PARP1/BRD4-IN-2 is a potent and selective PARP1 and BRD4 inhibitor with IC 50 values of 197 nM and 238 nM, respectively. PARP1/BRD4-IN-2 inhibits DNA damage repair, arrests G0/G1 transition and induces apoptosis. PARP1/BRD4-IN-2 has anti-tumor activity in MDA-MB-468 xenograft mouse model. PARP1/BRD4-IN-2 can be used for researching triple-negative breast cancer (TNBC).