Antimetastatic properties and DNA interactions of the novel class of dimeric Ru(III) compounds Na2[{trans-RuCl4(Me2SO)}2(μ-L)] (L=ditopic, non-chelating aromatic N-ligand). A preliminary investigation

doi:10.1016/S0162-0134(99)00231-7

Journal of Inorganic Biochemistry

Volume 79, Issues 1–4, 30 April 2000, Pages 173-177

https://doi.org/10.1016/S0162-0134(99)00231-7 Get rights and content

Abstract

A novel class of dianionic Ru(III) dimers of formula Na₂[{trans-RuCl₄(Me₂SO)}₂(μ-L)], with L=pyrazine (pyz, 1), pyrimidine (pym, 2), 4,4′-bipyridine (bipy, 3), and 1,2-bis(4-pyridine)ethane (etbipy, 4), was developed by us with the specific aim of assessing their antitumor properties. The dimers are in fact structurally related to the antimetastatic mononuclear compound (ImH)[trans-RuCl₄(Me₂SO)(Im)] (NAMI-A, Im=imidazole). Preliminary results concerning the antineoplastic activity of 1–4 against the murine MCa carcinoma model, a tumor which spontaneously metastasizes in the lungs, are reported. Similarly to what is normally observed with NAMI-A, the treatment with the dimeric complexes was scarcely effective against the growth of the primary tumor. However, dimers 1, 2, and 4 reduced very effectively the number and, in particular, the weight of lung metastases (to about 5% with respect to controls); in particular, Na₂[{trans-RuCl₄(Me₂SO)}₂(μ-etbipy)] (4) was as effective as NAMI-A in reducing the spontaneous metastases at a dosage which, in terms of moles of ruthenium, is about 3.5 times lower compared to that normally used for NAMI-A. Furthermore, in vitro tests showed that dimers 1–4 are capable of forming interstrand cross-links with linearized plasmidic DNA in a time-dependent manner. All the dimeric species are more active in inducing cross-links compared to NAMI-A, and the dimer bridged by the etbipy ligand (4) is the most effective among those tested.

Introduction

We recently reported the synthesis and characterization of novel dianionic Ru(III) dimers of formula Na₂[{trans-RuCl₄(Me₂SO)}₂(μ-L)] (Fig. 1), in which the two trans-RuCl₄(Me₂SO) units are bridged by a ditopic non-chelating aromatic N-ligand, such as pyrazine [1], [2]. Each half of these dimers maintains essentially the same coordination sphere (four trans chlorides, one S-bonded dimethyl sulfoxide and one heterocyclic N-ligand) that characterizes the mononuclear compound Na[trans-RuCl₄(Me₂SO)(Im)] (NAMI, Im=imidazole), whose selective antimetastatic properties against animal tumor models have been repeatedly reported by us [3], [4], [5]. The imidazolium salt of NAMI, NAMI-A, which has improved characteristics of stability in the solid state and a similar antineoplastic activity compared to NAMI [6], [7], [8], [9], [10], [11], is currently being tested in clinical phase I as an antimetastatic drug.

The new dimeric compounds were developed with the specific aim of assessing their antitumor properties. By virtue of the structural analogies, they might maintain the antineoplastic activity of the closely related mononuclear species but with some different, and possibly enhanced, selectivity and/or specificity. In fact, although the mechanism of action of NAMI-A has not yet been elucidated, DNA and/or proteins are among its most likely biological targets. The general dinuclear structure of the novel compounds might allow DNA intrastrand and interstrand cross-links, protein cross-links, as well as ternary complex formation of DNA-protein cross-links that are unavailable to the mononuclear analogs. The precedents in the field of platinum drugs, in which the dimers and trimers developed by Farrell et al. [12], [13] show remarkable activity also against tumor lines resistant to cisplatin, seemed particularly encouraging.

We report here some preliminary results on the antineoplastic activity against animal tumor models and on the in vitro interactions with DNA for four dimers of formula Na₂[{trans-RuCl₄(Me₂SO)}₂(μ-L)], with L=pyrazine (pyz, 1), pyrimidine (pym, 2), 4,4′-bipyridine (bipy, 3), and 1,2-bis(4-pyridine)ethane (etbipy, 4).

Section snippets

Materials and methods

The synthesis of dimers 1–4 was performed according to published procedures [1], [2].

Synthesis and chemical behavior

The synthesis, structural characterization and thorough chemical behavior in physiological solution of the new dimers have been recently described by us elsewhere [1], [2]. For the sake of clarity, we report here a brief summary of those aspects which might be relevant to the evaluation of the biological properties described below.

The dimers are synthesized in good yield by treatment of the precursor Na[trans-RuCl₄(Me₂SO)₂] with 0.5 equivalent of the bridging ligand. The complexes usually

Discussion

Although the nature of the biological target(s) of the antimetastatic NAMI-A is yet unknown, we have shown that mononuclear Ru(III) complexes, including NAMI-A, after hydrolysis of at least one chloride are capable of binding DNA [14] and also proteins such as transferrin [15] and albumine [16] in vitro; moreover, they were recently proved capable of inducing DNA-protein cross-links in isolated nuclei [17]. Thus, in vivo, the mononuclear Ru(III) complexes behave, very likely, as either

Acknowledgements

This work was supported by Italian MURST in the frame of the Project ‘Pharmacological and Diagnostic Properties of Metal Complexes’ (coordinator Professor G. Natile), by Polytech s.r.l. (Science Park of Trieste), and by EU COST Action D8 (Project D8/96/0017). We thank Johnson Matthey for the generous loan of hydrated RuCl₃.

References (17)

A. Barca et al.
Mutat. Res.
(1999)
E. Alessio, E. Iengo, G. Mestroni, G. Sava, Ital. Patent Applic. MI99A000811...
E. Iengo, G. Mestroni, M. Calligaris, S. Geremia, E. Alessio, J. Chem. Soc., Dalton Trans. (1999)...
G. Mestroni, E. Alessio, G. Sava, S. Pacor, M. Coluccia, in: B.K. Keppler (Ed.), Metal Complexes in Cancer...
G. Sava et al.
Drugs Future
(1993)
G. Mestroni et al.
Met.-Based Drugs
(1994)
G. Mestroni, E. Alessio, G. Sava, Int. Patent No. WO 98/00431 (8 Jan....
G. Sava et al.
Clin. Exp. Metastasis
(1998)

There are more references available in the full text version of this article.

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