The link between chronic inflammation and cancer development has lately gained extensive epidemiological and experimental support, particularly in organs like liver, stomach, colon, and lung. Although experimental models are available to study inflammation-driven tumorigenesis in the liver, stomach, and colon, no such models are available for lung cancer. Therefore, the objective of the present study is to develop a model for inflammation-driven lung tumorigenesis. A/J mice received four intraperitoneal injections (two doses/week) of the tobacco smoke carcinogen 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) at a dose level of 50 mg/kg body weight. Beginning one week after the last dose of NNK, the mice were given weekly intranasal instillations of lipopolysaccharide (LPS, 10ug/mouse), a potent inflammation-inducing agent, until the end of the study at week 27. Upon termination of the study, tumors on the surface of the lung were counted, their size determined and histopathologically analyzed. Moreover, we analyzed alterations in the expression of inflammation- and tumorigenesis-related proteins and microRNAs (miRs) by Western immunoblotting and qRT-PCR, respectively. Chronic exposure NNK-treated mice to LPS increased the number and size of lung tumors (47.3 ± 11 tumors/mouse for the NNK plus LPS group versus 28 ± 8 tumors/mouse in the NNK only group).

Furthermore, lung tumors in the NNK plus LPS treated mice were significantly larger than the lung tumors of the mice challenged with NNK alone.

Multiplicities of lung tumors in LPS-treated mice were similar to those mice given the vehicle. Multiplicities of the histopathological lesions pulmonary hyperplastic foci, adenoma, adenoma with dysplasia and adenocarcinoma in the NNK only group were 3.0 ± 1.2, 7.1 ± 2.9, 1.3 ± 1.1, and 0.3 ± 0.5/mouse, respectively. The corresponding frequencies of the lesions in the NNK plus LPS group were 3.1 ± 1.8, 11.8 ± 5.2, 3.9 ± 1.8, and 0.6 ± 0.7/mouse. Western immunoblotting studies showed that LPS exposure of NNK-treated mice enhanced activation of NF-kappaB, STAT3, and Akt but caused down-regulation of the tumor suppressor protein PTEN. Further, analyses of levels of five carcinogenesis-related microRNAs (miR-21, miR-146a, miR-150, miR-155 and miR-21, and miR-181b-1) showed increases in the expressions of miR-155 and miR-21. Levels of miR-155 and miR-21 were increased by 2.3-fold and 1.9-fold, respectively, in mice treated with NNK plus LPS group as compared to mice treated with NNK. Moreover, levels of miR-155 and miR-21 were increased by 10.5-fold and 4.7-fold, respectively, in LPS treated mice compared to vehicle-treated mice. In summary, our results demonstrate that LPS-induced chronic lung inflammation enhances lung tumorigenesis. This model could be a vey useful tool to understand the role inflammation in lung tumorigenesis and for identification of anti-inflammatory and lung cancer chemopreventive agents.

Citation Information: Cancer Prev Res 2011;4(10 Suppl):B41.