Imaging mass spectrometry on formalin-fixed paraffin-embedded tissue (FFPE): localization of various compartments in one tissue section: What it is possible today?

Background Imaging mass spectrometry (IMS) is an evolving technique which is able to detect hundreds of peptides in one experiment demonstrating at the same time their spatial distribution. In case of Whipple´s operation, many different tissue compartments are seen. The objective of this study is to show the possibilities of IMS to paint different histological structures by highlighting their peptide expression pattern. Methods A pancreatic tumor tissue was cut at 5 μm prior to deparaffinization and heat-induced epitope retrieval. Trypsin solution (0.1 μg/μl) was sprayed on the tissue section using a Bruker ImagePrep automatic spray devise. After digestion for 1.5 h, alpha-cyano-4-hydroxycinnamic acid (CHCA) matrix was sprayed and the tissue was analyzed for peptides in positive ion mode on a Bruker Autoflex Speed mass spectrometer. Ion peptide species were visualized using FlexImaging 4.0 software (Bruker) at 100 μm spatial resolution. Results IMS technique revealed distribution of peptide species specifically localized in the tumor and in pancreatic intraepithelial neoplasia (m/z 945.3), the duodenal epithelium (m/z 2264.1), normal pancreatic tissue (m/z 1506.9) and smooth muscle areas of the muscular wall of the duodenum as well as the smooth muscle of the vessel wall (m/z 1185.6). Thorough examination of different areas in the tissue revealed intratumoral heterogeneity. Conclusions IMS analysis allowed detection of several peptide species localized in specific regions of a pancreatic tumor tissue while retaining morphological information. This combination makes IMS a very valuable tool in cancer diagnostics by complementing other currently used approaches.