Dalton Transactions PAPER Cite this: Dalton Trans., 2018, 47, 13696 Received 17th July 2018, Accepted 30th August 2018 DOI: 10.1039/c8dt02903b rsc.li/dalton New gold pincer-type complexes: synthesis, characterization, DNA binding studies and cytotoxicity†‡ Snežana Radisavljević, a Ioannis Bratsos, b Andreas Scheurer, c Jana Korzekwa, c Romana Masnikosa, d Aleksandar Tot, e Nevenka Gligorijević, f Siniša Radulović f and Ana Rilak Simović * a With the aim of assessing whether Au(III) compounds with pincer type ligands might be utilized as poten- tial antitumor agents, three new monofunctional Au(III) complexes of the general formula [Au(N–N’–N)Cl] Cl 2 , where N–N’–N = 2,6-bis(5-tert-butyl-1H-pyrazol-3-yl)pyridine (H 2 L tBu , 1), 2,6-bis(5-tert-butyl-1- methyl-1H-pyrazol-3-yl)pyridine (Me 2 L tBu , 2) or 2,6-bis((4S,7R)-1,7,8,8-tetramethyl-4,5,6,7-tetrahydro- 1H-4,7-methanoindazol-3-yl)pyridine (Me 2 *L, 3) were synthesized. All complexes were characterized by elemental analysis, spectroscopic techniques (IR, UV-Vis, 1D and 2D NMR) and mass spectrometry (MALDI TOF MS). The chemical behavior of the complexes under physiological conditions was studied by UV-Vis spectroscopy, which showed that all compounds were remarkablystable and that the gold center remained in the 3+ oxidation state. The kinetics and the mechanism of the reaction of complexes 1–3 with guanine derivatives (i.e. guanosine (Guo) and guanosine-5’-monophosphate (5’-GMP)) and calf thymus DNA (CT DNA) were studied by stopped-flow spectroscopy. The three complexes displayed mod- erately different rate constants in their reactions with Guo, 5’-GMP and CT DNA, which can be explained by the steric hindrance and σ-donicity of the methyl substituent on the bis-pyrazolylpyridine fragment in complexes 2 and 3. The measured enthalpies and entropies of activation (ΔH ≠ > 0, ΔS ≠ < 0) supported an associative mechanism for the substitution process. The interaction of the newly synthesized complexes 1–3 with CT DNA was investigated by UV-Vis and fluorescence spectroscopy, and also by viscosity measurements, which all indicated that complexes 1–3 bound to CT DNA with moderate binding affinity (K b = 1.6–5.7 × 10 3 M −1 ) and stabilized the duplex of CT DNA. Molecular docking indicated that complexes 1–3 interacted with DNA via intercalation. Complex 1 reduced the cell survival of all the investigated cell lines (A549, A375, and LS-174) with IC 50 values being up to 20 μM. We have shown that 1 induced pertur- bations of the cell cycle and led to apoptosis in human melanoma A375 cells. Complex 1 also affected the level of reactive oxygen species (ROS) in the same cells. However, pre-treatment of A375 cells with NAC (ROS scavenger) reversed the effect of 1 on their survival. Introduction In the last few years gold(III) complexes have attracted growing attention in the design of new metal-based anticancer therapeutics. 1–6 Indeed, a number of structurally diverse gold(III) compounds were developed and tested both in vitro and in vivo with encouraging results. 7–9 One of the major challenges of the medical development of Au(III) complexes is their stability in aqueous solutions. 10–12 In order to enhance the stability of the Au(III) center, a number of several Au(III) complexes with multidentate ligands, namely [Au(en)Cl 2 ][Cl], [Au(dien)Cl][Cl 2 ], [Au(cyclam)][ClO 4 ] 2 [Cl], [Au(terpy)Cl][Cl 2 ] and [Au( phen) Cl 2 ][Cl], has been prepared. 13 Their cytotoxic properties were tested in vitro using the representative human ovarian tumor † This work is dedicated to the deceased Prof. Dr Živadin D. Bugarčić, a great scientist in the field of bio-inorganic reaction mechanisms, teacher and a real friend. ‡ Electronic supplementary information (ESI) available. See DOI: 10.1039/ c8dt02903b a University of Kragujevac, Faculty of Science, R. Domanovića 12, P. O. Box 60, 34000 Kragujevac, Serbia. E-mail: anarilak@kg.ac.rs; Fax: +381 (0)34 335040; Tel: +381 (0)34 300262 b I.N.N., Department of Physical Chemistry, NCSR “Demokritos”, 15310 Ag. Paraskevi, Athens, Greece c Inorganic Chemistry, Department of Chemistry and Pharmacy, University of Erlangen-Nürnberg, Erlangen, Germany d Department of Physical Chemistry, Vinča Institute of Nuclear Sciences, University of Belgrade, Mike Petrovića Alasa 12-14, 11000 Belgrade, Serbia e University of Novi Sad, Faculty of Sciences, Department of Chemistry, Biochemistry and Environmental Protection, Trg Dositeja Obradovića 3, 21000 Novi Sad, Serbia f Institute for Oncology and Radiology of Serbia, Pasterova 14, 11000 Belgrade, Serbia 13696 | Dalton Trans. , 2018, 47, 13696–13712 This journal is © The Royal Society of Chemistry 2018