Treatment of ALK-expressing cells with nutlin-3 stabilizes p53 leading to growth arrest. SUDHL-1 cells were treated with increasing doses of nutlin-3 (2.5-5 μM) for 48 hours, at which point cells were lysed and assayed by Western blot analysis for the expression of p53 and its downstream target p21 (A). Confocal microscopy of SUDHL-1 cytospin preparations revealed increased nuclear localization of p53 after nutlin-3 treatment for 48 hours (B). Transcript levels of p53 downstream targets were monitored by qRT-PCR after 48 hours of 20 μM nutlin-3 treatment (C). IPs for MDM2 were performed 48 hours after treatment with 20 μM nutlin-3 and bound p53 detected by Western blot analysis. Numbers represent ratios of arbitrary units after densitometric analysis of p53 and MDM2 protein levels (D). Cells were exposed to increasing doses of nutlin-3 for 6, 24, or 48 hours and monitored for cell growth by AlamarBlue incorporation (E). Error bars represent SDs of the mean. All experiments were performed at least in triplicate.