Identification of potential pancreatic cancer serum markers: Increased sialyl-Lewis X on ceruloplasmin

Pancreatic adenocarcinoma (PDAC) usually shows an enhanced expression of sialyl-Lewis X (sLex) and related epitopes. PDAC may secrete some of the proteins carrying such increased sLex determinant into serum, so they could be used as PDAC markers. Previously, we identified acute-phase proteins with increased sLex in both PDAC and in chronic pancreatitis patients. In this study, depleted sera from the main acute-phase proteins has been analysed for the search of proteins with increased sLex levels in PDAC. Sera from healthy controls, chronic pancreatitis and PDAC patients were depleted, electrophoresed and subjected to sLex immunodetection. Proteins that differentially expressed sLex in PDAC were trypsin digested and identified by LC-ESI-QTOF mass spectrometry. Five protein bands that differentially expressed sLex in PDAC were identified and corresponded to seven different acute-phase proteins. Among them, ceruloplasmin (CP) was selected for further analysis. N-glycan sequencing of CP confirmed the increase of sLex levels in CP in PDAC patients. Healthy controls, chronic pancreatitis and PDAC patients' sera were immunoprecipitated with anti-CP antibodies, and their sLex and CP levels were analysed by western blot. The sLex/CP ratio tended to be higher for the PDAC group, which altogether suggests that the sLex/CP ratio could be a useful biomarker for PDAC.