Effects of the PARP Inhibitor Niraparib on the Radiosensitivity of Human Lung and Cervical Cancer Cells

Abstract

DNA damage repair (DDR) initiated after DNA damage may lead to a decreased radiosensitivity of tumor cells or even radiation resistance. Previous studies indicate that PARP inhibitors block the repair of DNA single-strand breaks (SSBs), and unrepaired SSBs may continuously accumulate and form double-strand breaks (DSBs) that promotes tumor cell death. Studies have also shown that PARP inhibitors act synergistically with RT to inhibit DDR. In this study, we aim to investigate the effect of Niraparib, a clinically approved PARP inhibitor on the radiosensitivity of human lung and cervical cancer cells, and preliminarily explore the underlying mechanism. The human lung cancer cell line A549 and human cervical cancer cell line Siha were both treated with niraparib (for 1h), or X-ray (4Gy), or Niraparib (for 1h) combined with X-ray (4Gy). The effect was examined via measurements of cell proliferation by the cell counting kit-8 assay, and cell viability was detected by clone formation assays. Cell apoptosis and cell cycle distribution were investigated by flow cytometry. In human lung and cervical cancer cell lines, Niraparib combined with radiation therapy significantly inhibited cell proliferation. The proportion of apoptotic cells in cell lines treated with Niraparib plus radiation (the combination group) was significantly higher compared with control, radiation-only, and Niraparib-only groups. Additionally, the proportion of A549 cells in the G2/M phase was significantly increased in the combination group compared with the radiation-only group. The results support that PARP inhibitor Niraparib increases the radiosensitivity of tumor cells, promotes their apoptosis, and induces cell cycle redistribution. The possible mechanism is associated with the inhibition of radiation-induced DNA damage repair.