Visualizing glioma margins by real-time tracking of γ-glutamyltranspeptidase activity

Distinguishing tumor from adjacent non-cancerous tissue can be problematic during surgical treatment of malignant glioma. Consequently, a novel approach to selective discrimination is required. The goal of this study was to determine whether a fluorescent probe activated by γ-Glutamyltranspeptidase (GGT), an enzyme that is overexpressed on glioma cell membranes but only minimally expressed in normal brain tissue, could be used to visualize glioma margins. Here, we showed that the GGT-activatable fluorescent probe (NC-B-Cys-γ-Glu) provided real-time in situ tracking of enzyme activity that accurately distinguished glioma from healthy brain tissue. NC-B-Cys-γ-Glu, which featured distinct ratiometric fluorescence responsiveness after interaction with GGT, enabled monitoring of GGT activity in living cells and differentiation between glioma and normal cells. Topical spraying of NC-B-Cys-γ-Glu facilitated real-time in vivo identification of orthotopic glioblastomas in a mouse model. Importantly, the tumor, infiltrating area and surrounding normal tissue were distinguished in clinical glioma samples by real-time tracking of GGT activity. When coupled with auto fluorescence bronchoscopy, NC-B-Cys-γ-Glu offered diagnostic value for cancers overexpressing GGT. Therefore, NC-B-Cys-γ-Glu might offer a promising tool to guide maximal yet precise tumor resection while sparing non-cancerous tissue.