Objectives: Cigarette smoking is the leading cause of lung cancer worldwide. Carcinogens in cigarette smoke are responsible for airway epithelial changes, although our knowledge about the molecular events underlying lung tumorigenesis are still not very detailed. Our aim was first of all to establish an in vitro model which mimics chronic exposure conditions found in the airways of smokers and to more comprehensively characterize the chronological changes that occur in bronchial epithelial cells under those conditions.

Materials and methods: Total particulate matter (TPM) was generated from the 3R4F reference cigarette according to the ISO smoking regimen. Human bronchial epithelial cells (BEAS-2B; ATCC) were repeatedly exposed to TPM for 4 weeks. Gene regulation and expression were investigated using Affymetrix GeneChip® twice weekly during exposure, and data were analyzed using R scripts and Ingenuity Pathway Analysis® (IPA®). Phenotypic alterations due to exposure including, for example, cell cycle changes and epithelial-to-mesenchymal transition (EMT) were studied on a weekly basis and at the end of the exposure period, respectively, using high content imaging. The imaging data were subjected to statistical analysis using linear models (SAS 9.2).

Results: Treatment of BEAS-2B cells with TPM resulted in increased DNA damage after 1 week, continuously rising until the end of the 4-week exposure, although this trend was not statistically significant. We also observed a shift of the cell cycle to a G2/M-phase arrest, with a growing number of cells accumulating in this cell cycle phase over the treatment period. In addition, gradual activation of canonical pathways (e.g. PI3K/AKT, p53 and IL6 signaling) and enrichment in biological functions related to tumorigenesis over time was evidenced by overexpression of tumor promoting genes such as TP63, COX-2, GDF15, CCND1 and tumor suppressive genes like SERPINB5, THBS1, FAS and CDKN1A from as early as days 3-7. Furthermore, overexpression of miR-200 and miR-205 was identified first following 17 days of treatment, remaining significantly higher than controls until day 28. However, no visible morphological changes could be detected at the time when gene and miRNA expression changes first became significant. In contrast, those events typically occurred later.

Conclusion: Our experiments indicate that repeated exposure of bronchial epithelial cells to TPM induces ongoing alterations in gene expression as well as phenotypic changes related to tumorigenesis. The data here may lead to a better mechanistic understanding of the stepwise transformation of normal airway epithelial cells to full malignancy.

Citation Format: Marco van der Toorn, Niklas Kuehn, Stefan Frentzel, Diego Marescotti, Emmanuel Guedj, Nikolai Ivanov, Patrice Leroy, Manuel C. Peitsch, Julia Hoeng, Karsta Luettich. Characterization of molecular changes occurring during long-term treatment of human bronchial epithelial cells with cigarette smoke total particulate matter. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-091. doi:10.1158/1538-7445.AM2015-LB-091