PARP1 and cancer: PARP2 is able to partially compensate for the DNA repair functions of PARP1 after knockout of PARP1, while a double knockout of PARP1 and PARP2 is lethal [8].The inhibitors that affect catalytic activity of both PARP1 and PARP2 are used in clinics for the treatment of cancers with aberrations in DNA damage repair mechanisms [9–11].