Production and characterization of osteoclast-selective monoclonal antibodies that distinguish between multinucleated cells derived from different human tissues

Differential expression of filamin B splice variants in giant cell tumor cells

Giant cell tumor of bone (GCT) is the most commonly reported non-malignant bone tumor in Hong Kong. This kind of tumor usually affects people aged 20–40 years. Also, it is well known for recurrence locally, especially when the tumor cannot be removed completely. Filamins are actin-binding proteins which contain three family members, filamin A, B and C. They are the products of three different genes, FLNA, FLNB and FLNC, which can generate various transcript variants in different cell types. In this study, we focused on the effects of FLNBv2 and FLNBv4 toward GCT cells. The only difference between FLNBv2 and FLNBv4 is that FLNBv4 does not contain hinge 1 region. We found that the relative abundance of FLNBv4 varies among different GCT cell lines while the expression level of FLNBv4 in normal osteoblasts was only marginally detectable. In the functional aspect, overexpression of FLNBv4 led to upregulation of RANKL, OCN, OPG and RUNX2, which are closely related to GCT cell survival and differentiation. Moreover, FLNBv4 can have a negative effect on cell viability of GCT cells when compare with FLNBv2. In conclusion, splicing variants of FLNB are differentially expressed in GCT cells and may play a role in the proliferation and differentiation of tumor cells.

Giant cell tumor of bone

Giant cell tumor is a common benign bone tumor that possesses specific features including location at the end of long bone, a strong tendency toward local recurrence, and the rare capacity to metastasize to the lungs. Preferred treatment usually consists of extensive curettage and filling of the cavity with bone graft or cement. Debate still exists about the usefulness of local adjuvant treatment. Functional outcome is usually very good.

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.

The impact of genomics on drug discovery

High-throughput gene sequencing has revolutionized the process used to identify novel molecular targets for drug discovery. Thousands of new gene sequences have been generated but only a limited number of these can be converted into validated targets likely to be involved in disease. We describe here some of the approaches used at SmithKline Beecham to select and validate novel targets. These include the identification of selective tissue gene product expression, such as for cathepsin K, a novel osteoclast-specific cysteine protease. We also describe the discovery and functional characterization of novel members of the G-protein coupled receptor superfamily and their pairing with natural ligands. Lastly, we discuss the promises of gene microarrays and proteomics, developing technologies that allow the parallel analyses of tissue expression patterns of thousands of genes or proteins, respectively.

Spindle-shaped cells derived from giant-cell tumor of bone support differentiation of blood monocytes to osteoclast-like cells

Spindle-shaped cells were established from four giant-cell tumors of bone. When human blood monocytes were co-cultured with these cells, multinucleated giant-cell formation of monocytes was induced. Intriguingly, even when a filter (pore size: 0.45 microm) was interposed between monocytes and the spindle-shaped cells, polykaryocytes also appeared. These multinucleated giant cells were positive for tartrate-resistant acid phosphatase, expressed calcitonin receptor, and showed bone-resorption activity, characteristics of osteoclast-like cells. These findings indicate that soluble factors secreted from these cells play an important role in osteoclast-like cell formation from blood monocytes. These data additionally suggest that these cells support osteoclast-like cell formation in giant-cell tumors of bone. The cells also expressed mannose receptor, fibronectin, receptor activator of nuclear factorkappaB, and several cytokine mRNAs, including interleukin-6, receptor activator of nuclear factorkappaB ligand/osteoclast differentiation factor/osteoprotegerin ligand, and macrophage colony-stimulating factor. However, all of these molecules except receptor activator of nuclear factorkappaB ligand mRNA could also be detected in control HeLa and CV-1 cells. Although the soluble receptor activator of nuclear factorkappaB ligand has not been found under physiological conditions, it is possible that it is cleaved by cellular proteases and the truncated receptor activator of nuclear factorkappaB is released from cells. Identification of the soluble factors capable of inducing osteoclast formation from blood monocytes is a pressing problem to be solved.

CKbeta-8 [CCL23], a novel CC chemokine, is chemotactic for human osteoclast precursors and is expressed in bone tissues

We have previously demonstrated that a tartrate-resistant acid phosphatase (TRAP)-positive subpopulation of mononuclear cells isolated from collagenase digests of human osteoclastoma tissue exhibits an osteoclast phenotype and can be induced to resorb bone. Using these osteoclast precursors as a model system, we have assessed the chemotactic potential of 16 chemokines. Three CC chemokines, the recently described CKbeta-8, RANTES, and MIP-1alpha elicited significant chemotactic responses. In contrast, 10 other CC chemokines (MIP-1beta, MCP-1, MCP-2, MCP-3, MCP-4, HCC-1, eotaxin-2, PARC, SLC, ELC) and 3 CXC chemokines (IL-8, GROalpha, SDF-1) were inactive. None of these chemokines showed any chemotactic activity for either primary osteoblasts derived from human bone explants or the osteoblastic MG-63 cell line. The identity of the osteoclast receptor that mediates the chemotactic response remains to be established. However, all three active chemokines have been reported to bind to CCR1 and cross-desensitization studies demonstrate that RANTES and MIP-1alpha can partially inhibit the chemotactic response elicited by CKbeta-8. CKbeta-8, the most potent of the active CC chemokines (EC(max) 0.1-0.3 nM), was further characterized with regard to expression in human bone and cartilage. Although expression is not restricted to these tissues, CKbeta-8 mRNA was shown to be highly expressed in osteoblasts and chondrocytes in human fetal bone by in situ hybridization. In addition, CKbeta-8 protein was shown to be present in human osteophytic tissue by immunolocalization. These observations suggest that CKbeta-8, and perhaps other chemokines, may play a role in the recruitment of osteoclast precursors to sites of bone resorption.

Development and characterization of a human in vitro resorption assay: demonstration of utility using novel antiresorptive agents

A human in vitro resorption assay has been developed using osteoclastoma-derived osteoclasts and used to evaluate novel antiresorptive agents including antagonists of the alphavbeta3 integrin, and inhibitors of cathepsin K and the osteoclast ATPase. The potency of novel compounds in the in vitro resorption assay correlates with functional assays for each class of inhibitor: the human alphavbeta3-mediated cell adhesion assay for the vitronectin receptor antagonists (r2 = 0.82), the chick osteoclast vacuolar ATPase enzyme assay for the H+-ATPase inhibitors (r2 = 0.77) and the recombinant human cathepsin K enzyme assay for the cathepsin K inhibitors (r2 = 0.80). Cell suspensions, rich in osteoclasts, are prepared by collagenase digestion of the tumor tissue. These cells can be stored long-term in liquid nitrogen and upon thawing maintain their bone-resorbing phenotype. The cryopreserved cells can be cultured on bovine cortical bone for 24-48 h and resorption can be measured by either confocal microscopy or biochemical assays. The resorptive activity of osteoclasts derived from a number of tumors can be inhibited reproducibly using a number of mechanistically unique antiresorptive compounds. In addition, the measurement of resorption pits by laser confocal microscopy correlates with the release of type I collagen C-telopeptides or N-telopeptides, as measured by enzyme-linked immunosorbent assay. Resorption can be measured reproducibly using a 48-h incubation of osteoclasts on bone slices, or a 24-h incubation with bone particles. This in vitro human osteoclast resorption assay provides a robust system for the evaluation of inhibitors of osteoclastic function that may be developed for the treatment of metabolic bone diseases such as osteoporosis.

Inhibition of avian osteoclast bone resorption by monoclonal antibody 121F: a mechanism involving the osteoclast free radical system

Osteoclasts generate high levels of superoxide anions during bone resorption that contribute to the degradative process, although excessive levels of this free radical may be damaging. One mechanism for their removal is via superoxide dismutase (SOD), a protective superoxide scavenging enzyme. We have previously described a novel developmentally regulated 150 kDa plasma membrane glycoprotein of avian osteoclasts which is reactive with the osteoclast-specific monoclonal antibody (Mab) 121F and is related immunologically, biochemically, and in protein sequence to mitochondrial Mn2+/Fe2+ SOD. We hypothesized that this unusual osteoclast surface component may be involved in protection against superoxides generated during active bone resorption. Increasing concentrations of monovalent Fab fragments prepared from Mab 121F, but not those from another antiosteoclast Mab designated 29C, markedly inhibited both bone particle and bone pit resorption by avian osteoclasts, while reducing tartrate-resistant acid phosphatase activity and causing the morphological contraction of osteoclasts on bone. Thus, the SOD-related membrane antigen may be essential for osteoclast bone resorption. Osteoclast superoxide production, monitored kinetically by cytochrome c reduction and histochemically by nitroblue tetrazolium reduction staining, was significantly greater in the presence of 121F, but not 29C, Fab treatment. Furthermore, the release of another free radical known as nitric oxide, which is produced by osteoclasts, can scavenge superoxides, and acts to potently inhibit osteoclast bone resorption, was dose-dependently increased by 121F Fab in resorbing osteoclast cultures. Therefore, Mab 121F binding may block the potential protective function of the osteoclast plasma membrane SOD-related glycoprotein, leading to a rapid elevation of superoxide levels and a subsequent rise in osteoclast nitric oxide release, feedback messages which may be sensed by the osteoclast as signals to cease active bone resorption.

The new partnership of genomics and chemistry for accelerated drug development

Genomics and combinatorial chemistry are two methods that are revolutionizing drug discovery efforts. Analysis of gene sequences allows identification of novel proteins which are potential therapeutic targets. Recent advances relate to the rate of gene sequencing and data handling resulting from the enormous flow of new gene sequences. Cathepsin K, a cysteine protease involved in bone resorption, was recently identified from a bone cell cDNA library as a potential target for osteoporosis therapy. New sources of chemical agents will rely on advances in high throughput chemical synthesis and structure-based design.

Cloning and characterization of a novel integrin beta3 subunit

We have identified a novel integrin beta3 subunit, termed beta3C, from a human osteoclast cDNA library. The COOH-terminal sequence and 3'-untranslated region of the beta3C subunit differs from the previously reported beta3A (platelet) and beta3B (placenta) sequences, while the regions coding for the transmembrane and extracellular domains are identical. The beta3C cytoplasmic domain contains 37 amino acids, the last 17 of which are encoded by a novel exon located about 6 kilobase pairs downstream of exon 14 of the beta3A gene. HEK 293 cells were stably co-transfected with alphaV and either beta3C (HEKbeta3C) or beta3A (HEKbeta3A). The viability of HEKbeta3C cells was lower than that of HEKbeta3A cells, and HEKbeta3C cells in culture grew as clusters rather than as a monolayer. The novel cytoplasmic domain did not affect receptor binding affinity; both alphaVbeta3A and alphaVbeta3C isoforms exhibited high affinity binding to 125I-echistatin and cyclic and linear RGD peptides. However, in contrast to HEKbeta3A, HEKbeta3C cells failed to adhere to osteopontin, an alphaVbeta3 matrix protein. The data provide further support for the key role of the cytoplasmic domain of the beta3 integrin in cell adhesion and suggest a potential role for the beta3C integrin subunit in modulating cell-matrix interactions.

The radiographic stage of giant cell tumor related to stromal cells' proliferation. Tissue cultures in 13 cases

The clinical behavior of giant cell tumor is related to the radiological appearance. To test the hypothesis that in vitro proliferation of the neoplastic stromal cell population of giant cell tumors is related to the radiological appearance, this study was undertaken. A prospective analysis of the cells migrating from 13 consecutive tumors was conducted. Growth curves and population doubling-times (PDT) for first and fifth passages were calculated and alkaline phosphatase levels were measured and compared to preoperative radiographic staging. A strong negative correlation was found between PDT and the radiographic stage. Tumors in stages I and II (low aggressiveness) were found to have an average cell population doubling-time of 11 (SD 2.2) days, while those in stage III (high aggressiveness) showed a doubling-time of 6 (SD 2.2) days. Low alkaline phosphatase activity was noted in all cultures, a finding consistent with the putative preosteoblastic potential of these stromal cells. This putative origin is also indicated by the differentiation response to retinoic acid. The findings suggest that the in vitro proliferation of the mononuclear stromal cell population of giant cell tumors is related to the radiographic stage and may predict the clinical behavior of these tumors.

Bone-membrane interface in aseptic loosening of total joint arthroplasties

In 19 patients who underwent revision arthroplasty for aseptic loosening of total joint arthroplasty, specimens were taken at the time of operation to include the bone-membrane interface. In 16 (84%) of the specimens, sufficient visualization of the interface was possible to allow histologic interpretation. In 13 of these cases, there was prominent evidence of classic bone remodeling with osteoclast-mediated resorption and active new bone formation. These results suggest that the osteolysis in aseptic loosening is mediated through osteoclastic bone resorption and that the bone found in such areas is extremely active. The findings help to explain the efficacy of impacted morselized bone-graft in the treatment of bone lysis in aseptic loosening.

Purification and characterization of fully functional human osteoclast precursors

The identification and purification of human osteoclast precursors is essential to further our understanding of the mechanisms that control human osteoclast differentiation. Osteoclastoma tissue potentially provides a rich source of human osteoclast precursors, and in previous studies we have demonstrated the existence of a population of mononuclear cells within this tissue that is reactive with osteoclast-selective vitronectin receptor monoclonal antibodies. In this study, mononuclear cells expressing the vitronectin receptor, as defined by their ability to react with a murine monoclonal antibody to the beta 3 chain of the vitronectin receptor (87MEM1), were isolated from collagenase digests of osteoclastoma tissue using a fluorescence activated cell sorter. Based on their fluorescence signal and size, approximately 2-3% of the viable cells (typically 2 x 10(5)) were obtained and prepared for further phenotyping. The isolated cells demonstrated a number of phenotypic characteristics of osteoclasts: positive tartrate-resistant acid phosphatase (TRAP) activity, reactivity with human osteoclast-selective antibodies, expression of calcitonin receptors, cathepsin K (a novel osteoclast-selective cysteine proteinase) mRNA, and osteopontin mRNA and protein. These phenotypic characteristics were also detected in mononuclear cells within cryostat sections of the native osteoclastoma tissue as well as in resorption lacunae of sections of human bone. In contrast, isolated peripheral blood monocytes were negative for TRAP activity and osteopontin expression and, unlike the osteoclastoma-derived cells, demonstrated strong nonspecific esterase activity. Significantly, when the osteoclastoma-derived 87MEM1 positive cells were cocultured on whale dentine for 1-3 weeks with stromal cells, extensive resorption of the dentine surface was observed. This is the first demonstration of the purification of human osteoclast precursors. These cells provide an homogeneous cell population for studying cellular events that occur during human osteoclast differentiation.

Human osteoclastoma-derived stromal cells: correlation of the ability to form mineralized nodules in vitro with formation of bone in vivo

It has been suggested that the stromal element of human osteoclastomas contains osteoblastic cells. In this study, we demonstrate that osteoclast-depleted, passaged stromal cells express alkaline phosphatase and osteocalcin in vitro and form mineralized nodules under appropriate culture conditions. In addition, we describe a model in which severe combined immunodeficient (SCID) mice were used to support the differentiation of these putative human osteoblast progenitors in vivo. Lesions formed from human stromal cells were identified using the OKa blood group antigen and human procollagen type I antibodies. By 21 days, the lesion was a complete bone unit: a fully mineralized cortex, remodeling trabeculae, and a highly cellular marrow space. Stromal cells derived from six out of seven osteoclastomas produced identical lesions. Further studies have demonstrated that the capacity of the osteoclastoma-derived stromal cells to form bone in vivo and in vitro is passage dependent; early passages were osteogenic in both model systems, while later passages were not. In conclusion, we have developed a model in which the osteogenic nature of cells can be confirmed in vivo. Furthermore, human osteoclastoma-derived stromal cells provide a source of these osteogenic cells to study human osteoblast differentiation, both in vivo and in vitro.

Human osteoclasts, not osteoblasts, deposit osteopontin onto resorption surfaces: an in vitro and ex vivo study of remodeling bone

Osteopontin is a phosphorylated glycoprotein believed to be secreted by osteoblasts and deposited into the bone matrix to facilitate osteoclasts adhesion or to initiate osteoid mineralization. Previously we have presented contradictory evidence that osteoclasts express osteopontin mRNA in human remodeling bone. The aim of this study was to ascertain whether osteoclasts synthesize and deposit osteopontin in resorption lucunae. We characterized expression of osteopontin mRNA and protein expression in both intramembranous and endochondral ossification, as well as remodeling bone, in the human osteophyte. Osteopontin mRNA was expressed in osteoclast with tartrate-resistant acid phosphatase (TRAP) positivity within resorption lacunae. The osteoclasts and immediate resorption surfaces also expressed osteopontin. However, osteopontin mRNA and protein were weak (transient) or undetectable in osteoblasts at adjacent bone formation sites; no osteopontin expression was observed in the osteoid, although occasional reactivity was observed in osteocytes and the mineral-osteoid interface. In contrast, osteopontin was highly expressed in the osteoblasts and matrix of woven bone during intramembranous and endochondral ossification. The matrix expression correlated with mineralization; however, in some instances osteopontin deposition was observed prior to mineralization. Similarly, osteopontin expression was evident in cartilage matrix, solely at foci of mineralization. Chondroclasts expressed osteopontin mRNA and protein: the surfaces of resorbed calcified cartilage also expressed osteopontin. Abnormal, unmineralized matrices apparently lacked deposited osteopontin, but were nevertheless resorbed by osteoclasts; the osteoclasts and resorbed surfaces expressed no osteopontin protein. That osteoclasts are responsible for the deposition of osteopontin was confirmed in vitro, whereby resorption pits in whale dentine and bovine bone slices, produced by isolated human osteoclasts, contained deposited osteopontin. Osteopontin may facilitate the adhesion (or detachment) of the osteoclast to the bone surface. Alternatively, the possibility that osteopontin may act as a postresorptive signal to recruit osteoblasts, or to polarize and direct the mineralization of the formed osteoid, is discussed.

Osteoblasts and osteoclasts in adult human osteophyte tissue express the mRNAs for insulin-like growth factors I and II and the type 1 IGF receptor

Insulin-like growth factors (IGFs) are among the most abundant growth factors present in bone. In vitro, bone-derived cells both produce and respond to IGFs I and II, suggesting that these growth factors play an autocrine role in the regulation of bone turnover. In vivo, however, particularly in adult bone, their sites of expression have not been well documented. We have used, therefore, the technique of in situ hybridization to study the expression of the mRNAs for IGFs I and II and the type 1 IGF receptor in adult human osteophyte tissue. Throughout the developing osteophyte there was a strong association between osteogenesis and the expression of all three mRNA transcripts. The highest levels of expression were observed in active osteoblasts. Hybridization signals were weak or absent in flat cells lining quiescent surfaces and in cells of the bone marrow, including those that expressed alkaline phosphatase activity. Osteocytes and cells of the periosteum were negative. At sites of endochondral bone formation newly differentiated and hypertrophic chondrocytes expressed the mRNAs for IGFs and IGF receptor whereas cells of the perichondrium were negative. A striking finding of this investigation was that osteoclasts at sites of bone and calcified cartilage resorption expressed high levels of all three mRNA transcripts. These results support the hypothesis that locally produced IGFs are important regulators of bone formation. The differential expression of all three transcripts among cells of the osteoblast lineage suggests that IGFs may be involved in the maintenance of the mature osteoblast phenotype rather than in inducing the differentiation of marrow precursors or controlling the osteoblast-osteocyte transition.(ABSTRACT TRUNCATED AT 250 WORDS)

Are MG-63 and HOS TE85 human osteosarcoma cell lines representative models of the osteoblastic phenotype?

The aim of this study was to perform a systematic comparison of two widely used osteosarcoma cell lines and ascertain their relevance as experimental models for investigating osteoblast function. We have therefore compared growth, differentiated cell function, integrin expression and adhesive profiles of MG-63, HOS TE85, and human bone derived cells. Both osteosarcoma cell lines proliferated more rapidly than osteoblast-like cells with HOS cells exhibiting the shortest doubling time. HOS cells expressed higher levels of alkaline phosphatase than MG-63 cells under basal conditions but only MG-63 cells showed the increased enzyme activity following 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) administration, which is characteristic of bone derived cells. Osteocalcin was not detected in supernatants from any cells under basal conditions but levels produced by MG-63 cells on addition of 1,25(OH)2D3 were comparable with those of osteoblast-like cells. alpha 1, alpha 2, alpha 3, alpha 5, alpha V, and beta 1 integrin subunits were detected on all cells and there was no staining for alpha L, alpha M, beta 2, and beta 3. alpha 3 and beta 1 were the major subunits detected on MG-63, HOS, and bone derived cells but relative concentrations of other alpha subunits were dependent on cell type; alpha 4 and alpha 6 subunits could only be detected on osteosarcoma cell lines. Short term, serum-free cell adhesion assays showed that the three cell types adhered in a saturable manner to collagen I, fibronectin, and laminin.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoclonal antibodies with selective reactivity against osteoblasts and osteocytes in human bone

Monoclonal antibodies (MAb) may provide valuable tools for studying osteoblast differentiation. We therefore raised a panel of MAb reactive with cells of this phenotype using 1,25(OH)2D3-treated human trabecular osteoblast-like cells (HOBS) as the immunogen. Immunohistochemical studies on various tissues, including undecalcified cryostat sections of fetal and adult human bone, identified 11 bone cell-reactive MAb. Of these, 2 demonstrated particularly selective reactivities against osteocytes (OB/M) and osteoblasts (OB/L). These reactivities were also seen in developing bone from rat, rabbit, and marmoset. OB/L and OB/M demonstrated limited reactivity against a small number of human tissues from the extensive panel of substrates tested. Both MAb exhibited reactivity against discrete populations of cells in the large and small intestine. In addition, OB/L reacted with cells in the basal epidermis of skin and OB/M with cells in blood vessel walls. Both antibodies demonstrated reactivity against a variety of cultured osteoblast-like cell lines and other cultured cell types. These MAb may therefore provide a valuable means of studying osteoblast ontogeny.

The cell biology of bone

Bone remodelling and repair are accomplished by the co-ordinated activity of cells of the osteoclast and osteoblast lineages. Small changes in the balance between formation and resorption will, when magnified by repeated cycles, lead to significant reduction in bone mass and strength, ultimately resulting in fracture. This review focuses on the cellular features of bone remodelling and the known regulators of bone cell function. These include systemic and local factors, both soluble and contained within the complex extracellular matrix of bone.

Immunophenotype of multinucleated cells in giant cell lesions

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