The development of multidisciplinary therapy for Ewing’s sarcoma (ES) has increased current long-term survival rates to greater than 50%, but only 20% for patients with clinically detectable metastases at diagnosis, or not responding to therapy or with disease relapse. Anti-bone resorption bisphosphonates (BP) may represent promising adjuvant molecules to limit the osteolytic component of bone tumor.

The combination of zoledronic acid (ZOL) and ifosfamide (IFOS) or mafosfamide (MAFOS) was studied in ES models and in 8 human cell lines all expressing the EWS-FLI1 fusion gene. Cell proliferation, viability, apoptosis and cell cycle distribution were analysed. The ES models were developed in immuno-deficient mice by inoculating the human tumor cells either intra-muscular (soft tissue tumor development) or intra-osseous (bone tumor development). Mice were then treated with ZOL (100 μg/kg twice or 4 times/week) and/or ifosfamide (IFOS 30 mg/kg, one to 3 sequences of 3 injections).

All the cell lines studied were more or less sensitive to ZOL and MAFOS in terms of cell proliferation. Both drugs induced cell cycle arrest respectively in S and G2M phase and final apoptosis associated to caspase 3 activation. In vivo, ZOL had no effect on soft tumor progression although it dramatically inhibits ES development in bone site. When combined with IFOS, ZOL exerts synergistic effects in the soft tissue model leading to a similar quantitative inhibitory effect when associated with 1 sequence IFOS as compared to 3 sequences of IFOS alone. In the bone model, ZOL prevents tumor recurrence observed with a lonely sequence of IFOS.

Combination of ZOL with conventional chemotherapy showed promising results in both ES models and could allow the clinicians to diminish the doses of chemotherapy. Moreover, as ZOL and MAFOS induce cell death by different pathways, respective resistance may be circumvented.