Targeted In-Gel MRM: A Hypothesis Driven Approach for Colorectal Cancer Biomarker Discovery in Human Feces

Colorectal cancer (CRC) is the second most common cause of cancer-related deaths in both men and women. The fecal occult blood test is currently the first line method for CRC screening but has an unacceptably low sensitivity and specificity. Improved screening tests are therefore urgently required for early stage CRC screening. We have described a hypothesis-driven approach for a rapid biomarker discovery process whereby selected proteins previously implicated as colorectal cancer-associated proteins (CCAP), which can potentially be shed into the feces from a colorectal tumor, are targeted for excision from 1D-SDS-PAGE based on their predicted molecular weight followed by directed identification and relative quantification using multiple reaction monitoring (MRM). This approach can significantly reduce the time for clinical assay development with the added advantage that many proteins will have been validated by previous in vitro and/or in vivo studies. Sixty potential CCAPs were selected from the literature and appropriate MRM conditions were established for measurement of proteotypic peptides. Nineteen of these proteins were detected in the feces from a patient with colorectal cancer. Relative quantitation of these 19 CCAP across 5 CRC patients and 5 healthy volunteers were carried out, revealing hemoglobin, myeloperoxidase, S100A9, filamin A and L-plastin to be present only in the feces of CRC patients.