DNA-Binding and Cytotoxicity of Copper(I) Complexes Containing Functionalized Dipyridylphenazine Ligands

Synthesis, crystal structural description, DNA binding, molecular docking, and anticancer evaluation of the novel platinum(IV) supramolecular complex

A novel platinum(IV) supramolecular complex; [PtCl2(2,2'-bipy)2](PtCl6) was synthesized in aqueous acetonitrile solution at ambient temperature with constant stirring. The structure was confirmed by elemental analysis, FT-IR, UV-vis, NMR spectroscopy, and single-crystal X-ray diffraction, revealing a unique distorted octahedral geometry and a three-dimensional network stabilized by hydrogen bonding and π-π stacking. DNA binding studies, including electronic absorption titration and viscometry, indicated a groove binding mechanism with a binding constant (Kb) of 5.00 × 10⁶ M-1. Molecular docking with DNA (PDB ID: 1BNA) and cancer-related proteins (PDB codes: 3ig7, 3eqm, 4fm9) supports these interactions, while in vitro anticancer assays demonstrated potent cytotoxicity with IC₅₀ values of 41.37 μM for HepG2, 47.62 μM for HCT116, and 73.90 μM for MDA-MB-231 cells, outperforming cisplatin in selectivity. This study not only advances our understanding of structure-activity relationships in platinum-based complexes but also highlights the potential of this complex as a promising candidate for developing more effective and less toxic anticancer agents.

Tuning anticancer properties and DNA-binding of Pt(ii) complexes via alteration of nitrogen softness/basicity of tridentate ligands†

Nine tridentate Schiff base ligands of the type (N^N^O) were synthesized from reactions of primary amines {2-picolylamine (Py), N-phenyl-1,2-diaminobenzene (PhN), and N-phenyl-1,2-diaminoethane(EtN)} and salicylaldehyde derivatives {3-ethoxy (OEt), 4-diethylamine (NEt₂) and 4-hydroxy (OH)}. Complexes with the general formula Pt(N^N^O)Cl were synthesized by reacting K₂PtCl₄ with the ligands in DMSO/ethanol mixtures. The ligands and their complexes were characterized by NMR spectroscopy, mass spectrometry and elemental analysis. The DNA-binding behaviours of the platinum(ii) complexes were investigated by two techniques, indicating good binding affinities and a two-stage binding process for seven complexes: intercalation followed by switching to a covalent binding mode over time. The other two complexes covalently bond to ct-DNA without intercalation. Theoretical calculations were used to shed light on the electronic and steric factors that lead to the difference in DNA-binding behavior. The reactions of some platinum complexes with guanine were investigated experimentally and theoretically. The binding of the complexes with bovine serum albumin (BSA) indicated a static interaction with higher binding affinities for the ethoxy-containing complexes. The half maximal inhibitory concentration (IC₅₀) values against MCF-7 and HepG2 cell lines suggest that platinum complexes with tridentate ligands of N-phenyl-o-phenylenediamine or pyridyl with 3-ethoxysalicylimine are good chemotherapeutic candidates. Pt-Py-OEt and Pt-PhN-OEt have IC₅₀ values against MCF-7 of 13.27 and 10.97 μM, respectively, compared to 18.36 μM for cisplatin, while they have IC₅₀ values against HepG2 of 6.99 and 10.15 μM, respectively, compared to 19.73 μM for cisplatin. The cell cycle interference behaviour with HepG2 of selected complexes is similar to that of cisplatin, suggesting apoptotic cell death. The current work highlights the impact of the tridentate ligand on the biological properties of platinum complexes.

The article illustrates the design flexibility of tridentate ligands and the resultant platinum complexes, highlighting the impact of this design flexibility on the anticancer potential.

Tuning the anticancer properties of Pt(ii) complexes via structurally flexible N-(2-picolyl)salicylimine ligands

Three tridentate Schiff base ligands were synthesized from the reactions between 2-picolylamine and salicylaldehyde derivatives (3-ethoxy (OEt), 4-diethylamino (NEt2) and 4-hydroxy (OH)). Complexes with the general formula Pt(N^N^O)Cl were obtained from reactions between the ligands and K2PtCl4. The ligands and their complexes were characterized by NMR spectroscopy, mass spectrometry and elemental analysis. Further confirmation of the structure of Pt-OEt was achieved by single-crystal X-ray diffraction. The DMSO/chlorido exchange process at Pt-OEt was investigated by monitoring the change in conductivity, revealing very slow dissociation in DMSO. Moreover, solvent/chlorido exchange for Pt-OEt and Pt-NEt2 were investigated by NMR spectroscopy in DMSO and DMSO/D2O; Pt-NEt2 forms an adduct with DMSO while Pt-OEt forms adducts with DMSO and water. The DNA-binding behaviour of the platinum(ii) complexes was investigated by two techniques. Pt-NEt2 has the best apparent binding constant. The intercalation mode of interaction with ct-DNA was suggested by molecular docking studies and the increase in the relative viscosity of ct-DNA with increasing concentrations of the platinum(ii) complexes. However, the gradual decrease in the relative viscosity over time at constant concentration of platinum(ii) complexes indicated a shift from intercalation to a covalent binding mode. Anticancer activities of the ligands and their platinum(ii) complexes were examined against two cell lines. The platinum(ii) complexes exhibit superior cytotoxicity to that of their ligands. Among the platinum(ii) complexes, Pt-OEt possesses the best IC50 against both cell lines, its cytotoxicity being comparable to that observed for cisplatin. Cell cycle arrest in the HepG2 cell line upon treatment with Pt-OEt and Pt-NEt2 was investigated and compared to that of cisplatin; the change in the cell accumulation patterns supports the presumption of an apoptotic cell death pathway. The optimized structures of the B-DNA trimer adducts with the platinum complexes showed hydrogen-bonding interactions between the ligands and nucleobases, affecting the inter-strand hydrogen bonding within the DNA, and highlighting the strong ability of the complexes to induce conformational changes in the DNA, leading to the activation of apoptotic cell death. In summary, the current study demonstrates promising new anticancer platinum(ii) complexes with highly flexible tridentate ligands; the functional groups on the ligands are important in tuning their DNA binding/anticancer properties.

Synthesis and Evaluation of Antiproliferative Activity, Topoisomerase IIα Inhibition, DNA Binding and Non-Clinical Toxicity of New Acridine-Thiosemicarbazone Derivatives

In this study, we report the synthesis of twenty new acridine–thiosemicarbazone derivatives and their antiproliferative activities. Mechanisms of action such as the inhibition of topoisomerase IIα and the interaction with DNA have been studied for some of the most active derivatives by means of both in silico and in vitro methods, and evaluations of the non-clinical toxicities (in vivo) in mice. In general, the compounds showed greater cytotoxicity against B16-F10 cells, with the highest potency for DL-08 (IC₅₀ = 14.79 µM). Derivatives DL-01 (77%), DL-07 (74%) and DL-08 (79%) showed interesting inhibition of topoisomerase IIα when compared to amsacrine, at 100 µM. In silico studies proposed the way of bonding of these compounds and a possible stereoelectronic reason for the absence of enzymatic activity for CL-07 and DL-06. Interactions with DNA presented different spectroscopic effects and indicate that the compound CL-07 has higher affinity for DNA (Kb = 4.75 × 10⁴ M⁻¹; Ksv = 2.6 × 10³ M⁻¹). In addition, compounds selected for non-clinical toxicity testing did not show serious signs of toxicity at the dose of 2000 mg/kg in mice; cytotoxic tests performed on leukemic cells (K-562) and its resistant form (K-562 Lucena 1) identified moderate potency for DL-01 and DL-08, with IC₅₀ between 11.45 and 17.32 µM.

Synthetic approach toward spiro quinoxaline-β-lactam based heterocyclic compounds: Spectral characterization, SAR, pharmacokinetic and biomolecular interaction studies

Series of spiro quinoxaline-β-lactam based heterocyclic compounds (QL 1 - QL 21) were synthesized and characterized by spectroscopic techniques like ¹H-NMR, LC-MS, FT-IR spectroscopy and elemental analysis. The binding mode and binding strength between compounds and calf thymus-DNA were estimated by UV-visible spectroscopy, viscosity measurement and molecular docking studies. The compounds bind with the DNA through partial intercalation mode. In the absorption titration experiment, the K_b values for all the synthesized compounds were found in the range of 0.24-0.64 × 10⁵ M^-1. The protein binding studies of all the synthesized compounds were evaluated by absorption titration experiment, and the K_b value for all the compounds was obtained in the range of 0.030-1.571 × 10⁴ M^-1. The compounds were screened against two Gram (+ve) and three Gram (-ve) bacteria for antimicrobial activity. The MIC values for all the synthesized compounds were found in 95-255 µM. The LC₅₀ values (cytotoxicity) of the synthesized compounds (QL 1-QL 21) were found in the range of 4.00-12.89 µg/mL. The ADME study was carried out using the online platform SwissADME and admetSAR to evaluate the pharmacokinetic profile of all the synthesized compounds. All the compounds were screened for anticancer activity against the human osteosarcoma (MG-63) cell line. The result shows that all the compounds exhibit effective anticancer activity.Communicated by Ramaswamy H. Sarma.

Heteroleptic copper(II) complexes of prenylated flavonoid osajin behave as selective and effective antiproliferative and anti-inflammatory agents

Heteroleptic copper(II) complexes, containing prenylated flavonoid osajin isolated from the fruits of Maclura pomifera Schneid., were prepared and thoroughly characterized, including single crystal X-ray analysis. Some of the following complexes of the general composition [Cu(L)(bpy)]NO₃ (1), [Cu(L)(dimebpy)]NO₃·2MeOH (2) [Cu(L)(phen)]NO₃·H₂O (3), [Cu(L)(bphen)]NO₃ (4) and [Cu(L)(dppz)]NO₃ (5), where HL stands for 3-(4-hydroxyphenyl)-5-hydroxy-8,8-dimethyl-6-(3-methylbut-2-ene-1-yl)-4H,8H-benzo[1,2-b:3,4-b']dipyran-4-one (osajin), bpy = 2,2'-bipyridine, dimebpy = 4,4'-dimethyl-2,2'-bipyridine, phen = 1,10-phenanthroline, bphen = 4,7-diphenyl-1,10-phenanthroline and dppz = dipyrido[3,2-a:2',3'-c]phenazine, were also monitored for their solution stability and interactions with cysteine and glutathione by mass spectrometry. The in vitro cytotoxicity of the complexes was evaluated against a panel of eight human cancer cell lines: (MCF-7, HOS, A549, PC-3, A2780, A2780R, Caco-2, and THP-1). The results revealed high antiproliferative activity of the complexes with the best IC₅₀ values of 0.5-3.4 μM for complexes (4) and (5), containing the bulkier N,N'-donor ligands (bphen, and dppz, respectively). The complexes also revealed a relatively low toxicity towards human hepatocytes (IC₅₀ values are higher than 100 μM in some cases), and thus proved to be highly selective towards the cancer cells. On the other hand, the complexes showed a strong in vitro nuclease effect using the model pUC-19 plasmid. In the model of lipopolysaccharide-stimulated (LPS) THP-1 monocytes, the complexes revealed ability to lower the activity of nuclear factor kappa-B/activator protein 1 (NF-κB /AP-1) system and decrease the secretion of tumor necrosis factor alpha (TNF-α). Thus, the complexes have been identified as strong antiproliferative and anti-inflammatory compounds.

Evaluation of the Anticancer and DNA-Binding Characteristics of Dichloro(diimine)zinc(II) Complexes

Several metal diimine complexes have been reported to possess anticancer properties. To evaluate the anticancer properties of tetrahedral zinc(II) diimine complexes, six complexes were synthesized with the general formula M(N^N)Cl2 {where M = Zn, Pt and N^N = 2,2’-biquinoline (1), 2,2’-dipyridylketone (2) and 4-((pyridine-2-ylmethylene)amino)phenol (3)}. In general, the intrinsic DNA-binding constants for the different compounds exhibited values within close proximity; the changes in the viscosity of the CT-DNA upon binding to the compounds suggest intercalation-binding mode. Molecular docking study predicted that complexes containing the highly planar ligand 2,2’-biquinoline are capable to establish π–π interactions with nucleobases of the DNA; the other four complexes engaged in donor–acceptor interactions with DNA nucleobases. The six complexes and two reference drugs (cisplatin and sunitinib) were tested against two cancer cell lines (COLO 205 and RCC-PR) and one normal cell line (LLC-MK2), highlighting the better performance of the zinc(II) complexes compared to their platinum(II) analogues. Moreover, zinc(II) complexes have higher selectivity index values than the reference drugs, with promising anticancer properties.

Anticancer effect evaluation in vitro and in vivo of iridium(III) polypyridyl complexes targeting DNA and mitochondria

To investigate the antitumor effect of iridium complexes, three iridium (III) complexes [Ir(ppy)₂(dcdppz)]PF₆ (ppy = 2-phenylpyridine, dcdppz = 11,12-dichlorodipyrido[3,2-a:2',3'-c]phenazine) (Ir1), [Ir(bzq)₂(dcdppz)]PF₆ (bzq = benzo[h]quinoline) (Ir2) and [Ir(piq)₂(dcdppz)]PF₆ (piq = 1-phenylisoquinoline) (Ir3) were synthesized and characterized. Geometry optimization, molecular dynamics simulation and docking studies have been performed to further explore the antitumor mechanism. The cytotoxicity of Ir1-3 toward cancer cells was studied by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The localization of complexes Ir1-3 in the mitochondria, intracellular accumulation of reactive oxygen species (ROS) levels, the changes of mitochondrial membrane potential and morphological changes in apoptosis were investigated. Flow cytometry was applied to quantify fluorescence intensity and determine cell cycle distribution. Western blotting was used to detect the expression of apoptosis-related proteins. The anti-tumor effect of Ir1 in vivo was evaluated. The results showed that Ir1-3 had high cytotoxicity to most tumor cells, especially to SGC-7901 cells with a low IC₅₀ value. Ir1-3 can increase the intracellular ROS levels, reduce the mitochondrial membrane potential. Additionally, the complexes induce an increase of apoptosis-related protein expression, enhance the percentage of apoptosis. The complexes inhibit the cell proliferation at G0/G1 phase. The results obtained from antitumor in vivo indicate that Ir1 can significantly inhibit the growth of tumors with an inhibitory rate of 54.08%. The docking studies show that complexes Ir1-3 interact with DNA through minor-groove intercalation, which increases the distance of DNA base pairs, leading to a change of DNA helix structure. These experimental and theoretical findings indicate that complexes Ir1-3 can induce apoptosis in SGC-7901 cells through the mitochondrial dysfunction and DNA damage pathways, and then exerting anti-tumor activity in vitro and vivo.

Effect of Net Charge on DNA-Binding, Protein-Binding and Anticancer Properties of Copper(I) Phosphine-Diimine Complexes

The syntheses of [Cu(PPh3)2(L)]NO3 and [Cu(PPh3)2(L-SO3Na)]NO3 were achieved through the reaction of Cu(PPh3)2NO3 and equimolar amount of the ligands (L = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine; LSO3Na = 5,6-diphenyl-3-[2-pyridyl]-1,2,4-triazine-4,4′-disulfonic acid disodium salt). The complexes were characterized by NMR and IR spectroscopy and mass spectrometry. The compounds exhibit similar absorption and emission spectra, suggesting a similar electronic structure. Ct-DNA binding studies show the strong influence of the net charge as Cu-L (positively charged) is able to bind to ct-DNA while Cu-LSO3Na (negatively charged) is not. The net charge of the complexes affects the thermodynamic and kinetic binding parameters toward human serum albumin. HSA-binding of the complexes was further investigated by molecular docking, revealing different binding sites on the HSA protein as a function of the net charge. The different anticancer activities of the complexes towards ovcar-3 and hope-62 cancer cell lines are suggestive of a role for the overall charge of the complexes. Interaction with the DNA is not the major mechanism for this class of complexes. The overall net charge of the pharmacophore (anticancer agent) should be a key consideration in the design of anticancer metal complexes.

Synthesis, Structural Studies, and Anticancer Properties of [CuBr(PPh3)2(4,6-Dimethyl-2-Thiopyrimidine-κS]

CuBr(PPh3)2(4,6-dimethylpyrimidine-2-thione) (Cu-L) was synthesized by stirring CuBr(PPh3)3 and 4,6-dimethylpyrimidine-2-thione in dichloromethane. The crystal structure of Cu-L was obtained, and indicated that the complex adopts a distorted tetrahedral structure with several intramolecular hydrogen bonds. Moreover, a centrosymmetric dimer is formed by the intermolecular hydrogen bonding of the bromine acceptor created by symmetry operation 1−x, 1−y, 1−z to the methyl group (D3 = C42) of the pyrimidine–thione ligand. HSA-binding of Cu-L and its ligand were evaluated, revealing that Cu-L binds to HSA differently than its ligand. The HSA-bindings were modeled by molecular docking, which suggested that Cu-L binds to the II A domain while L binds between the I B and II A domains. Anticancer activities toward OVCAR-3 and HeLa cell lines were tested and indicated the significance of the copper center in enhancing the cytotoxic effect; negligible toxicities for L and Cu-L were observed towards a non-cancer cell line. The current study highlights the potential of copper(I)-phosphine complexes containing thione ligands as therapeutic agents.