Fig. 1Inhibitory effects of parthenolide (PT) and balsalazide on cell growth. HCT116 cells were exposed to the indicated concentrations of (A) balsalazide, (B) PT, or (C) 20 mM balsalazide and 10 or 20 µM PT for 24 h. The data represent the mean cell counts ± the standard error of the mean of three independent experiments. *P<0.05, †P<0.001, as compared to control and ‡P<0.05, as compared to PT-treated cells.
Fig. 2Apoptotic cell death was induced by parthenolide (PT) and balsalazide. (A) After treatment with PT and/or balsalazide for 24 h, cells were harvested and stained with annexin-V FITC/propidium iodide (PI). (B) Cell cycle modification induced by combination treatment. After treatment with PT and/or balsalazide for 24 h, cells were harvested, fixed, and stained with PI. The percentage of the population in sub-G1 is reported in each histogram and the total number of events analyzed for each condition was 10,000.
Fig. 3Down-regulation of nuclear factor-kappa B (NF-κB) signaling by parthenolide (PT) and balsalazide. (A) Nuclear and cytosolic protein extracts were prepared from HCT116 cells treated with PT, balsalazide, or PT and balsalazide for 24 h. Combined balsalazide and PT markedly suppressed nuclear translocation of the NF-κB p65 subunit and inhibitor of NF-κB alpha (IκB-α) phosphorylation. (B) Total protein extracts were prepared from HCT116 cells treated with PT (10, 20 µM), balsalazide (20, 40 mM), or both (10 µM PT plus 20 mM balsalazide) for 24 h. Combined balsalazide and PT dramatically suppressed p65 phosphorylation. Actin was used as the loading control.
Fig. 4Down-regulation of caspases by parthenolide (PT) and balsalazide. HCT116 cell lysates were prepared after treatment with PT, balsalazide, or PT and balsalazide for 24 h and then analyzed by western blotting with caspase-3 or caspase-8 antibodies. Combined treatment reduced the levels of full length caspase-3 and caspase-8. However, caspase-3 and caspase-8 did not change when cells were pre-treated with a pan-caspase inhibitor (Z-VAD-FMK). Actin was used as the loading control.
Fig. 5Levels of apoptosis-associated proteins following treatment with parthenolide (PT) and balsalazide. HCT116 cell lysates were prepared after treatment with PT, balsalazide, or PT and balsalazide for 24 h and analyzed by western blotting using B-cell lymphoma 2 (Bcl-2), B-cell lymphoma-extra large (Bcl-xL), Bid, Bcl-2-associated X protein (Bax), and cytochrome c antibodies. Actin was used as the loading control.