PARP1 and breast cancer: AZD-2461 can inhibit PARP-1, PARP-2, and PARP-3 with respective IC50 values of 5 nM, 2 nM, and 200 nM. It can also inhibit SSB repair in human A549 cells at a dose of 500 nM, and can cause resistance and expression of high levels of P-gp in BRCA2-deficient KB2P3.4 murine breast cancer cells. It also exhibits cytotoxicity when used to treat BT-20 cells at concentrations of 5–50 μM, increasing the frequency of these cells in the S and G2 phases of the cell cycle while having a limited effect on SKBr-3 cell cycle progression at doses of 5–20 μM