Fractionated ionizing radiation exposure induces apoptosis through caspase-3 activation and reactive oxygen species generation

Background: Radiation therapy (RT) is a well established therapeutic modality for the treatment of solid tumors. In particular, post-operative RT is considered the standard treatment adjuvant to surgery since its ability to prolong median survival of patients with malignant astrocytoma has been shown; nevertheless the ionizing radiation (IR) treatment fails in a considerable number of astrocytoma patients. Materials and Methods: Using an ADF human astrocytoma cell line the molecular mechanisms involved in the DNA damage induced by fractionated irradiation (FIR) and single IR treatment have been investigated. Results: FIR and single IR treatment inhibited the growth of the ADF human astrocytoma cell line. FACS analysis revealed that FIR treatment, but not single IR treatment, induced growth inhibition associated with the induction of apoptosis. Apoptosis was related to caspase-3 activation and reactive oxygen species (ROS) generation. ROS formation depends on the up-regulation of the cytochrome P450 enzyme gene. On the contrary, 12.5 Gy induced necrotic cell death up-regulating the HSPD1, HSPCB, HSPCA and HSPB1 genes. Conclusion: FIR treatment induced cell death through caspase-3 and ROS-mediated apoptosis.