Development of novel therapeutic strategies for lung cancer: targeting the cholinergic system

Abstract

One of the earliest descriptions of non-neuronal ACh synthesis was by Morris who reported that ACh was synthesized in the placenta [1]; furthermore, Falugi et al. showed the presence of AChE in human fibrosarcoma cells [2]. Afterward, the expression of ACh, AChE, and cholinergic receptors in non-neuronal cells was reported in several studies [3-16]. Indeed, recent data reported that SCLC expresses a cholinergic autocrine loop that can regulate cell growth. Such work demonstrates that SCLC cells have a cholinergic phenotype and that ACh exerts as an autocrine growth factor in human lung tumours [16]. Moreover, it has been recently reported that nicotine in lung adenocarcinoma A549 cells, potently induces Bad phosphorylation at serine (S)112, S136 and S155 in a mechanism involving activation of MAPKs, ERK1/2, PI3K/AKT and PKA through the linking to alpha7-receptors [9]. Bad phosphorylation results in sequestering Bad from mitochondria and subsequently interacting with 14-3-3 in the cytosol [9]. We have recently reported that human malignant pleural mesothelioma expresses a cholinergic system, involved in cell growth regulation. Hence, mesothelioma cells growth is modulated by the cholinergic system in which agonists (i.e. nicotine) have a proliferative effect and antagonists (i.e. curare or alpha-cobratoxin) have an inhibitory effect. Furthermore apoptosis mechanisms are under the control of the cholinergic system (nicotine antiapoptotic via induction of NF-kappaB complexes and phosphorylation of Bad at S112, curare proapoptotic via G0-G1 arrest p21waf-1-dependent, but p53-independent) [16]. The involvement of the non-neuronal cholinergic system in lung cancer and mesothelioma appears reasonable and opens up new translational research strategies.