1997;388:300C4. NSCLC cellular models. Consistent with our observations, this drug combination also significantly reduces tumor growth 4, mean SD) (A, B). H1975, PC9 and A549 cells treated with 5, 50, 500 nM RO3280 or 2, 20, 200 ng/ml rhTRAIL for 24 hours were prepared for western blot analysis to determine PARP cleavage levels (C, D). We further investigated three of these cell lines with representative genotypes: PC9 cells containing a single epidermal growth factor receptor (EGFR) mutation, H1975 cells containing a double EGFR mutation and A549 cells harboring a K-Ras mutation. The apoptotic effect of rhTRAIL (2C200 ng/ml) and RO3280 (5C500 ng/ml) as single therapy was tested in the three NSCLC cell lines by examining poly (ADP-ribose) polymerase (PARP) cleavage. As shown in Figure ?Figure1C,1C, rhTRAIL induced PARP cleavage in a dose dependent manner in TRAIL-sensitive PC9 cells and TRAIL-resistant H1975 cells. Single treatment with rhTRAIL resulted in low PARP activity in A549 cells, the most resistant of the tested cell lines. Treatment with RO3280 induced PARP cleavage in H1975 and PC9 cells in a dose-dependent manner, but to a Tyrosol lesser extent in A549 cells (Figure ?(Figure1D1D). RO3280 in combination with rhTRAIL synergistically reduces cell viability in NSCLC cells Next, we examined whether Tyrosol we could increase the sensitivity of NSCLC cells to TRAIL-induced anti-tumor activity by testing a combination of rhTRAIL (20 ng/mL) and RO3280 (50 nM) in all five NSCLC cell lines. Statistical tests revealed in all cell lines a significant reduction of cell viability when cells were treated with the drug combination compared to single agent treatments (Figure ?(Figure2A2A). Open in a separate window Figure 2 Synergistic effect of RO3280 and rhTRAIL combined treatment in NSCLC cellsCells were cultured simultaneously with 50 nM RO3280 Tyrosol and 20 ng/ml rhTRAIL (A, B) and an increased concentration of RO3280 (nM) and rhTRAIL (ng/ml): 1) 0:0; 2) 0.05:0.02; 3) 0.5:0.2; 4) 5:2; 5) 50:20; 6) 500:200; 7) 5000:2000 (C). Cell viability was analyzed by MTS assays after 72 hrs incubation (A) or at indicated time points (4, mean SD) (B). The combination index/fraction affected curve was calculated with the Compusyn program (C). We further investigated this drug combination in a time-course experiment. H1975, PC9 and A549 cells were simultaneously treated with RO3280 (50 nM) and rhTRAIL (20 ng/ml) for 24, 48, 72, and 96 hours respectively. The result demonstrates that the combined treatment reduces cell viability in a time-dependent manner in the three cell lines (Figure ?(Figure2B2B). To ascertain the additive or synergistic nature of this drug combination, we calculated the combination index (CI) [32]. RO3280 (0.05C500 nM) was combined with rhTRAIL (0.02C200 ng/ml) at a constant ratio in H1975, PC9 and A549 cells. Cell viability was assessed after 72 hours and the CI and fraction affected curve was calculated using the Compusyn software. Synergistic effects were observed at IC50/ED50 in all cells, with strong synergism (CI = 0.1C0.3) in H1975 and very strong synergism (CI 0.1) in A549 cells respectively (Figure ?(Figure2C2C). RO3280 enhances TRAIL-mediated apoptosis in NSCLC Apoptotic activity was assessed by examining caspase-3 and PARP cleavage by western blot analysis. As shown in Figure ?Figure3A,3A, caspase-3 activity was increased in H1975, PC9 and A549 cells treated with the combination of RO3280 (50 nM) and rhTRAIL (20 ng/ml) compared to control and single agent exposure. A similar result was also observed for PARP, where the Rabbit Polyclonal to LAMA3 combination treatment increased PARP cleavage in all tested cells (Figure ?(Figure3A3A). Open in a separate window Figure 3 PLK1 inhibition by RO3280 increase TRAIL-induced apoptosis in NSCLC cellsH1975, PC9, and A549 cells were treated with a combination of RO3280 (50 nM).