PARP1-IN-12 is a potent PARP1 inhibitor with an IC 50 of 2.99 nM. PARP1-IN-12 exhibits antiproliferative activity, can induce cell apoptosis and cause cycle arrest at G2/M phase. PARP1-IN-12 also can induce DNA double strand breaks (DSBs) in BRCA -deficient cells.