Glutathione Protects other Cellular Thiols against Oxidation by Cu^II-Dp44mT

Cu-thiosemicarbazones have been intensively investigated for their application in cancer therapy or as antimicrobials. Copper(II)-di-2-pyridylketone-4,4-dimethyl-thiosemicarbazone (Cu^II-Dp44mT) showed anticancer activity in the submicromolar concentration range in cell culture. The interaction of Cu^II-Dp44mT with thiols leading to their depletion or inhibition was proposed to be involved in this activity. Indeed, Cu^II-Dp44mT can catalyze the oxidation of thiols although with slow kinetics. The present work aims to obtain insights into the catalytic activity and selectivity of Cu^II-Dp44mT toward the oxidation of different biologically relevant thiols. Reduced glutathione (GSH), L-cysteine (Cys), N-acetylcysteine (NAC), D-penicillamine (D-Pen), and the two model proteins glutaredoxin (Grx) and thioredoxin (Trx) were investigated. Cu^II-Dp44mT catalyzed the oxidation of these thiols with different kinetics, with rates in the following order D-Pen>Cys≫NAC>GSH and Trx>Grx. Cu^II-Dp44mT was more efficient than Cu^II chloride for the oxidation of NAC and GSH, but not D-Pen and Cys. In mixtures of biologically relevant concentrations of GSH and either Cys, Trx, or Grx, the oxidation kinetics and spectral properties were similar to that of GSH alone, indicating that the interaction of these thiols with Cu^II-Dp44mT is dominated by GSH. Hence GSH could protect other thiols against potential deleterious oxidation by Cu^II-Dp44mT.