Continual Exposure to Cigarette Smoke Extracts Induces Tumor-Like Transformation of Human Nontumor Bronchial Epithelial Cells in a Microfluidic Chip

Introduction: Heavy cigarette smoking-related chronic obstructive pulmonary disease is an independent risk factor for lung squamous carcinoma. However, the mechanisms underlying the malignant transformation of bronchial epithelial cells are unclear. Methods: In our study, human tumor-adjacent bronchial epithelial cells were obtained from 10 cases with smoking-related chronic obstructive pulmonary disease and lung squamous carcinoma and cultured in an established microfluidic chip for continual exposure to cigarette smoke extracts (CSE) to investigate the potential tumor-like transformation and mechanisms. The integrated microfluidic chip included upstream concentration gradient generator and downstream cell culture chambers supplied by flowing medium containing different concentrations of CSE. Results: Our results showed that continual exposure to low doses of CSE promoted cell proliferation whereas to high doses of CSE triggered cell apoptosis. Continual exposure to CSE promoted reactive oxygen species production in human epithelial cells in a dose-dependent manner. More importantly, continual exposure to low dose of CSE promoted the epithelial-to-mesenchymal transition process and anchorage-independent growth, and increased chromosome instability in bronchial epithelial cells, accompanied by activating the GRP78, NF-kappa B, and PI3K pathways. Conclusions: The established microfluidic chip is suitable for primary culture of human tumor-adjacent bronchial epithelial cells to investigate the malignant transformation. Continual exposure to low doses of CSE promoted tumor-like transformation of human nontumor bronchial epithelial cells by inducing reactive oxygen species production and activating the relevant signaling.