Increased cure rate of glioblastoma using concurrent therapy with radiotherapy and arsenic trioxide

Patients with glioblastoma multiforme (GBM) do extremely poorly despite aggressive therapy with surgery, radiotherapy (RT), and chemotherapy. In an effort to increase the efficacy of therapy for GBM, we studied the efficacy of arsenic trioxide (ATO) combined with high-dose RT in GBM cells in vitro and GBM xenograft tumors in nude mice.

Human glioblastoma cell line SNB75 cells were irradiated in vitro with doses of 0-15 Gy with or without ATO. Clonogenic assays were used to generate radiation survival curves. Intracellular reactive oxygen species and apoptosis induced by ATO and RT were measured. The therapeutic efficacy of ATO alone, local tumor RT alone, and the combined therapy was tested in nude mice bearing established s.c. SNB75 tumors. A single RT dose of 20 Gy was administered locally to tumors. ATO at 10 mg/kg was injected i.p. 10 min after RT for the in vivo experiments.

Radiation survival curves of GBM SNB75 cells demonstrated that a dose of 0.2 microM ATO increased radiation-induced cell killing by 2 logs at 10 Gy. ATO at 1 microM decreased survival from 4 x 10(-2) after 7 Gy of RT alone to 4 x 10(-5). A time-course experiment demonstrated that the greatest level of cell killing occurred when ATO was administered immediately before or within 2 hours after RT. To test the therapeutic efficacy of this combined treatment regimen in vivo, nude mice with established SNB75 GBM tumors were treated with a single local tumor dose of 20 Gy of RT with or without ATO (10 mg/kg x two doses) administered weekly. Appropriate control groups were included as well. ATO alone did not inhibit tumor growth. RT at 20 Gy alone inhibited tumor growth by 45 days, with regrowth of tumors thereafter. The combination of RT and ATO resulted in complete regression of the tumors in 4 of 5 mice without tumor regrowth for up to 4 months. The fifth mouse in the combined treatment group had a 90% reduction in tumor size without progression during the 4-month follow-up period. Furthermore, ATO alone and in combination with RT did not produce any obvious signs of toxicity.

These results have demonstrated that ATO increases intracellular levels of reactive oxygen species, induces apoptosis, and enhances the radiation cell killing of GBM cells. RT combined with ATO was an effective treatment for GBM tumors in this preclinical model. These preclinical results are encouraging and provide a rationale for further study of ATO combined with RT for the treatment of GBM and other histologic types of brain cancer using a variety of RT schemes.