Inhibition of NNK-induced lung carcinogenesis by green tea polyphenols and their combination with atorvastatin

Lung cancer is the leading cause of cancer related deaths in the United States and one of the most common cancers worldwide. The identification of dietary constituents that prevent this cancer and the elucidation of their mechanisms of action are important areas of lung cancer research. The objectives of this study were: (1) to characterize the pathogenesis and molecular alterations in the 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK)-induced lung tumors in A1J mice; (2) to determine the inhibition of adenoma progression to adenocarcinoma in NNK model by tea polyphenols (Polyphenon E, a standardized green tea polyphenol preparation containing 65% EGCG) and caffeine; (3) to elucidate the possible mechanisms involved in the tumor inhibitory action of tea polyphenols (EGCG, the major tea catechins in Polyphenon E) and caffeine, and (4) to evaluate the combined efficacy of Polyphenon E with atorvastatin on the inhibition of lung tumor growth in H1299 cell line, H1299 cell xenograft tumors and NNK-induced lung tumors. NNK administration induced dramatic cell proliferation in bronchial epithelial cells, which might stabilize the NNK-induced gene mutation. K-Ras gene mutation is believed to be the driving force in NNK-induced lung tumorigenesis. In lung adenomas induced by NNK, K-Ras downstream MAPK pathway overactivation was found. In adenocarcinomas, upregulation of IGFR was observed, which resulted in much higher levels of cell proliferation through IGFR-Ras-MAPK pathway. Polyphenon E administration significantly reduced the incidence and multiplicity of lung adenocarcinoma. Caffeine also showed inhibitory effects, but these did not reach statistical significance. Polyphenon E and caffeine treatment inhibited cell proliferation and enhanced apoptosis in the adenomas and adenocarcinomas, with no effects in normal lung tissues. The cancer preventive effects of Polyphenon E and caffeine were associated with lowered levels of Erk and c-Jun phosphorylation, which was further confirmed by short-term treatments of EGCG and caffeine in NNK-induced lung adenomas. Combination of Polyphenon E and atorvastatin produced synergy in inhibiting H1299 cell growth. The combination also inhibited the growth of H1299 xenograft tumors. Polyphenon E and atorvastatin combination also significantly reduced tumor multiplicity and tumor burden in NNK model. The synergistic effect in inhibiting lung tumorigenesis was at least partially due to induction of apoptosis. The information obtained from the present study will be useful for the development of Polyphenon E and possibly its combination with atorvastatin as effective chemopreventive agents for human lung cancer.