Pretreatment with interferon-alpha radiosensitizes Daudi cells modulating gene expression and biomarkers.

BACKGROUND Interferon (IFN) potentiates cytotoxicity by X-ray irradiation. To elucidate the mechanism of this potentiation, the biological markers related to DNA damage and cell survival were studied. MATERIALS AND METHODS IFN-alpha-sensitive Daudi and its resistant cells were used. Survival after treatment was assessed by clonogenic assays. DNA breaks were studied by pulse-field gel electrophoresis (PFGE). Production of reactive oxygen metabolites was measured using flow cytometry. Messenger RNA and protein were examined by RT-PCR and immunoblot, respectively. RESULTS IFN-alpha treatment for 24 h before irradiation potentiated the sensitivity of Daudi cells to X-rays. This combination induced 50 kb DNA fragmentation and activated caspase-3 in Daudi cells. Pretreatment with IFN-alpha inhibited the production of reactive oxygen species by irradiation. IFN-alpha pretreatment down-regulated most of the double-strand break (DSB) repair-related mRNAs, but did not affect the repair of DSBs studied by PFGE. The induction and phosphorylation of p21(Cip1/WAF1) (p21) was prominently suppressed in cells pretreated with IFN-a. CONCLUSION Pretreatment with IFN-alpha potentiates the cytotoxic effects of X-rays. Inhibition of X-ray-induced p21 may cause the augmented sensitivity by IFN-alpha pretreatment.