Sensitive β-galactosidase-targeting fluorescence probe for visualizing small peritoneal metastatic tumours in vivo

Fluorescence-guided diagnostics is one of the most promising approaches for facile detection of cancer in situ. Here we focus on beta-galactosidase, which is overexpressed in primary ovarian cancers, as a molecular target for visualizing peritoneal metastases from ovarian cancers. As existing fluorescence probes are unsuitable, we have designed membrane-permeable HMRef-beta Gal, in which the optimized intramolecular spirocyclic function affords > 1,400-fold fluorescence enhancement on activation. We confirm that HMRef-bGal sensitively detects intracellular beta-galactosidase activity in several ovarian cancer lines. In vivo, this probe visualizes metastases as small as < 1 mm in diameter in seven mouse models of disseminated human peritoneal ovarian cancer (SHIN3, SKOV3, OVK18, OVCAR3, OVCAR4, OVCAR5 and OVCAR8). Because of its high brightness, real-time detection of metastases with the naked eye is possible. Endoscopic fluorescence detection of metastases is also demonstrated. The results clearly indicate preclinical potential value of the probe for fluorescence-guided diagnosis of peritoneal metastases from ovarian cancers.