Activation of abungarotoxin-sensitive nicotinic receptors in non small cell lung cancer A459 plays an important role in nicotine-induced proliferation

Nicotinic acetylcholine receptors (nAChRs) are expressed in normal bronchial epithelial and in non-small cell lung cancer (NSCLC) cells, and are involved in cell growth regulation. Nicotine is an nAChR exogenous ligand and through activation of nAChRs induces cell proliferation and stimulates lung cancer growth. To verify whether nicotine-induced A549 NSCLC cell proliferation was the result of nAChR activation, cells exposed to nicotine were co-incubated with the nicotinic α7 or α9 subtype-specific antagonists αbungarotoxin (α−Bgtx) or methyllycaconitine (MLA). As nicotine-induced cell proliferation was observed using the selective α7 agonist ICH3, we also treated the cells with Rg1 toxin, an α9-selective antagonist, in order to detect the possible involvement of α9-containing receptors. Co-incubation with Rg1 toxin completely blocked nicotine–induced proliferation and signalling. We have previously characterised 4-oxystilbene derivatives as selective α7 antagonists, and have now found that two of these compounds, F1 (previously called MG624) and F3, bind and block not only α7- but also α9- and α10-containing receptors. F1 and F3 treatment of A549 cells blocked their nicotine-induced proliferation and viability in a dose-dependent manner, but were much less active on SH-SY5Y and HepG2 cells. Finally, as A549 cells express high α5, α7 and α9 mRNA levels, and nAChRs containing these subunits are involved in nicotine-induced proliferation, we also screened for at least two short interfering RNAs (siRNAs) against the CHRNA5, CHRNA7 and CHRNA9 genes in order to knock down the expression of the subunits. RT-PCR and Western blotting showed that the siRNAs against CHRNA5 and CHRNA7 blocked nicotine-induced proliferation and intracellular signalling. In conclusions, our data show that the inhibition of Bgtx-sensitive receptors (α7 and/ or α9- containing receptors) by subtype-specific antagonists or RNA interference can inhibit A549 NSCLC cell proliferation in vitro.