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Immunofluorescent staining of tissues via in situ proximity ligation assay (isPLA) is now a well-established tool for highly sensitive detection of protein-protein interactions and their localization. It finds versatile applications in basic research, understanding of cellular processes, visualization of tissue architecture, and identification of biomarkers, among others. However, standard IF and isPLA techniques alike may suffer from high background. Tissues are particularly affected by background problems caused by autofluorescence and tissue infiltration of various cell types (e.g., immune, endothelial) where the fluorescently labelled oligos used for detection in isPLA may bind unspecifically. To address this, we developed a next generation isPLA-based technology for fluorescent detection of protein interactions in FFPE and fresh frozen human and mouse tissues, called NaveniFlex Tissue. In contrast to previously available protocols, it can visualize signal that would otherwise be obscured by background, thereby increasing sensitivity. Here, we compare the ability of NaveniFlex Tissue and similar commercial kits to detect the interaction between low abundance proteins Podocalyxin and Ezrin in the glomeruli of healthy kidney and in breast cancer, where co-expression is a prognostic marker for increased metastatic potential. While other kits generate high background which masks isPLA signal entirely, NaveniFlex Tissue dramatically reduces cell-based background and visualizes the interaction in its specific localization. Furthermore, in a TMA staining for the Mucin 16/Mesothelin interaction, our method successfully demonstrates strong and clear signal in stage III ovarian cancer. Moreover, it sensitively detects even low abundance interaction in a stage Ia tumor. In contrast, a different commercial kit detects significantly less interactions in the stage III tumor, while in the lower grade tumor it does not generate signals above background level. Therefore, NaveniFlex Tissue improves detection in tissues with varying disease progression, thus adding information and prognostic value to the staining. Taken together, our data illustrate that NaveniFlex Tissue outperforms current isPLA-based techniques by efficiently reducing background, which improves visualization of signal and signal-to-noise ratios in various healthy and diseased tissues. Citation Format: Hampus Elofsson, Doroteya Raykova, Agata Zieba Wicher. Powerful background reduction in fluorescent tissue stains with an improved proximity-based technology for detection of protein-protein interactions. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6772. |
