Molecular insight into the structural and functional aspects of arene Ru(II) complexes bearing bulky thiourea ligands

Herein we report four new arene ruthenium(II) complexes [RuII(η6-p-cymene)(L1)к1(S)Cl2] (C1), [RuII(η6-benzene)(L1)к1(S)Cl2] (C2) where L1 is N-((2,6-dimethylphenyl)carbamothioyl)benzamide (L1), and [RuII(η6-p-cymene)(L2)к1(S)Cl2] (C3), [RuII(η6-benzene)(L2)к1(S)Cl2] (C4) where L2 is N-((2,6-diisopropylphenyl)carbamothioyl)benzamide (L2) which were synthesized and evaluated for biological activity. The monodentate coordination of thione sulphur (S) to ruthenium ion along with two terminal chloride was confirmed by X-Ray diffraction analysis thus revealing a typical "piano-stool" pseudo tetrahedral geometry. DPPH radical scavenging activity showed that ligands were less efficient however on complex formation it showed significant efficacy with C4 showing the highest activity. The ligands and ruthenium complexes exhibited minimal to no cytotoxic effects on HEK cells within the concentration range of 10-300 μM. Evaluating the cytotoxicity against prostate cancer cells (DU145) L1, L2 and C1 displayed more pronounced cytotoxic activity with C1 showing high cytotoxicity against the cancer cells, in comparison to cisplatin indicating its potential for further investigation and analysis. Considering this, compound C1 was used to further study its interaction with BSA using fluorescence spectroscopy and it was found to be 2.64 × 106 M-1. Findings from CD spectroscopy indicate the binding in the helix region which was further confirmed with the molecular docking studies.

Promoting the Anticancer Activity with Multidentate Furan-2-Carboxamide Functionalized Aroyl Thiourea Chelation in Binuclear Half-Sandwich Ruthenium(II) Complexes

A new set of binuclear arene ruthenium complexes [Ru2(p-cymene)2(k4-N2OS)(L1-L3)Cl2] (Ru2L1-Ru2L3) encompassing furan-2-carboxamide-based aroylthiourea derivatives (H2L1-H2L3) was synthesized and characterized by various spectral and analytical techniques. Single-crystal XRD analysis unveils the N^O and N^S mixed monobasic bidentate coordination of the ligands constructing N, S, Cl/N, O, and Cl legged piano stool octahedral geometry. DFT analysis demonstrates the predilection for the formation of stable arene ruthenium complexes. In vitro antiproliferative activity of the complexes was examined against human cervical (HeLa), breast (MCF-7), and lung (A549) cancerous and noncancerous monkey kidney epithelial (Vero) cells. All the complexes are more efficacious against HeLa and MCF-7 cells with low inhibitory doses (3.86-11.02 μM). Specifically, Ru2L3 incorporating p-cymene and -OCH3 fragments exhibits high lipophilicity, significant cytotoxicity against cancer cells, and lower toxicity on noncancerous cells. Staining analysis indicates the apoptosis-associated cell morphological changes expressively in MCF-7 cells. Mitochondrial membrane potential (MMP) and reactive oxygen species (ROS) analyses reveal that Ru2L3 can raise ROS levels, reduce MMP, and trigger mitochondrial dysfunction-mediated apoptosis. The catalytic oxidation of glutathione (GSH) to its disulfide form (GSSG) by the complexes may simultaneously increase the ROS levels, alluding to their observed cytotoxicity and apoptosis induction. Flow cytometry determined the quantitative classification of late apoptosis and S-phase arrest in MCF-7 and HeLa cells. Western blotting analysis confirmed that the complexes promote apoptosis by upregulating Caspase-3 and Caspase-9 and downregulating BCL-2. Molecular docking studies unfolded the strong binding affinities of the complexes with VEGFR2, an angiogenic signaling receptor, and BCL2, Cyclin D1, and HER2 proteins typically overexpressed on tumor cells.

Design, synthesis, X-ray crystal structures, anticancer, DNA binding, and molecular modelling studies of pyrazole-pyrazoline hybrid derivatives

We have designed and synthesized three pyrazole analogs (4, 5a, 5b), pyrazole-based chalcones (6a-6d) and (8a-8h), and N-formyl/acetyl 1,3,5-trisubstituted pyrazoline analogs (7a-7d), (9a-9d). FT-IR, 1H, 13C NMR, and mass spectrometry techniques were used to describe the structures of all the synthesized analogs. The single crystal X-ray method was used to identify the molecular structure of derivatives 4 and 5a. All synthesized analogs were screened by MTT assay on two cancer cell lines, the human lung cancer cell line (A549) and cervical cancer cell line (HeLa). Among all compounds, analog 9d demonstrates significant anticancer activity against HeLa (IC50 = 23.6 μM) and A549 (IC50 = 37.59 μM). The non-interactive interaction of active compound (9d) with Calf thymus DNA (Ct-DNA) has been investigated through various methods, such as UV-vis absorption, emission, cyclic voltammetry and circular dichroism. The DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical has been used to measure the antioxidant capacity of the pyrazoline derivative (9d). The outcomes showed that active analog has significant antioxidant activity. In addition, MD simulation of the EGFR tyrosine kinase protein-ligand complex was performed at a time scale of 100 ns. The MMGBSA data of ligand-protein complex are showed stable interactions up to 100 ns.

Ru(II)-p-Cymene Complexes of Furoylthiourea Ligands for Anticancer Applications against Breast Cancer Cells

Half-sandwich Ru(II) complexes containing nitro-substituted furoylthiourea ligands, bearing the general formula [(η⁶-p-cymene)RuCl₂(L)] (1-6) and [(η⁶-p-cymene)RuCl(L)(PPh₃)]⁺ (7--12), have been synthesized and characterized. In contrast to the spectroscopic data which revealed monodentate coordination of the ligands to the Ru(II) ion via a "S" atom, single crystal X-ray structures revealed an unusual bidentate N, S coordination with the metal center forming a four-membered ring. Interaction studies by absorption, emission, and viscosity measurements revealed intercalation of the Ru(II) complexes with calf thymus (CT) DNA. The complexes showed good interactions with bovine serum albumin (BSA) as well. Further, their cytotoxicity was explored exclusively against breast cancer cells, namely, MCF-7, T47-D, and MDA-MB-231, wherein all of the complexes were found to display more pronounced activity than their ligand counterparts. Complexes 7-12 bearing triphenylphosphine displayed significant cytotoxicity, among which complex 12 showed IC₅₀ values of 0.6 ± 0.9, 0.1 ± 0.8, and 0.1 ± 0.2 μM against MCF-7, T47-D, and MDA-MB-231 cell lines, respectively. The most active complexes were tested for their mode of cell death through staining assays, which confirmed apoptosis. The upregulation of apoptotic inducing and downregulation of apoptotic suppressing proteins as inferred from the western blot analysis also corroborated the apoptotic mode of cell death. The active complexes effectively generated reactive oxygen species (ROS) in MDA-MB-231 cells as analyzed from the 2',7'-dichlorofluorescein diacetate (DCFH-DA) staining. Finally, in vivo studies of the highly active complexes (6 and 12) were performed on the mice model. Histological analyses revealed that treatment with these complexes at high doses of up to 8 mg/kg did not induce any visible damage to the tested organs.

Hinged Bipodal Furoylthiourea-Based Ru(II)-Arene Complexes: Effect of (ortho, meta, or para)-Substitution on Coordination and Anticancer Activity

We set out to design and synthesize bipodal ligands with the phenyl group as the spacer and varied the substitution on the spacer between ortho (L1), meta (L2), and para (L3). The respective ligands and complexes containing either p-cymene (PL1-PL3) or benzene (BL1-BL3) as the arene unit were synthesized and characterized successfully. The influence of the ligands due to substitution change on their coordination behavior was quite minimal; however, the differences were seen in the anticancer activity of the complexes. DFT studies revealed the structural variations between the three different substitutions, which was further confirmed by single-crystal X-ray diffraction studies. The anticancer activity of the complexes could be correlated with their rate of hydrolysis and their lipophilicity index as determined by UV-visible spectroscopy. The cell death mechanism of the active complexes was deduced to be apoptotic via staining assays, flow cytometry, and Western blot analysis.

In vitro biological and in silico molecular docking and ADME studies of a substituted triazine-coordinated cadmium(II) ion: efficient cytotoxicity, apoptosis, genotoxicity, and nuclease-like activity plus binding affinity towards apoptosis-related proteins

A cadmium(II) complex containing dppt ligand with the formula [CdCl₂(dppt)₂], where dppt is 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine was synthesized, elucidated and submitted to in vitro cytotoxicity studies against human breast (MCF-7), glioblastoma (U-87), and lung (A549) cancer cell lines as well as mouse embryo normal cell line (NIH/3T3), in comparison with cisplatin employing MTT assay over 24 and 48 h. The complex exhibited the highest cytotoxic effect against MCF-7 cells among the other three cell lines with IC₅₀ values of 8.7 ± 0.5 (24 h) and 1.2 ± 0.7 µM (48 h). Significantly, flow cytometric assessment of the complex-treated MCF-7 and U-87 cells demonstrated a dose-dependent induced apoptotic cell death. The cellular morphological changes were in concord with cytotoxicity and flow cytometric results. The results of comet assay showed that the complex is able to induce DNA damage in MCF-7 cells. These observations are of importance, as sustained damage to cellular DNA could lead to apoptotic cell death. The results of DNA-binding studies indicated that the complex fits into the DNA minor groove and interacts with DNA via a partial intercalation. Moreover, the complex was able to efficiently cleave pUC19 DNA through a hydrolytic mechanism. The binding affinity between the complex and apoptosis-relevant protein targets including APAF1, Bax, Bcl-2, Cas3, Cas7, and Cas9 was evaluated through molecular docking studies. In silico virtual studies revealed the complex's strong affinity towards apoptosis-related proteins; therefore the complex can act as a potential apoptosis inducer. Physicochemical, pharmacokinetics, lipophilicity, drug-likeness, and medicinal chemistry properties of the complex were also predicted through in silico absorption, distribution, metabolism and excretion studies.

Tunable Anticancer Activity of Furoylthiourea-Based RuII -Arene Complexes and Their Mechanism of Action

Fourteen new Ru^II -arene (p-cymene/benzene) complexes (C1-C14) have been synthesized by varying the N-terminal substituent in the furoylthiourea ligand and satisfactorily characterized by using analytical and spectroscopic techniques. Electrostatic potential maps predicted that the electronic effect of the substituents was mostly localized, with some influence seen on the labile chloride ligands. The structure-activity relationships of the Ru-p-cymene and Ru-benzene complexes showed opposite trends. All the complexes were found to be highly toxic towards IMR-32 cancer cells, with C5 (Ru-p-cymene complex containing C₆ H₂ (CH₃ )₃ as N-terminal substituent) and C13 (Ru-benzene complex containing C₆ H₄ (CF₃ ) as N-terminal substituent) showing the highest activity among each set of complexes, and hence they were chosen for further study. These complexes showed different behavior in aqueous solutions, and were also found to catalytically oxidize glutathione. They also promoted cell death by apoptosis and cell cycle arrest. Furthermore, the complexes showed good binding ability with the receptors Pim-1 kinase and vascular endothelial growth factor receptor 2, commonly overexpressed in cancer cells.

Utilization of Guanidine-Based Ancillary Ligands in Arene-Ruthenium Complexes for Selective Cytotoxicity

A family of three water-soluble half-sandwich arene-ruthenium complexes, depicted as C ₁ -C ₃ , having the general formula [Ru(p-cymene)(L)Cl]Cl has been synthesized, where L represents (1H-benzo[d]imidazol-2-yl)guanidine (L ₁ ) or (benzo[d]oxazol-2-yl)guanidine (L ₂ ) or (benzo[d]thiazol-2-yl)guanidine (L ₃ ). The crystal structure of complex C ₃ has been determined. The complexes show several absorption bands in the visible and ultraviolet regions, and they also show prominent emission in the visible region while excited near 400 nm. Studies on the interaction of ligands L ₁ -L ₃ and complexes C ₁ -C ₃ with calf thymus DNA reveal that the complexes are better DNA binders than the ligands, which is attributable to the imposed planarity of the ruthenium-bound guanidine-based ligand, enabling it to serve as a better intercalator. Molecular docking studies show that the complexes effectively bind with DNA through electrostatic and H-bonding interactions and partial intercalation of the guanidine-based ligands. Cytotoxicity studies carried out on two carcinoma cell lines (PC3 and A549) and on two non-cancer cell lines (BPH1 and WI-38) show a marked improvement in antitumor activity owing to complex formation, which is attributed to improvement in cellular uptake on complex formation. The C ₁ complex is found to exhibit the most prominent activity against the PC3 cell line. Inclusion of the guanidine-based ligands in the half-sandwich ruthenium-arene complexes is found to be effective for displaying selective cytotoxicity to cancer cells and also for convenient tracing of the complexes in cells due to their prominent emissive nature.

Synthesis, characterization, theoretical, molecular docking and in vitro biological activity studies of Ru(II) (η6-p-cymene) complexes with novel aniline substituted aroyl selenoureas

A sequence of aroyl selenourea ligands (L1-L3) substituted by aniline and their Ru(II) (η⁶-p-cymene) complexes (1-3), [Ru(II) (η⁶-p-cymene) L] (L = monodentate aroyl selenourea ligand) have been synthesized and characterized the composition of the ligands and their metal complexes. The molecular structures of ligand L1 and complex 3 were also confirmed by single XRD crystal method. The single-crystal XRD study showed that aroyl selenourea ligand coordinates with Ru via Se novel neutral monodentate atom. In vitro DNA interaction studies were investigated by Fluorescence and UV-Visible spectroscopic methods which showed that the intercalative mode of binding is in the order of 1 > 2 > 3 with Ru(II) (η⁶-p-cymene) complexes. Spectroscopic methods have been used for measuring the binding affinity of bovine serum albumin to complex. Moreover, the cytotoxic study of complexes (1-3) were evaluated against HeLa S3, A549, and IMR90 cells, resulting in complexes 1 and 2 showed promising cytotoxic activity against HeLa S3 cell with IC₅₀ values of 24 and 26 µM, respectively. Also, the morphological changes of HeLa S3 and A549 cells were confirmed by fluorescence microscope in the presence of complexes 1 and 2 using AO (acridine orange, 200 µM) and EB (ethidium bromide, 100 µM). In addition, the docking results strongly support the protein binding studies of the complexes.Communicated by Ramaswamy H. Sarma.

Identification and development of thiazole leads as COX-2/5-LOX inhibitors through in-vitro and in-vivo biological evaluation for anti-inflammatory activity

Treatment of inflammation using NSAIDs is coupled with a risk of severe gastric adverse events. Development of dual COX-2/5-LOX inhibitors turns out to be an imperative area devoted to safer NSAIDs. A series of thiourea, thiazole, and thiazolidene derivatives were synthesized by green synthetic approach and COX-1, COX-2 and 5-LOX inhibition screening resulted in the identification of a potent compound 6l with IC₅₀ of 5.55 µM, 0.09 µM, and 0.38 µM respectively. Compound 6l made significant decrease (60.82%) in the carrageenan-induced edema in male Wistar rats. qRT-PCR analysis and determination of PGE₂ and LTB₄ in the rat paw tissues indicated that this thiazole based dual inhibitor significantly reduced the expression of COX-2 and 5-LOX genes besides the marked reduction in both PGE₂ and LTB₄ levels. The gastric safety profiling revealed an enhanced gastrointestinal safety of the compound 6l on histopathological examination. Molecular docking studies at COX-2 and 5-LOX active sites were consistent with biological studies by significant protein-ligand interaction. Besides, results of in-vitro PGE₂ and LTB₄ studies on RAW 264.7 cells as well as antioxidant studies were parallel to the dual inhibitory activity. The present investigations identify a promising lead having anti-inflammatory potential with an improved gastric safety profile.

Design, Synthesis, DNA/HSA Binding, and Cytotoxic Activity of Half-Sandwich Ru(II)-Arene Complexes Containing Triarylamine-Thiosemicarbazone Hybrids

Organoruthenium complexes are potent alternatives for platinum-based complexes because of their superior anticancer activity. In this investigation, a series of new Ru(II)-arene complexes with triarylamine-thiosemicarbazone hybrid ligands with higher anticancer activity than cisplatin are reported. The molecular structure of the ligands and complexes was confirmed spectroscopically and supported by single-crystal X-ray crystallography. These complexes adopted a three-leg piano stool geometry. All the Ru(II)-arene complexes were systematically investigated for their in vitro cytotoxicity against human cervical (HeLa S3), lung (A549) cancer, and human normal lung (IMR-90) cell lines using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Interestingly, a pyrrolidine-attached Ru(II)-benzene complex exhibited superior activity against cancer cells with low IC₅₀ values, and colony formation study showed complete inhibition at 5 and 10 μM concentration. Furthermore, morphological changes assessed by acridine orange and propidium iodide staining revealed that the cell death occurred by apoptosis. In addition, the interaction between synthesized Ru(II)-arene complexes and DNA/protein was explored by absorption and emission spectroscopy methods. These synthesized new organoruthenium complexes can be used for developing new metal-based anticancer drugs.

Ruthenium(II) Complexes as Potential Apoptosis Inducers in Cancer Therapy

The compound cis-diamminedichloroplatinum(II) (cisplatin) is the most widely used anticancer drug, but due to its serious side effects (including gastrointestinal symptoms, renal tubular injury, neuromuscular complications, and ototoxicity), clinical applications of cisplatin are limited. Therefore, these limitations have provided an encouragement for further research into other transition metal complexes, with an aim to overcome the disadvantages related with cisplatin therapy. In the search for effective complexes that can be targeted against tumor cells, many research groups synthesized various ruthenium( II) complexes with different ligands. Also, newly synthesized ruthenium(II) complexes showed selective anticancer activity against different types of cancer cells. Activity of ruthenium(II) complexes in some cases was even higher than that of cisplatin against the same cells. Precise mechanism of action of ruthenium(II) complexes is not fully understood. The different examples mentioned in this review showed that ruthenium(II) complexes decreased viability of cancer cells by induction of apoptosis and/or by cell cycle arrest which implies their different mechanism of action against different types of cancer cells.

Synthesis and Anticancer Activity of [RuCl2(η6-arene)(aroylthiourea)] Complexes-High Activity against the Human Neuroblastoma (IMR-32) Cancer Cell Line

Eight new organometallic Ru(II)-arene complexes of the type [RuCl₂(η⁶-arene)(η¹-S-aroylthiourea)] (arene = p-cymene or benzene) were synthesized in order to evaluate the effect of the arene moiety and the substituent of the aroylthiourea ligand on the cytotoxicity of the complexes. The ligands (L1 and L2) and complexes (1-8) were characterized using analytical and spectroscopic (UV-visible, infrared, ¹H NMR, ¹³C NMR, and mass) methods. The structure of the ligands (L1 and L2) and complexes (1 and 3-6) was obtained from single-crystal X-ray diffraction studies. The cytotoxicity of the complexes was evaluated against four different cancer cell lines: MCF-7 (breast), COLO 205 (colon), A549 (lung), and IMR-32 (neuroblastoma). All the complexes showed good cytotoxicity and the highest was in the IMR-32 cell line, which articulates the specificity of these complexes toward the IMR-32 cancer cell line. The complexes 5, 7, and 8 exhibited remarkable cytotoxicity in the entire cancer cell lines tested, which was comparable with the standard drug, cisplatin. The anticancer mechanism of the complexes 3 and 7 in IMR-32 cells was evaluated by bright-field microscopy, intracellular reactive oxygen species (ROS), mitochondrial membrane potential (MMP), DNA damage, and caspase-3 analyses. The cells treated with the complexes showed upregulated caspase-3 compared to the control, and it was found that ROS and MMP were dose-dependent on analysis. Also, bright-field microscopy and 4',6-diamidino-2-phenylindole (DAPI) staining have correspondingly shown cellular membrane blebbing and DNA damage, which were morphological hallmarks of apoptosis. The study concluded that the complexes promoted the oxidative stress-mediated apoptotic death of the cancer cells through the generation of intracellular ROS, depletion of MMP, and damage of the nuclear material.

Half-sandwich Ru(η6-p-cymene) complexes featuring pyrazole appended ligands: Synthesis, DNA binding and in vitro cytotoxicity

Organometallic Ru(II)-arene complexes have emerged as potential alternatives to platinum appended agents due to their wide range of interesting features such as stability in solution and solid, significant activity, less toxicity and hydrophobic property of arene moiety, etc. Hence, a series of Ru(II)-p-cymene complexes, [(η⁶-p-cymene)Ru(η²-N,N-L1)Cl]Cl (1), [(η⁶-p-cymene)Ru(η¹-N-L2)Cl₂] (2) and [(η⁶-p-cymene)Ru(η¹-N-L3)Cl₂] (3) were prepared from pyrazole based ligands [2-(1H-pyrazol-3-yl)pyridine (L1), 3-(furan-2-yl)-1H-pyrazole (L2) and 3-(thiophen-2-yl)-1H-pyrazole (L3)], and [RuCl₂-(η⁶-p-cymene)] dimer. The new Ru(II)-p-cymene complexes were well characterized by elemental analysis, and spectroscopic (FT-IR, UV-Visible, ¹H NMR, ¹³C NMR and mass) and crystallographic methods. The Ru(II)-p-cymene complexes (1-3) were found to adopt their characteristic piano stool geometry around Ru(II) ion. The calf thymus DNA (CT-DNA) binding ability of the new complexes was investigated by electronic absorption spectroscopic titration and viscosity methods. The molecular docking study results showed that complex 1 strongly bound with targeted biomolecules than 2 and 3. Docked poses of bidentate pyrazole based Ru(II)-p-cymene complex 1 revealed that the complex formed a crucial guanine N⁷ position hydrogen bond with DNA receptor. Complexes 1-3 might hydrolyze under physiological conditions and form aqua complexes 4-8, and docking calculations showed that the aqua complexes bound strongly with the receptors than original complexes. The in vitro cytotoxicity of the Ru(II)-p-cymene complexes and cisplatin was evaluated against triple negative breast cancer (TNBC) MDA-MB-231 cells. Our results showed that the inhibitory effect of bidentate pyrazole based Ru(II)-p-cymene complex 1 on the growth of breast cancer cells was superior to other tested complexes.

Highly active copper(i) complexes of aroylthiourea ligands against cancer cells – synthetic and biological studies

Copper(i) complexes containing sulfur donor monodentate aroylthiourea ligands have been synthesized and evaluated for their biological applications.