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Tobacco Carcinogen-Induced Cellular Transformation Increases Akt Activation In Vitro and In Vivo* FREE TO VIEW

Kip A. West, PhD; Ilona R. Linnoila, MD; John Brognard, MS; Steven Belinsky, PhD; Curtis Harris, MD; Phillip A. Dennis, MD, PhD
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*From the Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD.

Correspondence to: Phillip Dennis, MD, PhD, Cancer Therapeutics Branch, Center for Cancer Research, National Cancer Institute, 8901 Wisconsin, Ave, Bethesda, MD 20889-5105; e-mail: pdennis@nih.gov

Chest. 2004;125(5_suppl):101S-102S. doi:10.1378/chest.125.5_suppl.101S
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Previously, we identified the serine/threonine kinase Akt as a molecular target in lung cancer, because Akt is constitutively active in non-small cell lung cancer cells in vitro and in vivo, and tobacco components activate Akt in primary cultures of human lung epithelial cells. To determine a role for Akt activation in the transformation of lung epithelial cells, we evaluated the PI3K/Akt pathway in immortalized human lung epithelial cells (BEAS-2B cells) or in BEAS-2B cells that were fully transformed by a tobacco-specific carcinogen (ie, BEAS-2B/4-[methylnitrosamino]-1-[3-pyridyl]-1-butanone [NNK] cells) in vitro, as well as NNK-induced murine lung lesions in vivo. Adding nicotine or NNK to BEAS-2B or BEAS-2B/NNK cells increased Akt activation in a time-dependent and dose-dependent manner, and increased cellular proliferation. Compared to immortalized BEAS-2B cells, tumorigenic BEAS-2B/NNK cells had higher levels of epidermal growth factor receptor (EGFR) phosphorylation, increased Akt activity, increased phosphorylation of multiple substrates downstream of Akt, and enhanced survival under conditions of serum starvation. Pharmacologic inhibitors of PI3K, Akt, or the EGFR decreased Akt activity and increased apoptosis of BEAS-2B and BEAS-2B/NNK cells, with the greatest relative induction of apoptosis observed with BEAS-2B/NNK cells.

To confirm these results, we infected BEAS-2B and BEAS-2B/NNK cells with adenoviruses expressing dominant-negative Akt. At lower doses of adenoviral infectivity, immortalized BEAS-2B cells underwent greater apoptosis than did BEAS-2B/NNK cells, but at the higher doses each cell type underwent apoptosis. To evaluate a spectrum of tobacco carcinogen-induced preneoplastic and neoplastic lesions in vivo, we performed an immunohistochemical analysis of the PI3K/Akt pathway in lung tissues derived from A/J mice treated with NNK. Active Akt and downstream components were detected in the normal bronchial epithelium, hyperplastic lesions, adenomas, and adenocarcinomas, with the most intense staining observed in adenocarcinomas. Collectively, these results show the following: (1) that tobacco components increase Akt activity and promote the growth of immortalized and tumorigenic lung epithelial cells; (2) that activation of the PI3K/Akt pathway increases with the phenotypic progression of lung epithelial cells caused by a tobacco carcinogen; and (3) that genetic or pharmacologic inhibition of Akt increases the apoptosis of immortalized and tumorigenic lung epithelial cells. These data suggest that therapeutic approaches that inhibit Akt might prevent the phenotypic progression of lung cancer.

Abbreviations: EGFR = epidermal growth factor receptor; NNK = 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone




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