Two bioluminogenic caged coelenterazine derivatives (bGalCoel and bGalNoCoel) were designed and synthesized to detect β-galactosidase activity and expression by means of bioluminescence imaging. Our approach addresses the instability of coelenterazine by introducing β-galactose caging groups to block the auto-oxidation of coelenterazine. Both probes contain β-galactosidase cleavable caging groups at the carbonyl group of the imidazo-pyrazinone moiety. One of the probes in particular, bGalNoCoel, displayed a fast cleavage profile, high stability, and high specificity for β-galactosidase over other glycoside hydrolases. bGalN-oCoel could detect β-galactosidase activity in living HEK-293T cell cultures that expressed a mutant Gaussia luciferase. It was determined that coelenterazine readily diffuses in and out of cells after uncaging by β-galactosidase. We showed that this new caged coelenterazine derivative, bGalNoCoel, could function as a dual-enzyme substrate and detect enzyme activity across two separate cell populations.
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