The Adrenergic System in Gastrointestinal Cancers

It has been demonstrated by clinical and animal studies that stress stimulation plays a pivotal role in the tumor development and progression. Adrenergic system activation mediates most of the effects resulting from stress stimulation. Various cigarette components have been indicated for inducing the secretion of stress hormones such as noradrenaline and adrenaline which activate the adrenoceptors expressed on tumor cells and initiate different biological effects. Gastrointestinal (GI) cancers, a common malignancy in the body are also influenced by stress stimulation to a great extent. Combined stress stimulation with cigarette smoking can further accelerate tumor progression, and even develop chemoresistance in cancer cells. Therefore the involvement of adrenoceptors in these biological processes and habitual behaviours are becoming interesting therapeutic targets. Indeed various adrenoceptor blockers are implicated as promising therapeutic agents to prevent and treat relevant cancers including those in the GI tract. In this review, we sum up the possible relationship between the adrenergic system and GI cancers and provide a mechanistic understanding on this relationship. Meanwhile, we also further discuss the roles of cigarette smoke and its active ingredient nicotine which is highly associated with the adrenergic system in the development of GI cancers.