Fluorescent probes for bioactive detection and imaging of phase II metabolic enzymes

Numerous enzymes with diverse structures and functions are distributed in nature, and their expressions and functions are easily influenced by genetic and environmental factors, resulting in their presence in different tissues, individuals and species. The metabolic enzymes are responsible for modification of functional groups (classified as phase I reactions) or conjugation with endogenous substituents (classified as phase II reactions) in the organism. Fluorescent probes are key tools in the characterization of metabolic enzymes, used in drug discovery, evaluation of drug-drug interactions, clinical diagnosis and treatment etc. Therefore, the use of fluorescent probes in the accurate and rapid detection of phase II metabolic enzymes and related applications are summarized in this review. In particular, the following enzymes will be covered: UGT (Uridine-diphosphate glucuronosyltransferase), COMT (Catechol-O-methyltransferase), NAT (N-acetyltransferase), GT (Glucosyltransferase), GST (Glutathione S-transferase), SULT (Sulfotransferase) and some other phase II metabolic enzymes. Their applications to biological imaging and high-throughput inhibitor screening are discussed in detail. In addition, future directions in the design and development of small molecular fluorescent probes for phase II enzymes are discussed in the final section.