腫瘍マーカー探索のためのペプチドミクス

抄録

Peptidomics provides a powerful approach to identify peptide markers for cancer. Peptides that are preferentially secreted from tumor cells and stable in circulation could serve as ideal markers since determination of their serum levels may aid in cancer diagnosis and management. Thanks to developing proteomics technologies, studies on disease marker discovery are increasingly popular worldwide. However, endogenous peptides remain largely disregarded because they are not covered by current proteomics. It should also be noted that no genome-based approach is applicable to the discovery of peptide fragments associated with a particular tumor phenotype. In an attempt to identify potential peptide markers, we have initiated a mass analysis of peptides secreted by cancer cell lines and non-malignant cells grown in serum-free conditions. The fact that tumor markers currently used in clinics are secreted by cell lines points to the advantage of the use of cultured cells to this end. Our principal analytical platform rests on surface enhanced laser desorption ionization (SELDI) mass spectrometry for profiling and tandem mass spectrometry for identification. As proof of principle, samples from 75 cultured cells were analyzed on a SELDI mass spectrometer to identify candidate peptides associated with pancreatic adenocarcinoma only. A 3333 Da peptide, which occurred in 6 cell lines derived from pancreatic adenocarcinoma, turned out to be a COOH-terminal 29 amino acid fragment of the putative tumor suppressor protein DMBT-1. Studies using a specific antibody revealed that the peptide is secreted by growing pancreatic cancer cell lines but not by two non-malignant cell lines of pancreatic duct origin. Immunoprecipitation studies on surgical pancreatic adenocarcinomas also revealed that it is expressed in a cancerous lesion but not in a matched control lesion in 4 out of 5 cases.