Activation of p53 by Nutlin-3a, an Mdm2 Antagonist, Induces Downregulation of Akt-mtor Oncogenic Signaling in Alk+ Anaplastic Large Cell Lymphoma (Alcl) Cells
E Drakos, GZ Rassidakis, E Schlette, J Li, JL Medeiros. MD Anderson Cancer Center, Houston, TX; Medical School, University of Athens, Athens, Greece
Background: p53, the most frequently mutated tumor suppressor gene in human cancer, is rarely mutated in anaplastic lymphoma kinase-positive (ALK+) ALCL tumors. We showed recently that activation of p53 by nutlin-3a, a MDM2 specific inhibitor, results in p53-mediated cell cycle arrest and apoptosis of ALK+ ALCL cells harboring potentially functional p53. The signaling of constitutively activated ALK, as a result of the t(2;5) (p23;q35) or variant translocations, is responsible for the oncogenesis in ALK+ALCL cells by promoting proliferation and survival. However, the effects of p53 activation on signaling pathways downsteam of constitutively activated ALK is unknown.
Design: We used three ALK+ ALCL cell lines, all harboring NPM-ALK translocation. These cell lines either had wild type (wt) p53 (SUP-M2), mutated but partially functional p53 (DEL), or mutated and nonfunctional (SUDHL1) p53. After sort-term treatment with nutlin-3a, in order to activate the p53 signaling pathway, and before the appearance of apoptotic events, we investigated by westen blot analysis the effect on activation status of STAT3, ERK and AKT, three of the most important downstream mediators of NPM-ALK oncogenic signaling.
Results: Treatment with nutlin-3a resulted predominantly in decreased AKT activation, as demonstrated by downregulation of p-ser473AKT. This was associated with downregulation of the mTOR signaling pathway operating downstream of AKT, as demonstrated by downregulation of phospholylated S6 and 4EBP1, two downstream targets of mTOR/Raptor signaling. Combined treatment with nutlin-3a and the PI3K inhibitor LY294002 resulted in dramatically enhanced antiproliferative and cytotoxic activity in ALK+ALCL cells harboring potentially functional p53. In contrast, treatment with the mTOR/Raptor inhibitor rapamycin increased only marginally the antitumor activity of nutlin-3a in ALK+ALCL cells. Also, treatment with nutlin-3a increased considerably the cytotoxic activity of the ALK inhibitor WHI-P154, specifically in ALK+ALCL cells harboring potentially functional p53.
Conclusions: Activation of the p53 pathway by the MDM2 inhibitor, nutlin-3a, induces downregulation of AKT signaling in ALK+ALCL cells harboring functional p53. Combined targeting of ALK, p53 and PI3K/AKT signaling may provide a new therapeutic approach for patients with ALK+ALCL.
Tuesday, March 23, 2010 9:30 AM
Poster Session III # 194, Tuesday Morning