PARP1 and cancer: While it is argued that for minor DNA damage, cancer cells activate PARP-1 to help in the cell survival by repairing the mild DNA lesions, for high-level DNA damage PARP-1 is overactivated and uses NAD+ as a donor of ADP ribose for ADP-ribosylation, driving the cell into an imbalance of NAD+/ATP ratio, NAD depletion and eventually resulting in an energy-deprived necrosis [8,52,53].