Identification and validation of SRC and phospho-SRC family proteins in circulating mononuclear cells as novel biomarkers for pancreatic cancer.

There is an urgent need to develop novel markers of pancreatic cancer to facilitate early diagnosis. Pancreatic carcinoma is characterized by marked stroma formation with a high number of infiltrating tumor-associated macrophages (TAMs) that originate from circulating mononuclear cells (MNCs). We hypothesized that differential analysis of protein expression and phosphorylation in circulating MNCs from healthy nude mice and nude mice bearing orthotopic human pancreatic cancer would identify a surrogate marker of pancreatic cancer. These differences were analyzed by two-dimensional gel electrophoresis followed by Western blot analysis using antibody against phosphorylated tyrosine proteins (pY). Protein and phosphorylated protein spots of interest were identified by mass spectrometry and validated by Western blot analysis as candidate markers for pancreatic cancer. We found that the expression and phosphorylation of Src family proteins were significantly higher in circulating MNCs from mice bearing pancreatic cancer than in circulating MNCs from healthy mice. TAMs in mice with pancreatic tumors also had higher Src family protein expression and phosphorylation than resident macrophages in the pancreas of healthy mice. The expression and phosphorylation of Src family proteins were correlated with tumor weight; however, increased Src expression and phosphorylation also occurred in MNCs from mice with chronic pancreatitis. This is the first report to explore novel pancreatic tumor markers in circulating MNCs. Although the specificity of the marker for pancreatic cancer was low, it could be used to monitor the disease or to select high-risk patients with chronic pancreatitis.