Identification of β-tubulin as a common immunogen in gastrointestinal malignancy by mass spectrometry of colorectal cancer proteome : implications for early disease detection

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To identify tumor-specific antigens in patients with colorectal cancer by mass spectrometry of cancer cell line proteins. To determine the number of patients with various types of gastrointestinal malignancy demonstrating anti-tumor antibodies. Proteins from the colorectal cancer cell line DLD-1 were separated by two-dimensional polyacrylamide gel electrophoresis and Western blotted onto P polyvinylidene fluoride membranes for immune reaction with sera from colorectal cancer patients. Immunoreactive spots were mapped and excised from Coomasie brilliant blue stained gels. In-gel trypsin digestion, peptide extraction and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was performed to identify immunogenic proteins. Sera from patients with gastrointestinal malignancies, other colorectal conditions and healthy subjects were tested for reactivity against identified proteins. One of the immunogenic proteins was identified as β-tubulin. Antibodies in patients were detected in 16/54 (30%) colorectal, 6/16 (38%) gastric, 2/10 (20%) esophageal and 4/10 (40%) pancreatic cancer, while in 2/3 (67%) colorectal adenoma, 0/2 colonic Crohn's and 0/1 carcinoid of the appendix. Only one healthy subject had antibodies making the specificity 96%. For those with colorectal cancer, the presence of anti-β-tubulin antibodies was associated with well differentiated lesions (p<0.05) while there were no correlations with disease stage or the presence of vascular and lymphatic invasion. Through a proteomics-based approach, we have successfully identified β-tubulin as a tumor-specific antigen in colorectal cancer and other gastrointestinal malignancies. Anti-β-tubulin antibodies may be a sensitive and measurable marker for early malignant disease.