Estrogen Receptor-positive Breast Cancer Cells are Sensitized by Piperine to Chemo/Radio Therapy through Lowering the expression of a NHEJ repair protein DNA-PK

Abstract Background Gamma radiation(γ) and other DNA targeted compounds generate highly lethal DNA double-stranded breaks (DSBs) inducing the cells to undergo apoptosis. Non-homologous end joining (NHEJ), one of the primary DSB repair pathways, plays an important role in providing cancer cells resistance against radio/chemotherapeutic agents resulting in cancer progression and relapse. Downregulating DNA-PK, a key protein in NHEJ could result in the accretion of DSBs, thereby sensitizing the cells towards radiation. Methods Cytotoxicity assays, Clonogenic assays, DNA damage assays, Flowcytometry analysis, Confocal Microscopy, immunofluorescence, and Immunoblotting were carried out. Combinatorial index calculations were done using Compusyn Analysis and data analysis was done using one-way ANOVA and two-way ANOVA, where a p-value of ≤ 0.0001 was considered significant. Results Here we found that the treatment of MCF7 cells with piperine, lead to the accumulation of DSBs induced by γ-radiation through lowering DNA-PK complex (comprising of DNA-PKcs/Ku70/Ku80), by altering the estrogen receptor (ER) α /β ratio. Piperine lowered DNA-PK mediated NHEJ repair through its transcription factor, ERα. Upregulation of ERβ, a nuclear hormone transcription factor promoting tumor suppression positively correlated with lowered expression of ERα and DNA-PK marked by the accumulation of radiation-induced DSBs and DNA damage response, cell cycle arrest leading to the intrinsic pathway of apoptosis. Conclusion Breast Cancer cells may be sensitized to radiation by altering the expression of DNA-PKc Complex, a key dsDNA repair protein machinery through selective estrogen receptor modulation. This study proposes a new strategy for combating acquired radioresistance through estrogen receptor-mediated modulation of the NHEJ pathway.