BEZ235-induced apoptosis correlates poorly with chemosensitivity and occurs independently of p53 and the p53-regulated BH3-only proteins PUMA and NOXA. (A) Five independently derived Eμ-Myc lymphomas were cultured for 24 hours with 20 nM etoposide and analyzed for annexin-V/PI positivity. (To facilitate comparison with Figure 2, the lymphomas have been stratified from most to least BEZ235 sensitive [at 125 nM] from left to right). The unique identifier for each lymphoma is provided above the bar graph. “R” denotes primary etoposide resistance (defined as AC₅₀ [50% apoptosis concentration] < 20 nM at 24 hours). (B) Correlation of the percentage of cells undergoing apoptosis at 24 hours for an extended panel of lymphomas (n = 11) treated with 250 nM BEZ235 or 20 nM of etoposide (r, Pearson’s correlation coefficient). (C) Eμ-Myc lymphomas derived on a p53 null background (p53 null) or with previously characterized inactivating p53 mutations (p53 mutated [mut.]) were treated for 24 hours with BEZ235 prior to analysis for annexin-V/PI positivity. (D) The same p53-incompetent lymphomas were treated with etoposide (20 nM) for 24 hours prior to analysis for annexin-V/PI positivity. (E) Lymphomas derived on a Puma- (Puma^−/−) or Noxa- (Noxa^−/−) deficient background and a Puma/Noxa-competent (#4242) control were treated with BEZ235 for 24 hours prior to analysis for annexin-V/PI positivity. All graphs represent the mean (± SEM) for at least 3 independent experiments. WT, wild-type.