This journal is c The Royal Society of Chemistry 2012 Chem. Commun., 2012, 48, 11623–11625 11623 Cite this: Chem. Commun., 2012, 48, 11623–11625 Medicinal gold compounds form tight adducts with the copper chaperone Atox-1: biological and pharmacological implicationsw Chiara Gabbiani, a Federica Scaletti, b Lara Massai, b Elena Michelucci, c Maria A. Cinellu d and Luigi Messori* b Received 11th September 2012, Accepted 15th October 2012 DOI: 10.1039/c2cc36610j Based on ESI-MS measurements, we show here that some repre- sentative cytotoxic gold(III) compounds produce stable adducts upon reaction with the copper chaperone Atox-1; notably, such adducts contain gold in the oxidation state +1. These findings are of interest to understand the intracellular metabolism of medicinal gold species and to develop new potent inhibitors of the copper trafficking system. The so called ‘‘copper trafficking system’’ is primarily involved in the regulation of copper transport and homeostasis inside cells. Details of the copper trafficking system were recently disclosed. 1 This system consists of a few proteins that assist copper entrance inside cells and then promote its transfer and delivery to essential copper-dependent cellular proteins 1 (Fig. 1). The sophisticated biochemical machinery of the copper trafficking system ensures a tight control of the intracellular concentrations of free copper ions that are potentially very deleterious to cells and are kept well below 10 À15 M. Atox-1 is an intracellular metallochaperone crucially involved in copper trafficking; structural details of Atox-1 were clarified through a few recent studies. 2 Most Atox-1 homologues are B70 amino acid proteins containing a conserved CXXC motif for copper(I) binding in the vicinity of the N-terminus. Previous investigations revealed that platinum based drugs do interact strongly with proteins belonging to the copper trafficking system; the latter, in turn, seems to play a key role in modulating cisplatin uptake. 3 A strict linkage between the copper trafficking system and resistance to cisplatin was also pinpointed. 4 More recent studies proved that cisplatin reacts eagerly with Atox-1 forming stable derivatives. 5 The structures of cisplatin derivatives of Atox-1 have been solved through X-ray diffraction 2 or NMR measurements 5 proving the inter- action of the platinum center with the CXXC motif. Interest- ingly, Arnesano et al. showed that cisplatin binding to Atox-1 comprises at least two steps: initially a cisplatin–Atox-1 adduct is formed; afterward, protein dimerization and concomitant loss of ammines from cisplatin take place. 5 In turn, a study by Pernilla Wittung et al. analysed the reaction of cisplatin with Atox-1 through various biophysical methods and demon- strated that copper(I) and platinum(II) ions may bind simulta- neously to this protein to nearby, yet independent and not mutually exclusive, anchoring sites. 6 During the last decade we were engaged in preparing and characterising a number of medicinal gold compounds as experimental cytotoxic and anticancer agents. 7 On the ground of basic concepts of coordination chemistry and of established HSAB principles, we hypothesised that medicinal gold compounds, especially those in the oxidation state +1, might interact strongly with proteins of the copper trafficking system. Indeed, a previous study revealed that the copper trafficking system is substantially inhibited by ‘‘soft’’ d 10 silver(I) ions, capable of binding Atox-1. 8 Gold(I) ions – with a d 10 electronic configuration – are even ‘‘softer’’ Lewis acids than silver(I) ions and, as such, should react eagerly with the copper(I) binding site of Atox-1; remarkably, a very recent study reported that copper transport proteins are involved in Fig. 1 Pathways of copper trafficking within a mammalian cell. Reproduced from ref. 5. a Department of Chemistry and Industrial Chemistry, via Risorgimento 35, 56126 Pisa, Italy b Laboratory of ‘‘Metals in Medicine’’ (METMED), Department of Chemistry ‘‘Ugo Schiff’’, University of Florence, Via della Lastruccia 3, 50019 Sesto Fiorentino, Firenze, Italy. E-mail: luigi.messori@unifi.it; Fax: +39 055 4573385; Tel: +39 055 4573388 c Mass Spectrometry Centre (CISM), University of Florence, Via U. Schiff 6, 50019 Sesto Fiorentino, Firenze, Italy d Department of Chemistry, University of Sassari, Via Vienna 2, 07100 Sassari, Italy w Electronic supplementary information (ESI) available: Experimental section and an additional figure. See DOI: 10.1039/c2cc36610j ChemComm Dynamic Article Links www.rsc.org/chemcomm COMMUNICATION Downloaded by Universita Studi di Firenze on 11 January 2013 Published on 16 October 2012 on http://pubs.rsc.org | doi:10.1039/C2CC36610J View Article Online / Journal Homepage / Table of Contents for this issue