The use of matrix coating assisted by an electric field (MCAEF) to enhance mass spectrometric imaging of human prostate cancer biomarkers

In this work, we combined a newly developed matrix coating technique – matrix coating assisted by an electric field (MCAEF) and matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) to enhance the imaging of peptides and proteins in tissue specimens of human prostate cancer. MCAEF increased the signal‐to‐noise ratios of the detected proteins by a factor of 2 to 5, and 232 signals were detected within the m/z 3500–37500 mass range on a time‐of‐flight mass spectrometer and with the sinapinic acid MALDI matrix. Among these species, three proteins (S100‐A9, S100‐A10, and S100‐A12) were only observed in the cancerous cell region and 14 proteins, including a fragment of mitogen‐activated protein kinase/extracellular signal‐regulated kinase kinase kinase 2, a fragment of cAMP‐regulated phosphoprotein 19, 3 apolipoproteins (C‐I, A‐I, and A‐II), 2 S100 proteins (A6 and A8), β‐microseminoprotein, tumor protein D52, α‐1‐acid glycoprotein 1, heat shock protein β‐1, prostate‐specific antigen, and 2 unidentified large peptides at m/z 5002.2 and 6704.2, showed significantly differential distributions at the p < 0.05 (t‐test) level between the cancerous and the noncancerous regions of the tissue. Among these 17 species, the distributions of apolipoprotein C‐I, S100‐A6, and S100‐A8 were verified by immunohistological staining. In summary, this study resulted in the imaging of the largest group of proteins in prostate cancer tissues by MALDI‐MS reported thus far, and is the first to show a correlation between S100 proteins and prostate cancer in a MS imaging study. The successful imaging of the three proteins only found in the cancerous tissues, as well as those showing differential expressions demonstrated the potential of MCAEF‐MALDI/MS for the in situ detection of potential cancer biomarkers. Copyright © 2015 John Wiley & Sons, Ltd.