Study on Interaction of DNA from Calf Thymus with 1,10-phenanthrolinehexyldithiocarbamatopalladium(II) nitrate as Potential Antitumor Agent

Abstract

A novel palladium(II) complex has been synthesized with hexyldithiocarbamate (Hex-dtc) and 1,10-phenanthroline (phen) by the reaction of [Pd(phen)(H₂O)₂](NO₃)₂ with sodium salt of hexyldithiocarbamate and a complex of type [Pd(Hex-dtc) (phen)]NO₃ has been obtained. The complex has been characterized by elemental analysis, molar conductance, ¹H NMR, IR and electronic spectroscopic studies. The dithiocarbamate ligand acts in bidentate fashion. This water-soluble complex was screened against chronic myelogenous leukemia cell line, K562, for cytotoxic effects and showed significant antitumor activity much lower than that of cisplatin. The interaction of this complex with calf thymus DNA (ctDNA) was extensively investigated by a variety of spectroscopic techniques. Absorbance titration experiments imply the interaction of 4 Pd(II) complex molecules per 1000 nucleotides on DNA with positive cooperativity in the binding process and the complex denature the DNA at very low concentration (～14.3 μM). Fluorescence titration spectra and fluorescence Scatchard plots suggest that the Pd(II) complex intercalate in DNA. The gel chromatograms obtained from Sephadex G-25 column experiments showed that the binding of metal complex with DNA is so strong that it does not readily break. Furthermore, some thermodynamic and binding parameters found in the process of UV-Visible studies are described. They may provide specificity of the compound with ctDNA.     

Synthesis,Characterization, and Cytotoxicity Studies of a Novel Palladium(II) Complex and Evaluation of DNA-Binding Aspects

A new water-soluble palladium(II) complex, [Pd(bpy)(pyr-Ac]NO₃ in which bpy = 2,2′-bipyridine and pyr-Ac is 1-pyrrolacetato, has been synthesized and characterized by spectroscopic methods (¹H NMR, FT-IR, and UV-Vis), molar conductivity measurements, and elemental analysis. The results obtained from elemental analysis and conductivity measurements confirmed the stoichiometry of ligand and its complex while the characteristic peaks in UV-Vis and FT-IR and resonance peaks in ¹H NMR spectra confirmed the formation of ligand frameworks around the palladium ion. The 50% cytotoxic concentration (Ic₅₀) of new synthesized Pd(II) complex was determined by using MTT assay against human breast cancer cell line, T47D. The interaction between the Pd(II) complex with calf thymus DNA was studied at different temperatures by using absorption spectroscopy, fluorescence titration spectra, ethidium bromide displacement, and gel chromatography studies. The results obtained by absorption spectroscopy revealed that the Pd(II) complex can bind to DNA cooperatively at low concentrations. Several binding parameters in the above interaction were calculated by the fluorescence quenching method. The quenching mechanism was suggested to be the static quenching. The thermodynamic parameters: enthalpy change (ΔH °), entropy change (ΔS °), and Gibbs free energy (ΔG °), showed that van der Waals and hydrogen binding are predominant intermolecular forces between Pd(II) complex and DNA. These results were also consistent with the results obtained from Scatchard's plots.     

Investigation of the Interaction Between Human Serum Albumin and Antitumor Palladium(II) Complex Containing 1,10-Phenanthroline and Dithiocarbamate Ligands

The interaction between [Pd(But-dtc)(phen)]NO₃ (where But-dtc = butyldithiocarbamate and phen = 1,10-phenanthroline) with HSA (Human Serum Albumin) was investigated by applying fluorescence, UV–Vis and circular dichroism techniques under physiological conditions. The results of fluorescence spectra indicated that the Pd(II) complex could effectively quench the fluorescence intensity of HSA molecules via static mechanism. The number of binding sites and binding constant of HSA–Pd(II) complex were calculated. Analysis of absorption titration data on the interaction between Pd(II) complex and HSA revealed the formation of HSA–Pd(II) complex with high-binding affinity. Thermodynamic parameters indicated that hydrophobic forces play a major role in this interaction. Furthermore, CD measurements were taken to explore changes in HSA secondary structure induced by the Pd(II) complex.     

Biological evaluations of newly-designed Pt(II) and Pd(II) complexes using spectroscopic and molecular docking approaches

To perform biological evaluations of newly-designed Pt(II) and Pd(II) complexes, the present study was conducted with targeted protein human serum albumin (HSA) and HCT116 cell line as model of human colorectal carcinoma. The binding of Pt(II) and Pd(II) complexes to HSA was analyzed using fluorescence spectroscopy and molecular docking. The thermal stability and alterations in the secondary structure of HSA in the presence of Pt(II) and Pd(II) complexes were investigated using the thermal denaturation method and circular dichroism (CD) spectroscopy. The cytotoxicity of the Pt(II) and Pd(II) complexes was studied against the HCT116 cell line using MTT assay. The binding analysis revealed that the fluorescence findings were well in agreement with docking results such that there is only one binding site for each complex on HSA. Binding constants of 8.7?×?10³ M^?1, 2.65?×?10³ M^?1, 0.3?×?10³ M^?1, and 4.4?×?10³ M^?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 25?°C, respectively. Also, binding constants of 1.9?×?10³ M^?1, 15.17?×?10³ M^?1, 1.9?×?10³ M^?1, and 13.1?×?10³ M^?1 were determined for Pd(II) and Pt(II) complexes (I–IV) at temperature of 37?°C, respectively. The results of CD and thermal denaturation showed that the molecular structure of HSA affected by interaction with Pt(II) and Pd(II) complexes is stable. Cytotoxicity studies represented the growth suppression effect of the Pt(II) and Pd(II) complexes toward the human colorectal carcinoma cell line. Therefore, the results suggest that the new designed Pt(II) and Pd(II) complexes are well promising candidates for use in cancer treatment, particularly for human colorectal cancer.

Communicated by Ramaswamy H. Sarma     

Synthesis of a novel linear polymer of a macrocyclic polyamine copper (II) complex and its interaction with plasmid DNA

The novel linear polymer of a macrocyclic polyamine copper (II) complex, which has many cyclen groups linked by epichlorohydrin, has been synthesized as a DNA cleavage agent. The structure of the polymer 3 was identified by ¹HNMR and IR and its molecular weight was measured by GPC. The result of agarose gel electrophoresis assay showed that Cu-(II) complex 4 could act as a powerful catalyst for the cleavage of plasmid DNA under physiological conditions.     

DNA interaction of new copper(II) complexes with sulfonamides as ligands

New copper(II) complexes with sulfonamide ligands have been prepared and characterized. Sulfonamide ligands were prepared through a reaction between 8-aminoquinoline and either 2-mesitylene (Hqmesa), 4-tert-butylbenzene (Hqtbsa), or alpha-toluene (Halphaqtsa) sulfonyl chlorides. The structural analysis carried out for complex [Cu(alphaqtsa)(2)] indicated that the local environment of the Cu(II) cation is between a square planar and a tetrahedral geometry, with stacking of the benzene rings of the sulfonyl ligands between neighbor molecules. Powder EPR spectra at room temperature gave rhombic spectra for the [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] complexes and an axial spectrum for the [Cu(qtbsa)(2)] complex, probably due to the steric hindrance of the methyl groups. Complexes [Cu(alphaqtsa)(2)] and [Cu(qmesa)(2)] are artificial chemical nucleases that degrade DNA in the presence of sodium ascorbate. A study of the radical scavengers revealed that the ROS (reactive oxygen species) involved in the DNA damage were hydroxyl, singlet oxygen-like species, and superoxide anion.     

Intercalation of a Zn(II) complex containing ciprofloxacin drug between DNA base pairs

In this study, an attempt has been made to study the interaction of a Zn(II) complex containing an antibiotic drug, ciprofloxacin, with calf thymus DNA using spectroscopic methods. It was found that Zn(II) complex could bind with DNA via intercalation mode as evidenced by: hyperchromism in UV–Vis spectrum; these spectral characteristics suggest that the Zn(II) complex interacts with DNA most likely through a mode that involves a stacking interaction between the aromatic chromophore and the base pairs of DNA. DNA binding constant (K_b = 1.4 × 10⁴ M^?1) from spectrophotometric studies of the interaction of Zn(II) complex with DNA is comparable to those of some DNA intercalative polypyridyl Ru(II) complexes 1.0 ?4.8 × 10⁴ M^?1. CD study showed stabilization of the right-handed B form of DNA in the presence of Zn(II) complex as observed for the classical intercalator methylene blue. Thermodynamic parameters (ΔH < 0 and ΔS < 0) indicated that hydrogen bond and Van der Waals play main roles in this binding prose. Competitive fluorimetric studies with methylene blue (MB) dye have shown that Zn(II) complex exhibits the ability of this complex to displace with DNA-MB, indicating that it binds to DNA in strong competition with MB for the intercalation.     

DNA binding behaviors and cleavage properties of a Ru(II) polypyridyl complex

A novel complex, [Ru(phen)₂pzip]²⁺1 (phen = 1,10-phenanthroline; pzip = 2-(pyrazine-2-yl)imidazo-[4,5-f][1,10]phenanthroline]), has been synthesized and characterized by elemental analysis, ES-MS, ¹H NMR. The DNA-binding behaviors of this complex were studied by spectroscopic methods and viscosity measurements. The results indicate that the complex can bind to CT-DNA in an intercalative mode. When irradiated at 365 nm, complex 1 can promote the cleavage of plasmid pBR322DNA. Furthermore, Zn²⁺ can trigger the DNA cleavage of complex 1 without irradiation. The mechanism studies revealed that the DNA cleavage by complex 1 in the presence of Zn²⁺ is likely to proceed via a hydrolytic cleavage process.     

Synthesis,DNA Binding,and Oxidative Cleavage Studies of Fe(II) and Co(III) Complexes Containing Bioactive Ligands

The two complexes containing bioactive ligands of the type and [Fe(L)] (PF₆)₂ (1) (where L = [1-{[2-{[2-hydroxynaphthalen-1-yl)methylidine]amino}phenyl)imino] methyl}naphthalene-2-ol]) and [Co(L₁L₂)] (PF₆)₃ (2) (where L₁L₂ = mixed ligand of 2-seleno-4-methylquinoline and 1,10-phenanthroline in the ratio 1:2, respectively) were synthesized and structurally characterized. The DNA binding property of the complexes with calf thymus DNA has been investigated using absorption spectra, viscosity measurements, and thermal denaturation experiments. Intrinsic binding constant K_b has been estimated at room temperature. The absorption spectral studies indicate that the complexes intercalate between the base pairs of the CT-DNA tightly with intrinsic DNA binding constant of 2.8 × 10⁵ M^?1 for (1) and 4.8 × 10⁵ M^?1 for (2) in 5 mM Tris-HCl/50 mM NaCl buffer at pH 7.2, respectively. The oxidative cleavage activity of (1) and (2) were studied by using gel electrophoresis and the results show that complexes have potent nuclease activity.     

Synthesis, crystal structure and DNA cleavage activity of a novel Ni(II)-Cd(II) coordination polymer

A novel one-dimensional heterometallic complex, {Cd₂[NiL]₂(SCN)₄(H₂O)}_n (1), has been synthesized and characterized by single-crystal X-ray analysis, where L is dianion of 2,3-dioxo-5,6,13,14-dibenzo-9,10-cyclohexyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene. The most striking feature of 1 is that in the structure there is one type of S-S bond (1.823(13) Å) formed by two thiocyanate groups which has not been reported to our knowledge. The DNA cleavage activity of 1 in the presence of H₂O₂ was compared with those of nickel(II) ion, cadmium(II) ion and corresponding mononuclear precursor NiL (2). The DNA cleavage kinetics was studied and the corresponding activation parameters of 1 were obtained.     

Platinum(II) Complexes with 1,10‐Phenanthroline and Hydrophilic Alkoxyacetate Ligands as Potential Antitumor Agents

Four platinum complexes, formulated as [Pt(phen)(OCOCH₂OR)₂] (phen=1,10‐phenanthroline, R=Me, Et, ⁱPr, or ^tBu), have been synthesized and well characterized by elemental analysis, IR, ¹H‐NMR, ¹³C‐NMR and ESI‐MS spectroscopy. Replacing chloride groups of the precursor Pt(phen)Cl₂ with alkoxyacetate anions greatly improved the aqueous solubility and cytotoxicity of the resulting platinum complexes. The in vitro cytotoxicity study revealed that complexes 1 – 3 were active in vitro towards four human tumor cell lines, especially complex 1 which exhibited prominent in vitro cytotoxic activity against HCT‐116 cell lines comparable to cisplatin and oxaliplatin. Flow cytometry assay indicated that representative complexes 1 and 2 exerted cytotoxicity on HCT‐116 cell lines through inducing cell apoptosis and blocking cell cycle progression in the S or G2/M phases. The interaction of representative complexes with pET28a plasmid DNA was tested by agarose gel electrophoresis, which demonstrated that complexes 1 and 2 were capable of distorting plasmid DNA mainly by covalent binding and degradation effect.     

Cytotoxicity and DNA damage induced by a new platinum(II) complex with pyridine and dithiocarbamate

A new platinum(II) complex containing a pyridine nucleus and a dithiocarbamate moiety as ligands ([Pt(ESDT)(Py)Cl]) was evaluated for in vitro cytotoxicity in the cisplatin-sensitive human ovarian 2008 and in the isogenic-resistant C13* cell lines. In both cell types, a tumor cell growth inhibition greater than cisplatin and a complete lack of cross-resistance in C13* cells were found. Despite its molecular size, [Pt(ESDT)(Py)Cl] accumulation was much higher than cisplatin both in parent and resistant cells. Studying the mechanism of action in cell-free media, we established that [Pt(ESDT)(Py)Cl] more efficiently interacts with DNA in vitro compared to cisplatin maintaining a binding preference for GG rich sequences of DNA. On the contrary, DNA platination in vivo by [Pt(ESDT)(Py)Cl] was found lower than cisplatin. An analysis of the type of DNA lesions induced by [Pt(ESDT)(Py)Cl] suggests that the cytotoxic efficacy and the ability to overcome cisplatin resistance seem to be related to a different mechanism of interaction with DNA and/or with other key cellular components.     

DNA binding affinity of a macrocyclic copper(II) complex: Spectroscopic and molecular docking studies

The interaction of a novel macrocyclic copper(II) complex, ([CuL(ClO₄)₂] that L is 1,3,6,10,12,15-hexaazatricyclo[13.3.1.1^6,10]eicosane) with calf thymus DNA (ct-DNA) was investigated by various physicochemical techniques and molecular docking at simulated physiological conditions (pH = 7.4). The absorption spectra of the Cu(II) complex with ct-DNA showed a marked hyperchroism with 10 nm blue shift. The intrinsic binding constant (K_b) was determined as 1.25 × 10⁴ M^?1, which is more in keeping with the groove binding with DNA. Furthermore, competitive fluorimetric studies with Hoechst33258 have shown that Cu(II) complex exhibits the ability to displace the ct-DNA-bound Hoechst33258 indicating that it binds to ct-DNA in strong competition with Hoechst33258 for the groove binding. Also, no change in the relative viscosity of ct-DNA and fluorescence intensity of ct-DNA-MB complex in the present of Cu(II) complex is another evidence to groove binding. The thermodynamic parameters are calculated by van't Hoff equation, which demonstrated that hydrogen bonds and van der Waals interactions played major roles in the binding reaction. The experimental results were in agreement with the results obtained via molecular docking study.     

Synthesis,characterization, DNA and HSA binding studies of isomeric Pd (II) antitumor complexes using spectrophotometry techniques

Two new Palladium(II) isomeric complexes, [Pd (Gly)(Leu)](I) and [Pd (Gly)(Ile)](II), where Gly is glycine, and Leu and Ile are isomeric amino acids (leucine and isoleucine), have been synthesized and characterized by elemental analysis, molar conductivity measurements, FT-IR, ¹H NMR, and UV–Vis. The complexes have been tested for their In vitro cytotoxicity against cancer cell line K₅₆₂ and their binding properties to calf thymus DNA (CT-DNA) and human serum albumin (HSA) have also been investigated by multispectroscopic techniques. Interactions of these complexes with CT-DNA were monitored using gel electrophoresis. The energy transfer from HSA to these complexes and the binding distance between HSA and the complexes (r) were calculated. The results obtained from these studies indicated that at very low concentrations, both complexes effectively interact with CT-DNA and HSA. Fluorescence studies revealed that the complexes strongly quench DNA bound ethidium bromide as well as the intrinsic fluorescence of HSA through the static quenching procedures. Binding constant (K_b), apparent biomolecular quenching constant (k_q), and number of binding sites (n) for CT-DNA and HSA were calculated using Stern–Volmer equation. The calculated thermodynamic parameters indicated that the hydrogen binding and vander Waals forces might play a major role in the interaction of these complexes with HSA and DNA. Thus, we propose that the complexes exhibit the groove binding with CT-DNA and interact with the main binding pocket of HSA. The complexes follow the binding affinity order of I > II with DNA- and II > I with HSA-binding.     

Palladium(II) binding to N(7) of acyclovir: DNA interaction and herpes simplex virus (HSV-1) inhibitory activity

Cytotoxicity and herpes simplex virus (HSV-1) inhibitory activity of acyclovir (ACV), 9-[(2-hydroxyethoxy)methyl]guanine, and the palladium(II) coordination complex cis-[PdCl₂(H₂O)(N7-ACV)] · ACV · xH₂O have been tested in African green monkey kidney (Vero line) epithelial cell cultures. The N(7) position of ACV represents the preferred binding site to afford a pseudo-chelate N7/O6 Pd(II) complex involving H-bonds with the cis H₂O molecule. The Pd(II)-ACV complex has been structurally characterized by FTIR and ¹H NMR spectroscopy techniques, chemical composition was measured by elemental analysis, and the thermoanalytical study was performed by TG/DTA. The recognition of secondary ACV molecules by the Pd(II) derivative promotes cooperatively potent HSV-1 inhibitory activity which, in turn, strongly depends on concentration conditions. At the optimal concentration of 10 μM, this complex exhibits antiviral efficiency in vitro, approximately hundred-fold (ca. 1.87 log₁₀) more effective in herpes-infected cells when compared with that of the parent ACV molecules. The molecular-level observation of noticeable modifications caused by the complex on the morphology of the plasmid pBR322 DNA was monitored by AFM, whose mutual interaction evolves to eventually afford DNA condensates upon increasing the period of incubation.     

Synthesis,cytotoxicity assessment,and interaction and docking of novel palladium(II) complexes of imidazole derivatives with human serum albumin

Imidazole analogs are the agents that attract both bioinorganic chemist and drug designer. Numerous methods have been proposed for synthesis of imidazole derivatives. In this study, a series of heterocyclic system with p-conjugated system such as 2-aryl-imidazo[4,5-f][1,10]phenanthroline analogs were synthesized. Then, three new palladium(II) complexes containing 2-(Furan-2-yl)-1H-Imidazo[4,5-f][1,10]Phenanthroline (FIP) and 2-(thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline (TIP) ligands were synthesized. The structures of the compounds, [Pd(Phen)(TIP)](NO₃)₂, [Pd(Phen)(FIP)](NO₃)₂, and [Pd(FIP)₂]Cl were determined by spectroscopic methods and elemental analysis. Biological activity of the complexes synthesized was assessed against chronic myelogenous leukemia cell line, K562. Also, the interactions of human serum albumin with complexes were investigated using isothermal titration in the Tris buffer, pH 7.4. According to the results obtained, it was found that there is a set of six binding sites for these complexes on HSA with positive cooperativity in the binding process. Docking technique was also applied to confirm the experimental results. The results showed that smaller complexes have higher interaction affinity.     

Synthesis,characterization, DNA interaction,and cytotoxicity of novel Pd(II) and Pt(II) complexes

Four complexes [Pd(L)(bipy)Cl]·4H₂O (1), [Pd(L)(phen)Cl]·4H₂O (2), [Pt(L)(bipy)Cl]·4H₂O (3), and [Pt(L)(phen)Cl]·4H₂O (4), where L = quinolinic acid, bipy = 2,2’-bipyridyl, and phen = 1,10-phenanthroline, have been synthesized and characterized using IR, ¹H NMR, elemental analysis, and single-crystal X-ray diffractometry. The binding of the complexes to FS-DNA was investigated by electronic absorption titration and fluorescence spectroscopy. The results indicate that the complexes bind to FS-DNA in an intercalative mode and the intrinsic binding constants K of the title complexes with FS-DNA are about 3.5?×?10⁴ M^?1, 3.9?×?10⁴ M^?1, 6.1?×?10⁴ M^?1, and 1.4?×?10⁵ M^?1, respectively. Also, the four complexes bind to DNA with different binding affinities, in descending order: complex 4, complex 3, complex 2, complex 1. Gel electrophoresis assay demonstrated the ability of the Pt(II) complexes to cleave pBR322 plasmid DNA.     

ROS-Mediated Antitumor Activity,Apoptosis, and Molecular Docking Studies of Platinum(II) Coordination Complexes Bearing 2-(Diphenylphosphino)pyridine Ligands

Platinum-based drugs have been widely used in cancer treatment. However, their severe side effects have limited their use. So, researchers have been striving to find compounds with fewer side effects and greater efficacy, to overcome these drawbacks. Here, the cytotoxicity of platinum(II) complexes containing 2-(diphenylphosphino)pyridine ligands have been studied on human lung (A549), ovarian (SKOV3), breast (MCF-7) cancer, and normal breast (MCF-10A) cell lines. The most potent compound exhibits a marked cell growth-inhibitory effect against ovarian and lung cancer cells with IC₅₀ values of 9.41 and 5.58 μM, respectively, which were significantly better than that observed for cisplatin (19.02, and 8.64 μM). Additionally, all complexes achieved significantly lower cytotoxicity towards MCF-10A. To investigate the interaction of complexes with DNA, an electrophoresis mobility shift assay was conducted, which indicated that complexes bind to DNA and affect its electrophoretic mobility. An analysis of apoptosis in A549 cells supported the conclusion that they inhibits cell proliferation via induction of apoptosis in a concentration-dependent manner. Molecular docking was also used to investigate the interactions of compounds with different DNA structures. These compounds have the ability to be a suitable pharmaceutical compound with further investigations in the field of cancer research.     

DNA Binding Studies of Hematoxylin-Dy(Ш) Complex by Spectrometry Using Acridine Orange as a Probe

The interaction of a hematoxylin(HE)-Dy(Ш) complex with herring sperm DNA(hsDNA) was studied using acridine orange(AO) as a probe by UV-vis absorption, circular dichroism(CD), fluorescence spectroscopy and viscosity measurements. From the results of the probe experiment, we found that the HE-Dy(Ш) complex could compete with AO for intercalating into hsDNA. The binding constants of the HE-Dy(Ш) complex to hsDNA was obtained by the double reciprocal method and indicated that the affinity between hsDNA and the complex is weaker than that between hsDNA and classical intercalators. The thermodynamic parameters(ΔH°, ΔG°, ΔS°) were calculated from the UV-vis absorption data measured at two different temperatures. Further experimental results suggested that there exist groove binding and partial intercalation binding between hsDNA and HE-Dy(Ш) complex.