Multicolor imaging of endoplasmic reticulum-located esterase as a prodrug activation enzyme.

The carboxylesterase families of enzymes are key participants in phase I drug metabolism processes. Carboxylesterase families 1 and 2 are of particular clinical relevance. These enzymes produce endoplasmic reticulum localization signals, are primarily localized in the endoplasmic reticulum, and hydrolyze a wide range of ester-containing prodrugs into an activated form. In order to detect enzymes belonging to both families, we developed an optical multicolor imaging technique, which provides a distinct color window for multicolor imaging. This technique required the design and synthesis of three new mechanistic colored probes that fluoresce red, green, or blue and are based on the quinone methide cleavage process. These activity-based probes allow rapid and clear visualization with high specificity against the endoplasmic reticulum in cultured cells based on endoplasmic reticulum localized esterases including both families of carboxylesterase enzymes.