Elsevier

Journal of Inorganic Biochemistry

Volume 153, December 2015, Pages 315-321
Journal of Inorganic Biochemistry

Ruthenium(II) p-cymene complex bearing 2,2′-dipyridylamine targets caspase 3 deficient MCF-7 breast cancer cells without disruption of antitumor immune response

https://doi.org/10.1016/j.jinorgbio.2015.09.006Get rights and content

Highlights

  • [Ru(η6-p-cymene)Cl(dpaR)][PF6], dpa = 2,2′-dipyridylamine; R = H (1), (CH2)4COOEt (2).

  • Ru(II) complex 1 is more active against tumor cells than 2.

  • 1 is the most efficient against caspase 3 deficient MCF-7 breast cancer cells.

  • 1 is not active against cells of the adaptive immune system.

  • 1 does not exert a general immunosuppressive effect on cytokine production.

Abstract

[Ru(η6-p-cym)Cl{dpa(CH2)4COOEt}][PF6] (cym = cymene; dpa = 2,2′-dipyridylamine; complex 2) was prepared and characterized by elemental analysis, IR and multinuclear NMR spectroscopy, as well as ESI-MS and X-ray structural analysis. The structural analog without a side chain [Ru(η6-p-cym)Cl(dpa)][PF6] (1) as well as 2 were investigated in vitro against 518A2, SW480, 8505C, A253 and MCF-7 cell lines. Complex 1 is active against all investigated tumor cell lines while the activity of compound 2 is limited only to caspase 3 deficient MCF-7 breast cancer cells, however, both are less active than cisplatin. As CD4+ Th cells are necessary to trigger all the immune effector mechanisms required to eliminate tumor cells, besides testing the in vitro antitumor activity of 1 and 2, the effect of ruthenium(II) complexes on the cells of the adaptive immune system have also been evaluated. Importantly, complex 1 applied in concentrations which were effective against tumor cells did not affect immune cell viability, nor did exert a general immunosuppressive effect on cytokine production. Thus, beneficial characteristics of 1 might contribute to the overall therapeutic properties of the complex.

Graphical abstract

Synthesis and characterization of [Ru(η6-p-cym)Cl{dpa(CH2)4COOEt}][PF6] (cym = cymene; dpa = 2,2′-dipyridylamine; 2) as well as its antitumor activity and that of [Ru(η6-p-cym)Cl(dpa)][PF6] (1) is described. The most prominent activity was observed for 1 against caspase deficient MCF-7 breast cancer cells without affect to the immune cells and cytokine production.

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Introduction

Over the last few decades many efforts have been made in the field of cancer therapy [1], [2], [3], [4]. The treatment of many types of cancer has cisplatin and its analogs as mainstay drugs in current clinical chemotherapy. However, the clinical drawbacks of cisplatin are apparent, including the limited applicability, the intrinsic or acquired resistance, and the serious side effects [5]. In recent years, ruthenium-based complexes have emerged as promising antitumor and antimetastatic agents with equal or even greater antitumor activity and lower toxicity [6].

Superiority of ruthenium complexes from the classical platinum-based drugs reflect not only in their cytotoxic activity, but also in the extremely low toxicity against normal cells [7], [8], [9]. Up to now, various ruthenium complexes were investigated as potential anticancer agents [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]. Two families of ruthenium(II) complexes were the mostly investigated as potential agents in treatment of cancer. Thus, octahedral ruthenium(III) complexes, such as [LH]trans-[RuCl4(L-κ-N)n(S-DMSO)2–n] (n = 1, L = imidazole; n = 2, L = indazole) which reached clinical trials [20], [21], [22], [23], [24], [25] as well as ruthenium(II) arene complexes, “piano stool” type, i.e. [Ru(η6-arene)Cl(NN)]X (NN = chelating diamine ligand; X = Cl, PF6, BPh4), showed promising anticancer activity in both in vitro and in vivo studies [26], [27].

Inflammation and immunity affect all phases of tumor growth from initiation to progression and dissemination [28]. T helper (Th) cells are fundamental for optimal induction of both humoral and cellular effector mechanisms [29]. Both innate and adaptive immunity have been shown to participate in this response. Adaptive immune responses to Ags released by dying cells play a critical role in the spontaneous as well as therapy-induced tumor rejection [30]. Ample studies have identified proinflammatory cytokines as crucial mediators in cancer treatments. Recently, the binuclear ruthenium(II) complex, [{Ru(η6-p-cym)Cl2}2μ-{(3-py)COO(CH2CH2O)4CO(3-py)}] (py = pyridine), was reported, which modulates immune system cell functions in vitro by inhibiting T cell differentiation toward pathogenic Th1/Th17 phenotype and inducing a regulatory phenotype characterized by IL-10 and IL-4 production [31]. This ruthenium(II) complex was found ineffective against several tumor cell lines [32].

This paper focuses on the synthesis and characterization of [Ru(η6-p-cym)Cl{dpa(CH2)4COOEt}][PF6] (cym = cymene; dpa = 2,2′-dipyridylamine; complex 2) as well as its biological activity and of its structural analog [Ru(η6-p-cym)Cl(dpa)][PF6] (1). With the aim to contribute to the understanding of the antitumor action mechanism of ruthenium(II) compounds the in vitro activity of 1 and 2 was investigated against tumor cells along with normal cells of the adaptive immune system.

Section snippets

Materials and measurements

All reactions and manipulations were carried out under argon using standard Schlenk techniques. NMR spectra (1H, 13C, 31P) were recorded at 27 °C on Varian Gemini VXR 400 spectrometers. Chemical shifts are relative to solvent signals (acetone-d6, δΗ 2.06, δC 30.5, 206.8; CDCl3, δΗ 7.24, δC 77.0) as internal references; δ(31P) is relative to external H3PO4 (85%). Microanalyses (C, H) were performed in the Microanalytical Laboratory of the University of Halle using a CHNS-932 (LECO) elemental

Synthesis and characterization

[Ru(η6-p-cym)Cl(dpa)][PF6] (dpa = 2,2′-dipyridylamine; 1) was obtained by an adapted literature procedure (Scheme 1) [35]. Dichlorido(p-cymene)ruthenium(II) dimer was reacted with dpa(CH2)4COOEt in the presence of [PF6] forming the cationic complex [Ru(η6-p-cym)Cl{dpa(CH2)4COOEt}][PF6] (2) in a good yield. The ruthenium(II) complex 2 was characterized by elemental analysis, IR and multinuclear (1H, 13C, 31P) NMR spectroscopy as well as single-crystal X-ray structure analysis.

ESI-MS of 2,

Conclusions

Herein, the synthesis of [Ru(η6-p-cym)Cl{dpa(CH2)4COOEt}][PF6] (2) is described. 2 was characterized by spectroscopic methods and X-ray structural analysis. Structural analog [Ru(η6-p-cym)Cl(dpa)][PF6] (1) and 2 were tested for their in vitro antitumoral potential. The most efficient complex 1 showed higher activity against MCF-7 cells (the caspase 3 deficient cell line, more resistant to chemotherapy). Decreased viability was due to blockade of cell division and subsequent apoptotic cell death

Acknowledgements

The authors would like to acknowledge financial support from the European Union and the Free State of Saxony (project No. 100099597) and the Ministry of Education, Science and Technological Development of the Republic of Serbia (project No. 173013). We would like to thank Dr. Peter Lönnecke (Leipzig University) for the X-ray structural measurement of complex 2.

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