Immunohistochemical detection of the CXCR4 expression in tumor tissue using the fluorescent peptide antagonist Ac-TZ14011-FITC.

Pathology is fundamental in grading, staging, and treatment planning of malignancies. One relatively novel biomarker that may become more important in therapy and diagnostics is the chemokine receptor 4 (CXCR4). Ac-TZ14011 peptide derivatives, functionalized with a radiolabel, can be used for molecular imaging of tumors. Direct fluorescent labeling of the small peptide Ac-TZ14011 with the fluorescent dye fluorescein isothiocyanate (FITC), however, provides an alternative for the detection of CXCR4 expression levels in cells and tumor tissue. In this study, Ac-TZ14011-FITC was validated for CXCR4 staining in human breast cancer cell lines MDAMB231 and MDAMB231(CXCR4+) during flow cytometric analysis. Its efficacy was compared to commercially available antibodies. Competition experiments validated the staining specificity. Confocal imaging revealed that CXCR4 staining was predominantly found on the cell membrane and/or in vesicles formed after endocytosis. Next to being able to differentiate "high" and "low" CXCR4-expressing tumor cells, the fluorescent peptide demonstrates potential in fluorescent immunohistochemistry of tumor tissue. Ac-TZ14011-FITC was able to differentiate MDAMB231 from MDAMB231(CXCR4+) tumor cells and tissue, proving its applicability in the detection of differences in CXCR4 expression levels.