DNA interaction, antimicrobial, antioxidant and anticancer studies on Cu(II) complexes of Luotonin A

doi:10.1016/j.jphotobiol.2016.11.024

Journal of Photochemistry and Photobiology B: Biology

Volume 167, February 2017, Pages 20-28

https://doi.org/10.1016/j.jphotobiol.2016.11.024 Get rights and content

Highlights

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Cu(II) complexes 1 & 2 are prepared from a natural alkaloid L.
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The newly prepared complexes 1 & 2 are characterized of by various spectral studies.
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Complex 1 has effective DNA binding, antimicrobial and antioxidant ability.
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Complex 1 comprise potent cytotoxic action on both MCF-7 and HeLa cancer cells.
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The normal cytotoxic activity of L is increased when chelated with Cu(II)

Abstract

Luotonin A (L), a novel natural cytotoxic and anti-inflammatory alkaloid, chelated with copper(II) to improve its cytotoxic effect against the cancer cells. The complexes [Cu(L)H₂OCl]Cl (1) and [Cu(L)₂]Cl₂ (2) are prepared by using copper(II) chloride and L with ligand/metal molar ratio of 1:1 and 2:1 respectively. A solution of complexes 1 & 2 are characterized by physical spectroscopic methods using Ultraviolet-visible (UV–Vis) spectrophotometer, Fourier Transform–Infra red (FT-IR) spectroscopy, Electron Para magnetic Resonance Spectroscopy (EPR) and by electrochemical methods. The interaction of these complexes 1 & 2 with calf thymus (CT-DNA) have been investigated by physical methods to propose the modes of DNA binding with the complexes 1 & 2. Absorption spectral titration studies of complex 1 with CT-DNA shows a red-shift of 5 nm with the DNA binding affinity of K_b, 8.65 × 10³ M^− 1, but complex 2does not show any red-shift with binding constant K_b, 7.32 × 10³ M^− 1 reveals that the complex 1 binding with DNA strongly than complex 2 and the binding occurs in between the base pairs of DNA as intercalation. Strong interactions of the two complexes 1 & 2 with CT-DNA have also been confirmed by fluorescence spectral titration studies. The evaluated values of K_SV and K_ass shows that, the complexes 1 & 2 interact with DNA through the intercalation, coincide with other partial intercalators strongly than the free ligand L. Complex 1 exhibits potent antioxidant activity with SC₅₀ value of 23.9 ± 0.69 μM is evaluated by DPPH radical scavenging assay and which has potent antimicrobial activity against pathogens than 2 and L. The anticancer activity of L, complexes 1 & 2 against human breast cancer cell line (MCF-7) and cervical cancer cell line (HeLa) has also been studied by using fluorescence staining method. The IC₅₀ values of L, complexes 1& 2 against MCF-7 and HeLa cell lines with the incubation time intervals of 24 hrs are 1 (5.0 ± 0.25, 12.0 ± 0.30 μM) < 2 (6.5 ± 0.27, 15.0 ± 0.30 μM) < L (7.0 ± 0.15, 25.0 ± 0.35 μM) respectively. Interestingly, complex 1 exhibits anticancer activity more potent than L against both MCF-7 and HeLa cell lines. The result of anticancer activity studies show that the cytotoxic activity of L against MCF-7 and HeLa cells is increased, when chelated with Cu(II).

Graphical Abstract

Introduction

The potent biological activities and clinical applications of pyrrologinazoline chromophore incorporated alkaloids had attracted intense attention worldwide and that have been isolated from natural sources [1]. A typical example is Luotonin A (L), pyrrolo–quinazolino–quinoline alkaloid originally isolated from a Chinese medicinal herb peganumnigellastrum that had been used to treat rheumatism, abscesses and inflammation [2], [3], [4]. It had been already reported that Luotonin A is a human DNA topoisomerase I inhibitor and exhibits potent cytotoxicity against murine leukemia P388 cell line by stabilizing the topoisomerase I/DNA complex with an IC₅₀ value of 6.3 μM [5]. Luotonin A is structurally identical to another anticancer drug camptothecin which has strong topoisomerase I characteristics [6], [7]. There is a considerable interest in the study of biological properties of Luotonin A, because of its lower toxicity a higher chemical stability compared with campatothecin [8], [9], [10]. The biological activities such as anticancer, topoisomerase I inhibition) of natural products (Curcumin, Salinomycin, etc.) were enhanced by complex formation with metals. The discovery of anticancer drugs is one of the most rapidly developing areas in biological research [11] and it is essential to increase the variety of metal based natural products for achieving higher activity, enabling the administration of a lower dose, apoptosis on different types of tumor cells; it exhibits better selectivity and lower toxicity than cisplatin [12], [13], [14]. The Cu(II) adducts of 4-methoxypyrrolic marine natural products have also shown potent antitumor properties against breast, liver cancer cells by facilitating apoptosis [15], [16], [17], [18], [19], [20]. A Cu(II) complex prepared from Hypyramol shows interesting cytotoxic properties in selected cancer cell lines, comparable to the anticancer drug cisplatin [21]. Based on this view and our continuing interest [22], [23], [24], [25],the present report accounts for the preparation, characterization, DNA binding modes, antimicrobial screening studies and antitumor activities of Luotonin A centered on Cu(II) complexes 1 & 2 are described. Both complexes have potential screening effect against human breast cancer cell line (MCF-7) and cervical cancer cell line (HeLa) to understand their antitumor activity. The use of L in these complexes 1 & 2 is of considerable interest because several Cu(II) complexes of diimines strongly bind to DNA and exhibit potent anticancer activities by inducing cell death [26].

Section snippets

Materials and Instrumentation

Luotonin A (L) and copper(II) chloride by SIGMA, DMSO by MERCK are used for over all experiments as purchased. All other reagents and solvents are of analytical, spectroscopic grade and they are used without further purification. The Cu(II) complexes 1 & 2 are greenish yellow in color with DMSO.

Infrared spectra are recorded with KBr pellets using Perkin Elmer FT-IR 8000 spectrophotometer scans between 400 and 4000 cm¹.Electronic spectra are recorded with a JASCO double beam UV–Vis

UV–Vis Spectral Analysis

The electronic spectra of L and its Cu(II) complexes 1 & 2 are recorded in DMSO at room temperature. The spectra of free ligand exhibit three absorption bands at 257, 344 and 362 nm as shown in Fig. S1. These bands are arises from π-π* and n-π* transition of the L. The electronic spectra of the complexes 1 & 2 in DMSO exhibit a intra ligand transition band at 254 nm and LMCT band at 327 nm, which confirms the complex formation of L with Cu(II) and evidently, the square planar stereochemistry

Electronic Absorption Spectra

The absorption spectral titration studies of complexes 1 & 2 with CT-DNA are shown in Fig. 2. Upon increasing the addition of DNA to Cu(II) complexes 1 & 2, the intensity changes occurred in intra ligand transition band at 254 nm and LMCT band at 324 nm. Hence, the DNA binding ability of complex 1 & 2 is studied by following the hypochromism of intra ligand transition band at 324 nm. For complex 1, the absorption bands of the ligand exhibits hypochromism with red shift of 5 nm. However, the

Antibacterial Screening

Antibacterial screening of the L and its Cu(II) complexes 1 & 2 (Fig. 6) have been carried out against the Escherichia coli, Staphylococcus aureus, Klebsiella pneumonia, Pseudomonas aeruginosa, Aeromonashydrphilia, Serratiamarcescenes and Proteus vulgari using Mueller-Hinton agar by well-diffusion method using DMSO as solvent [47], standard drug Amoxycillin. The comparative antimicrobial screening capability (in mm) of ligand L, complex 1, 2 and standard drug (Amoxycillin) are shown as in Fig. 6

DPPH Radical Scavenging Assay

A stock solution of DPPH prepared in DMSO to 3 × 10^− 3 M. To explore the antioxidant activity of L, complex 1 & 2, free radical scavenging experiment carried out by the addition of different volumes of samples (40–160 μl) into 150 μl of stock solution of DPPH and is made up to 3 ml with DMSO. The reaction mixture is incubated in dark condition at room temperature for 20 min. After 20 min, the absorbance of the mixture is read at 520 nm. 3 ml of diluted DPPH is taken as control. The percentage of

MTT Cytotoxic Assay

The comparative cytotoxic activities of ligand L and its Cu(II) complexes 1 & 2 have been studied against human breast cancer cells MCsF-7 and HeLa cell lines by using MTT assay. The graphical representation of IC₅₀ values for these compounds is given in Fig. 9. The IC₅₀ values of L, complexes 1 & 2 against MCF-7 and HeLa cell lines with the incubation time intervals of 24 h are 1 (5.0 ± 0.25, 12.0 ± 0.30 μM) < 2 (6.5 ± 0.27, 15.0 ± 0.30 μM) < L (7.0 ± 0.15, 25.0 ± 0.35 μM) respectively. However, L and its Cu(II)

Conclusion

A new Cu(II) metal complexes 1 & 2 have been successfully prepared and characterized. The DNA binding mode of these complexes 1 & 2 with CT-DNA have been evaluated using absorption, emission spectral studies and viscosity measurements. A comparative antimicrobial screening and antitumor activities of prepared Cu(II) complexes 1 & 2 with ligand L have been studied. From absorption and emission spectral studies, complex 1 has higher DNA binding constant, Stern-Volmer constant and association

Acknowledgements

The authors gratefully acknowledge the DST-SERB (Ref. No: SB/FT/CS-130/2012) for financial assistance. The authors sincerely thank the management of Sethu Institute of Technology, Kariapatti and Mohamed Sathak Engineering College, Kilakarai for their lab and instrumental facilities.

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DNA interaction, antimicrobial, antioxidant and anticancer studies on Cu(II) complexes of Luotonin A

Highlights

Abstract

Graphical Abstract

Introduction

Section snippets

Materials and Instrumentation

UV–Vis Spectral Analysis

Electronic Absorption Spectra

Antibacterial Screening

DPPH Radical Scavenging Assay

MTT Cytotoxic Assay

Conclusion

Acknowledgements

Tetrahedron

Bioorg. Med. Chem. Lett.

Bioorg. Med. Chem. Lett.

J. Inorg. Biochem.

Bioorg. Med. Chem. Lett.

J. Inorg. Biochem.

J. Inorg. Biochem.

J. Mol. Struct.

Spectrochim. Acta A Mol. Biomol. Spectrosc.

J. Mol. Struct.

Polyhedron

Eur. J. Med. Chem.

Spectrochim. Acta A

J. Mol. Struct.

J. Inorg. Biochem.

Polyhedron

J. Mol. Struct.

J. Mol. Struct.

J. Inorg. Biochem.

J. Photochem. Photobiol. B

Inorg. Chem. Commun.

A catalyst-free rapid, practical and general synthesis of 2-substituted quinazolin-4(3H)-ones leading to luotonin B and E, bouchardatine and 8-norrutaecarpine

RSC Adv.

One-pot synthesis of luotonin A and its analogues

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Luotonin A. A naturally occurring human DNA topoisomerase I poison

J. Am. Chem. Soc.