Synthesis, topoisomerase I inhibition and antitumor cytotoxicity of 2,2':6',2"-, 2,2':6',3"- and 2,2':6',4"-terpyridine derivatives

Exploring the binding properties of DNA/BSA and cytotoxicity studies with new terpyridine-ester-based metal complexes (M = Fe(III), Ni(II), Cu(II) and Ru(III)) - A comparative analysis

Many terpyridines and their metal complexes are known to exhibit remarkable potential for the interaction of biological targets. Notably, a subtle change in the structure of the ligand can influence these interactions significantly. In this regard, it would be very interesting to assess the binding affinity of functionalized molecules with DNA/BSA. In this work, a novel ester-based terpyridine (L) and the corresponding four metal complexes with Ni(II) (MC1), Cu(II) (MC2), Fe(III) (MC3) and Ru(III) (MC4) were prepared and structurally characterized using various spectroscopic and analytical techniques including the validation of molecular structures of ligand (L) and Ni(II)-Tpy complex (MC1). The EPR data demonstrate that MC1 is diamagnetic and other complexes (MC2-MC4) exhibit paramagnetic behavior. Additionally, the structures of ligands and metal complexes were determined using DFT studies and the same were utilized for the docking studies. Interestingly, MC3 and MC4 exhibit a predominant lowest binding energy of -9.62 Kcal/mol (with DNA) and -10.05 Kcal/mol (with BSA) respectively. The binding affinity of the ligand and its complexes with protein and DNA was evaluated by spectroscopic techniques. Notably, the cytotoxicity studies of L and MC1-MC4 were performed against the MCF-7 (human breast cancer) cell lines. The complex MC4 displayed great activity with an IC50 of 3.5 ± 1.75 μM among all synthesized compounds and comparable with cisplatin.

Fe(II) complexes of 2,2':6',2''-terpyridine ligands functionalized with substituted-phenyl groups: synthesis, crystal structures and anticancer potential

With the aim of developing potential anticancer drug candidates, a series of Fe(II) complexes were synthesized using nine 2,2':6',2''-terpyridine ligands functionalized with substituted-phenyl groups, and their biological activities were systematically investigated. Their bis-terpyridine sandwich-like structures were determined by single crystal X-ray crystallography. In vitro antiproliferative experiments based on three human cancer cell lines, including human hepatoma cancer cell line (Bel-7402), human esophageal cancer cell line (Eca-109), and human cervical squamous cancer cell line (SiHa), indicate the high antiproliferation activities of these complexes compared with commercial cisplatin. And their toxicity to normal cells was estimated based on human normal hepatocyte (HL-7702) cell line. In particular, when the phenyl in terpyridine ligand was modified by a carboxyl group, the corresponding complex 3 exhibited much higher antiproliferation to cancer Bel-7402 cells (IC50 = 3.653 μmol L-1) than cisplatin and low toxicity to normal HL-7702 cells (IC50 = 99.92 μmol L-1), implying a significant selectivity for 3 in killing hepatoma cancer cells. Combined with the fact that iron element is more accessible than platin, this series of Fe(II) complexes comprises potential candidates for anticancer drugs with specific inhibition of hepatoma cancer. UV titration experiments and circular dichroism (CD) showed a strong binding affinity between these nine complexes and CT-DNA. However, molecular docking simulation revealed the competitive binding of DNA and protein to these complexes. Further, the interactions between these complexes and bovine serum albumin (BSA) have been studied by fluorescence titration and CD spectroscopy.

Platinum(terpyridine) complexes with N-heterocyclic carbene co-ligands: high antiproliferative activity and low toxicity in vivo

Pt(terpyridine) complexes are well-known DNA intercalators. The introduction of an NHC co-ligand rendered such a complex highly antiproliferative in cancer cells compared to its chlorido derivative. Despite the high potency, zebrafish embryos tolerated the compound well, especially compared to cisplatin. DNA interaction studies support a mode of action related to intercalation.

Terpyridines as promising antitumor agents: an overview of their discovery and development

INTRODUCTION

The fused aromatic system of terpyridines makes them good, innocent ligands for various metals. The resulting complexes have been extensively studied for both their biological activity and physico-chemical properties. However, although free ligands also have an interesting biological activity, their share in recent research is considerably limited.

AREAS COVERED

This review covers the literature on the anticancer activity of terpyridines with special attention being paid to their use as free ligands. Whenever possible, the mechanism of action has been discussed, thereby providing evidence of the substantial differences between sole ligands or less stable complexes and those that have heavier elements.

EXPERT OPINION

The existing literature indicates that there is a specific attitude for investigating terpyridines and their transition metal complexes. While the latter have been well explored and recognized in the scientific community, the free terpyridines are considered to be useful solely due to their complexing ability. At the same time, terpyridines could have similar or even higher anticancer potency than their complexes. Moreover, a mechanistic analysis of the stability and intracellular activity would provide information that would be useful for designing new drugs.

New derivatives of 4'-phenyl-2,2':6',2″-terpyridine as promising anticancer agents

Terpyridine derivatives are known from their broad application including anticancer properties. In this work we present the newly synthesized 4'-phenyl-2,2':6',2″-terpyridine group with high antiproliferative activity. We suggest that these compounds influence cellular redox homeostasis. Cancer cells are particularly susceptible to any changes in the redox balance because of their handicapped and inefficient antioxidant cellular systems. The antiproliferative activity of the studied compounds was tested on five different cell lines that represent several types of tumours; glioblastoma, leukemia, breast, pancreatic and colon. Additionally, we also tested their selectivity towards normal cells. We performed molecular biology studies in order to detect the response of a cell to its treatment with the compounds that were tested. We looked at the in-depth changes in the proteins and cellular pathways that lead to cell cycle inhibition (G0/G1 and S), and consequently, death on the apoptosis and autophagy pathways. We proved that the studied compounds targeted DNA as well. Special attention was paid to the targets connected with ROS generation.

Study on the substitution effects of zinc benzoate terpyridine complexes on photoluminescence, antiproliferative potential and DNA binding properties

Six zinc(II) complexes, [Zn(OCOPh)₂L^R] (R = 1, 2, 3, 4, 5, 6) were synthesized by the reaction of zinc benzoate and six para-substituted 4-phenyl-terpyridine complexes and their structures were confirmed by elemental analysis, FT-IR, ¹H NMR and X-ray single crystal diffraction analysis. Their photoluminescent properties in solid and in solutions of DMSO were studied. Three human cancer cell lines were used for antiproliferative potential: human lung cancer cell line (A549), human esophageal cancer cell line (Eca-109) and human breast cancer cell line (MCF-7). The results have shown that these zinc complexes have good inhibitory effects on cancer cells, which are better than that of the commonly used clinical drug cisplatin. The ability of the complexes to binding to CT-DNA was studied by UV spectroscopy and fluorescence titration, while the interaction between the complexes and CT-DNA, AT6, GC6 short-chain DNA sequences and G-quadruplex were analyzed by circular dichroism (CD). It is found that these complexes can bind to DNA, and the binding mode is mainly intercalator. The docking of the complexes with the DNA fragment was simulated using molecular docking software. All the results clearly display that the substituents at these ligands of the complexes have the substitution effects on the properties of photoluminescence, antiproliferative potential and DNA binding study.

Molecular Design, Synthesis and Docking Study of Alkyl and Benzyl Derivatives of Robustic Acid as Topoisomerase I Inhibitors

Robustic acid is reported to be a bioactive compound, isolated from the medicinal plant Dalbergia benthamii Prain. Ten alkyl and benzyl derivatives (2a-2j) of robustic acid were designed and synthesized based on molecular docking approaches. The biological activities of most of the synthesized compounds (such as 2g, 2h, and 2i) were closely consistent with the docking results. In particular, 4-O-phenylpropyl substituted compound 2g displayed potent topoisomerase I inhibitory activity as well as cytotoxicity against SMMC-7721, HepG2, and HeLa cell lines. Further biological testing suggests that compound 2g acted mainly by an arrest of the tumor cells in G1 phase of the cell cycle and suppressed cell proliferation by inducing apoptosis. The findings of this study are encouraging with respect to potential utilization of these compounds as new topoisomerase I inhibitors.

A comprehensive review of topoisomerase inhibitors as anticancer agents in the past decade

The topoisomerase enzymes play an important role in DNA metabolism, and searching for enzyme inhibitors is an important target in the search for new anticancer drugs. Discovery of new anticancer chemotherapeutical capable of inhibiting topoisomerase enzymes is highlighted in anticancer research. Therefore, biologists, organic chemists and medicinal chemists all around the world have been identifying, designing, synthesizing and evaluating a variety of novel bioactive molecules targeting topoisomerase. This review summarizes types of topoisomerase inhibitors in the past decade, and divides them into nine classes by structural characteristics, including N-heterocycles compounds, quinone derivatives, flavonoids derivatives, coumarin derivatives, lignan derivatives, polyphenol derivatives, diterpenes derivatives, fatty acids derivatives, and metal complexes. Then we discussed the application prospect and development of these anticancer compounds, as well as concluded parts of their structural-activity relationships. We believe this review would be invaluable in helping to further search potential topoisomerase inhibition as antitumor agent in clinical usage.

Synthesis, characterization, DNA binding, topoisomerase I inhibition and antiproliferation activities of three new functionalized terpyridine platinum(II) complexes

Three new platinum(II) complexes with pendent morpholine were synthesized, namely complex 1 ([Pt(L)Cl]CF₃SO₃), complex 2 ([Pt(L)(NH₃)](CF₃SO₃)₂) and complex 3 ([Pt(L)(PPh₃)](CF₃SO₃)₂), where L = 4'-[4-(4-morpholinobutyloxy)phenyl]-2,2':6',2″-terpyridine and PPh₃ = triphenylphosphine. The detailed molecular structures of complex 3, L and its precursor L' (1,4'-[4-(4-bromobutyloxy)phenyl]-2,2':6',2″-terpyridine) were determined by single crystal X-ray diffraction. An evaluation of in vitro cytotoxicity for both ligand and complexes was performed by methyl thiazolyl tetrazolium (MTT) assay in three cancer cell lines and normal cells as the control, respectively. IC₅₀ values of complexes 1-3 were lower than those exhibited for the reference drug cisplatin, and selectivity of these complexes were greater than cisplatin. Among them, complex 3 with a leaving group PPh₃ was found to be the most efficacious complex against certain cell lines, especially for cisplatin-resistant A549cisR cells. These complexes were found to bind DNA, induce efficient DNA unwinding. Meanwhile, topoisomerase (Topo) I inhibitory activities by three complexes were detected, and a minimum inhibitory concentration of 15 μM of complex 3 was found totally inhibit Topo I activity.

Stepwise synthesis, characterization, DNA binding properties and cytotoxicity of diruthenium oligopyridine compounds conjugated with peptides

Although the interactions of oligopyridine ruthenium complexes with DNA have been widely studied, the biological activity of similar diruthenium oligopyridine complexes conjugated with peptides has not been investigated. Herein, we report the stepwise synthesis and characterization of diruthenium complexes with the general formula [(L^a)Ru(tppz)Ru(L^b)]ⁿ⁺ (tppz = 2,3,5,6-tetra(2-pyridyl)pyrazine, L^a = 2,2':6',2''-terpyridine or 4-phenyl-2,2':6',2''-terpyridine and L^b = 2,2':6',2''-terpyridine-4'-CO(Gly¹-Gly²-Gly³-LysCONH₂) (5), (6), n = 5; 2,2':6',2''-terpyridine-4'-CO(Gly¹-Gly²-Lys¹-Lys²CONH₂) (7), (8), n = 6; 2,2':6',2''-terpyridine-4'-CO(Ahx-Lys¹Lys²CONH₂) (9), (10), n = 5, Ahx = 6-aminohexanoic acid). The compounds [(trpy)Ru(tppz)Ru(trpy-CO₂H)](PF₆)₄, (2)(PF₆)₄, [(ptrpy)Ru(tppz)Ru(trpy-CO₂H)](PF₆)₄, (3)(PF₆)₄ and [(ptrpy)Ru(tppz)Ru(trpy)](PF₆)₄, (4)(PF₆)₄ were also characterized by single crystal X-ray methods. Moreover, the interactions of the chloride salts (5), (6) and (4) with the self-complementary dodecanucleotide duplex d(5'-CGCGAATTCGCG-3')₂ were studied by NMR spectroscopic techniques. The results show that complex (4) binds in the central part of the oligonucleotide, from the minor groove through the ligand ptrpy, while the ligand trpy, which was located on the other side of the diruthenium core, does not contribute to the binding. Complex (5) binds similarly, through the ligand ptrpy. However, the induced upfield shifts of the ptrpy proton signals are significantly lower than the corresponding ones in the case of (4), indicating much lower binding affinity. This is clear evidence that the tethered peptide Gly¹-Gly²-Gly³-Lys¹CONH₂ hinders the complex binding, even though it contains groups that are able to assist it (e.g., the positively charged amino group of lysine, the peptidic backbone, the terminal amide). Complex (6) shows a non-specific binding, interacting through electrostatic forces. The chloride salts of (4), (5) and (6) had insignificant effects on the cell cycle distribution and marginal cytotoxicity (IC₅₀ > 750 μM) against human lung cancer cell lines H1299 and H1437, indicating that their binding to the oligonucleotide is not a sufficient condition for their cytotoxicity.

Photorelease of nitric oxide (NO) on ruthenium nitrosyl complexes with phenyl substituted terpyridines

Transandcisisomers of ruthenium nitrosyl complexes release NO upon irradiation by visible light and give a unique photoproduct.

Synthesis, characterization, thermal properties and antiproliferative potential of copper(II) 4'-phenyl-terpyridine compounds

Reactions between 4'-phenyl-terpyridine (L) and several Cu(II) salts (p-toluenesulfonate, benzoate and o-, m- or p-hydroxybenzoate) led to the formation of [Cu(p-SO3C6H4CH3)L(H2O)2](p-SO3C6H4CH3) (1), [Cu(OCOPh)2L] (2), [Cu(o-OCOC6H4OH)2L] (3), [Cu(m-OCOC6H4OH)2L]4·MeOH (·MeOH) and [Cu(p-OCOC6H4OH)2L]5·2H2O (·2H2O), which were characterized by elemental and TG-DTA analyses, ESI-MS, IR spectroscopy and single crystal X-ray diffraction, as well as by conductivimetry. In all structures the Cu atoms present N3O3 octahedral coordination geometries, which, in 2-5, are highly distorted as a result of the chelating-bidentate mode of one of the carboxylate ligands. Intermolecular π···π stacking interactions could also be found in 2-5 (in the 3.569-3.651 Å range and involving solely the pyridyl rings). Medium-strong hydrogen bond interactions lead to infinite 1D chains (in 1 and 4) and to an infinite 2D network (in 5). Compounds 1 and 4 show high in vitro cytotoxicity towards HCT116 colorectal carcinoma and HepG2 hepatocellular carcinoma cell lines. The antiproliferative potential of compound 1 is due to an increase of the apoptotic process that was confirmed by Hoechst staining, flow cytometry and RT-qPCR. All compounds able to non-covalently intercalate the DNA helix and induce in vitro pDNA double-strand breaks in the absence of H2O2. Concerning compound 1, the hydroxyl radical and singlet oxygen do not appear to be involved in the pDNA cleavage process and the fact that this cleavage also occurs in the absence of molecular oxygen points to a hydrolytic mechanism of cleavage.

A convenient route to symmetrically and unsymmetrically substituted 3,5-diaryl-2,4,6-trimethylpyridines via Suzuki-Miyaura cross-coupling reaction

A series of differently substituted 3,5-diaryl-2,4,6-trimethylpyridines were prepared and characterized using the Suzuki-Miyaura coupling reaction with accordingly selected bromo-derivatives and arylboronic acids. The reaction conditions were carefully optimized allowing high yield of isolated products and also the construction of unsymmetrically substituted diarylpyridines, difficult to access by other methods.

Facile synthesis of heavily-substituted alkynylpyridines via a Sonogashira approach

A robust synthesis of highly-substituted alkynylpyridines via a Sonogashira approach is described, providing a library of functionalized pyridines for biological studies.

A water-soluble Pd(ii) complex with a terpyridine ligand: experimental and molecular modeling studies of the interaction with DNA and BSA; and in vitro cytotoxicity investigations against five human cancer cell lines

[Pd(4-OHPh-tpy)Cl]Cl was prepared. The complex interacts with DNA via a combination of covalent, intercalation, and hydrogen bonding interactions.

Phosphonate-functionalized heteroleptic ruthenium(II) bis(2,2′:6′,2″-terpyridine) complexes

The heteroleptic complexes [Ru(1)(4)][PF6]2, [Ru(2)(4)][PF6]2, [Ru(Phtpy)(4)][PF6]2, and [Ru(pytpy)(4)][PF6]2 (Phtpy = 4′-phenyl-2,2′:6′,2″-terpyridine, pytpy = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine, 1 and 2 = 4-methyl ester substituted derivatives of Phtpy and pytpy, 4 = ethyl 2,2′:6′,2″-terpyridine-4′-phosphonate) have been prepared. The single crystal structure of ligand 1 (1 = methyl 4-carboxy-4′-phenyl-2,2′:6′,2″-terpyridine) is reported. The introduction of the 4-methyl ester group causes a small red shift in the MLCT band of the ruthenium(II) complexes and a small shift to a more positive potential for the Ru2+/Ru3+ couple. The new complexes should serve as a useful starting point for development of ruthenium(II) dyes suited for sensitization of p-type semiconductors.

Synthesis of 4'-(2-ferrocenyl)-2,2':6'2''-terpyridine: characterization and antiprotozoal activity of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) complexes

A terpyridine ligand Fctpy was reacted with divalent metals (Cu, Co, Mn, Ni and Zn), yielding five complexes of general formula [Metal(Fctpy)2][PF6]2. The structure of Fctpy was determined by single crystal X-ray diffraction studies. The complexes characterized using various spectroscopic techniques suggested an octahedral geometry around the central metal ion. These complexes were screened for their antiamoebic, trypanocidal and antimalarial activities. It was found that, complexes 2 and 3 showed better IC50 values than metronidazole against HM1:IMSS strain of Entamoeba histolytica. A substantial parasitic inhibition was not observed for the trypanocidal activity. However, for the erythrocytic stage of W2 strain of Plasmodium falciparum, the complexes inhibited β-hematin formation. At the concentration of 10 μg/mL, these complexes did not display toxicity.

Syntheses and applications of furanyl-functionalised 2,2':6',2''-terpyridines

Different synthetic routes leading to terpyridines functionalised with furan heterocycles are reviewed. The methodologies used to prepare such compounds include the ring closure of 1,5-diketones and cross-coupling reactions. These versatile terpyridines and their derived metal complexes find applications in various fields including coordination chemistry, medicinal chemistry and material sciences.