Searching for serum tumor markers for colorectal cancer using a 2-D DIGE approach.

Identification of specific protein markers for colorectal cancer (CRC) could provide a basis for its early diagnosis and detection, as well as clues to the molecular mechanisms governing cancer progression. In the present study, 2-D DIGE coupled with MS was used to screen for biomarker candidates in the serum proteome of ten human CRC samples and ten healthy control samples. After pooling identical amounts of serum proteins (based on total protein concentration), albumin/IgG was depleted under partially denaturing conditions. Subsequently, the serum samples were labeled with three different CyDyes, and separated by 2-D DIGE. After analysis with the biological variation analysis module of the DeCyder software, only three spots were found to be significantly elevated in all patient groups (with ratios from 1.52 to 9.08), whereas five spots were significantly down-regulated in patients (with ratios from -1.23 to -10.21) (t-test; p<0.05). Finally, two potential biomarkers, Transaldolase 1 and thyroid receptor interactor, were chosen for validation and analysis by ELISA with the serum of 30 CRC patients and 30 healthy controls. The serum levels of the two proteins correlated well with the 2-D DIGE results. Thus, 2-D DIGE approaches show great promise for biomarker discovery in CRC.