Serum proteomic-based analysis of pancreatic carcinoma for the identification of potential cancer biomarkers

Abstract

To identify new biomarkers that improve the early diagnosis and lead to possible therapeutic targets in pancreatic carcinoma, we performed a proteomic approach to compare serum protein expression patterns of pancreatic carcinoma patients with that of gastric cancer patients, other pancreatic disease patients, and healthy volunteers. By two-dimensional gel electrophoresis (2-DE) analyses and mass spectroscopic identification, 10 protein spots were found significantly changed in pancreatic carcinoma and 5 proteins including cyclin I, Rab GDP dissociation inhibitor β (GDI2), α-1 antitrypsin precursor, Haptoglobin precursor, and Serotransferrin precursor were successfully identified. The increased levels of cyclin I and GDI2 found to be associated with pancreatic carcinoma were further confirmed by Western blot analyses in an independent series of serum samples and/or pancreatic juice samples. Applying immunohistochemistry, we further validated expression of cyclin I and GDI2 in additional pancreatic carcinomas. These results indicate that cyclin I and GDI2 may be potential molecular targets for pancreatic cancer diagnostics and therapeutics.

Introduction

In the United States, pancreatic cancer accounts for only 2% of all new cancers each year, but is the fourth leading cause of cancer deaths and the five-year survival rate of 4–5% is the lowest among all cancers [1]. In China, the incidence of pancreatic cancer is rising, and despite diagnostic and therapeutic efforts, pancreatic cancer-related mortality continues to rise [2]. Of all the treatment modalities for pancreatic cancer, only surgical resection offers the opportunity for a cure. However, at the time of diagnosis, approximately half of the patients already have metastases and approximately one third of patients are diagnosed as having locally advanced disease, whereas only a small proportion of patients are eligible for surgery [3]. Most symptoms related to this malignancy occur only after disease advancement to an unresectable stages and the early diagnosis of pancreatic cancer remains challenging. Although the serum tumor marker CA19-9 has been widely used in the diagnosis of pancreatic cancer, it is not sufficiently sensitive and accurate, and could not screening small and resectable cancer [4]. To increase the proportion of pancreatic cancer patients with a chance of a cure, there is an urgent need to develop an effective screening system for asymptomatic individuals and to improve the diagnostic accuracy for pancreatic cancer in its early stage [3].

In recent years, the rapid development of Proteomics technologies has provided new technology platforms to find a new tumor-marker. 2-DE-based comparative proteome analysis has been applied successfully to screen potential biomarkers for pancreatic cancer in cell lines [5] and tumor tissues [6]. But cell lines and tumor tissues are not as clinically useful as blood, especially for screening or early diagnosis. Recently, Yu et al. identified pancreatic cancer biomarkers in human serum using differential in-gel electrophoresis (DIGE) and tandem mass spectrometry (MS/MS), and apolipoprotein E, α-1-antichymotrypsin, and inter-α-trypsin inhibitor were confirmed to be increased in cancer serum [7]. More recently, Bloomston et al. investigated serum samples from normal and pancreatic cancer patients by means of 2-DE and mass spectrometry (MS), and fibrinogen γ, a protein associated with the hypercoagulable state of pancreatic cancer, was identified to be a potential tumor marker in pancreatic cancer [8]. However, the specific link between pancreatic cancer and the identified proteins of the two above studies need to be further investigated. Using a larger sample size, different control groups, different ethnic populations and sample treatments may increase the chance of finding different and specific serum proteins reflective of pancreatic cancer carcinogenesis or progression. In the present work, we used 2-DE and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to screen potential serum biomarkers for the detection of pancreatic cancer for the first time from the Chinese population. We compared the gel image from pancreatic cancer group with those from gastric cancer, other pancreatic disease, and healthy volunteer groups, respectively. Commonly differentially expressed proteins were identified. By using Western blot analysis and immunohistochemistry, two newly screened proteins (cyclin I and GDI2) were validated to be potential pancreatic cancer biomarkers.