Ligand-induced glutathione transferase degradation as a therapeutic modality: Investigation of a new metal-mediated affinity cleavage strategy for human GSTP1-1

Glutathione transferases (GST, EC. 2.5.1.18) are overexpressed in cancer cell and have been shown to be involved in cancer cell growth, differentiation and the development of multi-drug resistance (MDR) mechanism. Therefore, GST inhibitors are emerging as promising chemosensitizers to manage and reverse MDR. The present work aims to the synthesis, characterization and assessment of a new active-site chimeric inhibitor towards the MDR-involved human GSTP1-1 isoenzyme (hGSTP1-1). The inhibitor [BDA–Fe(III)] was designed to possess two functional groups: the anthraquinone moiety, as recognition element by hGSTP1-1 and a metal chelated complex [iminodiacetic acid-Fe(III)] as a reactive moiety, able to generate reactive oxygen species (ROS), through Fenton reaction. Upon binding of the BDA–Fe(III) to hGSTP1-1 in the presence of hydrogen peroxide, reactive oxygen species (ROS) are generated, which promoted the specific cleavage of hGSTP1-1 in a time and concentration-dependent manner. Electrophoretic analysis showed that each enzyme subunit is cleaved at a single site. Amino acid sequencing as well as molecular modelling studies established that the cleaved peptide bond is located between the amino acids Tyr103 and Ile104. This ligand-induced hGSTP1-1 degradation and inactivation strategy is discussed as a new approach towards chemosensitization of MDR cancer cells.