Date on Master's Thesis/Doctoral Dissertation
Pharmacology and Toxicology
Pharmacology and Toxicology, MS
Lungs--Cancer; Nicotine--Health aspects; Nicotine--Physiological effect
Lung cancer is the leading cause of cancer death in men and women worldwide. Tobacco exposure represents the major risk factor. Nicotine, an addictive plant alkaloid found in tobacco, has been demonstrated to stimulate lung carcinoma cells directly via nicotinic acetylcholine receptors (nAChRs) that trigger downstream signals capable of promoting lung cancer growth and progression. Attention has been given to α7 nAChRs, while less is known about α4 nAChRs. However, most studies evaluating these receptors relied on chemical inhibitors notorious for their off-target effects. Consequently, the true role of α4 and α7 nAChRs in lung cancer remains unclear. To address this, we performed in vitro and in vivo studies using Lewis Lung Carcinoma (LLC) cells silenced with shRNA for α4 or α7 nAChRs. As expected, nicotine stimulated the proliferation of LLC cells in vitro. However, tumor cells treated with specific inhibitors of α4 or α7 nAChRs independently, did not inhibit nicotine-induced proliferation; inhibition of proliferation required that receptors be targeted concomitantly with a broad-spectrum inhibitor. Similar observations were made when the receptors were silenced separately with shRNA; however cells showed increased proliferation at baseline when silenced for nAChRs. In LLC cells silenced for α4 nAChRs we observed fewer colonies on soft agar, decreased migration, and decreased apoptosis in response to cisplatin, when compared to untransfected cancer cells and cells transfected with control shRNA. Cells silenced for α7 nAChRs did not differ from untransfected cancer cells or cells transfected with control shRNA, with respect to colony formation, migration, and apoptosis. In a lung cancer xenograft model, silencing of α4 and α7 nAChRs in cancer cells resulted in no significant differences in tumor size, and did not alter overall survival. While exploring the role of host cell receptors, no differences were observed in tumor number or size in a spontaneous tumor formation model in animals carrying KRAS and α7 nAChR mutations. In contrast, larger tumors were observed in α7 nAChR knockout mice injected with wildtype LLCs. These studies suggest differential roles for α4 and α7 nAChRs in murine lung carcinoma cells, with α4 nAChRs having a predominant role in vitro. However, studies performed in animals suggest that targeting these receptors independently in tumor cells may not affect tumor progression in vivo, while targeting host receptors may.
Greenwell, John Caleb, "Exploring the roles of host and tumor cell α4 and α7 nicotinic acetylcholine receptors in lung cancer." (2015). Electronic Theses and Dissertations. Paper 2153.