Rational Development of Activatable Prodrugs of the GSTP1 Inhibitor NBDHEX: Turn-On NIR Fluorogenic Drug Delivery with Selective Anticancer Activity.

Glutathione-S-transferase pi (GSTP1), overexpressed in cancer cells, is known to inactivate many electrophilic anticancer drugs by glutathionylation. While NBDHEX is a potent and selective inhibitor of GSTP1 with good anticancer activity, it suffers from poor aqueous solubility and bioavailability. Herein, we report the reactive oxygen species (ROS)-responsive fluorogenic prodrug RK-251 of NBDHEX, by coupling it to a dual positively charged NIR fluorophore (QCy7) and a ROS-responsive unit. ROS-mediated activation of RK-251 in aqueous medium resulted in rapid uncaging of NBDHEX, with turn-on NIR fluorescence and potent GSTP1 inhibition. Moreover, RK-251 exhibited potent anticancer activity against triple-negative breast cancer (MDA-MB-231) cells compared with nonmalignant cells, with the modulation of key cancer marker genes. Endogenous ROS-mediated activation of RK-251 led to the turn-on red fluorescence, which was further validated in developing zebrafish embryos, confirming the concomitant release of QCy7 without any noticeable abnormalities or acute toxicities, supporting the translational potential of the prodrug.