Bone formation in vitro and in nude mice by human osteosarcoma cells

Roles of bone morphogenetic protein signaling in osteosarcoma

PURPOSE

Since the original extraction of bone morphogenetic proteins (BMPs) from bovine bone, research interest and clinical use has increased exponentially. With this, a concomitant analysis of BMP expression in bone tumours has been performed. BMP ligands, receptors, and signaling activity have been observed in diverse benign and malignant bone tumours. However, the reported expression, function, and importance of BMPs in bone tumours, and specifically osteosarcomas, have been far from uniform. This review highlights recent advances in understanding the role of BMP signaling in osteosarcoma biology, focusing on the sometimes divergent findings by various researchers and the challenges inherent in the study of osteosarcoma.

METHODS

We performed a literature review of all studies examining BMP signaling in osteosarcoma.

RESULTS

Overall, multiple BMP ligands and receptors are expressed in most osteosarcoma cell lines and subtypes, although BMP signaling may be reduced in comparison with benign bone-forming tumours. Studies suggest that osteosarcomas with different lineages of differentiation may have differential expression of BMP ligands. Although significant disagreement in the literature exists, the presence of BMP signaling in osteosarcoma may impart a worse prognosis. On the cellular level, BMP signaling appears to mediate promigratory effects in osteosarcoma and chondrosarcoma cell types, possibly via interaction and activation of Integrin β1.

CONCLUSIONS

BMP signaling has clear biologic importance in osteosarcoma, although it is not yet fully understood. Future questions for study include assessing the utility of BMP signaling in prognostication of osteosarcoma and the potential modulation of BMP signaling for inhibition of osteosarcomagenesis, growth and invasion.

Observation of collagen fibrils produced by osteosarcoma cells using atomic force microscopy

The present study examined the three-dimensional process of collagen fibril formation in the human osteosarcoma cell line NOS-1 by conventional scanning electron microscopy (SEM) and atomic force microscopy (AFM). SEM images showed collagen fibril formation on the bottom of culture dishes after 1 week of culture. The collagen fibrils had diameters of 30-100 nm. The surfaces of individual fibrils had characteristic grooves and ridges with periodicities of 60-70 nm. AFM images showed that the newly formed collagen fibrils were 30-300 nm in diameter and possessed characteristic grooves and ridges with periodicities of 60-70 nm. The thicker collagen fibrils contained thinner (approximately 30 nm thick) subfibrils that ran in a helical direction along the long axis of the thicker fibrils. Furthermore, twisted structures of collagen fibrils, which possessed a characteristic rope-like structure, were also identified. The ultrastructure of the collagen fibrils was clearly imaged in liquid medium by AFM, and the process of collagen fibril assembly was successfully analyzed under conditions much closer to the physiological state than those afforded by transmission electron microscopy or SEM. AFM also provided a precise morphological measurement, particularly of the vertical distance, of collagen fibrils with nanometer-scale resolution in liquid conditions.

RUNX2 expression in developing human bones and various bone tumors

The heterozygous germline mutation of runt-related protein 2 (RUNX2) causes cleidocranial dysplasia. To clarify the involvement of RUNX2 in human osteogenesis, fetal bones and various bone tumors were immunohistochemically examined. During both membranous and endochondral ossification in the fetus (n= 8), RUNX2 was expressed not only in osteoblastic cells but also in surrounding mesenchymal cells and early stage chondrocytes. Such an expression pattern was recapitulated in bone tumors: RUNX2 was unequivocally expressed in osteosarcoma (n= 20) and fibrous dysplasia (n= 10), regardless of the site of occurrence, cell morphology or amount of neoplastic osteoid. RUNX2 expression was limited to less differentiated cells in chondrogenic tumors (n= 20). We further analyzed whether RUNX2 expression was regulated by bone morphogenetic protein-2 (BMP-2), which is critical for osteoblastic differentiation. With real-time polymerase chain reaction, the RUNX2 mRNA level was correlated with BMP-2 mRNA level, and both levels were significantly higher in three osteosarcoma cell lines than in three chondrosarcoma cell lines. With treatment of recombinant BMP-2, the RUNX2 mRNA level was significantly altered in these cell lines. RUNX2 expression is constitutive in developing and neoplastic human osteogenesis, and is most likely to be regulated by BMP-2.

The influence of elementary silver versus titanium on osteoblasts behaviour in vitro using human osteosarcoma cell lines

Purpose. The antimicrobial effect of a silver-coated tumor endoprosthesis has been proven in clinical and experimental trials. However, in the literature there are no reports concerning the effect of elementary silver on osteoblast behaviour. Therefore, the prosthetic stem was not silver-coated because of concerns regarding a possible inhibition of the osseointegration. The aim of the present study was to investigate the effect of 5–25 mg of elementary silver in comparison to Ti-6Al-4V on human osteosarcoma cell lines (HOS-58, SAOS). Methods. Cell viability was determined by measuring the MTT proliferation rate. Cell function was studied by measuring alkaline phosphatase (AP) activity and osteocalcine production. Results. In the HOS-58 cells, the AP activity was statistically significant (P < 0.05) higher at a supplement of 5–10 mg of silver than of Ti-6 Al-4V at the same doses. For both cell lines, a supplement above 10 mg of silver resulted in a reduced AP activity in comparision to the Ti-6 Al-4V group, but a statistically significant difference (P < 0.05) was observed at a dose of 25 mg for the SAOS cells only. At doses of 20–25 mg in the HOS-58 cells and 10–25 mg in the SAOS cells, the reduction of the proliferation rate by silver was statistically significant (P < 0.05) compared to the Ti-6 Al-4V supplement. Discussion. In conclusion, elementary silver exhibits no cytotoxicity at low concentrations. In contrast, it seems to be superior to Ti-6 Al-4V concerning the stimulation of osteogenic maturation at these concentrations, whereas at higher doses it causes the known cytotoxic properties.

Behavior of two osteoblast-like cell lines cultured on machined or rough titanium surfaces

BACKGROUND

Two osteosarcoma-derived cell lines have been extensively used to investigate the biological events occurring on titanium surfaces: MG63 and Saos-2. However, the behavior of the two lines on different titanium surfaces has never been compared.

AIM

The aim of the present study was to compare the behavior of MG63 and Saos-2 cells on two different titanium surfaces, machined and rough (sandblasting and acid-etched). We compared cell proliferation and morphology, alkaline phosphatase (ALP) activity and secretion of osteocalcin (OC).

RESULTS

The most pronounced difference between the two cell lines was that ALP activity in the Saos-2 cells was 10-fold higher than in the MG63 cells. The proliferation rate of the MG63 cells was much higher than that of the Saos-2 cells at all the tested cell concentrations. MG-63 cells, but not Saos-2 cells, grown on rough surface titanium proliferated more rapidly than cells grown on machined surfaces. Morphological analysis revealed that Saos-2 cells and cells grown on the rougher surface, displayed a more mature phenotype. The level of OC secreted by the Saos-2 cells, but not the MG63 cells, were higher on the rough surface than on the machined surface.

CONCLUSIONS

This study shows that Saos-2 cells exhibit a more mature osteoblast phenotype, compared with that of MG63 cells, rendering them a good candidate for an in vitro model of osseointegration.

Bone morphogenetic proteins in bone tumors

Bone morphogenetic proteins (BMPs), inducers of ectopic bone formation in vivo, are present in a number of osteosarcomas. BMPs are responsible for reactive bone formation, including periosteal reactions by normal osteoblasts, rather than production of tumorous osteoid by tumor cells. Osteosarcomas producing BMPs contain less-differentiated mesenchymal cells, resulting in a poorer prognosis for those patients. BMPs are also expressed in malignant fibrous histiocytomas (MFHs) of bone and dedifferentiated chondrosarcomas exhibiting undifferentiated features. However, BMPs in MFH do not show any osteoinductive activity in vivo, suggesting that those BMPs may be inactive forms and have additional functions unrelated to bone formation. Among benign bone tumors, BMPs are expressed in osteoid osteomas or osteoblastomas and effect reactive bone formation such as a surrounding sclerosis. BMPs and a BMP receptor (BMPRIB) are also detected in the cartilage cap in osteochondroma, suggesting that BMP signaling via BMPRIB might be involved in the pathogenesis of osteochondroma. Clinically, BMPs have utility as diagnostic and prognostic markers for characterizing the stage of differentiation of mesenchymal cells and mesenchymal tumors, and they may be of value in predicting the prognosis of sarcoma patients. This article reviews the accumulated information on BMPs in bone tumors, including the most recent findings, and discusses the biological and clinical significance of BMPs in bone tumors.

Sclerosing epithelioid fibrosarcoma with der(10)t(10;17)(p11;q11)

Sclerosing epithelioid fibrosarcoma is a recently described, rare mesenchymal neoplasm. We report a case of sclerosing epithelioid fibrosarcoma that occurred in the lower leg of a 48-year-old man. The karyotype of the tumor exhibited der(1)t(1;10)(p31;p11), der(10)t(10;17)(p11;q11), and der(17) t(11;17)(?;q11). Rearrangement of 10p11 was also found in one previous reported case of this uncommon tumor.

Regulation of fibroblast growth factor 2 and fibroblast growth factor receptors by transforming growth factor beta in human osteoblastic MG-63 cells

Fibroblast growth factor 2 (FGF-2) and its receptors (FGFRs) are important regulators of bone cell function. Although FGF-2 is a major modulator of bone cell function, its expression and regulation in human osteoblasts have not been investigated. We examined FGF-2 messenger RNA (mRNA) expression and regulation in the human osteosarcoma MG-63 cells. Northern analysis revealed that MG-63 cells expressed FGF-2 mRNA transcripts of 7, 4, 2.2, and 1.3 kilobases (kb). In the absence of serum, treatment with transforming growth factor beta (TGF-beta; 0.1-10 ng/ml) increased all FGF-2 mRNA transcripts. Maximal increase was seen with 1 ng/ml of TGF-beta. TGF-beta increased FGF-2 mRNA expression within 2 h and this was sustained for 24 h. Phorbal myristate acetate (PMA; 1 microM) also increased FGF-2 mRNA at 6 h. Time course studies showed that TGF-beta did not significantly alter FGFR1 or FGFR2 mRNA expression in MG-63 cells. Western blotting with anti-human FGF-2 revealed that MG-63 cells synthesize three isoforms of FGF-2 protein of approximately 18, 22/23, and 24 kDa, which were increased after either 6 h or 24 h of treatment with TGF-beta. Increased FGF-2 mRNA and protein expression in response to TGF-beta was markedly reduced by the protein kinase A (PKA) inhibitor H-89. Immunogold labeling of MG-63 cells treated with TGF-beta showed increased labeling for FGF-2 and FGFR2 in the nuclei. In contrast, TGF-beta treatment significantly decreased FGFR1 labeling in the nuclei. These data show that TGF-beta regulates FGF-2 gene expression in human osteosarcoma cells. Furthermore, TGF-beta modulates the cellular localization of FGF-2 and its receptors.

A murine osteosarcoma cell line with a potential to develop ossification upon transplantation

An osteosarcoma cell line has been established from a soft tissue tumor that occurred spontaneously in a BALB / c mouse. This cell line showed ossification when transplanted into syngeneic mice. To examine the mechanism of bone formation, the expression of mRNAs for osteoblastic and chondroblastic markers and factors associated with ossification has been investigated. In culture, the cells exhibited a spindle shape in the growth phase, but had a polygonal shape in the stationary phase. Reverse transcription-polymerase chain reaction analysis showed that the cells expressed mRNAs for pro-alpha1(I) chain of type I collagen, alkaline phosphatase, osteopontin, osteocalcin, and core binding factor alpha1, suggesting differentiation into the stage of osteoblasts during the stationary phase. After transplantation, histological examination revealed small foci of pale blue material and basophilic networks that were scattered in the tumor tissues at one week. The former stained positive with alcian blue, suggesting a chondroid matrix. Pro-alpha1(II) chain of type II collagen mRNA was expressed at one week. A large part of tumors at two and three weeks consisted of basophilic networks, which stained positive via von Kossa's method, indicating a calcified woven bone. In situ hybridization analysis showed strong expression of osteopontin and osteocalcin mRNAs in tumor cells surrounding the bone matrix. Bone morphogenetic protein-6 and -7 mRNAs were detected in transplanted tumors, but not in cultured cells. These results suggest that the cell line has the properties of an osteoblastic lineage when cultured in vitro and has an ossifying ability through endochondral bone formation processes when transplanted in vivo.

Effects of bone morphogenetic protein-2 on human tumor cell growth and differentiation: a preliminary report

The effects of recombinant human bone morphogenetic protein-2 (rhBMP-2) on cell growth were studied in three human osteosarcoma cell lines, NOS-1, HuO9, and HuO-3N1; one human prostate cancer cell line, PC-3; and one human breast cancer cell line, OCUB-1M. The growth of these cell lines was not promoted by rhBMP-2 at concentrations of 50, 100, 250, and 500 ng/ml, as evaluated by colorimetric 3 (4,5-dimethyl-thiazol-2-yl)-2,5 diphenyl tetrazolium bromide (MTT) assay. Furthermore, the protein induced osteogenic differentiation, characterized by increased alkaline phosphatase activity, and increased production of type I collagen and gamma-carboxylated osteocalcin in NOS-1 cells. The results of this study may suggest the feasibility of using rhBMP-2 for the reconstruction of bone defects caused by malignant tumors, although the data are still preliminary and require further investigation.

Growth of collagen fibrils produced by human osteosarcoma cells: high-resolution scanning electron microscopy

To demonstrate three-dimensionally the process of the collagen fibril growth, the bottom of culture dishes with human osteosarcoma cells (NOS-1) and their extracts were examined by conventional scanning electron microscopy (SEM). Backscattered electron (BSE) imaging of SEM was also applied to the specimens, which were stained with phosphotungustic acid and uranyl acetate. Conventional SEM images showed several stages of collagen fibril assembly. Short collagen fibrils with tapered ends were distributed at the bottom of the dish just beneath and/or around the cultured cells; they were 1 microm long and 20-30 nm in diameter at the thickest middle portion. These fibrils were often twisted and united in a right helical direction, and consequently increased in length (5-10 microm) and diameter (more than 100 nm). In BSE images, the periodical bands stained with phosphotungstic acid and uranyl acetate were visualized throughout the individual fibrils. The banding pattern indicated that the polarity of the collagen molecules was unidirectional; namely, that all molecules were pointed in the same direction throughout the length of the fibrils.

Human osteosarcoma (OST) induces mouse reactive bone formation in xenograft system

To distinguish the origin of bone-forming cells in the osteosarcoma (OST) tumor inoculated into nude mice, we have developed a novel in situ hybridization technique. The system used digoxygenin (DIG) labeled DNA probes that encoded human specific repetitive gene, Alu, and mouse specific repetitive gene, mouse L1 (m-L1). The chondrogenic and osteogenic cells in the tumor had strongly positive signals for m-L1 probe without any signals for Alu probe. The expression of bone matrix proteins was also examined by in situ hybridization. The bone-forming cells were positive for mRNAs of mouse osteonectin, osteopontin, and osteocalcin relating to calcification during bone formation, while these were negative for human mRNAs of these bone matrix proteins. The OST cells in the tumor expressed the human bone morphogenetic proteins (BMPs) mRNAs by RT-PCR. These data indicated that the mouse cells, not the human sarcoma cells, are responsible for cartilage and bone formation in the OST tumor inoculated into nude mice, and we speculated that BMPs, at least in part, could play an important role in this ossification.

Clear cell chondrosarcomas arising from rare sites

Three cases are reported of clear cell chondrosarcoma arising from unusual sites: talus, rib and vertebra. Radiographically, two tumors showed osteolytic features and the vertebral tumor showed osteoplastic change. Histologically, all tumors consisted of clear cells that had a centrally placed nucleus surrounded by clear cytoplasm, osteoclast-like giant cells, areas of conventional chondrosarcoma, and various amounts of reactive bone. The tumor in the talus was initially diagnosed as benign chondroblastoma, but it recurred. The rib tumor showed marked cystic formation stimulating aneurysmal bone cyst. The osteoplastic radiographic feature in vertebral tumor was considered to be due to the abundant bone formation.