A Rationally Designed Prodrug for the Fluorogenic Labeling of Albumin and Theranostic Effects on Drug-Induced Liver Injury

The development of small-molecular fluorogenic tools for the chemo-selective labeling of proteins in live cells is important for the evaluation of intracellular redox homeostasis. Dynamic imaging of human serum albumin (HSA), an antioxidant protein under oxidative stress with concomitant release of antioxidant drugs to maintain redox homeostasis, affords potential opportunities for disease diagnosis and treatment. In this work, we developed a nonfluorogenic prodrug named TPA-NAC, by introducing N-acetyl-l-cysteine (NAC) into a conjugated acceptor skeleton. Through combined thiol and amino addition, coupling with HSA results in fluorescence turn-on and drug release. It was reasoned that the restricted intramolecular motion of the probe under an HSA microenvironment after covalent bonding inhibited the nonradiative transitions. Furthermore, the biocompatibility and photochemical properties of TPA-NAC enabled it to image exogenous and endogenous HSA in living cells in a wash-free manner. Additionally, the released drug evoked upregulation of superoxide dismutase (SOD), which synergistically eliminated reactive oxygen species in a drug-induced liver injury model. This study provides insights into the design of new theranostic fluorescent prodrugs for chemo-selective protein labeling and disease treatments.