Abstract PR4: Neuroplastic changes and pain-related behavior in a transgenic mouse model of pancreatic ductal adenocarcinoma (PDAC).

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is associated with significant morbidity and mortality. Morbidity in PDAC is partly due to the severe pain reported by patients with the disease. Tumor-nerve interactions including intrapancreatic perineural invasion, neurogenic inflammation, and neuritis are key features of pancreatic malignancies and are thought to play an important role in pancreatic cancer-related pain. Furthermore, neurotrophic factors such as nerve growth factor (NGF), glial cell line-derived neurotrophic factor (GDNF), GDNF family member artemin (Artn), and brain-derived neurotrophic factor (BDNF) have been implicated in the development of PDAC-related pain. These neurotrophic factors have been shown to produce hypersensitivity in sensory afferents and may drive the neuropathology underlying PDAC pain. Thus, we hypothesized that neurotrophic factors would be increased in the pancreas of PDAC mice as tumors develop, leading to altered pancreatic innervation and changes in pain-related behavior. Experiments were performed with transgenic mice that have pancreas-specific expression of a mutated Kras oncogene and heterozygous deletion of the p53 tumor suppressor gene (p48Cre; LSL-KRASG12D; p53lox/+). PDAC mice demonstrated a varied disease time course but generally developed multifocal pancreatic cancer by week 16 as evidenced by nodular-appearing pancreata. Obstruction of the biliary tree, tumor involvement throughout the mesentery, and metastases to the liver were also observed in some PDAC mice at more advanced stages of disease (> 25 weeks). Sex- and age-matched littermate transgenic controls were used for all experiments. Pancreas RNA was isolated from PDAC mice and controls at 16-30 weeks of age and levels of neurotrophic factor and neurotrophic factor receptor mRNA expression was measured using PCR and qRT-PCR. Indeed, expression of NGF, the NGF receptor TrkA, Artn, GDNF, the GDNF receptor GFRα1, BDNF, and the BDNF receptor TrkB were all increased in the pancreas of PDAC mice compared to controls. Immunohistochemical studies were performed to examine the density and distribution of nerve fibers in the pancreas of PDAC mice. Large nerve bundles that stained intensely with the pan-neuronal marker PGP 9.5, tyrosine hydroxylase (TH; NGF-responsive sympathetic fibers), calcitonin gene-related peptide (CGRP; sensory fibers), and growth-associated protein 43 (GAP-43; nerve sprouting) were observed in the pancreas of PDAC mice but not controls. Open-field, exploratory behavior was monitored in PDAC mice between 16 30 weeks of age. Specifically, animals were placed in Plexiglas boxes and their activity in both the horizontal plane and vertical plane was measured photoelectrically for a period of 15 minutes. PDAC mice spent less time moving horizontally and vertically, had a reduced number of reaching movements into the vertical plane, traveled less distance in the vertical plane, and made fewer movements in the vertical plane. These data indicate that significant changes in pancreatic innervation and neurotrophic factor expression occur in a transgenic mouse model of pancreatic cancer and these changes correlate with pain-related decreases in ambulatory and reaching activity. Thus, this animal model will enable us to systematically study the impact of neuroplastic changes in the PDAC microenvironment on the development of pancreatic cancer-related pain. This proffered talk is also presented as Poster A81. Citation Format: Rachelle E. Stopczynski, Kathryn M. Albers, Klaus Bielefeldt, Ronald A. DePinho, Haoqiang Ying, Brian M. Davis. Neuroplastic changes and pain-related behavior in a transgenic mouse model of pancreatic ductal adenocarcinoma (PDAC). [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Progress and Challenges; Jun 18-21, 2012; Lake Tahoe, NV. Philadelphia (PA): AACR; Cancer Res 2012;72(12 Suppl):Abstract nr PR4.