Effects of Notch1 silencing and of inhibition of p53 transcriptional activity on Nutlin-3–mediated cytotoxicity in leukemic cell lines. (A,B) OCI and SKW6.4 cells were either not transfected or transfected with control scrambled (scr) siRNA or Notch1 siRNA before treatment with Nutlin-3 (10 μM), as indicated. (C) SKW6.4 cells were preincubated either with control vehicle or with PFTα (25 μM) before treatment with Nutlin-3 (10 μM). Levels of Notch1 and p53 proteins were assessed by Western blot analysis of cell lysates; tubulin staining is shown as loading control. Representative examples of Western blot results of 3 independent experiments for each cell line are shown. After densitometric analyses, for each of the indicated experimental conditions, results were expressed as fold of Notch1 protein induction in Nutlin-3–treated cultures with respect to the untreated cultures. Data are reported as means ± SD of results from 3 independent experiments. In parallel, cell viability in Nutlin-3–treated cells was calculated as percentage with respect to the untreated cultures in each of the indicated experimental conditions. Data are reported as means ± SD of results from 3 independent experiments. A,B: *P < .05 with respect to either cells transfected with a scrambled (scr) control siRNA or cells not transfected. C: *P < .05 with respect to Nutlin-3–treated cells.