Biomarkers for pancreatic carcinogenesis

Abstract

Pancreatic cancer is a devastating disease. Most pancreatic cancers (approximately 85%) are diagnosed at a late, incurable stage. The poor prognosis and late presentation of pancreatic cancer patients underscore the importance of early detection, which is the sine qua non for the fight against pancreatic cancer. It is hoped for the future that the understanding of genetic alterations will lead to the rapid discovery of an effective biomarker of pancreatic carcinogenesis. In this thesis we visited the publicly available online SAGE libraries to evaluate global gene expression in pancreatic cancer and to select novel differentially expressed genes that might serve as diagnostic markers or as a lead for further research to therapeutic targets. We confirmed the differential expression of seven genes, involved in multiple cellular processes such as signal transduction (MIC-1), differentiation (DMBT1 and Neugrin), immune response (CD74), inflammation (CXCL2), cell cycle (CEB1) and enzymatic activity (Kallikrein 6). To provide an additional set of novel potential biomarkers for pancreatic ductal adenocarcinoma we used bioinformatics tools to reanalyze microarray data in the setting of pancreatic cancer. We characterized 60 previously unassigned ESTs (expressed sequence tags) and mapped most of them to known genes. The differential expression of a subset of genes was confirmed at the protein level by immunohistochemical labeling of tissue microarrays (Inhibin Beta A and CD29) and/or at the transcript level by RT-PCR (Inhibin Beta A, AKAP12, ELK3, EIF5A2, and EFNA5). In addition, we studied the expression and prognostic significance of 14-3-3sigma and ERM family protein expression in pancreatic ductal adenocarcinomas. The protein expression was significantly more common in poorly differentiated pancreatic cancers. Moreover, we showed that pancreatic cancer is a promising cancer type to explore novel chemotherapeutic strategies to exploit the selective loss of MTAP function. We found that immunolabeling for the MTAP gene product mirrored gene status and that approximately 30% of infiltrating pancreatic adenocarcinomas had complete loss of MTAP expression. In the future, those patients whose cancers show a complete loss of MTAP expression could be offered treatment with inhibitors of the de novo purine synthesis pathway. In addition, we immunolabeled a series of pancreatic intraepithelial neoplasia (PanIN) lesions of various histologic grades for the p16 and MTAP gene products using a high-throughput PanIN tissue microarray format. We demonstrated concordant loss of p16 and MTAP protein expression in 6/73 (8%) PanINs, including five high-grade lesions and one low-grade lesion. The concordant loss of expression of both genes in PanIN lesions demonstrated that homozygous deletions of the p16 tumor suppressor gene can occur in noninvasive precursor lesions. In summary, in this thesis we described potential clinically useful biomarkers for pancreatic carcinogenesis, discovered by analyzing unique cancer specific genetic alterations, differential expressed mRNA genes and protein changes in pancreatic cancer. Our increased knowledge of the molecular changes in pancreatic cancer and in different PanIN stages may provide the basis for developing more sensitive screening strategies for early detection, to achieve or final goal; “catching the horse before it has fled the barn”.