NS knockdown cells are sensitized to QC-induced DNA damage and QC sensitizes OC cells to PARPi. (A) Alkaline COMET assay shows increase in DSDBs following QC treatment in both OVCAR5 NTC and NS KD cells. (B) Quantified tail moment from the COMET assay was represented ** (p < 0.001), *** (p < 0.0001), # (p < 0.00001). (C) Cell viability was assessed in both NTC and NS KD cells upon dose dependent Veliparib treatment using MTT assay. (D) Colony formation assays using OVCAR5 cells upon treatment with indicated concentrations of QC alone or in combination with Rucaparib was shown. * (p < 0.01), ** (p < 0.001), *** (p < 0.0001). (E) The combination index (CI) was plotted as a function of dose combination, with average CIs for the drug combination reported in panel. The additive isobole is depicted in this panel as a red straight line, with synergistic dose combinations labeled below the isobole. An average CI of 1 indicates an additive effect, CI < 1 a synergistic effect, and CI > 1 an antagonistic effect. (F) Cell viability assay for 48 h using OVCAR8 cells upon treatment with indicated concentrations of QC alone or in combination with Rucaparib was shown. * (p < 0.01), ** (p < 0.001), *** (p < 0.0001), **** (p < 0.00001). (G) The combination index (CI) was plotted as mentioned above. Abbreviations: QC: Quinacrine; NS: Nucleostemin; NTC: non-targeted control, sh_NS: shRNA-mediated NS downregulation; COMET: single cell gel electrophoresis assay.