Comparative studies on DNA-binding and in vitro antitumor activity of enantiomeric ruthenium(II) complexes
Graphical abstract
Molecular docking models of energy-minimized structure of DNA dodecamer duplex, d(CGCGAATTCGCG)2 with Δ-[Ru(bpy)2PBIP]2 + {bpy = 2,2′-bipyridine, PBIP = 2-(4-bromophenyl)imidazo[4,5-f]1,10-phenanthroline} (A) and Λ-[Ru(bpy)2PBIP]2 + (B). Both enantiomers intercalate between base pairs of DNA in minor groove, and that the Δ form intercalates into DNA more deeply than the Λ form does.
Introduction
The discovery of cisplatin as antitumor drug by Rosenberg et al. opens the new pathway for cancer chemotherapy [1], [2]. However, the platinum-based anticancer complexes have some side effects such as nephrotoxicity, myelotoxicity, ototoxicity, peripheral neuropathy, nausea et al. [3]. In addition, many tumor cells are resistant to platinum drugs [4]. Since then, other metal-based anticancer small molecules have been widely explored in drug discovery, especially for ruthenium complexes. Sadler's group [5] focused on the anticancer potential of half-sandwich Ru(II) arene complexes of the type [(η6-arene)Ru(YZ)(X)], where YZ is a bidentate chelating ligand and X is a good leaving group (e.g. Cl). These half sandwich ‘piano-stool’ complexes offer much scope for design, with the potential to vary in each of the building blocks to enable modifications of thermodynamic and kinetic parameters. Trivalent ruthenium complexes (III) were assembled together with heterocycle compounds in Keppler's group for the treatment and prevention of cancers as well as the associated pain and suffering [6], [7]. Also, some dimethylsulphoxide ruthenium(II) complexes exerted greater efficacy against cancer metastases [8], [9]. Ruthenium complexes with their suitable properties are being designed to overcome the platinum complex limitation [10]. Currently, several types of ruthenium complexes have been synthesized and investigated for their anticancer application [11].
A couple of mechanisms have been explored in detailed for the anticancer activities including the interaction with biomolecules [12], [13], inhibition of metastasis [14], [15], production of reactive oxygen species [16], and induction of apoptosis [17]. In addition, the formation of metal-DNA adducts are capable of inhibiting DNA and RNA synthesis, and inducing programmed cell death [18], [19]. Polypyridyl ruthenium(II) complexes can bind to DNA in a non-covalent fashion such as electrostatic binding for cations, groove binding for large ligands, intercalative binding for planar ligands and partial intercalative binding for incompletely planar ligands [20], [21]. Many useful applications of these complexes require that the complexes bind to DNA through an intercalative mode. On the other hand, it has been well known that, interaction of DNA with chiral complex is generally enantioselective [22], [23], [24]. And the DNA cross-links of metal complexes with enantiomeric carrier ligands can exhibit different conformational features, leading to be processed differently response by the cellular machinery [25]. Therefore, it is very important and interesting to study the enantioselectivity of ruthenium(II) complexes interacting with DNA. And many other factors such as steric matching and binding strength [26], DNA binding modes, binding geometry [27], DNA sequence and length of the duplexes [28] have been proposed to govern the enantioselectivity for octahedral complexes' binding to DNA. However, only a few papers concentrated on the relationship between the enantioselectivity of metal complexes binding to DNA and their anti-tumor activities by comparative studies on the interactions of a pair of enantiomers with DNA [29], [30], [31].
As well known, substituents in phenyl ring are divided into two categories: ortho-para directing group and meta directing group. Generally, the former activates the phenyl ring for substituent reaction and the later inactivates the phenyl ring except halogens, which are ortho-para directing groups but inactivate the phenyl ring weakly. Comparative studies on the interactions of DNA with ruthenium(II) complexes containing both the two categories of typical phenyl substituents in the main ligand with 2-phenyl-imidazo[4,5-f]1,10-phenanthroline as the mother compound, have already been reported [32], [33]. And there is no any paper about the interactions of enantiomers containing halogen substituents in this class of main ligand with DNA up to now.
As our ongoing focus on the interactions of polypyridyl ruthenium(II) complexes with DNA [20], [22], [34], [35], [36], herein, we report the syntheses of a pair of enantiomic ruthenium(II) polypyridyl complexes, Δ- and Λ-[Ru(bpy)2PBIP]2 + {bpy = 2,2′-bipyridine, PBIP = 2-(4-bromophenyl)imidazo[4,5-f]1,10-phenanthroline}, along with their different DNA-binding behaviors and cytotoxic activities in tumor cell line. This study could provide useful information about chiral discrimination in DNA-targeting drugs and molecular probes.
Section snippets
Syntheses
The complex cis-[Ru(bpy)2Cl2]·2H2O [37] and 1,10-phenanthroline-5,6-dione [38] were prepared according to the literature procedures. Other reagents and solvents were purchased commercially and used without further purification. Resolution of cis-[Ru(bpy)2(py)2]2 + [39] was achieved by addition of 19.0 mL of a 0.5 M aqueous solution of disodium O,O′-dibenzoyl-d-tartrate to cis-[Ru(bpy)2(py)2]Cl2 (1.95 g) in 30 mL water and stirring for 10 min. Red crystals of the pure Δ-[Ru(bpy)2(py)2][O,O′-dibenzoyl-d
Syntheses and resolving of enantiomers
Isolation of the enantiomers was achieved by using Δ- and Λ-[Ru(bpy)2(py)2]2 + as enantiomerically pure chiral building blocks, which have shown high thermal stereochemical stability and have been widely used to prepare stereochemically pure ruthenium complexes [49]. The enantiomeric purity of these complexes was assayed by CD spectroscopy. The CD spectra of the Δ and Λ enantiomer are shown in Fig. 2. Assignment of the absolute configuration of the enantiomers was made by the molecular
Conclusions
Spectroscopic studies together with viscosity measurements show that both the enantiomers bind to CT DNA via intercalative mode, and that the Δ form binds to CT DNA more strongly than the Λ form does. Molecular simulation further shows that both the two enantiomers intercalate between base pairs of DNA in minor groove, and that the Δ form intercalates into DNA more deeply than the Λ form does. In addition, the MTT assays show that the Δ form induces a greater cytotoxicity than the Λ form on
Abbreviations
- bpy
2,2′-bipyridine
- PBIP
2-(4-bromophenyl)imidazo[4,5-f]1,10-phenanthroline
- CT DNA
calf thymus DNA
- py
pyridine
- Tris
tris(hydroxymethyl)-aminomethane
- MTT
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
- FBS
fetal bovine serum
- DMEM
Dulbecco's Modified Eagle's Medium
- DMSO
dimethylsulphoxide
- IR
inhibitory rate
- MLCT
metal-to-ligand charge transfer
- IC50
50% growth inhibition concentration;
- cisplatin
cis-diamineplatinum(II) dichloride
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant 31540012, 31470431, 30570421, 81501213), Guangdong Natural Science Foundation for Major cultivation project (2014A030308017), Shenzhen Science and Technology Innovation Committee Grants (JSGG20160229120821300, JCYJ20150625103526744, JCYJ20150324140036823, JCYJ20120613112512654, JCYJ20140414090541801, JCYJ20160427172335974 JSGG20130411160539208, KQCX20140522111508785, CXZZ20150601110000604, ZDSYS201506031617582),
References (57)
- et al.
Drug Discov. Today
(2009) - et al.
Pharmacol. Res.
(1989) - et al.
Eur. J. Cancer
(1993) - et al.
J. Inorg. Biochem.
(2011) - et al.
J. Inorg. Biochem.
(2011) - et al.
J. Inorg. Biochem.
(2010) - et al.
Biochem. Pharmacol.
(2012) - et al.
Eur. J. Med. Chem.
(2014) - et al.
Inorg. Chem. Commun.
(2010) - et al.
Eur. J. Med. Chem.
(2011)
J. Inorg. Biochem.
J. Inorg. Biochem.
Eur. J. Med. Chem.
J. Inorg. Biochem.
J. Inorg. Biochem.
J. Inorg. Biochem.
J. Inorg. Biochem.
Int. J. Biol. Macromol.
J. Inorg. Biochem.
Nature
Cancer Chemother. Pharmacol.
Chem. Soc. Rev.
Oncogene
Nat. Commun.
Dalton Trans.
Sci. Rep.
Cited by (37)
Organoruthenium-bipyridyl complexes – A platform for diverse chemistry and applications
2024, Coordination Chemistry ReviewsRuthenium complexes
2023, Nucleic Acids: A Natural Target for Newly Designed Metal Chelate Based DrugsCombination of light and Ru(II) polypyridyl complexes: Recent advances in the development of new anticancer drugs
2022, Coordination Chemistry ReviewsCitation Excerpt :Ruthenium(II) complexes are indeed emerging as adjuvants to platinum-based chemotherapics [19], even outclassing them from certain points of view. For example, they show lower systemic toxicity, hence fewer side effects, as a consequence of their higher selectivity for cancer vs healthy cells [14,15,20,21], which can be in turn a result of a higher uptake by the former than the latter [22]. Notably, ruthenium complexes have shown to overcome several resistance mechanisms of platinum anticancer drugs, achieving an adequate accumulation and retention in platinum-resistant cancer cells [23-29] and making their way to a possible therapeutic alternative to cisplatin.
Covalent and noncovalent interactions of coordination compounds with DNA: An overview
2021, Journal of Inorganic BiochemistryEvaluation of DNA-binding and DNA-photocleavage ability of tetra-cationic porphyrins containing peripheral [Ru(bpy)<inf>2</inf>Cl]<sup>+</sup> complexes: Insights for photodynamic therapy agents
2020, Journal of Photochemistry and Photobiology B: Biology
H⋯ etc.) responsible for the stabilization of crystal lattices. Calculations based on Density functional theory (B3LYP/DFT), have been carried out to obtain energies of Frontier molecular orbitals. Comparative in vitro binding profile of complexes 1 and 2 with ct–DNA was evaluated employing various biophysical techniques viz., UV–vis, fluorescence, circular dichroism and cyclic voltammetry which suggested non-covalent intercalative binding mode with more avid binding propensity of complex 1 compared to complex 2. The cleavage experiments of complex 1 was performed by gel electrophoretic assay which revealed efficient cleavage mediated via oxidative pathway. Furthermore, topoisomerase I enzymatic activity of complex 1 was carried out employing gel electrophoretic assay which demonstrated significant inhibitory effects at a low concentration of 25 µM. The cytotoxic potential of complex 1 was analyzed by SRB assay on a panel of selected human cancer cell lines which revealed selective activity for MCF-7 (breast cancer) cell line with GI50 = 16.21 µg/ml.