Small-molecule optical probes for cell imaging of protein sulfenylation and their application to monitor cisplatin induced protein oxidation

Abstract Reactive oxygen species (ROS) are considered versatile second messengers mediating fundamental biological functions. A molecular pathway by which ROS determine functional diversity is the selective oxidation of cysteine residues to form sulfenic acid (SOH) products, known as sulfenylation or S -hydroxylation. This crucial post-translational modification is responsible for the alteration of protein stability, function and signalling. Despite considerable advances on the identification of sulfenic residues on individual proteins, improved methods are needed for direct visualization and accurate quantification of the extent of total protein sulfenylation. Herein we present the synthesis of two new cell-permeable fluorescent probes containing dimedone (a cyclic β-diketone with high specificity for sulfenic acids), and apply them to study oxidation processes in individual cells via microscopy. The low cytotoxicity, cell permeability and optical features of the probes allowed us to visualize and quantify the oxidation of cysteine residues in live cells during H 2 O 2 -mediated oxidative burst ( i.e. exogenously administered H 2 O 2 ). We present preliminary cellular imaging studies with these probes to analyse the oxidation process in cells treated with the anticancer drug cisplatin.