Near-infrared phenothiazine-fused rhodol with large Stokes shift for fluorogenic imaging of butyrylcholinesterase in vivo.

Butyrylcholinesterase (BChE) is a serine hydrolase that plays diverse roles in physiological and pathological processes, and imaging BChE activity is of great importance for disease diagnosis and drug development. Here we develop a new activatable near-infrared (NIR) fluorescent probe, DR760, for high contrast imaging of BChE activities in vivo. A new NIR fluorophore with a large Stokes shift is engineered by fusing phenothiazine with rhodol. We further develop a fluorogenic probe for BChE by caging the hydroxyl group with a cyclopropyl ester moiety. It is shown that BChE-mediated release of the caging group results in a fluorescence enhancement of 81-fold at 760 nm. The probe is further explored to image BChE activity and monitor changes in BChE activity in a drug-treated Alzheimer's disease (AD) cellular model. The capability of the probe for imaging BChE activity in vivo is demonstrated using a tumor-bearing mice model. Collectively, this study shows that DR760 affords a new molecular tool for detecting BChE activity in vitro and in vivo.