PARP1-IN-27 (Compound 9B) is the inhibitor for PARP1 and PARP2 , with IC 50 of 2.53 nM and 6.45 nM in cell SUM149PT. PARP1-IN-27 inhibits the proliferation of BRCA-mutated cancer cells SUM149PT, HCC1937 and Capan-1, with IC 50 of 0.62, 1.91 and 4.26 μM respectively. PARP1-IN-27 aggravates DNA double-strand breaks, increases ROS generation, arrests cell cycle at G2/M phase, and induces apoptosis in SUM149PT.