(P 030) OSTEOSARCOMA PATIENT-DERIVED-XENOGRAFTS A RELEVANT MODEL TO STUDY CHEMOTHERAPEUTIC AND METASTATIC EVENTS

Objective: Osteosarcoma (OS) is the most common malignant bone tumor in the pediatric and young adults' population. Localized primary disease in the bone has been efficiently managed since the 1980 with the introduction of high-dose cytotoxic neo-adjuvant chemotherapy. Metastatic disease in the lungs, that develops despite selective pressure of treatment, is currently the most challenging aspect of the therapeutic management of OS patients. Almost no improvement has been introduced for these patients in the last two decades, and the 5-year survival rate remains dramatically low. Metastatic dissemination is nowadays the leading cause of death in osteosarcoma patients. In OS there are few spontaneous metastatic models and most transplantation models (patient-derived orthotopic xenografts, PDOX) are focused on primary disease, this paucity of human-derived relapse and metastatic models contributes to the slow advances in patients' care.

Methods: We sought to develop clinically relevant OS PDOXs from OS patients' biopsies, starting from tumor samples naïves of any treatment. The PDOXs models were engineered to express the Luciferase and then implanted orthotopically in immunocompromised mice. We applied fractionated high-dose chemotherapy to tumor-bearing mice using Doxorubicin, Cisplatin, and Methotrexate (MAP regimen). At the tumor volume cut-off of 0.5cm3, the hindlimb was amputated, and the mouse was monitored by BLI until the appearance of metastatic disease progression before being euthanized. Primary, relapses, and metastases are then profiled by next-generation sequencing at the bulk and single-cell level.

Results: Similarly to what is observed in patients, MAP chemotherapy efficiently reduces tumor growth but does not entirely prevent metastatic spreading. Some of the PDOXs OS tumors responded very well to chemotherapy before escaping the therapy and growing back, generating chemotherapy-resistant tumors that were amputated. The monitoring of these mice revealed the presence of macro-metastases in the lungs by BLI months after the implantation. Similarly to patients, the frequency of metastases is not significantly different between the treated and non-treated groups, indicating that chemotherapy does not induce an increase in distant metastases. MAP chemotherapy-treated mice have better overall survival and even achieve complete cure when compared to mice treated with surgery alone.

Conclusion: OS metastatic relapses can be modeled in vivo using PDOX in mice and fractionated, high-dose chemotherapy. Mice and humans show a similar rate of response or relapse. The collected macro-metastases samples are being molecularly profiled by RNAseq (bulk and single-cell) and Whole Exome Sequencing to identify the most promising candidates' driver genes of the metastatic and chemo-resistant OS. These models, close to OS clinical features will allow to better understand the metastatic spreading of primary OS under chemotherapy treatment.

1_Tumor growth OS PDX.pdf

2_Survival.pdf

3_ BLI whole mouse.pdf