumour-bone interface.

Discussion

Our findings indicate that, although variable, some malignant bone tumours (e.g. osteosarcoma, GCTB) are more commonly associated with a pronounced inflammatory cell infiltrate than others (e.g. chondrosarcoma. Ewing sarcoma); the infiltrate is composed mainly of TAMs but includes a significant DC, T lymphocyte and MC infiltrate.

Conclusion

Tumours that contain a heavy inflammatory cell response, which includes DCs, TAMs and T lymphocytes, may be more amenable to immunomodulatory therapy. MCs are present mainly at the tumour edge and are likely to contribute to osteolysis and tumour invasion.

Bone microenvironment signals in osteosarcoma development

The bone is a complex connective tissue composed of many different cell types such as osteoblasts, osteoclasts, chondrocytes, mesenchymal stem/progenitor cells, hematopoietic cells and endothelial cells, among others. The interaction between them is finely balanced through the processes of bone formation and bone remodeling, which regulates the production and biological activity of many soluble factors and extracellular matrix components needed to maintain the bone homeostasis in terms of cell proliferation, differentiation and apoptosis. Osteosarcoma (OS) emerges in this complex environment as a result of poorly defined oncogenic events arising in osteogenic lineage precursors. Increasing evidence supports that similar to normal development, the bone microenvironment (BME) underlies OS initiation and progression. Here, we recapitulate the physiological processes that regulate bone homeostasis and review the current knowledge about how OS cells and BME communicate and interact, describing how these interactions affect OS cell growth, metastasis, cancer stem cell fate and therapy outcome.

Uterine leiomyosarcoma with osteoclast-like giant cells associated with high expression of receptor activator of nuclear factor κB ligand

The occurrence of osteoclast-like giant cells (OLGCs) in uterine leiomyosarcomas (LMSs) is a rare phenomenon. The nature of OLGCs and the significance of their accumulation in these tumors are poorly understood. Recent studies revealed that the formation of osteoclasts requires a specific cytokine, receptor activator of nuclear factor κB ligand (RANKL), in bone. In this study, we investigated the expression of RANKL in 2 cases of uterine LMS with OLGCs by means of immunohistochemistry and compared the extent of RANKL expression with that in conventional uterine LMSs and leiomyomas by using real-time reverse-transcription quantitative polymerase chain reaction. Our cases of uterine LMS with OLGCs showed markedly high expression of RANKL messenger RNA with clear RANKL immunoreactivity compared with messenger RNA expression and immunoreactivity of conventional uterine LMSs and leiomyomas. These findings suggest that the tumors producing RANKL may account for accumulation of OLGCs in tumor tissue because of RANKL-related osteoclastogenesis.

Reciprocal osteoblastic and osteoclastic modulation in co-cultured MG63 osteosarcoma cells and human osteoclast precursors

Osteosarcoma is usually associated with a disturbed bone metabolism. The aim of this work was to characterize the reciprocal interactions between MG63 osteosarcoma cells and osteoclasts, in a co-culture system. Co-cultures were characterized throughout 21 days for the osteoclastogenic response and the expression of osteoblastic markers. Monocultures of MG63 cells and peripheral blood mononuclear cell (PBMC) and co-cultures of PBMC + human bone marrow cells (hBMC) were also performed. Compared to PBMC cultures, co-cultures yielded significantly increased gene expression of osteoclast-related markers, tartarate-acid resistant phosphatase (TRAP) activity, TRAP-positive multinucleated cells, cells with actin rings and vitronectin receptors (VNR) and calcitonin receptors (CTR) and calcium phosphate resorbing ability. Results showed that the development of functional osteoclasts required a very low number of MG63 cells, suggesting a high osteoclastogenic-triggering capacity of this cell line. Subjacent mechanisms involved the pathways MEK and NF-kB, although with a lower relevance than that observed on PBMC monocultures or co-cultures of hBMC + PBMC; PGE2 production also had a contribution. Compared to MG63 cell monocultures, the co-culture expressed lower levels of COL1 and ALP, and higher levels of BMP-2, suggesting that PBMC also modulated the osteoblastic behavior. While M-CSF appeared to be involved in the osteoclastogenic response on the MG63 + PBMC co-cultures, RANKL does not seem to be a key player in the process. On the other hand, sphingosine-1-phosphate production might contribute to the modulation of the osteoblastic behavior. Results suggest that the reciprocal modulation between osteosarcoma and osteoclastic cells might contribute to the disturbed bone metabolism associated with bone tumors.

Impact of oncopediatric dosing regimen of zoledronic acid on bone growth: preclinical studies and case report of an osteosarcoma pediatric patient

Osteosarcoma and Ewing sarcoma represent the two most frequent primary bone tumors that arise in the pediatric population. Despite recent improvement in their therapeutic management, no improvement in survival rate has been achieved since early 1980 s. Among new therapeutic approaches, bisphosphonates are promising candidates as potent inhibitors of bone resorption. However, their effects on bone growth must be studied at dosing regimen corresponding to pediatric protocols. To this aim, several protocols using zoledronic acid (ZOL) were developed in growing mice (50 µg/kg every 2 days × 10). Parameters of bone remodeling and bone growth were investigated by radiography, micro-computed tomography, histology, and biologic analyses. Extramedullar hematopoiesis was searched for in spleen tissue. A transient inhibitory effect of ZOL was observed on bone length, with a bone-growth arrest during treatment owing to an impressive increase in bone formation at the growth plate level (8- to 10-fold increase in BV/TV). This sclerotic band then shifted into the diaphysis as soon as endochondral bone formation started again after the end of ZOL treatment, revealing that osteoclasts and osteoblasts are still active at the growth plate. In conclusion, endochondral bone growth is transiently disturbed by high doses of ZOL corresponding to the pediatric treatment of primary bone tumors. These preclinical observations were confirmed by a case report in a pediatric patient treated in the French OS2006 protocol over 10 months who showed a growth arrest during the ZOL treatment period with normal gain in size after the end of treatment.

RANKL expression is related to treatment outcome of patients with localized, high-grade osteosarcoma

BACKGROUND

The receptor activator of nuclear factor κB ligand (RANKL/TNFSF11) is expressed in metastatic bone cancer cells and has been suggested to play a key role in cell migration and metastatic behavior. We determined whether RANKL expression is correlated to clinical behavior of localized, high-grade osteosarcoma.

PATIENTS AND METHODS

This retrospective, immunohistochemical study was performed using materials obtained from 40 patients treated at Korea Cancer Center Hospital between 1995 and 2007. Prechemotherapy biopsy samples were stained for RANKL and correlations between RANKL expression and clinical characteristics and outcomes were evaluated. Staining was interpreted in a semiquantitative manner using an intensity based scoring system.

RESULTS

Thirty cases (75.0%) stained positively for RANKL; 15 (50.0%) had a high RANKL score (≥ 4) and the other 15 a low RANKL score (≤3). RANKL expression and RANKL scores were not related to age, sex, tumor location, tumor volume, or pathologic subtype. However, RANKL expression was related to a poor response to preoperative chemotherapy (P = 0.03) and a high RANKL score was associated with inferior survival. The 5-year event-free survival of patients with RANKL score ≥4 was 17.8 ± 10.5%, which was far worse than those with RANKL scores 1-3 or 0 (50.0 ± 15.8%, 56.0 ± 13.7%, respectively, P = 0.02).

CONCLUSIONS

The RANKL-RANK-OPG axis might be a promising target for the treatment of osteosarcoma, but further studies are needed to verify our data in a larger cohort.

Skeletal imaging effects of pamidronate therapy in osteosarcoma patients

BACKGROUND

After observing metaphyseal changes in pediatric and young adult patients with osteosarcoma who were treated with pamidronate, we initiated a retrospective study to identify bone findings on computed radiography of the chest and extremities, chest CT, extremity MRI, and radionuclide bone scans in this population.

OBJECTIVE

To review the generalized skeletal imaging findings on computed radiography, CT, and MR examinations in patients with osteosarcoma (OS) receiving pamidronate.

MATERIALS AND METHODS

A retrospective review of 40 patients with newly diagnosed OS (mean age, 16.5 years) receiving pamidronate with chemotherapy were identified at one institution. Computed radiography, CT, MR, and bone scans on 36 patients were reviewed for osseous changes.

RESULTS

Dense metaphyseal bands at the growth plates in long bones, epiphyseal ossification centers, anterior rib ends, sternum and spine were observed. Osseous changes occurred on CT in 69% of patients, and on computed chest radiography in 53%. Bone-within-bone appearance in the spine and ossification centers was identified on computed radiography in 36%.

CONCLUSION

OS patients treated with pamidronate can develop metaphyseal sclerotic bands as well as epiphyseal and vertebral endplate sclerosis progressing to a bone-within-bone appearance. Findings occur more frequently in younger patients with open epiphyses.

Therapy for osteosarcoma: where do we go from here?

Osteosarcoma is the most common malignant primary bone tumor in children and adolescents. Current optimal treatment for osteosarcoma consists of multi-agent chemotherapy and aggressive surgical resection of all sites of disease involvement. The current national and international cooperative trial for patients with newly diagnosed osteosarcoma builds upon the backbone of cisplatin, doxorubicin, and methotrexate. This protocol is designed to clarify whether (i) the addition of ifosfamide and etoposide to postoperative chemotherapy with cisplatin, doxorubicin, and methotrexate improves the event-free survival and overall survival for patients with resectable osteosarcoma and a poor histologic response to 10 weeks of preoperative chemotherapy; and (ii) the addition of pegylated interferon-alpha-2b as maintenance therapy after postoperative chemotherapy with cisplatin, doxorubicin, and methotrexate improves the event-free survival and overall survival for patients with resectable osteosarcoma and a good histologic response to 10 weeks of preoperative chemotherapy. However, the optimal treatment strategy (or strategies) for patients with relapsed or metastatic disease has yet to be defined. This remains one of the persistent challenges in the treatment of osteosarcoma. Recent therapeutic advances have focused on circumventing chemotherapy resistance mechanisms, incorporation of non-classical agents into upfront therapy, targeting of the tumor micro-environment, and investigating the role of novel delivery mechanisms. In patients with localized disease the 5-year survival rate is at least 70%; patients with metastatic or recurrent disease have <20% chance of long-term survival despite aggressive therapies. These figures have changed little in the past 2 decades. This review focuses on the current therapy for osteosarcoma, and highlights emerging strategies that will hopefully change the outlook for patients with this disease.

Current status and perspectives regarding the treatment of osteo-sarcoma: chemotherapy

Osteosarcoma is the most common primary bone tumor in childhood and adolescence. The use of combination chemotherapy and surgery enables long-term survival in approximately 60-70% of cases. However, the necessity for surgery, the poor prognosis of patients with metastatic or recurrent disease (long-term survival in only about 20% of cases), and the lack of establishment of second-line chemotherapy suggest that improvements in chemotherapy are desperately needed. Currently, in an effort to extend the protocol with the chemotherapy drugs that already exist, high-dose chemotherapy with/without autologous peripheral blood stem cell transplantation, and tumor-targeted drug delivery systems are under investigation. Future drug developments will no doubt lie in the direction of immunotherapy and anti-angiogenic therapy, as well as the use of cytotoxic drugs. Identifying the genes and signal transduction pathways responsible for the development of osteosarcoma or for the occurrence of malignancy in cases of osteosarcoma will undoubtedly lead to the identification of pathway-specific agents, or possible gene therapy. Furthermore, as increased light is shed on the character of osetoblastic differentiation in osteosarcoma, this will certainly give rise to new treatments utilizing differentiation therapy. This article reviews the current status and perspectives regarding the treatment of osteosarcoma in terms of chemotherapy.

Reduction of urinary levels of pyridinoline and deoxypyridinoline and serum levels of soluble receptor activator of NF-kappaB ligand by etanercept in patients with rheumatoid arthritis

The effects of soluble TNF-alpha receptor, etanercept, on bone metabolism were investigated in patients with rheumatoid arthritis (RA). Thirty RA patients were administered etanercept once or twice a week for more than 6 months. We evaluated clinical and laboratory parameters and measured urinary excretion levels of pyridinoline (PYD), deoxypyridinoline (DPD), cross-linked N-telopeptides of type I collagen (NTX), and serum levels of bone alkaline phosphatase (BAP), osteoprotegerin (OPG), and soluble receptor activator of NFkappaB ligand (sRANKL) at the baseline and at 3 and 6 months after initial treatment with etanercept. Etanercept treatment resulted in an improvement of symptoms due to RA and in a reduction of urinary excretion levels of PYD and DPD as well as serum sRANKL levels, with a significant difference at 6 months, and an increase of serum BAP levels at 3 and 6 months after the initial treatment with etanercept. Urinary NTX and serum OPG levels did not show a significant change at 3 and 6 months after the initial treatment, but serum OPG levels did show a reverse correlation with serum CRP levels, suggesting that the regulation of inflammation in RA may result in an induction of OPG production. Etanercept may have the ability to reduce the levels of bone resorption markers and to increase the levels of a bone formation marker while reducing sRANKL formation in RA patients.

Human osteosarcoma cells express functional receptor activator of nuclear factor-kappa B

RANK, RANK ligand (RANKL) and osteoprotegerin (OPG) are the key regulators of bone metabolism, both in normal and pathological conditions. Previous data have demonstrated that human osteosarcoma biopsies express RANKL as well as OPG, and functional RANK is expressed in a murine osteosarcoma cell line. As RANK expression in human osteosarcoma remains controversial, the aim of the present study was to analyse its expression in vitro in human osteosarcoma cell lines, ex vivo using pathological tissues, and then to determine its functionality in terms of signal transduction pathways modulated by RANKL. RT-PCR analysis and immunohistochemistry experiments revealed that RANK is expressed at both transcriptional and protein levels in MNNG/HOS, Saos-2 and MG-63 human osteosarcoma cell lines, in contrast to the U-2 OS osteosarcoma cell line and human osteoblasts, which were negative. RANK was also expressed in 57% of osteosarcoma biopsies. Furthermore, western blot experiments clearly demonstrated the functionality of RANK. Thus, RANKL significantly induced the phosphorylation of ERK1/2, p38 and IkappaB in RANK-positive osteosarcoma cells. This study is the first report of functional RANK expression in human osteosarcoma cells: this strengthens the involvement of the RANK-RANKL-OPG axis in primary bone tumour biology and identifies novel therapeutic approaches targeting RANK-positive osteosarcoma.

Immunomodulatory effects of statins and autoimmune rheumatic diseases: novel intracellular mechanism involved

Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, known as statins, are the most commonly prescribed agents for the treatment of hypercholesterolemia. However, the effects of statins may extend beyond their influences on serum cholesterol levels resulting in cholesterol-independent or pleiotropic effects. Clinical, animal and in vitro studies suggest that statins have additional clinical uses because of their anti-inflammatory and immunomodulatory effects, in part due to their capacity to interfere with the mevalonate pathway and inhibit prenylation of Rho family GTPases. This review focuses on the molecular mechanisms of the anti-inflammatory and immunomodulatory effects of statins. In base to all these information, we suggest that statins could have similar inhibitory effects on MAPKs pathways in cells from RA patients, including osteoclasts and fibroblasts.

MKK3/6-p38 MAPK signaling is required for IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells

Coupled bone turnover is directed by the expression of receptor-activated NF-kappaB ligand (RANKL) and its decoy receptor, osteoprotegerin (OPG). Proinflammatory cytokines, such as interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) induce RANKL expression in bone marrow stromal cells. Here, we report that IL-1beta and TNF-alpha-induced RANKL requires p38 mitogen-activating protein kinase (MAPK) pathway activation for maximal expression. Real-time PCR was used to assess the p38 contribution toward IL-1beta and TNF-alpha-induced RANKL mRNA expression. Steady-state RANKL RNA levels were increased approximately 17-fold by IL-1beta treatment and subsequently reduced approximately 70%-90% when p38 MAPK was inhibited with SB203580. RANKL mRNA stability data indicated that p38 MAPK did not alter the rate of mRNA decay in IL-1beta-induced cells. Using a RANKL-luciferase cell line receptor containing a 120-kB segment of the 5' flanking region of the RANKL gene, reporter expression was stimulated 4-5-fold by IL-1beta or TNF-alpha treatment. IL-1beta-induced RANKL reporter expression was completely blocked with specific p38 inhibitors as well as dominant negative mutant constructs of MAPK kinase-3 and -6. In addition, blocking p38 signaling in bone marrow stromal cells partially inhibited IL-1beta and TNF-alpha-induced osteoclastogenesis in vitro. Results from these studies indicate that p38 MAPK is a major signaling pathway involved in IL-1beta and TNF-alpha-induced RANKL expression in bone marrow stromal cells.

Effect of interleukin-18 on metastasis of mouse osteosarcoma cells

The effect of interleukin-18 (IL-18) on metastasis of highly metastatic LM8 mouse osteosarcoma cells was investigated using nude mice treated with anti-asialo GM1 serum to exclude anti-tumor actions of IL-18 through activation of T and natural killer cells. Injection of LM8 cells which do not express IL-18 receptor beta into a tail vain resulted in the formation of pulmonary and hepatic metastatic foci. Daily injection of mice with IL-18 starting the fifth day from the cell injection had no significant effect on the number of metastatic foci, while five daily injections of IL-18 before and after the cell injection resulted in marked decreases. Culture of LM8 cells with IL-18 for 5 days before the injection into mice produced no significant effect on the number of pulmonary and hepatic metastatic foci. In contrast, pretreatment of mice with IL-18 for 5 days before the cell injection markedly decreased metastatic foci. The retention of LM8 cells in the lung 24 h after their injection was also reduced by the pretreatment of mice with IL-18. Serum obtained from mice pretreated with IL-18 for 5 days suppressed mobility of LM8 cells but IL-18 itself did not. These results suggest that IL-18 inhibits metastasis of LM8 cells partly by inducing a factor(s) in the host which suppresses cell mobility.

Chemotherapy resistance in osteosarcoma: current challenges and future directions

For patients with osteosarcoma, the use of chemotherapy has improved survival from 11% with surgical resection alone in the 1960s, to 70% by the mid-1980s. However, survival has since plateaued, despite advances in anticancer therapy. Elucidation of the mechanisms of chemoresistance and implementation of strategies to overcome chemoresistance will likely be pivotal to improving survival. In this review, the focus is on the current understanding of the mechanisms of resistance to the most commonly used agents in the treatment of osteosarcoma and the methods employed to overcome chemotherapy resistance.

RANKL protein is expressed at the pannus-bone interface at sites of articular bone erosion in rheumatoid arthritis

OBJECTIVES

Receptor activator of NF-kappaB ligand (RANKL) and osteoprotegerin (OPG) have been demonstrated to be critical regulators of osteoclast generation and activity. In addition, RANKL has been implicated as an important mediator of bone erosion in rheumatoid arthritis (RA). However, the expression of RANKL and OPG at sites of pannus invasion into bone has not been examined. The present study was undertaken to further elucidate the contribution of this cytokine system to osteoclastogenesis and subsequent bone erosion in RA by examining the pattern of protein expression for RANKL, OPG and the receptor activator of NF-kappaB (RANK) in RA at sites of articular bone erosion.

METHODS

Tissues from 20 surgical procedures from 17 patients with RA were collected as discarded materials. Six samples contained only synovium or tenosynovium remote from bone, four samples contained pannus-bone interface with adjacent synovium and 10 samples contained both synovium remote from bone and pannus-bone interface with adjacent synovium. Immunohistochemistry was used to characterize the cellular pattern of RANKL, RANK and OPG protein expression immediately adjacent to and remote from sites of bone erosion.

RESULTS

Cellular expression of RANKL protein was relatively restricted in the bone microenvironment; staining was focal and confined largely to sites of osteoclast-mediated erosion at the pannus-bone interface and at sites of subchondral bone erosion. RANK-expressing osteoclast precursor cells were also present in these sites. OPG protein expression was observed in numerous cells in synovium remote from bone but was more limited at sites of bone erosion, especially in regions associated with RANKL expression.

CONCLUSIONS

The pattern of RANKL and OPG expression and the presence of RANK-expressing osteoclast precursor cells at sites of bone erosion in RA contributes to the generation of a local microenvironment that favours osteoclast differentiation and activity. These data provide further evidence implicating RANKL in the pathogenesis of arthritis-induced joint destruction.

Cytological properties of stromal cells derived from giant cell tumor of bone (GCTSC) which can induce osteoclast formation of human blood monocytes without cell to cell contact

When human blood monocytes were cocultured with stromal cells derived from human giant cell tumor of bone (GCTSC) and a Millipore filter (0.4 microm) was interposed between monocytes and GCTSC, multinucleated giant cell formation of monocytes was induced. The multinucleated giant cells have characters as osteoclast-like cells, indicating that a soluble osteoclast-inducing factor(s) is secreted from GCTSC expressing RANK, RANKL/ODF/OPGL and TACE mRNA. Furthermore, OCIF/OPG inhibited GCTSC-induced osteoclastogenesis, showing that the RANK-RANKL system is involved in GCTSC-induced osteoclastogenesis and that soluble form of ODF/RANKL induces osteoclasts from monocytes. GCTSC expressed the cytokine mRNAs such as M-CSF, GM-CSF, IL-3, IL-4, IL-6, and IFN-gamma mRNAs. None of IL-1ralpha, IL-1alpha, IL-1beta, IL-2, IL-4, IL-10, IL-18, TNF-alpha, G-CSF and IFN-gamma could be detected in all culture media. A significant amount of IL-6 could be detected in the culture media of all GCTSC. IL-8 was found in the culture media of two GCTSC and two osteosarcoma-derived cells. M-CSF was detected in all culture media. GCTSC express CaSR, and stimulation of GCTSC with either extracellular Ca(2+) or neomycin, agonist of CaSR, augmented the expression of RANKL. Some lines of GCTSC expressed alkaline phosphatase, osteocalcin and Cbfa1, suggesting that GCTSC are intimately related to osteoblastic lineage.

RANK ligand and TNF-alpha mediate acid-induced bone calcium efflux in vitro

Chronic metabolic acidosis stimulates net calcium efflux from bone due to increased osteoclastic bone resorption and decreased osteoblastic collagen synthesis. Previously, we determined that incubation of neonatal mouse calvariae in medium simulating physiological metabolic acidosis leads to a significant, cyclooxygenase-dependent, increase in RNA for bone cell receptor activator of NF-kappaB ligand (RANKL) compared with incubation in neutral pH medium. In this study, we tested the hypothesis that the acid-mediated increase in RANKL expression is a primary mechanism for the stimulated osteoclastic resorption. Acid medium increased the medium concentration of sRANKL without altering the concentration of the decoy receptor osteoprotegerin (OPG). Inhibition of the RANKL pathway with concentrations of OPG up to 25 ng/ml, far greater than physiological, did not significantly decrease the robust acid-induced Ca efflux from bone nor did incubation of the calvariae with a different inhibitor, RANK/Fc (up to 50 ng/ml). Thus acid-induced net Ca efflux appears to involve mechanisms in addition to the RANK/RANKL pathway. Osteoblasts also produce TNF-alpha, another cytokine that stimulates the maturation and activity of osteoclasts. Incubation of calvariae in acid medium caused a significant increase in TNF-alpha levels. Incubation of calvariae with anti-TNF (up to 250 ng/ml) did not significantly decrease acid-induced net Ca efflux. However, the combination of RANK/Fc plus anti-TNF caused a significant but subtotal reduction in acid-induced Ca efflux, whereas the combination of RANK/Fc plus an isotype-matched control for the anti-TNF had no effect on Ca release. Thus simultaneous inhibition of RANKL and TNF-alpha is necessary to reduce acid-induced, cell-mediated net Ca efflux from bone; however, additional osteoblast-produced factors must also be involved in acid-induced, cell-mediated bone resorption.

Human trabecular bone-derived osteoblasts support human osteoclast formation in vitro in a defined, serum-free medium

While it has been assumed that osteoblasts in the human support osteoclast formation, in vitro evidence of this is currently lacking. We tested the ability of normal human trabecular bone-derived osteoblasts (NHBCs) to support osteoclast formation from human peripheral blood mononuclear cells (PBMC) in response to treatment with either 1alpha,25-dihydroxyvitamin D3 (1,25D) or parathyroid hormone (PTH), using a serum-replete medium previously used to support human osteoclast formation on a stroma of murine ST-2 cells. Under these conditions, NHBC did not support osteoclast formation, as assessed by morphological, histochemical, and functional criteria, despite our previous results demonstrating a link between induction of RANKL mRNA expression and NHBC phenotype in these media. We next tested a defined, serum-free medium (SDM) on NHBC phenotype, their expression of RANKL and OPG, and their ability to support osteoclast formation. SDM, containing dexamethasone (DEX) and 1,25D, induced phenotypic maturation of NHBC, based on the expression of STRO-1 and the bone/liver/kidney isoform of alkaline phosphatase (AP). PTH as a single factor did not induce phenotypic change. 1,25D and DEX induced the greatest ratio of RANKL:OPG mRNA, predictive of supporting osteoclast formation. Consistent with this, co-culture of NHBC with CD14+ PBMC, or bone marrow mononuclear cell (BMMC), or CD34+ BMMC precursors in SDM + 1,25D + DEX, resulted in functional osteoclast formation. Osteoclast formation also occurred in PTH + DEX stimulated co-cultures. Interestingly, SDM supplemented with recombinant RANKL (25-100 ng/ml) and M-CSF (25 ng/ml), did not induce osteoclast formation from any of the osteoclast precursor populations in stromal-free cultures, unlike serum-replete medium. This study demonstrates that under the appropriate conditions, adult human primary osteoblasts can support de novo osteoclast formation, and this model will enable the detailed study of the role of both cell types in this process.

Inhibition by interleukin-18 of the growth of Dunn osteosarcoma cells

To examine the usefulness of interleukin-18 (IL-18) in the treatment of osteosarcomas, the effect of IL-18 on the growth of Dunn osteosarcoma cells was investigated. Daily intraperitoneal (i.p.) injection of mouse recombinant IL-18 (2 microg/mouse) suppressed the growth of Dunn osteosarcoma cells transplanted subcutaneously (s.c.) into syngeneic C3H mice. This IL-18-induced suppression was not affected by simultaneous treatment with anti-asialo GM1 serum, which inactivates natural killer (NK) cells. However, IL-18 failed to suppress the growth of Dunn osteosarcoma cells transplanted into BALB/c-nude mice devoid of T lymphocytes or C3H-gld/gld mice deficient in functional Fas ligand (FasL). IL-18 also failed to suppress the growth of Dunn osteosarcoma cells in vitro, although expression of IL-18 receptor mRNA and MyD88 mRNA as well as Fas mRNA was detected by reverse transcriptase-polymerase chain reaction (RT-PCR). On the other hand, antimouse Fas antibody showed cytotoxicity against Dunn osteosarcoma cells in a dose-dependent manner in vitro. In addition, treatment of C3H mice with IL-18 enhanced the cytotoxic activity of CD8(+) T lymphocytes against Dunn osteosarcoma cells. These results indicate that IL-18 inhibits the growth of Dunn osteosarcoma cells in vivo by enhancing the cytotoxic activity of CD8(+) T lymphocytes through the FasL-Fas system.

In vitro blockade of receptor activator of nuclear factor-?B ligand prevents osteoclastogenesis induced by neuroblastoma cells

Proliferation and differentiation of osteoclasts are regulated by a cytokine system that includes RANKL, which binds 2 receptors: RANK, which activates osteoclast differentiation, and osteoprotegerin (OPG), a decoy receptor that limits RANKL action. We investigated the role of the OPG/RANKL/RANK network in the pathogenesis of skeletal metastasis in neuroblastoma. Four different neuroblastoma cell lines (NB100, CHP212, SH-SY5Y, SJ-NK-P) showed a large amount of OPG and RANKL transcripts. Soluble RANKL was detectable in all cell lines, but poor release of OPG was observed. SH-SY5Y showed the lowest OPG-to-RANKL ratio and promoted osteoclastic differentiation of FLG29.1 and peripheral mononuclear cells, inducing expression of the osteoclast markers RANK, c-src, c-fos, cathepsin-K and TRAP. SJ-N-KP, which released both OPG and RANKL, did not show the same capability. OPG, neutralizing anti-RANKL antibody and antisense oligonucleotides were evaluated for their ability to inhibit RANKL activity. The neutralizing antibody hampered osteoclastic differentiation by blocking both the juxtacrine and the paracrine activity of RANKL. Our findings confirm that neuroblastoma cells induce osteoclastogenesis via RANKL and suggest that the RANKL expression associated with lack of the decoy receptor OPG could be a peculiarity of some tumors that makes them able to induce metastatic osteolysis. Moreover, our results suggest that RANKL could be a relevant target in the adjuvant therapy of bone metastatic neuroblastoma as proper neutralization revokes completely osteoclastic differentiation.

The nitrogen-containing bisphosphonate, zoledronic acid, influences RANKL expression in human osteoblast-like cells by activating TNF-alpha converting enzyme (TACE)

Bisphosphonates are used to prevent osteoclast-mediated bone loss. Zoledronic acid inhibits osteoclast maturation indirectly by increasing OPG protein secretion and decreasing transmembrane RANKL expression in human osteoblasts. The decreased transmembrane RANKL expression seems to be related to the upregulation of the RANKL sheddase, TACE.

INTRODUCTION

Bisphosphonates (BPs) exhibit high affinity for hydroxyapatite mineral in bone and are used extensively to treat malignancy-associated bone disease and postmenopausal bone loss by inhibiting osteoclast (OC)-mediated bone resorption.

MATERIALS AND METHODS

We examined the effect of the most potent nitrogen-containing BP available, zoledronic acid (ZOL), on the expression of RANKL and osteoprotegerin (OPG), critical factors in the regulation of OC formation and activation, in primary osteoblast (OB)-like cells derived from human bone, using flow cytometry, ELISA, semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR), in situ immunofluorescence staining, and Western blotting.

RESULTS

Our studies show that ZOL, while not significantly affecting RANKL or OPG gene expression, markedly increased OPG protein secretion and reduced transmembrane RANKL protein expression in OB-like cells. The reduction in transmembrane RANKL expression was preceded by a marked increase in the expression of the metalloprotease-disintegrin, TNF-alpha converting enzyme (TACE). In addition, the decreased transmembrane expression of RANKL could be partially reversed by a TACE inhibitor, TAPI-2.

CONCLUSIONS

Our studies indicate that ZOL, in addition to its direct effects on mature OCs, may inhibit the recruitment and differentiation of OCs by cleavage of transmembrane RANKL in OB-like cells by upregulating the sheddase, TACE.

Metabolic acidosis stimulates RANKL RNA expression in bone through a cyclo-oxygenase-dependent mechanism

Metabolic acidosis inhibits osteoblastic bone formation and stimulates osteoclastic resorption. To determine whether acidosis alters expression of RNA for the osteoclastic differentiation factor RANKL, mouse calvariae were incubated in neutral or physiologically acidic media. Acidosis resulted in a significant cyclo-oxygenase-dependent increase in RANKL RNA levels, which would be expected to induce the associated increase in bone resorption.

INTRODUCTION

Metabolic acidosis increases net calcium efflux from bone, initially through physicochemical mechanisms and later through predominantly cell-mediated mechanisms. Acidosis decreases osteoblastic bone formation and increases osteoclastic resorption. The growth and maturation of osteoclasts, derived from hematopoietic precursors in the monocyte/macrophage lineage, are dependent on the interplay of a number of factors. Commitment of pre-osteoclasts to osteoclasts is induced by the interaction of the osteoclastic cell-surface receptor RANK with a ligand expressed by osteoblasts, RANKL. The RANK/RANKL interaction not only initiates a differentiation cascade that culminates in mature bone-resorbing osteoclasts but also increases osteoclastic resorptive capacity and survival.

METHODS

To test the hypothesis that metabolic acidosis increases expression of RANKL, we cultured neonatal mouse calvariae in acidic (initial medium pH approximately 7.1 and [HCO3-] approximately 11 mM) or neutral (initial medium pH approximately 7.5 and [HCO3-] approximately 25 mM) medium for 24 and 48 h. We determined the relative expression of RANKL RNA by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitated the expression by Northern analysis.

RESULTS

In this model of metabolic acidosis, there was significantly increased expression of RANKL RNA at both 24 (2-fold) and 48 h (5-fold) compared with respective controls. Net calcium efflux from bone was also increased in acidic medium compared with control medium. At 48 h, net calcium efflux correlated directly with RANKL expression (r = 0.77, n = 15, p < 0.001). Inhibition of prostaglandin synthesis with indomethacin blocked the acid-induced increase in RANKL RNA as well as the increased calcium efflux.

CONCLUSIONS

Metabolic acidosis induces osteoblastic prostaglandin synthesis, followed by autocrine or paracrine induction of RANKL. This increase in RANKL would be expected to augment osteoclastic bone resorption and help explain the increase in cell-mediated net calcium efflux.

Bone destruction in arthritis

Rheumatoid arthritis (RA) is characterised by the presence of an inflammatory synovitis accompanied by destruction of joint cartilage and bone. Destruction of cartilage matrix results predominantly from the action of connective tissue proteinases released by RA synovial tissues, chondrocytes, and pannus tissue. Several lines of evidence in RA and in animal models of arthritis support a role for osteoclasts in the pathogenesis of bone erosions. RA synovial tissues produce a variety of cytokines and growth factors that may increase osteoclast formation, activity, and/or survival. These include interleukin 1alpha (IL1alpha) and beta, tumour necrosis factor alpha (TNFalpha), IL11, IL17, and macrophage colony stimulating factor (M-CSF). Receptor activator of NFkappaB ligand (RANKL) is an essential factor for osteoclast differentiation and also functions to augment T cell-dendritic cell cooperative interactions. CD4+ T cells and synovial fibroblasts derived from RA synovium are sources of RANKL. Furthermore, in collagen induced arthritis (CIA), blockade with osteoprotegerin (OPG), a decoy receptor for RANKL, results in protection from bone destruction. To further evaluate the role of osteoclasts in focal bone erosion in arthritis, arthritis was generated in the RANKL knockout mouse using a serum transfer model. Despite ongoing inflammation, the degree of bone erosion in arthritic RANKL knockout mice, as assessed by microcomputed tomography and correlated histopathological analysis, was dramatically reduced compared with that seen in arthritic control mice. Cartilage damage was present in both the arthritic RANKL knockout mice and in arthritic control littermates, with a trend toward milder cartilage damage in the RANKL knockout mice. This study supports the hypothesis that osteoclasts play an important part in the pathogenesis of focal bone erosion in arthritis, and reveals distinct mechanisms of cartilage destruction and bone erosion in this animal model of arthritis. Future directions for research in this area include the further investigation of a possible direct role for the RANKL/RANK/OPG system in cartilage metabolism, and the possible role of other cell types and cytokines in bone erosion in arthritis.