QUANTITATIVE PROTEOMIC ANALYSIS OF HUMAN GASTRIC FLUID FOR BIOMARKER DISCOVERY

Abstract

Gastric cancer (GC) is a significant public health burden, being the third leading cause of cancer-related deaths worldwide. Its lethality is mainly due to the lack of specific markers and clinically acceptable techniques for diagnosing early-stage GC. We and others have identified human gastric fluid as a potential source of GC biomarkers because of its anatomic proximity to the site of disease. However, as we have reported previously, gastric fluid present significant challenges for biomarker discovery using conventional protein-centric approaches because of its unique intrinsic properties. The aims of my thesis project were therefore to identify informative biomarkers in gastric fluid using peptide-centric approaches and to develop clinical tests of potential biomarkers for early GC detection. Using the iTRAQ® approach, I identified 193 differentially expressed proteins in gastric fluid of GC patients compared to non-cancer controls. Of these, 136 were up-regulated and 57 were down-regulated in GC. Notably, several of the identified proteins were expressed exclusively in the stomach and/or GI tract. I then analyzed the expression of candidate biomarkers in primary gastric tumors to verify their expression and to determine their clinical utility. I selected 4 promising candidates to develop quantitative assays in gastric fluid using standard-flow liquid chromatography (LC) coupled with the highly sensitive and specific multiple reaction monitoring (MRM) technology for potential clinical applications. My study shows that human gastric fluid is a valuable source for identifying GC biomarkers. Additionally, it highlights the utility of LC-MRM/MS for targeted quantification of protein markers in human body fluids for clinical applications.