Detection and Cellular Imaging of Human Cancer Enzyme Using a Turn-On, Wavelength-Shiftable, Self-Immolative Profluorophore

A frontier
area in the development of activatable (turn-on) fluorescence-based
probes is that concerned with rapid and selective stimulus triggering
of probe activation so as to allow for biomarker identification and
cellular imaging. The work here is concerned with a cloaked fluorophore
composed of a reporter whose fluorescence is efficiently quenched
by it being bound to an activatable trigger group through a novel
self-immolative linker. Highly selective and rapid activation of the
trigger group is achieved by chemical and enzymatic means that result
in activated trigger group detachment from the self-immolative linker,
with the latter subsequently cleaved from the reporter autonomously,
thereby unmasking intense, red-shifted fluorescence emission. To achieve
this success, we used a trimethyl-locked quinone propionic acid trigger
group and an N-methyl-p-aminobenzyl
alcohol self-immolative linker attached to the reporter. Delineated
here are the synthesis and characterization of this cloaked fluorophore
and the evaluation of its triggered turning on in the presence of
an up-regulated enzyme in human cancer cells, NAD­(P)­H:quinone oxidoreductase-1
(NQO1, DT-diaphorase, EC 1.6.99.2).