Determination of the small cell lung cancer associated biomarker pro-gastrin-releasing peptide (ProGRP) using LC-MS

Small cell lung cancer is a rapidly growing neoplasm with high mortality. A recently discovered biomarker, pro-gastrin-releasing peptide (ProGRP), is used as a specific diagnostic marker for the disease. The present methods of quantification are based on the immunoassay techniques RIA and ELISA. Our object was to develop an LC-MS method for the detection and quantification of ProGRP using specific tryptic digestion products from the recombinant peptide ProGRP (31-98), a sequence common to three isoforms of ProGRP. The conditions for enzymatic cleavage were optimized and MS compatibility was obtained. Digestion of ProGRP (31-98) yielded an array of peptide products and these were evaluated for further method development. The peptide product NLLGLIEAK proved to be the preferable candidate to monitor ProGRP due to signal intensity, column retention, and peptide specificity. The identity of this product was verified by means of LC-MS/MS and the linearity of the calibration curve evaluated. LOD was calculated to be 13.9 pg on column (O.C.). Plasma samples spiked with ProGRP (31-98) prior to digestion verified the suitability of this digest product for the determination of ProGRP. LC-MS may prove to be a valuable tool for biomarker mediated diagnosis in the future.