Selective Near-Infrared Fluorescent Chemosensors for Human Carboxylesterase 1 Activity

Carboxylesterase 1 (CES1) is an enzyme that is crucial for drug metabolism by hydrolyzing a range of ester- and amide-containing drugs, which, in turn, influences drug efficacy and safety. Accurate monitoring of CES1 activity bears importance for the clinical setting, providing invaluable guidance in the utilization of numerous drugs that undergo metabolism by CES1. An approach to achieve monitoring involves designing near-infrared (NIR) probes, which also have the advantages of reducing autofluorescence, enhancing sensitivity, and allowing noninvasive imaging of molecular processes in biological systems. Herein, we developed NIR probes with selectivity for CES1. Our lead design, 1-Me, a Cy7 derivative, exhibited excellent photophysical properties under physiological conditions. In vitro enzymatic assays demonstrated that 1-Me offers a rapid and highly selective fluorogenic response to CES1 over CES2, undergoing efficient hydrolysis to yield a strong NIR fluorescence signal at 775 nm with 64× within 1 h and a limit of detection of 0.085 μg/mL. Furthermore, 1-Me exhibited minimal cytotoxicity across a range of concentrations in mammalian cells. Its utility was convincingly demonstrated in live-cell imaging experiments, where it accurately reported endogenous CES1 activity in human cell lines. This capability enables isoform-specific imaging, which holds promise for accelerating drug discovery, understanding CES1's biological roles, and guiding precision pharmacotherapy.