Search

Osteosarcoma, the most common malignant primary bone tumor, is currently treated with chemotherapy and surgery. The effectiveness of chemotherapy is evaluated by means of histological analysis of tumor necrosis, known as "the Huvos score". However, 25% of the patients initially considered good responders will relapse. In our practice, strong tissue heterogeneity around the residual viable cells of the osteosarcoma is observed, but this is not taken into account by the Huvos score, as it is only an average. The objective is to determine whether heterogeneity in the osteosarcoma's microenvironment can play a role in the histological response to chemotherapy. Two complementary approaches have been developed: (i) the therapeutic response to several monotherapies (ifosfamide, cisplatin, doxorubicin) has been compared to tumor growth and the necrosis levels in different preclinical syngeneic osteosarcoma models, mimicking various microenvironments by injecting the tumor cells into subcutaneous, intra-muscular paratibial, or intra-osseous sites; (ii) a retrospective analysis was performed on patients' osteoblastic osteosarcoma biopsies. Tissue localization mapping of residual live tumor cell colonies was evaluated for potential correlation with overall survival. The results of the preclinical studies showed a difference in tumor growth depending on the osteosarcoma model, with a higher rate in bone sites compared to subcutaneous tumors. For the therapeutic response, a higher response to doxorubicin was observed in the intra-osseous model compared to the intra-muscular model for tumor growth (P = 0.013) and necrosis (P = 0.007). These data strongly suggest that the microenvironment plays a role in how osteosarcoma responds to chemotherapy. The retrospective analysis showed no significant survival difference between residual cell sites, although the soft tissues may be seen as a potential negative factor., Competing Interests: None.

Osteosarcoma, the most frequent malignant primary bone tumor in pediatric patients is characterized by osteolysis promoting tumor growth. Lung metastasis is the major bad prognosis factor of this disease. Zoledronic Acid (ZA), a potent inhibitor of bone resorption is currently evaluated in phase III randomized studies in Europe for the treatment of osteosarcoma and Ewing sarcoma. The beneficial effect of the liposomal form of Muramyl-TriPeptide-Phosphatidyl Ethanolamine (L-mifamurtide, MEPACT®), an activator of macrophage populations has been demonstrated to eradicate lung metastatic foci in osteosarcoma. The objective of this study was to evaluate the potential therapeutic benefit and the safety of the ZA and L-mifamurtide combination in preclinical models of osteosarcoma, as a prerequisite before translation to patients. The effects of ZA (100 μg/kg) and L-mifamurtide (1 mg/kg) were investigated in vivo in xenogeneic and syngeneic mice models of osteosarcoma, at clinical (tumor proliferation, spontaneous lung metastases development), radiological (bone microarchitecture by microCT analysis), biological and histological levels. No interference between the two drugs could be observed on ZA-induced bone protection and on L-mifamurtide-induced inhibition of lung metastasis development. Unexpectedly, ZA and L-mifamurtide association induced an additional and in some cases synergistic inhibition of primary tumor progression. L-mifamurtide has no effect on tumor proliferation in vitro or in vivo, and macrophage population was not affected at the tumor site whatever the treatment. This study evidenced for the first time a significant inhibition of primary osteosarcoma progression when both drugs are combined. This result constitutes a first proof-of-principle for clinical application in osteosarcoma patients.