Orbitrap Analysis Identifies Potential New Serum Biomarker for Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a killer, with fewer than 5% of patients alive five years after diagnosis. Effective and timely treatment is often delayed because the disease is not noticed in time; its symptoms are vague and there is no reliable biomarker for early identification. One biomarker, carbohydrate antigen 19-9 (CA19.9), exists but it lacks sensitivity and specificity. Patients often present in late stage, when the tumor is not surgically removable or has already aggressively metastasized, at which point the prognosis is extremely poor.

Kosanam et al.¹ took advantage of recent developments in liquid chromatography–tandem mass spectrometry (LC-MS/MS) technology and went hunting for a more reliable biomarker. Taking malignant and adjacent benign tissue biopsies from four PDAC patients, they screened the proteome for potential diagnostic markers. Out of the 2,190 non-redundant proteins identified, 16 were selected as candidates. This pool was further narrowed down to four potential serum biomarkers.

Tissue biopsies harvested from four PDAC patients underwent trypsin digestion prior to strong cation-exchange chromatography (SCX) column fractionation. After C18 Trap column and reversed-phase liquid chromatography (RPLC) preparation, the purified products were examined by LTQ-Orbitrap XL MS (Thermo Scientific, San Jose, CA).

The 2,190 proteins identified were scored according to a selective algorithm designed to pull out the most promising candidates. The algorithm ranked the proteins according to cellular location and consistent recovery, among other criteria. At this step, the 16 candidates were identified; they underwent further investigation in serum samples from 20 PDAC patients that were compared with matched samples from patients with benign pancreatic cysts.

The four most promising candidate biomarkers were desmoplakin (DSP), laminin gamma C2 (LAMC2), Golgi membrane protein-2 (GP73) and desmoglein-2 (DSG2). Potential pathway analysis confirmed the suitability of each as a tumor-associated protein marker, and their serum concentrations were confirmed by commercial enzyme-linked immunosorbent assay (ELISA). Further investigation showed that tissue mRNA expression was raised in tumor biopsies. Additionally, three of the biomarkers were also found in ascitic fluid associated with PDAC.

With preliminary testing, LAMC2 appeared the most promising serum biomarker. In the initial serum testing, circulating concentrations in PDAC patients were significantly elevated compared with the matched control group (p<0.05).

This was further confirmed by expanding the study to three geographically distinct cohorts of PDAC patients in Germany, the United States and Japan, where LAMC2 consistently outperformed CA19.9 in identifying PDAC patients. Moreover, concentrations were raised where CA19.9 was undetectable, suggesting that LAMC2 might identify early-stage disease.

The authors conclude that LAMC2 is a strong candidate for a circulating PDAC tumor marker. Further investigation, however, is merited.

Reference

1. Kosanam, H., et al. (2013, June) “LAMC2: A promising new pancreatic cancer biomarker identified by proteomic analysis of pancreatic adenocarcinoma tissues,” Mol. Cell. Proteomics (first published June 24), doi:10.1074/mcp.M112.023507.