Two new Cu(II) dipeptide complexes based on 5-methyl-2-(2′-pyridyl)benzimidazole as potential antimicrobial and anticancer drugs: Special exploration of their possible anticancer mechanism

doi:10.1016/j.ejmech.2018.05.023

European Journal of Medicinal Chemistry

Volume 154, 25 June 2018, Pages 220-232

https://doi.org/10.1016/j.ejmech.2018.05.023 Get rights and content

Highlights

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Two new Cu(II) complexes were synthesized and characterized.
•
The complexes exhibited good antimicrobial and anticancer activities.
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The biological activities of 2 were greater than those of 1.
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The possible anticancer mechanism of the complexes was explored.

Abstract

In the search for more effective anticancer drugs with less toxic side effects, dipeptides were introduced into the Cu(II) complex of 5-methyl-2-(2′-pyridyl)benzimidazole (HPBM). Analytical and spectroscopic techniques were employed to thoroughly characterize complexes [Cu(Gly-gly)(HPBM)(H₂O)]ClO₄·0.5H₂O (1) and [Cu(Gly-L-leu)(HPBM)(H₂O)]ClO₄ (2) (where Gly-gly = Glycyl-glycine anion, Gly-L-leu = Glycyl-l-leucine anion). The solution stability studies performed by ultraviolet–visible (UV–Vis) spectroscopy confirmed the stability of the complexes in the buffer solutions. The DNA binding affinity was evaluated using multi-spectroscopy, viscosity measurement and molecular docking methods and further quantified by K_b and K_app values, revealing an intercalative mode. Moreover, gel electrophoresis analysis revealed that the complexes could damage CT DNA through a hydroxyl radical pathway in the presence of ascorbic acid. All the complexes displayed favorable antimicrobial and cytotoxic activities toward the tested microorganisms (Bacillus subtilis, Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa) and cancer cells (A549, HeLa and PC-3). Most importantly, the possible anticancer mechanism of the complexes was explored by determining the cells morphological changes, intracellular reactive oxygen species (ROS) levels, location in mitochondria, mitochondrial membrane potentials and the expression of Bcl-2 family proteins. The results showed that the complexes could induce apoptosis in HeLa cells through an ROS-mediated mitochondrial dysfunction pathway, which was accompanied by the regulation of Bcl-2 family proteins.

Graphical abstract

Two new Cu(II) dipeptide complexes based on HPBM were synthesized and characterized. The complexes were found to bind to CT DNA by an intercalative mode. The complexes exhibited good antimicrobial and cytotoxic activities. Moreover, the possible anticancer mechanism of the complexes was explored by determining the cells morphological changes, intracellular reactive oxygen species (ROS) levels, location in mitochondria, mitochondrial membrane potentials and the expression of Bcl-2 family proteins.

Introduction

Based on the wide range of coordination numbers, inconstant geometries and available redox states, metal complexes have become one hotspot in the research of anticancer agents [[1], [2], [3], [4]]. Among various anticancer agents, cisplatin as a potent agent against numerous malignancies has been widely used. But the side effects and drug resistance of cisplatin still limited its clinical applications and future development. Therefore, some strategies based on different metals and ligands were proposed by chemists to search more efficacious anticancer agents with less side effects, in which copper complexes have been clearly considered as the most promising anticancer agents [[5], [6], [7]].

As an endogenous metal element, copper has less toxic side effects compared with exogenous metals (platinum, ruthenium and rhenium etc.) [7]. The unique spectroscopic properties as well as excellent redox properties make its complexes have favorable DNA oxidative cleavage [8] and various biological activities, such as antimicrobial, anticancer and anti inflammatory activities [[9], [10], [11]]. It was reported that the anticancer activity of some copper complexes was more prominent and more effective than that of cisplatin drug, especially for human cancer cell which generates traditional platinum resistance [12]. In this case, copper complexes based on benzimidazole and their derivatives have gained great attention due to their better antimicrobial and anticancer activities [[13], [14], [15], [16], [17]], but some of them still have severe toxic side effects [18].

Dipeptides, formed by the dehydration condensation of two amino acids, are structurally similar to proteins, hence the introduction of dipeptides as an auxiliary ligand could effectively enhance the biological compatibility and recognition of the complexes, and reduce the toxic side effects [[19], [20], [21], [22]]. For instance, the copper-dipeptide complexes, [Cu(Ala-Phe)] (Ala-Phe = L-Alanyl-l-Phenylalanine anion) and [Cu(Phe-Ala)] (Phe-Ala = L-Phenylalanyl-l-Alanine anion), were found to possess effective cytotoxicity against breast cancer and less toxic effects against normal cells [23]. The similar results have been reported in numerous other studies [8,24,25]. Most importantly, it has been found that the activities of ternary copper-dipeptide complexes based on benzimidazole ([Cu(glygly)(HPB)Cl]·2H₂O, HPB = 2-(2′-pyridyl)benzimidazole) [26] were stronger than that of the corresponding binary complex ([CuCl₂(pbzH)], pbzH = 2-(2′-pyridyl)benzimidazole) [27]. Therefore, further study of ternary Cu(II)-dipeptide complexes with benzimidazole derivatives should be favorable for the development of new anticancer drugs with high efficiency and low toxicity.

In our previous work, a series of ternary mixed copper dipeptide complexes based on benzimidazole derivatives, their cytotoxic activities have been reported [[28], [29], [30], [31]]. However, the mechanism of their anticancer action has not been explored. Herein, as our continuous and deep work in this area, two new copper complexes [Cu(Gly-gly)(HPBM)(H₂O)]ClO₄·0.5H₂O (1) and [Cu(Gly-L-leu)(HPBM)(H₂O)]ClO₄ (2) were synthesized and characterized. The interaction of the complexes with CT DNA was investigated via spectroscopic experiments, hydrodynamics, gel electrophoresis and molecular docking technique. The in vitro cytotoxicity and antimicrobial activity of the complexes were tested by MTT, oxford cup and broth dilution methods, respectively. Most importantly, the possible anticancer mechanism of the complexes was explored by determining the cells morphological changes, intracellular reactive oxygen species (ROS) levels, location in mitochondria, mitochondrial membrane potentials and the expression of Bcl-2 family proteins.

Section snippets

Synthesis and characterization of the complexes

The syntheses of HPBM and the complexes were schematically presented in Scheme 1. The complexes were characterized by elemental analysis, molar conductivity measurement, and various spectroscopic techniques (IR, UV–Vis, ESI-MS and ESR). The elemental analytic results for the complexes match well with their theoretical values, which confirm the compositions of the complexes. The molar conductivities of complexes 1 and 2 in MeOH are 89.3 and 97.8 S cm² mol^-1, respectively, indicating their 1:1

Conclusions

Two mixed-ligand copper(II) complexes [Cu(Gly-gly)(HPBM)(H₂O)]ClO₄·0.5H₂O (1), [Cu(Gly-L-leu)(HPBM)(H₂O)]ClO₄ (2) were synthesized and well characterized. The complexes could bind to CT DNA through an intercalation mode, in which hydrophobic interactions were dominant. The binding sites and modes were further confirmed by molecular docking techniques. DNA cleavage experiments revealed that the complexes could oxidatively damage CT DNA in the presence of ascorbic acid. In addition, all the

Materials and methods

All reagents were of commercial reagent grade and were used without further purification, and deionized water was used throughout the experiments. The 5-methyl-2-(2′-pyridyl)benzimidazole was synthesized according to the reported method [55]. The ligands glycyl-glycine and glycyl-l-leucine were purchased from Aladdin. CT DNA, ethidium bromide (EB = 3,8-diamino-5-ethyl-6-phenyl-phenanthridinium bromide), dimethylsulfoxide (DMSO), RPMI-1640 and DMEM were purchased from sigma, and pBR322 DNA was

Acknowledgements

This work was supported by the Natural Science Foundation of Guangdong Province (No. 2015A030313423).

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Research paperTwo new Cu(II) dipeptide complexes based on 5-methyl-2-(2′-pyridyl)benzimidazole as potential antimicrobial and anticancer drugs: Special exploration of their possible anticancer mechanism

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Synthesis and characterization of the complexes

Conclusions

Materials and methods

Acknowledgements

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Eur. J. Med. Chem.

Polyhedron

Eur. J. Med. Chem.

Mater. Sci. Eng. C

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J. Inorg. Biochem.

J. Lumin.

Eur. J. Med. Chem.

J. Inorg. Biochem.

J. Photochem. Photobiol., B

J. Inorg. Biochem.

Spectrochim. Acta, Part A

J. Inorg. Biochem.

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J. Inorg. Biochem.

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Spectrochim. Acta, Part A

Spectrochim. Acta, Part A

Eur. J. Med. Chem.

J. Photochem. Photobiol., B

J. Inorg. Biochem.

J. Inorg. Biochem.

Spectrochim. Acta, Part A

Eur. J. Med. Chem.

Eur. J. Med. Chem.

Research paper
Two new Cu(II) dipeptide complexes based on 5-methyl-2-(2′-pyridyl)benzimidazole as potential antimicrobial and anticancer drugs: Special exploration of their possible anticancer mechanism