Role of PARP Trapping in Regulation of DSB Repair and PARP Inhibitor Sensitivity in Triple Negative Breast Cancers

Abstract

PARP inhibitors have exhibited clinical success in inherited breast cancers with mutations in the BRCA1/2 tumor suppressor genes. Novel PARPi have been shown to function not only by catalytic inhibition of PARP1/2 activity, but also by "trapping" PARP to sites of DNA damage. In this study, we investigated whether PARP catalytic inhibition versus trapping had distinct effects on regulation of DNA DSB repair in breast cancer cells, highlighting inhibitor efficacy. To test our hypothesis, we utilized breast cancer cell lines with stably integrated GFP-reporter plasmids designed to assess interchromosomal DSB repair activity. We showed combination PARPi/MMS led to increased PARP trapping, and overall resulted in decreased HR and increased ALT-NHEJ. Knockdown of PARP1 did not affect HR activity, but decreased the ALT-NHEJ activity in the PARPi/MMS combination. Our data shows that PARP1 is not the only signaling molecule for ALT-NHEJ, and that ALT-NHEJ may compensate for lack in HR activity.