Published evidence compiled in this review supports the hypothesis that the development, progression, and responsiveness to prevention and therapy of the most common human cancers is strongly influenced, if not entirely orchestrated, by an imbalance in stimulatory and inhibitory neurotransmission. The neurotransmitters acetylcholine, adrenaline, and noradrenaline of the autonomic nervous system act as powerful upstream regulators that orchestrate numerous cell and tissue functions, by releasing growth factors, angiogenesis factors and metastasis factors, arachidonic acid, proinflammatory cytokines, and local neurotransmitters from cancer cells and their microenvironment. In addition, they modulate proliferation, apoptosis, angiogenesis, and metastasis of cancer directly by intracellular signaling downstream of neurotransmitter receptors. Nicotine and the tobacco-specific nitrosamines have the documented ability to hyperstimulate neurotransmission by both branches of the autonomic nervous system. The expression and function of these neurotransmitter pathways are cell type specific. Lifestyle, diet, diseases, stress, and pharmacological treatments modulate the expression and responsiveness of neurotransmitter pathways. Current preclinical testing systems fail to incorporate the modulating effects of neurotransmission on the responsiveness to anticancer agents and should be amended accordingly. The neurotransmitter γ-aminobutyric acid has a strong inhibitory function on sympathicus-driven cancers whereas stimulators of cyclic adenosine monophosphate/protein kinase A signaling have strong inhibitory function on parasympathicus-driven cancers. Marker-guided restoration of the physiological balance in stimulatory and inhibitory neurotransmission represents a promising and hitherto neglected strategy for the prevention and therapy of neurotransmitter-responsive cancers.
Experimental Oncology Laboratory, Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville, Tennessee, USA
Correspondence to Hildegard M. Schuller, Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, TN, 37996, USA
Tel: +865 974 8217; fax: +8650974 5616; e-mail: firstname.lastname@example.org
Received 18 February 2008 Revised form accepted 27 March 2008