PARP1 and cancer: This is called, “PARP trapping.” This is also the reason why PARPi is more destructive towards cancer cells than knocking out the PARP gene itself (Kim et al., 2020); on the other hand, PARPi can competitively bind to the NAD+ site, directly inhibit the activity of PARP1/2, and block the DNA repair process mediated by it, so that the SSB in DNA cannot be repaired and converted into DNA double-strand break (DSB).