Candidate serum biomarkers for early intestinal cancer using ¹⁵N metabolic labeling and quantitative proteomics in the Apc^Min/+ mouse

Current screening procedures for colorectal cancer are imperfect and highly invasive and result in increased mortality rates due to low compliance. The goal of the experiments reported herein is to identify potential blood-based biomarkers indicative of early stage intestinal cancers using the Apc ^Min/+ mouse model of intestinal cancer as an experimental system. Serum proteins from tumor-bearing Apc^Min/+ mice were quantitatively compared to tumor-free Apc^+/+ wild-type mice via in anima metabolic labeling with ¹⁴N/¹⁵N-labeled Spirulina algae and an LTQ Orbitrap mass spectrometer. Out of 1116 total serum proteins quantified, this study identified 40 that were differentially expressed and correlated with the increase in intestinal neoplasms. A subset of these differentially expressed proteins underwent a secondary quantitative screen using selected reaction monitoring-mass spectrometry with stable isotope-labeled peptides. Using both quantitative techniques, we identified MGAM and COL1A1 as downregulated and ITIH3 and F5 as upregulated in serum. All but COL1A1 were similarly differentially expressed in the mRNA of neoplastic colonic tissues of Apc ^Min/+ mice compared to normal wild-type tissue. These differentially expressed proteins identified in the Apc^Min/+ mouse model have provided a set of candidate biomarkers for future validation screens in humans.