PARP inhibitor Olaparib increases the sensitization to radiotherapy in FaDu cells

Radioresistance causes a major problem for improvement of outcomes of patients treated with radiation. Targeting for DNA repair deficient mechanisms is a hallmark of sensitization to resistance. We tested whether Olaparib, a (poly) ADP-ribose polymerase (PARP) inhibitor, can sensitize the radioresistant FaDu cells to radiotherapy. Radioresistant FaDu cells, called FaDu-RR cells, were used as the radioresistant hypopharyngeal cancer models. The expression of PARP1 was detected in both FaDu and FaDu-RR cells. The role of Olaparib in radiosensitization was analysed with several assays including clonogenic cell survival, cell proliferation and cell cycle, and radioresistant xenograft. High expression of PARP1 had a significant effect on enhancing radioresistance in FaDu-RR cells compared with FaDu cells. After treatment of Olaparib, FaDu-RR cells showed significantly less and smaller surviving colonies, lower proliferation ability and G2/M arrest than those in the group without treatment. Moreover, Olaparib significantly reduced growth of tumours in FaDu-RR cell xenografts treated with ionizing radiation. Olaparib can significantly inhibit PARP1 expression and consequently has significant effects on radiosensitization in FaDu-RR cells. These results indicate that Olaparib may help individualize treatment and improve their outcomes of hypopharyngeal cancer patients treated with radiation.