Cisplatin (cis-diamminedichloroplatinum, CDDP) is one of the most used drugs for osteosarcoma chemotherapy. By using a series of CDDP-resistant variants, which were established from the U-2OS and Saos-2 human osteosarcoma cell lines, we found that CDDP resistance was mainly associated with the increase of both the intracellular level and enzymatic activity of glutathione S-transferase P1 (GSTP1). On the basis of these findings, we evaluated the clinical effect of GSTP1 in a series of 34 high-grade osteosarcoma patients and we found that the increased expression of GSTP1 gene was associated with a significantly higher relapse rate and a worse clinical outcome. These indications prompted us to assess the in vitro effectiveness of 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX), a promising new anticancer agent that is a highly efficient inhibitor of GSTP1. NBDHEX was tested on a panel of 10 human osteosarcoma cell lines and 20 variants of the U-2OS or Saos-2 cell lines that were resistant to CDDP, doxorubicin, or methotrexate. NBDHEX proved to be very active on the vast majority of these cell lines, including those with higher GSTP1 levels and enzymatic activity. Drug combination studies showed that NBDHEX can be used in association with CDDP and provided useful information about the best modality of their combined administration. In conclusion, our findings show that GSTP1 has a relevant effect for both CDDP resistance and clinical outcome of high-grade osteosarcoma and that targeting GSTP1 with NBDHEX may be considered a promising new therapeutic possibility for osteosarcoma patients who fail to respond to conventional chemotherapy.

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On the basis of the information that has emerged so far, it can be predicted that in the next 5 - 10 years, new agents to be included in innovative treatment strategies for selected subgroups of high-grade OS patients may become available.

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The results of this study show that EMF can act in concert with IGF-I in stimulating PG synthesis in bovine articular cartilage explants. As this effect is not maintained in chondrocyte monolayers, the native cell-matrix interactions in the tissue may be fundamental in driving the EMF effects. These data suggest that in vivo the combination of both EMF and IGF may exert a more chondroprotective effect than either treatment alone on articular cartilage.

CD99 is a cell surface protein with unique features and only partly defined mechanisms of action. This molecule is involved in crucial biological processes, including cell adhesion, migration, death, differentiation and diapedesis, and it influences processes associated with inflammation, immune responses and cancer. CD99 is frequently overexpressed in many types of tumors, particularly pediatric tumors including Ewing sarcoma and specific subtypes of leukemia. Engagement of CD99 induces the death of malignant cells through non-conventional mechanisms. In Ewing sarcoma, triggering of CD99 by specific monoclonal antibodies activates hyperstimulation of micropinocytosis and leads to cancer cells killing through a caspase-independent, non-apoptotic pathway resembling methuosis. This process is characterized by extreme accumulation of vacuoles in the cytoplasmic space, which compromises cell viability, requires the activation of RAS-Rac1 downstream signaling and appears to be rather specific for tumor cells. In addition, anti-CD99 monoclonal antibodies exhibit antitumor activities in xenografts in the absence of immune effector cells or complement proteins. Overall, these data establish CD99 as a new opportunity to treat patients with high expression of CD99, particularly those that are resistant to canonical apoptosis-inducing agents.

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The effect of the glutathione transferase P1-1 (GSTP1-1) targeting has been investigated in both sensitive (U-2OS) and cisplatin-resistant (U-2OS/CDDP4 mg) human osteosarcoma cell lines. Despite the different enzyme's content, inhibition of GSTP1-1 by 6-(7-nitro-2,1,3-benzoxadiazol-4-ylthio)hexanol (NBDHEX) causes the activation of c-Jun N-terminal kinase (JNK) and apoptosis in both cell lines. However, different time courses of JNK activation and cell responses are observed. Whereas in the U-2OS/CDDP4 mg cell line drug treatment results in an early increase of caspase activity and secondary necrosis, in the U-2OS cells it mainly causes an early cell cycle arrest followed by apoptosis. In order to elucidate the action mechanism of NBDHEX we performed a proteomic investigation by label-free nLC-MS E . The high-throughput analysis associated with a bioinformatic tool suggested the involvement of the TNF receptor associated factor (TRAF) family in the cellular response to the drug treatment. We report experimental evidence of the interaction between GSTP1-1 and TRAF2 and we demonstrate that NBDHEX is able to dissociate the GSTP1-1 : TRAF2 complex. This restores the TRAF2 : ASK1 signaling, thereby leading to the simultaneous and prolonged activation of JNK and p38. These mitogenactivated protein kinases (MAPKs) mediate different effects: JNK is crucial for apoptosis, whereas p38 causes an increase in the p21 level and a concomitant cell cycle arrest. Our study shows that GSTP1-1 plays an important regulatory role in TRAF signaling of osteosarcoma and discloses new features of the action mechanism of NBDHEX that suggest potentially practical consequences of these findings.