The diagnosis and treatment of prostate cancer (PCa) is largely dependent on clinical and pathologic staging based on cellular morphology of tissues examined under a light microscope. Multiple molecular alterations at the protein level can be monitored in situ both qualitatively and quantitatively with a recently developed technique, matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Direct profiling of proteins in tissue sections using MALDI-IMS can link morphological and molecular changes, enhancing the ability to identify candidates for new PCa biomarkers. However, critical questions remain regarding the integration of this technique with clinical decision making. To address these questions for prostate cancer, a cohort of 36 PCa and 61 adjacent benign frozen tissue samples were analyzed by MALDI-IMS. Multiple protein/peptide expression changes were identified that correlated with the presence or absence of PCa, including the over-expression of a single peptide (m/z = 4355) that accurately distinguished primary cancer tissue from adjacent normal tissue. Tandem mass spectrometry identified this peptide as a fragment of MEKK2, a member of the MAP kinase signaling pathway. MEKK2 over-expression in clinical tissues as determined by immunohistochemistry correlated with expression of m/z=4355 via MALDI-IMS. The downstream targets of MEKK2, MEK5/ERK5, are known to be over-expressed in high grade PCa. Interestingly, we found that in cases of well differentiated PCa MEKK2 expression was highest and decreased in high grade poorly differentiated PCa. MEK5 staining of the same tissues showed an inverse relationship with MEKK2 staining. The morphological features associated with the expression of both MEKK2 protein and m/z 4355 also included infiltrating lymphocytes, indicating a potential role for MEKK2 as a marker for atrophic lesions. We also examined clinical prostate tissues subjected to an alcohol based fixative (Unfix, Sakura) as a model system for parallel analysis of the same tissue by IHC/morphology/MALDI-IMS. This system yielded the same results as frozen tissue and thus provides a clinically viable alternative to formalin fixation. Our results highlight the potential of MALDI-IMS in biomarker discovery and analysis, as well as a scenario for the integration of this technique into the clinical pathologic assessment of PCa.

Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4739.

100th AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO

American Association for Cancer Research
2009