Rational design of gold(III)-dithiocarbamato peptidomimetics for the targeted anticancer chemotherapy Morelle Negom Kouodom a , Giulia Boscutti a , Marta Celegato b , Marco Crisma c , Sergio Sitran d , Donatella Aldinucci b , Fernando Formaggio a , Luca Ronconi a, ⁎, Dolores Fregona a, ⁎⁎ a Department of Chemical Sciences, University of Padova, Via F. Marzolo 1, Padova 35131, Italy b Division of Experimental Oncology 2, Centro di Riferimento Oncologico (CRO-IRCSS), Via F. Gallini 2, Aviano (PN) 33081, Italy c Institute of Biomolecular Chemistry, CNR, Padova Unit, Via F. Marzolo 1, Padova 35131, Italy d Institute of Inorganic and Surfaces Chemistry, CNR Research Area, Corso Stati Uniti 4, Padova 35127, Italy abstract article info Article history: Received 1 April 2012 Received in revised form 30 May 2012 Accepted 3 July 2012 Available online 11 July 2012 Keywords: Gold Dithiocarbamates Peptidomimetics Anticancer activity Drug delivery Peptide transporters (PEPTs) As a further extension of our research work focusing on the development of gold(III)-dithiocarbamato dtc deriv- atives of oligopeptides as potential anticancer agents, complexes [Au III X 2 (dtc-Sar-L-Ser(t-Bu)-O(t-Bu))] (X=Br (1a)/Cl (1b)), [Au III X 2 (dtc-AA-Aib 2 -O(t-Bu))] (AA=Sar (sarcosine, N-methylglycine), X=Br (2a)/Cl (2b); AA=D,L-Pro, X=Br (3a)/Cl (3b)), [Au III X 2 (dtc-Sar-Aib 3 -O(t-Bu))] (X=Br (4a)/Cl (4b)), and [Au III X 2 (- dtc-Sar-Aib 3 -Gly-OEt)] (X=Br (5a)/Cl (5b)) (Aib = “alpha”-aminoisobutyric acid, 2-methylalanine) were designed to obtain metal-based peptidomimetics that may specifically target two peptide transporters (namely, PEPT1 and PEPT2) upregulated in several human tumor cells. All the compounds were characterized by means of FT-IR and mono- and multidimensional NMR spectroscopy. According to in vitro cytotoxicity studies, complex [Au III Cl 2 (dtc-D,L-Pro-Aib 2 -O(t-Bu))] (3b) turned out to be the most effective toward the four human tumor cell lines evaluated (PC3, 2008, C13, and L540), for which the IC 50 values were lower than cisplatin. Remarkably, it showed no cross-resistance with cisplatin itself and was proved to inhibit tumor cell proliferation by inducing almost exclusively late apoptosis/necrosis. Biological results are here reported and discussed in terms of the structure–activity relationship. © 2012 Elsevier Inc. All rights reserved. 1. Introduction Notwithstanding the therapeutic efficacy, conventional anticancer agents suffer from several drawbacks including high toxicity, chemical instability, unsuitable pharmacokinetic and pharmacodynamic profiles, no oral bioavailability, and poor specificity [1]. Consequently, much effort has been recently focusing on shifting from cytotoxic non-specific chemotherapies to molecularly-targeted rationally designed drugs [2], because of the potential for minimizing unwanted side-effects as well as for improving tumor selectivity while retaining the desirable thera- peutic effectiveness [3]. Tumor cells express many biomarkers and receptors that can be specifically targeted. Thus, current research has been devoted to the development of efficient and innovative delivery systems in which conjugated drugs incorporate a tumor targeting group (carrier) and a cytotoxic agent (cargo). These systems should ideally reach the tis- sue of interest and deliver their cargo directly into the cells where it can exert its therapeutic activity [4]. So far, a number of strategies have been suggested as drug delivery systems, including liposomes, nanoparticles and polymers, but very few have reached the preclinical or clinical trial stage [5–8]. Among them, drug functionalization with specific peptides may offer higher flexibility over other approaches [9], and, accordingly, much attention has been recently given to peptide-based delivery systems targeting peptide transporters (PEPTs). The proton-coupled peptide transporters PEPT1 and PEPT2 are integral membrane carrier proteins that mediate the uptake of most possible physiologically occurring di- and tripeptides. The carriers are symporters that cotransport H + and substrates across cell membranes, the inwardly directed proton gradient providing the driving force for the accumulation of a substrate against its concentration gradient [10]. Besides their physiological substrates, PEPTs are also responsible for membrane transport of many pharmacologically active peptidomimetic drugs and prodrugs owing to their structural resem- blance to di- and tripeptides [11,12]. They are expressed in some mam- malian tissues/organs, including small intestine, kidney, pancreas, bile duct, liver, mammary glands, lung and choroid plexus, but, remarkably, seem to be overexpressed in some types of tumors [13]. In fact, cancer cells require larger amounts of peptide-bound amino acids for growth and metabolism and, consequently, peptide transporters might be upregulated [14]. Intriguingly, it was recently shown that PEPTs are largely overexpressed in several types of tumor cells but not in the Journal of Inorganic Biochemistry 117 (2012) 248–260 ⁎ Corresponding author. Tel.: +39 049 8275214; fax: +39 02 700538450. ⁎⁎ Corresponding author. Tel.: +39 049 8275159; fax: +39 02 700500560. E-mail addresses: luca.ronconi@unipd.it (L. Ronconi), dolores.fregona@unipd.it (D. Fregona). 0162-0134/$ – see front matter © 2012 Elsevier Inc. All rights reserved. doi:10.1016/j.jinorgbio.2012.07.001 Contents lists available at SciVerse ScienceDirect Journal of Inorganic Biochemistry journal homepage: www.elsevier.com/locate/jinorgbio