Carcinogenesis Advance Access published online on January 8, 2009
Carcinogenesis, doi:10.1093/carcin/bgp010
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Nicotine stimulates pancreatic cancer xenografts by systemic increase in stress neuro-transmitters and suppression of the inhibitory neurotransmitter 
-aminobutyric acid.
1 Experimental Oncology Laboratory, Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, Knoxville, TN, USA
2 Experimental Oncology Laboratory, Sana'a University, Sana'a, Yemen
3 Author for correspondence and reprint requests: Hildegard M. Schuller, Experimental Oncology Laboratory, Department of Pathobiology, College of Veterinary Medicine, University of Tennessee, 2407 River Drive, Knoxville, TN 37996, USA, Phone: 865-974-8217, Fax: 865-974-5616, E-mail: hmsch{at}utk.edu
Pancreatic ductal adenocarcinoma (PDAC) is a leading cause of cancer mortality in Western countries. We have previously shown that four representative human PDAC cell lines were regulated by beta-adrenoreceptors via cAMP-dependent signaling. In the current study, we have tested the hypothesis that nicotine stimulates the growth of PDAC xenografts in nude mice by increasing the systemic levels of the stress neurotransmitters adrenaline and noradrenaline, which are the physiological agonists for beta-adrenoreceptors, and that inhibition by 
-aminobutyric acid (GABA) of the adenylyl cyclase-dependent pathway downstream of adrenoreceptors blocks this effect. The size of xenografts from PDAC cell line Panc-1 were determined 30 days after inoculation of the cancer cells. Stress neurotransmitters in serum as well as cAMP in the cellular fraction of blood and in tumor tissue were assessed by immunoassays. Levels of GABA, its synthesizing enzymes GAD65 and GAD67 and beta-adrenergic signaling proteins in the tumor tissue were determined by Western blotting. Nicotine significantly increased the systemic levels of adrenaline, noradrenaline and cAMP while increasing xenograft size and protein levels of cAMP, p-CREB and p-ERK1/2 in the tumor tissue. Nicotine additionally reduced the protein levels of both GAD isozymes and GABA in tumor tissue. Treatment with GABA abolished these responses to nicotine and blocked the development of xenografts in mice not exposed to nicotine. These findings suggest that the development and progression of PDAC is subject to significant modulation by stimulatory stress neurotransmitters and inhibitory GABA and that treatment with GABA may be useful for marker-guided cancer intervention of PDAC.
Received August 5, 2008; revised November 29, 2008; accepted December 29, 2008.