The microtubule stabilizer patupilone (epothilone B) is a potent radiosensitizer in medulloblastoma cells

Concurrent radiochemotherapy for medulloblastoma includes the microtubule disrupting agent vincristine; however, vincristine alone or as part of a combined treatment regimen is highly toxic. A major goal is therefore to replace vincristine with novel potent chemotherapeutic agents-in particular, with microtubule stabilizing and destabilizing compounds-with a larger therapeutic window. Here, we investigated the antiproliferative, cytotoxic and radiosensitizing effect of patupilone (epothilone B [EPO906]), a novel, non-taxane-related and nonneurotoxic microtubule-stabilizing agent in human medulloblastoma cell lines. The antiproliferative and cytotoxic effects of patupilone alone and in combination with ionizing radiation was determined in the 3 representative human medulloblastoma cell lines D341Med, D425Med, and DAOY. Patupilone alone effectively reduced the proliferative activity and clonogenicity of all medulloblastoma cell lines tested at picomolar concentrations (50-200 pM) and resulted in an at least additive anticlonogenic effect in combination with clinically relevant doses of ionizing radiation (2 or 5 Gy). Cell-cycle analysis revealed a sequential G2-M arrest and sub-G1 accumulation in a dose-and treatment-dependent manner after exposure to patupilone. In tumor xenografts derived from D425Med cells, a minimal treatment regimen with patupilone and fractionated irradiation (1 x 2 mg/kg plus 3 x 3 Gy) resulted in an extended tumor growth delay for the 2 single treatment modalities alone and a supra-additive treatment response for the combined treatment modality, with complete tumor regressions. These results demonstrate the potent efficacy of patupilone against medulloblastoma cell lines and indicate that patupilone represents a promising candidate to replace vincristine as part of a combined treatment strategy with ionizing radiation.