Ruthenium(II)/triphenylphosphine complexes: An effective way to improve the cytotoxicity of lapachol

doi:10.1016/j.poly.2017.04.005

Polyhedron

Volume 130, 7 July 2017, Pages 108-114

https://doi.org/10.1016/j.poly.2017.04.005 Get rights and content

Abstract

This study reports on the synthesis of a new ruthenium(II) complex, cis-[Ru(PPh₃)₂(lap)₂] (1) with two molecules of the natural product known as lapachol [lap = (2-hydroxy-3-(3-methyl-2-buthenyl)-1,4-naphthoquinone)] coordinated as bidentated by oxygen atoms and two monodentate PPh₃ (triphenylphosphine) in a cis configuration. This neutral complex was characterized by spectroscopic analysis, single-crystal X-ray diffraction, elemental analysis, molar conductivity and cyclic voltammetry. In this study, ruthenium complex trans-[Ru(lap)(PPh₃)₂(phen)]PF₆ (2) was used for comparison purposes. The interaction of ruthenium complexes (1) and (2) with CT-DNA was evaluated by UV–Vis and circular dichroism and it was observed that the complexes interact weakly with the CT-DNA. The fluorescence measurements suggest that complex (1) shows stronger interaction with HSA and BSA proteins compared to complex (2). Cytotoxicity assays against A549 (lung cancer), MDA-MB-231 (breast cancer) and V79 (non-tumoral lung) revealed that complex (2) is more active (lower IC₅₀ values) than complex (1) and the cisplatin, used as a reference.

Graphical abstract

Ruthenium(II)/triphenylphosphine complexes containing the natural product lapachol as ligand with improved cytotoxicity activity against lung and breast cancer cells is reported in this work. Interaction studies of the synthesized complexes with biomolecules (DNA, BSA and HSA) are carried out to provide valuable data to explain the improvement of cytotoxicity.

Introduction

A strategy to improve the activity of molecules that already show some biological activity is to synthesize coordination compounds containing these species as ligands in order to enhance the biological activities thereof [1]. Thus, currently, many research groups have synthesized a number of metal complexes containing different classes of ligands, generating new complexes with a remarkable biological activity [2], [3], [4], [5], [6], [7]. Examples of compounds with quinolone [8], flavone [7], naphthoquinone [9], [10] with different metals have been reported.

Among the various metals used, ruthenium is an interesting option due to the variety of structures, reactivities and applications [11], [12], [13]. Lapachol (2-hydroxy-3-(3-methylbut-2-enyl)naphthalene-1,4-dione) is a naphthoquinone isolated from plants of the Bignoniaceae family. This compound is characterized by a variety of properties such as antiviral, antifungal, antiparasitic, antimicrobial and anticancer [6], [14], [15]. This can be highlighted by recent reports of ruthenium/lapachol complexes endowed of anticancer, antileishmanial and antiplasmodial properties compared to the free molecule [4], [5], [6], [16].

We have reported on some ruthenium complexes containing different phosphines that exhibit properties such as anticancer, antitubercular, antileishmanial and antiplasmodial [6], [17], [18], [19]. In this context, we prepared a new Ru(II)/triphenylphosphine complex with lapachol, cis-[Ru(PPh₃)₂(lap)₂] (1), which was obtained and characterized. Furthermore, the trans-[Ru(lap)(PPh₃)₂(phen)]PF₆ (2) complex, previously published by us [6], was also obtained and its cytotoxicities were evaluated against two tumor cell lines (breast MDA-MB-231 and lung A549) and against the V79, a non-tumoral lung cell line. Considering that the DNA is a possible target for anticancer drugs, the interaction of this molecule with the compounds under study has been widely investigated, mainly due to the cisplatin mechanism of action that acts by binding covalently with pairs of nitrogenous bases of DNA [20]. The complexes/DNA-binding affinity was also investigated by spectroscopic titration and circular dichroism.

Albumin is an abundant protein in the circulatory system and it is responsible for transporting endogenous and exogenous substances to specific targets [21], [22], [23]. Thus, regarding the development of new compounds as possible drug candidates, an issue that should always be considered is the interaction of the compounds of interest with the plasma proteins, to find out their pharmacodynamics and pharmacokinetics properties. Thus, the behavior of complexes (1) and (2) was investigated in the presence of two albumins (human and bovine) using fluorescence spectroscopy.

Section snippets

Materials and reagents

All manipulations involving solutions were performed under argon atmosphere. All solvents used in this work were purified using standard methods. Chemicals were of analytical grade. RuCl₃.3H₂O, triphenylphosphine (PPh₃), calf-thymus DNA (CT-DNA), bovine serum albumin (BSA), human serum albumin (HSA) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) (Sigma Aldrich) were used as received from Sigma Aldrich. Lapachol was obtained according to the procedure described in [24].

Synthesis and characterization

Complex (1) was obtained as a blue dark powder, according to Scheme 1 below:

The elemental analysis (C and H) and spectroscopic data of complex (1) are in agreement with the structure containing two lapachol molecules coordinated to the metal center. The molar conductivity of the complex, in dichloromethane, presents a value equal to 0.23 S m² mol⁻¹, which is compatible with a neutral complex [33], as expected for the complex containing two lapachol molecules, negatively charged.

Considering that

Conclusions

In this study, the new ruthenium complex, cis-[Ru(PPh₃)₂(lap)₂], containing two lapachol molecules was synthesized and fully characterized. The ³¹P{¹H} NMR spectrum of the complex presents two doublets indicating the cis configuration of the two phosphorus atoms, where they are trans positioned to different oxygen atoms of the lapachol coordinated ligand, as confirmed by the X-ray diffraction studied. This new complex shows an oxidation potential (Ru^II/Ru^III) close to 729 mV, against Ag/AgCl.

Acknowledgments

We would like to thank to Laboratório Farmacêutico do Estado de Pernambuco (LAFEPE) for kindly supplying the lapachol. This work was supported by CAPES, CNPq and FAPESP of Brazil. K.M. Oliveira would like to thank FAPESP (2014/04147-9) for the doctoral scholarship.

References (43)

G. Agonigi et al.
Organometallics
(2016)
R. Hernández-Molina et al.
Polyhedron
(2007)
M.I.F. Barbosa et al.
J. Inorg. Biochem.
(2014)
K.D. Mjos et al.
J. Inorg. Biochem.
(2016)
A. Farias Moreira da Silva et al.
Polyhedron
(2017)
E.K. Beloglazkina et al.
Polyhedron
(2016)
L. Tabrizi et al.
J. Organomet. Chem.
(2016)
R.S. Correa et al.
J. Inorg. Biochem.
(2015)
L. Colina-Vegas et al.
J. Inorg. Biochem
(2015)
F.R. Pavan et al.
Eur. J. Inorg. Chem.
(2011)

J.-L. Li et al.

J. Inorg. Biochem.

(2015)

T.S. Morais et al.

J. Inorg. Biochem.

(2014)

S. Thangavel et al.

Polyhedron

(2016)

T.A. Stephenson et al.

J. Inorg. Nucl. Chem.

(1966)

M. Gopalakrishnan et al.

Inorg. Chem. Commun.

(2014)

W.J. Geary

Coord. Chem. Rev.

(1971)

I. Singh et al.

Tetrahedron

(1968)

R.S. Corrêa et al.

J. Inorg. Biochem.

(2016)

R.A. Farfán et al.

J. Coord. Chem.

(2009)

F. Caruso et al.

Inorg. Chem.

(2009)

W. Kandioller et al.

Chem. Commun.

(2013)

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Citation Excerpt :
The 2-hydroxy-3-(3-methylbut-2-en-1-yl)naphthalene-1,4-dione, commonly known as lapachol, originally isolated from species of the Bignoniaceae family, represents an important naphthoquinone, mainly due to its anti-cancer properties [5]. Thus, we, and other research groups, have been investigating the anti-cancer potential of lapachol (Lap) and other naphthoquinones, free or coordinated to a metal, because ruthenium complexes containing Lap as a ligand, for instance, show a wide range of biological properties, including activities on various cancer cell lines [6–15]. In light of those favorable results described in the literature, we herein designed two new Ru(II)-bipyridine/phenanthroline complexes with lapachol, with formula [Ru(bipy)2(Lap)]PF6 (1) and [Ru(Lap)(phen)2]PF6 (2) (bipy = 2,2′-bipyridine; phen = 1,10-phenantroline).
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Ruthenium(II)/triphenylphosphine complexes: An effective way to improve the cytotoxicity of lapachol

Abstract

Graphical abstract

Introduction

Section snippets

Materials and reagents

Synthesis and characterization

Conclusions

Acknowledgments

Organometallics

Polyhedron

J. Inorg. Biochem.

J. Inorg. Biochem.

Polyhedron

Polyhedron

J. Organomet. Chem.

J. Inorg. Biochem.

J. Inorg. Biochem

Eur. J. Inorg. Chem.

J. Inorg. Biochem.

J. Inorg. Biochem.

Polyhedron

J. Inorg. Nucl. Chem.

Inorg. Chem. Commun.

Coord. Chem. Rev.

Tetrahedron

J. Inorg. Biochem.

J. Coord. Chem.

Inorg. Chem.

Chem. Commun.