Choline Acetyltransferase: A novel drug target in lung adenocarcinoma patients who are exposed to tobacco smoke

Purpose of the study : Lung cancer is not a single disease entity; it represents a spectrum of malignancies. Out of these lung adenocarcinoma (LUAD) accounts for about 65% of all lung cancers and shows a strong etiological correlation with smoking. Clinical studies show that about 30% of LUAD patients continue to smoke after being diagnosed with lung cancer. In addition, many others are exposed to nicotine via secondhand smoke and smoking cessation devices. Nicotine, the addictive component of tobacco smoke, accelerates the growth of human LUADs via the by nicotinic acetylcholine receptors (nAChRs) on target cells. The first-line therapy for LUAD patients involves the administration of tyrosine kinase inhibitors (TKIs) targeting EGFR, ALK, MET kinases. Such targeted therapies show potent anti-cancer activity in non-smokers and never smokers but show poor efficacy in patients who continue to smoke after their diagnosis. The primary objective of our research is to evaluate the potential of choline acetyltransferase (ChAT, the enzyme which synthesizes acetylcholine) as a drug target for LUAD in smokers. We evaluated the anti-neoplastic activity of BW813U (small molecule inhibitor of ChAT) in LUADs associated with moderate-heavy smoking history. We also investigated the anti-angiogeneic activity of BW813U (as a molecular mechanism underlying its growth-inhibitory effects) LUAD. Experimental procedures . Primary human microvascular endothelial cells from the lung (HMEC-L) were used for all the experiments. These cells were used between passage 3-7. The anti-angiogenic activity of BW813U was measured in cell culture models by using the “MATRIGEL ASSAY”. The results obtained from the “MATRIGEL ASSAY” were confirmed using chicken chorioallantoic membrane (CAM) angiogenesis experiments. Finally, the anti-tumor activity of BW813U was measured in vivo by using xenograft model systems in SCID mice. Our studies also investigated the signaling pathways underlying the anti-angiogenic activity of BW813U, using chemical inhibitors and siRNA methodology. Results : BW813U robustly suppressed angiogenesis in Matrigel assays and CAM model systems. The administration of BW813U potently decreased the growth rate of H838 tumors xenotransplanted in SCID mice. Immunohistochemical staining experiments revealed that the anti-tumor activity of BW813U was correlated with decrease of CD31 angiogenic biomarker in H838 tumor sections. The anti-angiogenic activity of BW813U was mediated by the alpha7-nAChR pathway and involved the nitric oxide pathway. Taken together, our studies show that ChAT may be a valuable drug target for the therapy of LUAD. Conclusions: ChAT antagonists like BW813U decrease the growth of LUAD by suppressing tumor angiogenesis.