In Situ N-Glycosylation Signatures of Epithelial Ovarian Cancer Tissue as Defined by MALDI Mass Spectrometry Imaging

SIMPLE SUMMARY: Altered glycosylation of proteins was shown to be implicated in various steps of malignant transformation and tumor progression. For that reason, it is frequently referred to as the next hallmark of cancer. In epithelial ovarian cancer (EOC), a female gynecological malignancy of the highest mortality, N-glycosylation alterations were predominantly investigated at the level of serum glycoproteins and OC cell lines. By contrast, data on in situ N-glycosylation in OC tissue are still very limited, particularly with respect to terminal sialylation. This is despite the increasing number of studies supporting the role of sialylated N-glycans in tumor progression, angiogenesis, and metastasis. In this work, MALDI mass spectrometry imaging (MALDI-MSI) was implemented in combination with chemical sialic acid derivatization to determine tissue type-specific N-glycosylation of less common histotypes of EOC and non-malignant ovarian disease. ABSTRACT: The particularly high mortality of epithelial ovarian cancer (EOC) is in part linked to limited understanding of its molecular signatures. Although there are data available on in situ N-glycosylation in EOC tissue, previous studies focused primarily on neutral N-glycan species and, hence, still little is known regarding EOC tissue-specific sialylation. In this proof-of-concept study, we implemented MALDI mass spectrometry imaging (MALDI-MSI) in combination with sialic acid derivatization to simultaneously investigate neutral and sialylated N-glycans in formalin-fixed paraffin-embedded tissue microarray specimens of less common EOC histotypes and non-malignant borderline ovarian tumor (BOT). The applied protocol allowed detecting over 50 m/z species, many of which showed differential tissue distribution. Most importantly, it could be demonstrated that α2,6- and α2,3-sialylated N-glycans are enriched in tissue regions corresponding to tumor and adjacent tumor-stroma, respectively. Interestingly, analogous N-glycosylation patterns were observed in tissue cores of BOT, suggesting that regio-specific N-glycan distribution might occur already in non-malignant ovarian pathologies. All in all, our data provide proof that the combination of MALDI-MSI and sialic acid derivatization is suitable for delineating regio-specific N-glycan distribution in EOC and BOT tissues and might serve as a promising strategy for future glycosylation-based biomarker discovery studies.