Figure 1. PARP1 and CHK1 inhibitors interact to kill breast cancer cells. (A) Fulvestrant resistant MCF7F cells were treated with AZD2281 (1 μM), ABT888 (1 μM), NU1025 (10 μM), UCN-01 (50 nM) and AZD7762 (25 nM), and these agents in combination as presented in the panel. Cells were isolated 48h after exposure, and viability was determined using trypan blue exclusion. (n = 3 ± SEM) * p < 0.05 value greater than corresponding vehicle control. Inset blot: Cells were treated with vehicle (DMSO) or AZD7762 (25 nM); cells were isolated after 60 min and the phosphorylation of CDC25C determined. (B) BT474, MCF7 and MMTV-HER2 cells were treated with AZD2281 (1 μM), LY2603618 (1 μM) or the drugs in combination. Cells were isolated 24h after exposure, and viability was determined using trypan blue exclusion. (n = 3 ± SEM) * p < 0.05 value greater than corresponding vehicle control. Inset blot: BT474 cells were treated with AZD2281 (1 μM), LY2603618 (1 μM) or the drugs in combination. Cells were isolated 30 min after exposure and blotting performed to determine P-ERK and P-CHK1 levels. The fold change in P-ERK to total ERK and P-CHK1 to total CHK1 levels is presented. (C) BT474, MCF7 and MMTV-HER2 cells were treated with Rucaparib (1 μM), LY2603618 (1 μM) or the drugs in combination. Cells were isolated 24h after exposure, and viability was determined using trypan blue exclusion. (n = 3 ± SEM). * p < 0.05 value greater than corresponding vehicle control. (D) BT474 cells were infected with an empty vector virus (CMV) or viruses to express BCL-XL, dominant negative caspase 9 or c-FLIP-s. Twenty four h after infection cells are treated with vehicle (DMSO) or AZD2281 (1 μM) and LY2603618 (1 μM). Cells were isolated 24h after exposure, and viability was determined using trypan blue exclusion. (n = 3 ± SEM). # p < 0.05 value less than corresponding virus control. (E) BT474 cells were transfected with scrambled siRNA (siSCR, 20 nM) or an siRNA to knock down ATM expression. Lower Graph: 24h after transfection cells were treated with vehicle (DMSO) or with [UCN-01, 50 nM + AZD2281, 1 μM] or [AZD7762, 25 nM + AZD2281 1 μM]. Cells were isolated 48h after exposure, and viability was determined using trypan blue exclusion. (n = 3 +/− SEM). * p < 0.05 value greater than corresponding siSCR control. Upper blots: 24h after transfection cells were treated with vehicle (DMSO) or with [UCN-01, 50 nM] or [AZD7762, 25 nM]. Cells were isolated 30 min after exposure and blotting performed to determine P-ERK and P-CHK1 levels.