Synthesis, photophysical characterisation, quantum-chemical study and in vitro antiproliferative activity of cyclometalated Ir(III) complexes based on 3,5-dimethyl-1-phenyl-1H-pyrazole and N,N-donor ligands

In this paper, we present the synthesis of four new complexes: the dimeric precursor [Ir(dmppz)2(μ-Cl)]2 (1) (Hdmppz - 3,5-dimethyl-1-phenyl-1H-pyrazole) and heteroleptic bis-cyclometalated complexes: [Ir(dmppz)2(Py2CO)]PF6·½CH2Cl2 (2), [Ir(dmppz)2(H2biim)]PF6·H2O (3), and [Ir(dmppz)2(PyBIm)]PF6 (4), with auxiliary N,N-donor ligands: 2-di(pyridyl)ketone (Py2CO), 2,2'-biimidazole (H2biim) and 2-(2'-pyridyl)benzimidazole (PyBIm). In the obtained complexes, SC-X-ray analysis revealed that Ir(III) has an octahedral coordination sphere with chromophores of the type {IrN2C2Cl2} (1) or {IrN4C2} (2-4). The complexes obtained, which have been fully characterised by physicochemical methods (CHN, TG, FTIR, UV-Vis, PL and 1H, 13C, 15N NMR), were used to continue our studies on the factors influencing the cytotoxic properties of potential chemotherapeutic agents (in vitro). To this end, the following studies are presented: (i) comparative analysis of the effects on the biological properties of N,N-donor ligands and C,N-donor ligands in the studied complexes, (ii) studies of the interactions of the compounds with the selected molecular target: DNA and BSA (UV-Vis, CD and PL methods), (iii) and the reactivity towards redox molecules: GSH, NADH (UV-Vis and/or ESI-MS methods), (iv) cytotoxic activity (IC50) of potential chemotherapeutics against MCF-7, K-562 and CCRF-CEM cell lines.

Advances in peptide-based drug delivery systems

Drug delivery systems (DDSs) are designed to deliver drugs to their specific targets to minimize their toxic effects and improve their susceptibility to clearance during targeted transport. Peptides have high affinity, low immunogenicity, simple amino acid composition, and adjustable molecular size; therefore, most peptides can be coupled to drugs via linkers to form peptide-drug conjugates (PDCs) and act as active pro-drugs. PDCs are widely thought to be promising DDSs, given their ability to improve drug bio-compatibility and physiological stability. Peptide-based DDSs are often used to deliver therapeutic substances such as anti-cancer drugs and nucleic acid-based drugs, which not only slow the degradation rate of drugs in vivo but also ensure the drug concentration at the targeted site and prolong the half-life of drugs in vivo. This article provides an profile of the advancements and future development in functional peptide-based DDSs both domestically and internationally in recent years, in the expectation of achieving targeted drug delivery incorporating functional peptides and taking full advantage of synergistic effects.

Metal Peptide Conjugates in Cell and Tissue Imaging and Biosensing

Metal complex luminophores have seen dramatic expansion in application as imaging probes over the past decade. This has been enabled by growing understanding of methods to promote their cell permeation and intracellular targeting. Amongst the successful approaches that have been applied in this regard is peptide-facilitated delivery. Cell-permeating or signal peptides can be readily conjugated to metal complex luminophores and have shown excellent response in carrying such cargo through the cell membrane. In this article, we describe the rationale behind applying metal complexes as probes and sensors in cell imaging and outline the advantages to be gained by applying peptides as the carrier for complex luminophores. We describe some of the progress that has been made in applying peptides in metal complex peptide-driven conjugates as a strategy for cell permeation and targeting of transition metal luminophores. Finally, we provide key examples of their application and outline areas for future progress.

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.

Syntheses, crystal structures of two Fe(III) Schiff base complexes with chelating o-vanillin aroylhydrazone and exploration of their bio-relevant activities

Two novel Fe(III) complexes, Fe(HL¹)₂Cl·1.25H₂O (1) and Fe(HL²)₂·Et₃NH·H₂O (2) (H₂L¹ = o-vanillin benzoylhydrazone, H₃L² = o-vanillin salicylhydrazone) are prepared. X-ray single crystal diffraction confirms that the hydrazone ligands can be chelated to iron centre resulting in a six-coordinate octahedral configuration. Both complexes show major intercalation effect to the herring sperm deoxyribonucleic acid (HS-DNA) with high binding constants of 2.01 × 10⁴ M^-1 and 2.24 × 10⁴ M^-1, respectively. Molecular docking studies reveal both complexes can intercalate at the gap of DC5-DG2 and DG6-DC1 base pairs of DNA hexamer (1Z3F). The interaction of the complex 1 with plasmid pBR322 DNA induces distinguishable alterations of the DNA morphology. Further, the structure of plasmid pBR322 DNA treated with complex 1 in the presence of ascorbic acid has been damaged probably due to the reactive oxygen species (ROS) generation. What's more, both complexes show high affinity with bovine serum albumin (BSA), the binding constants measured by fluorescence techniques are 5.75 × 10⁶ M^-1 and 4.39 × 10⁷ M^-1, respectively. Molecular docking demonstrates that the complexes prefer the binding pocket of site III (subdomain IIB) of BSA (PDB ID: 4F5S). Similarly, dynamic light scattering (DLS) reveals that the complexes not only bind to BSA but also induce bigger size aggregates as the concentration increases.

Novel Quinoline-based Ir(III) Complexes Exhibit High Antitumor Activity in Vitro and in Vivo

Eight novel Ir(III) complexes listed as [Ir(H-P)₂(P)]PF₆ (PyP-Ir), [Ir(H-P)₂(dMP)]PF₆ (PydMP-Ir), [Ir(H-P)₂(MP)]PF₆ (PyMP-Ir), [Ir(H-P)₂(tMP)]PF₆ (PytMP-Ir), [Ir(MPy)₂(P)]PF₆ (MPyP-Ir), [Ir(MPy)₂(dMP)]PF₆ (MPydMP-Ir), [Ir(MPy)₂(MP)]PF₆ (MPyMP-Ir), [Ir(MPy)₂((tMP)]PF₆ (MPytMP-Ir) with 2-phenylpyri-dine (H-P) and 3-methyl-2-phenylpyridine (MPy) as ancillary ligands and pyrido-[3,2-a]-pyrido[1',2':1,2]imidazo[4,5-c]phenazine (P), 12,13-dimethyl pyrido-[3,2-a]-pyrido[1',2':1,2]-imidazo-[4,5-c]-phenazine (dMP), 2-methylpyrido [3,2-a]-pyrido-[1',2':1,2]-imidazo-[4,5-c]-phenazine (MP), and 2,12,13-trimethylpyrido-[3,2-a]-pyrido-[1',2':1,2]-imidazo-[4,5-c]-phenazine (tMP) as main ligands, respectively, were designed and synthesized to fully characterize and explore the effect of their toxicity on cancer cells. Cytotoxic mechanism studies demonstrated that the eight Ir(III) complexes exhibited highly potent antitumor activity selectively against cancer cell lines NCI-H460, T-24, and HeLa, and no activity against HL-7702, a noncancerous cell line. Among the eight Ir(III) complexes, MPytMP-Ir exhibited the highest cytotoxicity with an IC₅₀ = 5.05 ± 0.22 nM against NCI-H460 cells. The antitumor activity of MPytMP-Ir in vitro could be contributed to the steric or electronic effect of the methyl groups, which induced telomerase inhibition and damaged mitochondria in NCI-H460 cells. More importantly, MPytMP-Ir displayed a superior inhibitory effect on NCI-H460 xenograft in vivo than cisplatin. Our work demonstrates that MPytMP-Ir could potentially be developed as a novel potent Ir-based antitumor drug.

Third-strand stabilizing effects of the RNA poly(U)·poly(A)*poly(U) triplex by a ruthenium(II) polypyridine complex and its hexaarginine peptide conjugate

In this work, a Ru(II) complex [Ru(bpy)₂(pip-CO₂H)]²⁺ (Ru1) and its hexaarginine peptide conjugate [Ru(bpy)₂(pic-Arg₆)]⁸⁺ (Ru2) have been synthesized and characterized. The binding of Ru1 and Ru2 with poly(U)•poly(A)*poly(U) triplex has been studied. Results suggest that Ru1 binds in the surface of the minor groove while Ru2 binds to the minor groove of the triplex. Consequently, the triplex stabilization is barely affected by Ru1, while with Ru2 the triplex stabilizing effect is so strong that that dissociation of the triplex shows an overlapping of both melting processes with the melting temperature increased to a maximum of 56.1 °C at the C_Ru2/C_UAU ratio of 0.05, where ΔT_m1 and ΔT_m2 are 19.6 and 10.1 °C, respectively. Furthermore, the effect of Ru2 stabilizing the third strand at such a low binding ratio of 0.05 is more marked than what obsereved for flavone luteolin and [Ru(bpy)₂(mdpz)]²⁺, which are so far the strongest triplex stabilizers in the reported organic small molecules and metal complexes, respectively. Considering the structure natures of Ru2, conceivably except for electrostatic interaction, the forces stabilizing the triplex should also involve hydrophobic interaction and hydrogen bingding. To our knowledge, this work represents a first example of improving the triplex stabilization by a metallopeptide.

Selective G-quadruplex binding by oligoarginine-Ru(dppz) metallopeptides

We demonstrate that both the R₈ functionalization and its interplay with the ancillary ligand have and an important role in the G-quadruplex recognition process by Ru(dppz) metallopeptides.

Membrane-disrupting iridium(iii) oligocationic organometallopeptides

A series of oligoarginine peptide derivatives containing cyclometallated iridium(iii) units display remarkable cytotoxicity, comparable to that of cisplatin. In vitro studies with unilamellar vesicles support a membrane-disrupting mechanism of action.