CD99 regulates neural differentiation of Ewing sarcoma cells through miR-34a-Notch-mediated control of NF-κB signaling.

Sarcomas are mesenchymal tumors characterized by blocked differentiation process. In Ewing sarcoma (EWS) both CD99 and EWS-FLI1 concur to oncogenesis and inhibition of differentiation. Here, we demonstrate that uncoupling CD99 from EWS-FLI1 by silencing the former, nuclear factor-κB (NF-κB) signaling is inhibited and the neural differentiation program is re-established. NF-κB inhibition passes through miR-34a-mediated repression of Notch pathway. CD99 counteracts EWS-FLI1 in controlling NF-κB signaling through the miR-34a, which is increased and secreted into exosomes released by CD99-silenced EWS cells. Delivery of exosomes from CD99-silenced cells was sufficient to induce neural differentiation in recipient EWS cells through miR-34a inhibition of Notch-NF-κB signaling. Notably, even the partial delivery of CD99 small interfering RNA may have a broad effect on the entire tumor cell population owing to the spread operated by their miR-34a-enriched exosomes, a feature opening to a new therapeutic option.

Prognostic significance of miR-34a in Ewing sarcoma is associated with cyclin D1 and ki-67 expression.

BACKGROUND: At diagnosis, identification of reliable biological indicators of prognosis to allow stratification of patients according to different risks is an important but still unresolved aspect in the treatment of Ewing sarcoma (EWS) patients. This study aimed to explore the role of miR-34A expression on prognosis of EWS patients. PATIENTS AND METHODS: Specimens from 109 patients with non-metastatic EWS treated at the Rizzoli Institute with neoadjuvant chemotherapy (protocols ISG/SSGIII, EW-1, EW-2, EW-REN2, EW-REN3, EW-PILOT) and 17 metastases were studied. Sixty-eight patients (62%) remained disease-free and 41 (38%) relapsed (median follow-up: 67 months, range 9-241 months). Expression of miR-34a and of some of its targets (cyclin D1, bcl-2, SIRT1 and YY1) was evaluated by qRT-PCR using TaqMan MicroRNA Assays and/or by immunohistochemistry on tissue microarrays from the same patients. RESULTS: High expression of miR-34a in localized tumors was significantly related to better event-free and overall survival (P = 0.004). Relevance of miR-34a was confirmed by using different calibrators (normal mesenchymal stem cells and different normal tissues). By multivariate Cox regression analysis, low miR-34a expression as well as nontotal necrosis and high levels of lactate dehydrogenase were all confirmed as independent risk factors associated with poor outcome. Expression of miR-34a was lower in metastases than in primary tumors. It inversely correlated with expression of cyclin D1 and Ki-67. CONCLUSIONS: By demonstrating its relationship with clinical outcome, we propose evaluation of miR-34a at diagnosis of EWS patients to allow early risk stratification. Validation of these results would nonetheless ultimately need a prospective assessment.

CD99 suppresses osteosarcoma cell migration through inhibition of ROCK2 activity.

CD99, a transmembrane protein encoded by MIC2 gene is involved in multiple cellular events including cell adhesion and migration, apoptosis, cell differentiation and regulation of protein trafficking either in physiological or pathological conditions. In osteosarcoma, CD99 is expressed at low levels and functions as a tumour suppressor. The full-length protein (CD99wt) and the short-form harbouring a deletion in the intracytoplasmic domain (CD99sh) have been associated with distinct functional outcomes with respect to tumour malignancy. In this study, we especially evaluated modulation of cell-cell contacts, reorganisation of the actin cytoskeleton and modulation of signalling pathways by comparing osteosarcoma cells characterised by different metastasis capabilities and CD99 expression, to identify molecular mechanisms responsible for metastasis. Our data indicate that forced expression of CD99wt induces recruitment of N-cadherin and ß-catenin to adherens junctions. In addition, transfection of CD99wt inhibits the expression of several molecules crucial to the remodelling of the actin cytoskeleton, such as ACTR2, ARPC1A, Rho-associated, coiled-coil containing protein kinase 2 (ROCK2) as well as ezrin, an ezrin/radixin/moesin family member that has been clearly associated with tumour progression and metastatic spread in osteosarcoma. Functional studies point to ROCK2 as a crucial intracellular mediator regulating osteosarcoma migration. By maintaining c-Src in an inactive conformation, CD99wt inhibits ROCK2 signalling and this leads to ezrin decrease at cell membrane while N-cadherin and ß-catenin translocate to the plasma membrane and function as main molecular bridges for actin cytoskeleton. Taken together, we propose that the re-expression of CD99wt, which is generally present in osteoblasts but lost in osteosarcoma, through inhibition of c-Src and ROCK2 activity, manages to increase contact strength and reactivate stop-migration signals that counteract the otherwise dominant promigratory action of ezrin in osteosarcoma cells.

Efficacy of and resistance to anti-IGF-1R therapies in Ewing's sarcoma is dependent on insulin receptor signaling.

Identification of patient selection criteria and understanding of the potential mechanisms involved in the development of resistance are crucial for an appropriate and successful design of clinical trials with anti-insulin-like growth factor (IGF)-1R therapies. Few Ewing's sarcomas are highly sensitive to IGF-1R targeting and understanding the reason why, may hold the secret to improve successful treatments. In this paper, we show that a major mechanism of resistance to highly specific inhibitors of IGF-1R, either antibodies or tyrosine kinase inhibitors may involve enhanced insulin receptor (IR)-A homodimer formation and IGF-2 production. Resistant cells are able to switch from IGF-1/IGF-1R to IGF-2/IR-A dependency to maintain sustained activation of AKT and ERK1/2, proliferation, migration and metastasis. These cells also showed higher proliferative response to insulin, in keeping with a switch towards insulin pathways sustaining proliferation and malignancy, rather than metabolism. Our findings demonstrate a role for IR-A in eliciting intrinsic and adaptive resistance to anti-IGF-1R therapies. Thus, we indicate that tumors with low IGF-1R:IR ratio are unlikely to greatly benefit from anti-IGF-1R therapies and that the efficacy of anti-IGF-1R therapies should be evaluated in relationship to the IR-A:IGF-1R ratio in cancer cells. Moreover, we provide evidences supporting IR-A as an important target in sarcoma therapy.

Clinical impact of the methotrexate resistance-associated genes C-MYC and dihydrofolate reductase (DHFR) in high-grade osteosarcoma.

BACKGROUND: Aims of this study were the validation of C-MYC involvement in methotrexate (MTX) resistance and the assessment of clinical impact of C-MYC and dihydrofolate reductase (DHFR) in osteosarcoma (OS). MATERIALS AND METHODS: The involvement of C-MYC in MTX resistance was validated with an antisense approach. C-MYC and DHFR protein levels at diagnosis were assessed by immunohistochemistry on series of patients treated with either a MTX-based protocol (IOR/OS-1; 72 patients) or with a standard four-drug regimen (ISG/SSG 1; 61 patients). RESULTS: Down-regulation of C-MYC significantly decreased the MTX resistance level of OS cells, demonstrating its causal involvement in this phenomenon. In clinical samples, a worse outcome was associated with increased levels of DHFR and C-MYC at diagnosis in the IOR/OS-1 patients and of C-MYC in the ISG/SSG 1 patients. CONCLUSIONS: Meanwhile the adverse clinical impact of DHFR overexpression appeared to be closely related to the relevance of MTX in the chemotherapeutic protocol, that of C-MYC overexpression was more general and not strictly MTX related. The assessment of C-MYC and DHFR at diagnosis, together with that of other known prognostic markers, can be considered for an early identification of subgroups of OS patients with higher risk of adverse outcome.

CD99 isoforms dictate opposite functions in tumour malignancy and metastases by activating or repressing c-Src kinase activity.

CD99 gene encodes two distinct proteins, produced by alternative splicing of CD99 gene transcript. Full-length CD99 isoform (CD99wt) is formed by an extracellular domain, followed by a transmembrane domain and a 36 amino-acid intracytoplasmic domain, which is partially deleted in the truncated, short form (CD99sh). A differential expression of these two CD99 molecules can lead to distinct functional outcomes in lymphocytes. To investigate the functional effects of CD99 molecules on malignancy, forced overexpression of the two CD99 isoforms was induced in osteosarcoma and prostate cancer cells. The two isoforms exhibited opposite functions: the major form dramatically inhibits anchorage-independent growth, anoikis resistance, migration and metastasis, whereas the CD99sh remarkably favours the phenomena. A mechanistic analysis of CD99-transfected osteosarcoma cells points to involvement of c-Src family kinase activity in regulating CD99 functions in malignancy. Ser168 residue of CD99 plays a pivotal role in the reversion of the malignant phenotype. Our findings highlight the involvement of CD99 in crucial processes of cancer malignancy, serving as a curtain raiser for this, so far neglected molecule. In addition, a dualistic role for the two CD99 isoforms was shown in agreement with what was observed for other cell adhesion molecules.

RNA interference as a key to knockdown overexpressed cyclooxygenase-2 gene in tumour cells.

Silencing those genes that are overexpressed in cancer and contribute to the survival and progression of tumour cells is the aim of several researches. Cyclooxygenase-2 (COX-2) is one of the most intensively studied genes since it is overexpressed in most tumours, mainly in colon cancer. The use of specific COX-2 inhibitors to treat colon cancer has generated great enthusiasm. Yet, the side effects of some inhibitors emerging during long-term treatment have caused much concern. Genes silencing by RNA interference (RNAi) has led to new directions in the field of experimental oncology. In this study, we detected sequences directed against COX-2 mRNA, that potently downregulate COX-2 gene expression and inhibit phorbol 12-myristate 13-acetate-induced angiogenesis in vitro in a specific, nontoxic manner. Moreover, we found that the insertion of a specific cassette carrying anti-COX-2 short hairpin RNA sequence into a viral vector (pSUPER.retro) greatly increased silencing potency in a colon cancer cell line (HT29) without activating any interferon response. Phenotypically, COX-2 deficient HT29 cells showed a significant impairment of their in vitro malignant behaviour. Thus, the retroviral approach enhancing COX-2 knockdown, mediated by RNAi, proved to be an useful tool to better understand the role of COX-2 in colon cancer. Furthermore, the higher infection efficiency we observed in tumour cells, if compared to normal endothelial cells, may disclose the possibility to specifically treat tumour cells without impairing endothelial COX-2 activity.

The molecular mechanisms responsible for resistance to ET-743 (Trabectidin; Yondelis) in the Ewing's sarcoma cell line, TC-71.

Identification of new active agents against sarcoma is considered an important challenge in medical oncology. ET-743 (Trabectidin; Yondelis) has recently emerged as the first active drug developed against sarcoma in the last two decades, with promising results especially against soft-tissue sarcoma and Ewing's sarcoma (ES). In this study, we analyzed the molecular mechanisms responsible for resistance to ET-743 in ES cells. Three resistant cell variants (TC/ET 3 nM, TC/ET 6 nM and TC/ET 12 nM) were obtained, showing 28-, 47- and 102-fold increase in ET-743 resistance. Cross-resistance to other drugs was analyzed. Comparative genomic hybridization and cDNA microarray technology were employed to characterize and compare the gene expression profile of two TC/ET variants with the parental cell line. TC/ET cells show a conventional multidrug resistance phenotype and P-glycoprotein overexpression was found to significantly contribute to ET-743 resistance. However, functional studies with the cyclosporine analogue, PSC-833, indicate that other mechanisms are involved in resistance to ET-743. The gene expression profile of TC/ET cells indicated, among up-regulated genes, an increase in expression of insulin-like growth factor receptor-I (IGF-IR) and one of its major intracellular mediators, insulin receptor substrate-1. Functional studies using a neutralizing antibody anti-IGF-IR confirmed involvement of this signaling pathway in resistance to ET-743. Simultaneous blockage of both P-glycoprotein and IGF-IR completely restored sensitivity to ET-743 in ES cells. Overall, these findings provide impetus for future studies testing the therapeutic value of new specific inhibitors of P-glycoprotein and IGF-IR, which could represent a concrete therapeutic option for ES patients refractory to conventional agents.

Reversal of multidrug-resistance using Valspodar (PSC 833) and doxorubicin in osteosarcoma.

High-grade osteosarcoma is an extremely aggressive neoplasm, where over 80% of patients present with life-threatening micrometastases at diagnosis. Systemic control of the disease is therefore critical for the treatment of these patients and neoadjuvant chemotherapy using various drugs, including doxorubicin (DXR), which has been demonstrated to be the most effective regimen. Multidrug resistance (MDR) to some anticancer agents, including DXR, mediated by the MDR1 gene product P-glycoprotein (Pgp), has been shown to be a major cause of chemotherapy failure in osteosarcoma. We analyzed the effect of a cyclosporine A derivate Valspodar (PSC 833) on MDR human osteosarcoma cells. We also evaluated Pgp expression in sporadic appendicular canine osteosarcoma. Moreover, dogs were treated with combined administration of DXR and PSC 833. Several blood samples were collected for the determination of DXR and PSC 833 levels. PSC 833 induced a complete reversal of the resistant phenotype at concentrations compatible with the clinical use. Pgp was present in 12/18 (66.6%) of the cases. At the time of DXR administration, adequate blood concentrations of PSC 833, to provide a complete MDR reversal, were obtained without clinical or laboratory findings of toxicity. Combination therapy with DXR and PSC 833 allowed a 30% decrease in DXR dose infusion with equivalent therapeutic exposure. The high incidence of Pgp expression in osteosarcoma confers to the study a rationale for an effective regimen based on down-modulation of MDR.

Effectiveness of Type I interferons in the treatment of multidrug resistant osteosarcoma cells.

P-glycoprotein overexpression is an important adverse prognostic marker for osteosarcoma (OS) patients, which is associated with higher risk for developing metastases as a consequence of the limited responsiveness to standard treatments of P-glycoprotein overexpressing OS cells. The use of cytokines has been advocated as a possible therapeutic approach to overcome multidrug resistance (MDR), being active on cell lines that are resistant to conventional drugs. In this study, we evaluated in vitro effects of interferons (IFNs) on MDR P-glycoprotein overexpressing OS cells. Type I IFNs, but not IFNgamma, showed tangible inhibitory effects on OS cell growth, which were higher in MDR cell lines compared to parental cells. The higher sensitivity of P-glycoprotein overexpressing cells to Type I IFNs correlates with higher expression of the activator of the transcription (STAT)-2 and (STAT)-3, two intracellular mediators of the IFNalpha and IFNbeta signaling pathways, whereas no differences were observed with respect to the expression or activation of the Type I IFN receptor and STAT-1. Exposure of OS MDR cells to Type I IFN decreased the expression of P-glycoprotein. This effect resulted in a significantly increased chemosensitivity of MDR cells to doxorubicin. Therefore, our data support the use of IFNalpha or IFNbeta in the treatment of osteosarcoma patients who overexpress P-glycoprotein in their primary tumors, and respond insufficiently to current therapeutic regimens.

Analysis of dihydrofolate reductase and reduced folate carrier gene status in relation to methotrexate resistance in osteosarcoma cells.

BACKGROUND: To evaluate the impact of dihydrofolate reductase (DHFR) and reduced folate carrier (RFC) genes on methotrexate (MTX) resistance in osteosarcoma cells in relation to retinoblastoma (RB1) gene status. MATERIALS AND METHODS: A series of human osteosarcoma cell lines-either sensitive or resistant to MTX-and 16 osteosarcoma tumour samples were used in this study. RESULTS: In U-2OS MTX-resistant variants, and in other RB1-positive cell lines, MTX resistance was associated with increased levels of DHFR and with a slight decrease of RFC gene expression. In Saos-2 MTX-resistant variants, and in another RB1-negative cell line, development of MTX resistance was associated with a decrease in expression of RFC, without any significant involvement of DHFR. In osteosarcoma clinical samples, amplification of the DHFR gene at clinical onset appeared to be more frequent in RB1-positive compared with RB1-negative tumours. CONCLUSIONS: Amplification of the DHFR gene may occur more frequently in the presence of RB1-mediated negative regulation of its activity and can be present at clinical onset in osteosarcoma patients. Simultaneous evaluation of RFC, DHFR and RB1 gene status at the time of diagnosis may become the basis for the identification of potentially MTX-unresponsive osteosarcoma patients, who could benefit from treatment protocols with alternative antifolate drugs.

Impact of IGF-I/IGF-IR circuit on the angiogenetic properties of Ewing's sarcoma cells.

The insulin-like growth factor receptor I (IGF-I)-mediated circuit is a major autocrine loop for Ewing's sarcoma (ES) cells, and plays a role the pathogenesis and malignancy of this tumor. IGF-I receptor (IGF-IR) has emerged as a good therapeutic site for ES patients. In this study, we analyzed the impact of strategies targeting the IGF-IR on the regulation of VEGFs, which are of fundamental importance in angiogenesis, and TGFbeta, CTGF and Cyr61, which are factors primarily involved in skeletal growth control and angiogenesis. IGF-I increases expression of VEGF-A, TGFbeta, CTGF and Cyr61 mRNA. However, only the modulation of VEGF-A expression appears to be mediated by IGF-IR. Functional assays on endothelial cells indicate a strict correlation between survival and proliferation of HUVECs and VEGF-A levels, confirming a major role for this factor in angiogenesis. Blockage of IGF-IR functions by neutralizing antibody or antisense strategies significantly reduced the expression and secretion of VEGF-A by ES cells, and supernatants of treated cells were unable to sustain the survival and proliferation of HUVECs. Analysis of the signaling mechanisms involved in constitutive or IGF-induced expression and secretion of VEGF-A indicated that PI3-K and MAPK signaling pathways are both required for VEGF expression and production in ES cells. Selective inhibitors LY294002 or PD98059 were highly effective in reducing the ability of ES cells to produce VEGF-A and stimulate survival and proliferation of HUVECs. Taken together, these findings add a new activity to the IGF-I repertoire in ES and highlight how disruption of IGF-IR functions may constitute an effective tool for the control of neovascularization in this tumor.

Simultaneous paired analysis of numerical chromosomal aberrations and DNA content in osteosarcoma.

Relatively little is known about the biologic relevance of numerical chromosomal changes in relation to DNA content in osteosarcoma. In this study, by using a series of human osteosarcoma cell lines, we standardized a method for the assessment, on the same nuclei specimen, of both specific chromosome copy numbers by fluorescence in situ hybridization (FISH) and the DNA content by static cytofluorometry or image cytometry. On the same cell lines, we also evaluated the DNA content by using flow cytometry and the chromosome number distribution by metaphase analysis. Comparison between these different methods showed that DNA ploidy level as determined by FISH or metaphase analysis is frequently lower than the ploidy pattern as defined by cytometric methods. By using comparative genomic hybridization, we were able to demonstrate that these discrepancies were due to the presence of several unbalanced chromosome aberrations, specifically gains and high-level amplifications, which affect the total DNA content with less effect on the total chromosome number. Thus, evaluation of DNA ploidy in osteosarcoma cells is needed for a correct interpretation of FISH or cytogenetic data concerning numerical chromosomal changes. Evaluation of tumor ploidy in a series of clinical samples demonstrated that in high-grade osteosarcoma, flow cytometry sometimes may give false results because of the presence of high proportions of contaminating, nonneoplastic cells that cannot be excluded from the flow cytometric assessment but that do not interfere with the evaluation of DNA ploidy by static cytofluorometry or image cytometry, in which only tumor cells are selected for the analysis. The possibility of using this method to evaluate, on the same nuclei sample, both specific chromosomal aberrations and DNA ploidy may allow a better determination of numerical chromosomal changes that may be relevant for the biologic behavior of osteosarcoma.

Inhibition of insulin-like growth factor I receptor increases the antitumor activity of doxorubicin and vincristine against Ewing's sarcoma cells.

Innovative treatment modalities are needed for Ewing's sarcoma (ES), a neoplasm with a disappointingly low survival rate despite the use of aggressive multimodal therapeutic approaches. We and others (D. Yee et al., J. Clin. Investig., 86: 1806-1814, 1990; K. Scotlandi et al., Cancer Res., 56: 4570-4574, 1996) have previously shown the existence and the pathogenetic relevance of an autocrine loop, mediated by the insulin-like growth factor-I receptor (IGF-IR), which is crucial for survival and proliferation of ES cells in vitro. Moreover, we reported that the IGF-IR-blocking monoclonal antibody (MAb), alphaIR3, as well as suramin, a drug that can interfere with growth factor by binding to the receptors, inhibited both the tumorigenic and the metastatic ability of ES cells in athymic mice. In this study, we analyzed whether agents that can block the IGF-IR-mediated loop are of value in association with conventional cytotoxic drugs for the design of more effective therapeutic regimens. Both alphaIR3 MAb and suramin treatment significantly increased the antitumor in vitro effects of doxorubicin and vincristine, two drugs with a leader action on ES. These findings were obtained by both simultaneous and sequential treatments. Analysis of the proliferation rate and of apoptosis revealed that alphaIR3 MAb and suramin significantly enhanced the G(1)-phase rate induced by doxorubicin, without substantially affecting doxorubicin-G(2)-M-blockage of cell cycle, and significantly increased the induction of apoptosis, which confirmed that the specific blockage of IGF-IR deprives ES cells of an important tool for the prevention of drug-induced apoptosis. Moreover, combination treatments of doxorubicin plus alphaIR3 MAb significantly increase the doxorubicin-induced impairment of the ability of ES cells to form colonies in soft agar. In conclusion, we showed that, in ES, the blockage of IGF-IR by a neutralizing MAb or by suramin may greatly potentiate the antitumor activity of conventional chemotherapeutic drugs.

CD99 engagement: an effective therapeutic strategy for Ewing tumors.

CD99 is a Mr 32,000 transmembrane molecule that shows a high level of expression on cells of the hemopoietic system as well as on Ewing tumor cells. Within the hematopoietic system, CD99 has been implicated in cell adhesion and cell death, participating in this way in the differentiation of T-cell precursors. In this study, we demonstrate that engagement of CD99 significantly inhibits the in vitro and in vivo growth ability of Ewing tumor cells by delivering an apoptotic stimulus and reducing the malignant potential of these cells. Moreover, we show that anti-CD99 monoclonal antibodies may be advantageously used in association with conventional anticancer agents. These results provide a novel entry site for therapeutic intervention, which may have application in the care of patients with Ewing tumor, and warrant additional studies to clarify the molecular mechanisms activated by CD99 engagement.

Identification of EWS/FLI-1 transcripts in giant-cell tumor of bone.

The EWS/FLI-1 fusion gene, resulting from a t(11;22) translocation, plays a key role in the pathogenesis of Ewing's sarcoma. We demonstrate the presence of EWS/FLI-1 hybrid transcripts also in giant-cell tumor, a bone neoplasm featuring intermediate characteristics between benign and malignant lesions. Chimeric products were detected by semi-nested PCR after 2 cycles of amplification in 13/15 cases of giant-cell tumor, and their presence was confirmed by Southern and Western blots and fluorescence in situ hybridization. Moreover, 3/8 primary cultures of giant-cell tumor showed the same type of hybrid transcript observed in the original tumor sample. Sequencing of PCR products confirmed the presence of EWS and FLI-1 sequences in these products. Detection of EWS/FLI-1 fusion transcripts in giant-cell tumor of bone provides a model for the study of the transforming mechanisms of the EWS/FLI-1 fusion gene in mesenchymal tumors.

Prognostic significance of nuclear accumulation of c-myc and mdm2 proteins in synovial sarcoma of the extremities.

We retrospectively analysed a group of primary tumours from 32 patients with synovial sarcomas of the extremities by using immunohistochemistry on paraffin-embedded tissue samples in order to investigate the prognostic significance of the nuclear accumulation of c-myc and mdm2 proteins. Nuclear positive immunostaining for c-myc or mdm2 proteins were revealed in 9/32 cases (28%) and in 6/30 cases (20%), respectively. Since c-myc protein appears to be a key factor for keeping cells in an active proliferative stage, we also analysed the growth compartment of each tumour by using the MIB1 monoclonal antibody, specific for Ki-67 antigen. A high MIB1 index was found in 8/31 cases (26%) but was not associated either with c-myc or mdm2 nuclear positivity. Analysis of clinical outcome was performed in a subgroup of 27 patients with a minimum follow-up of 24 months. Among the clinicopathologic parameters and the biological markers, only the nuclear accumulation of c-myc was significantly associated with a higher relapse rate (p = 0.03). Accordingly, survival analysis confirmed a trend toward a poor event-free survival rate and a worse outcome in c-myc-positive cases (p = 0.12). These data demonstrate that assessment of c-myc nuclear accumulation can be useful to identify high-risk subsets of patients with synovial sarcoma of the extremities.

Reversal of malignant phenotype in human osteosarcoma cells transduced with the alkaline phosphatase gene.

Alkaline phosphatases are a family of glycoproteins that are able to hydrolize various monophosphate esters at a high pH optimum. Liver/bone/kidney (L/B/K) alkaline phosphatase (ALP) is one of the four major isoenzymes that belong to this family. Apart from its role in normal bone mineralization, other functions of L/B/K ALP remain obscure, both in physiological and in neoplastic conditions, including the bone-forming tumor osteosarcoma. In this study, we transfected the U-2 OS osteosarcoma cell line, which does not show any basal expression of this enzyme, with the full-length gene of L/B/K ALP, and analyzed the in vitro and in vivo features of four transfectants showing different expression of L/B/K ALP. A reduced in vitro ability to invade Matrigel and to grow in a semi-solid medium, together with a lower tumorigenic and metastatic ability in athymic mice, was found to be associated with a high level of cell surface L/B/K ALP activity. Moreover, L/B/K ALP transfectants showed a reduced secretion of matrix metalloproteinase-9 enzyme. These findings indicate a loss of aggressiveness of osteosarcoma cells after the expression of L/B/K ALP on their surface and suggest a new role for this enzyme.

Murine model for skeletal metastases of Ewing's sarcoma.

Ewing's sarcoma shows a strong tendency to metastasize to the lungs or the skeleton, or both. A peculiar feature of the secondary involvement of bone with this tumor is that it may also appear in the absence of clinically evident lung metastases, both at clinical presentation and during the course of the disease. Although osseous metastases are critically relevant for prognosis, the pathogenesis of this peculiar feature of Ewing's sarcoma is poorly understood, partly due to the lack of appropriate experimental in vivo models. We show that the intravenous injection of TC-71 Ewing's sarcoma cells into athymic 4-5-week-old Crl/nu/nu (CD1) BR mice reproducibly colonizes specific sites of the skeleton in addition to the lungs and lymph nodes. The distribution and the morphologic appearance of these experimental bone metastases mimic the pattern of skeletal involvement observed in humans. This experimental model of bone metastasis of Ewing's sarcoma may be the basis for future studies aimed at understanding the pathophysiology and treatment of Ewing's sarcoma.

The expression of P-glycoprotein is causally related to a less aggressive phenotype in human osteosarcoma cells.

The relationship between P-glycoprotein expression and malignancy is controversial. We have recently found that, in osteosarcoma, multidrug resistance (MDR) is associated with a less aggressive behavior, both in vitro and in clinical settings. In this study, we evaluated whether P-glycoprotein overexpression has a cause-effect relationship with the reduced metastatic potential of MDR cells, or rather reflects a more complex phenotype. MDR1 gene-transfected osteosarcoma cell clones, showing different levels of P-glycoprotein expression, were analysed for their in vitro characteristics and their tumorigenic and metastatic ability in athymic mice. Apart from the different levels of P-glycoprotein, no significant change in the expression of surface antigens or in the differentiative features were observed in the MDR1 gene transfectants compared to the parental cell lines or control clones, obtained by transfection with neo gene alone. In contrast to controls, however, MDR1 transfectants showed a significantly lower ability to grow in semi-solid medium and were completely unable to grow and give lung metastases in athymic mice. These findings indicate that P-glycoprotein overexpression is causally associated with a low malignant potential of osteosarcoma cells, and open new insights on the role and functions of P-glycoprotein activity.