PARP deficiency causes hypersensitivity to Taxol through oxidative stress induced DNA damage

Taxol is an antitumor drug derived from the bark of the Pacific Yew tree that inhibits microtubule disassembly, resulting in cell cycle arrest in late G2 and M phases. Additionally, Taxol increases cellular oxidative stress by generating reactive oxygen species. We hypothesized that the inhibition of specific DNA repair machinery/mechanisms would increase cellular sensitivity to the oxidative stress capacity of Taxol. Initial screening using Chinese hamster ovary (CHO) cell lines demonstrated that base excision repair deficiency, especially PARP deficiency, caused cellular Taxol hypersensitivity. Taxane diterpenes-containing Taxus yunnanensis extract also showed hypertoxicity in PARP deficient cells, which was consistent with other microtubule inhibitors like colcemid, vinblastine, and vincristine. Acute exposure of 50 nM Taxol treatment induced both significant cytotoxicity and M-phase arrest in PARP deficient cells, but caused neither significant cytotoxicity nor late G2-M cell cycle arrest in wild type cells. Acute exposure of 50 nM Taxol treatment induced oxidative stress and DNA damage. The antioxidant Ascorbic acid 2 glucoside partially reduced the cytotoxicity of Taxol in PARP deficient cell lines. Finally, the PARP inhibitor Olaparib increased cytotoxicity of Taxol in wild type CHO cells and two human cancer cell lines. Our study clearly demonstrates that cytotoxicity of Taxol would be enhanced by inhibiting PARP function as an enzyme implicated in DNA repair for oxidative stress.