The ability of the unaided human eye to detect small
cancer foci or accurate borders between
cancer and normal tissue during surgery or endoscopy is limited.
Fluorescent probes are useful for enhancing visualization of small
tumors but are typically limited by either high background signal or the requirement for administration hours to days before use. We synthesized a rapidly activatable,
cancer-selective fluorescence imaging probe, γ-glutamyl hydroxymethyl
rhodamine green (gGlu-HMRG), with intramolecular spirocyclic caging for complete quenching. Activation occurs by rapid one-step cleavage of
glutamate with γ-glutamyltranspeptidase (GGT), which is not expressed in normal tissue, but is overexpressed on the cell membrane of various
cancer cells, thus leading to complete uncaging and dequenching of the fluorescence probe. In vitro activation of gGlu-HMRG was evident in 11 human
ovarian cancer cell lines tested. In vivo in mouse models of disseminated human peritoneal
ovarian cancer, activation of gGlu-HMRG occurred within 1 min of topically spraying the
tumor, creating high signal contrast between the
tumor and the background. The gGlu-HMRG probe is practical for clinical application during surgical or endoscopic procedures because of its rapid and strong activation upon contact with GGT on the surface of
cancer cells.