Study on the Multimodal Anticancer Mechanism of Ru(II)/Ir(III) Complexes Bearing a Poly(ADP-ribose) Polymerase 1 Inhibitor

A series of novel ruthenium(II) and iridium(III) complexes (Ru1-Ru3 and Ir1-Ir3) with different ancillary ligands and a PARP-1-inhibitory chelating ligand 2-(2,3-dibromo-4,5-dimethoxybenzylidene)hydrazine-1-carbothioamide (L1) were designed and prepared. The target complexes were structurally characterized by NMR and ESI-MS techniques. Among them, the crystal and molecular structures of Ir1 and Ir2 were also determined by X-ray crystallography. These complexes retained the PARP-1 enzyme inhibitory effect of L1 and showed potent antiproliferative activity on the tested cancer cell lines. The ruthenium(II) complexes Ru1-Ru3 were found to be more cytotoxic than the iridium(III) complexes Ir1-Ir3. Further investigations revealed that the most active complex Ru3 induced apoptosis in MCF-7 cells by multiple modes, inclusive of inducing DNA damage, suppressing DNA damage repair, disturbing cell cycle distribution, decreasing the mitochondrial membrane potential, and increasing the intracellular reactive oxygen species levels.

Heteronuclear Ru(II)-Re(I) complexes as potential photodynamic anticancer agents with anti-metastatic and anti-angiogenic activities

Herein, three heterometallic Ru(II)-Re(I) complexes, [Ru(NN)₂(tpphz)Re(CO)₃Cl](PF₆)₂ (N-N = 2,2'-bipyridine (bpy, in RuRe1), 1,10-phenanthroline (phen, in RuRe2), 4,7-diphenyl-1,10-phenanthroline (DIP, in RuRe3), tpphz = tetrapyrido[3,2-a:2',3'-c:3″,2″-h:2″',3″'-j]phenazine), using tpphz as a bridging ligand to connect Ru(II) polypyridyl moiety and Re(I) tricarbonyl moiety were designed and synthesized. Cytotoxicity tests revealed that RuRe1-3 exhibited high phototoxicities against several cancer cell lines tested, with IC₅₀ values ranging from 0.8 to 6.8 μM. Notably, RuRe2 exhibited the most significant increase in cytotoxicity against human prostate cancer (PC3) cells under light (450 nm) irradiation, with phototoxicity index (PI) value increasing by >112.3-fold. Further mechanistic studies of RuRe2 revealed that RuRe2-mediated PDT could induce tumor cell apoptosis through the mitochondrial pathway. Moreover, RuRe2-mediated PDT could inhibit PC3 cell scratch healing and reduce the expression levels of matrix metalloproteinases 2 (MMP-2), matrix metalloproteinases 9 (MMP-9) and vascular endothelial growth factor receptor VEGFR2. Finally, angiogenic activity assays performed in human umbilical vein endothelial cells (HUVECs) showed that RuRe2 exerted an anti-angiogenesis effect. Our study demonstrated that RuRe1-3 were promising PDT antitumor agents with potential anti-metastatic and anti-angiogenic activities.

Comparative Studies on DNA-Binding Mechanisms between Enantiomers of a Polypyridyl Ruthenium(II) Complex

A pair of ruthenium(II) complex enantiomers, Δ- and Λ-[Ru(bpy)₂MBIP]²⁺ (bpy = 2,2'-bipyridine, MBIP = 2-(3-bromophenyl)imidazo[5,6-f]phenanthroline), were designed, synthesized, and characterized. Comparative studies between the enantiomers on their binding behaviors to calf thymus DNA (CT-DNA) were conducted using UV-visible, fluorescence, and circular dichroism spectroscopies, viscosity measurements, isothermal titration calorimetry, a photocleavage experiment, and molecular simulation. The experimental results indicated that both the enantiomers spontaneously bound to CT-DNA through intercalation stabilized by the van der Waals force or the hydrogen bond and driven by enthalpy and that Δ-[Ru(bpy)₂MBIP]²⁺ intercalated into DNA more deeply than Λ-[Ru(bpy)₂MBIP]²⁺ did and exhibited a better DNA photocleavage ability. Molecular simulation further indicated that Δ-[Ru(bpy)₂MBIP]²⁺ more preferentially intercalated between the base pairs of CT-DNA to the major groove, and Λ-[Ru(bpy)₂MBIP]²⁺ more favorably intercalated to the minor groove. These research findings should be very helpful to the understanding of the stereoselectivity mechanism of DNA-bindings of metal complexes, and be useful for the design of novel metal-complex-based antitumor drugs with higher efficacy and lower toxicity.

Nuclease-like metalloscissors: Biomimetic candidates for cancer and bacterial and viral infections therapy

Despite the extensive and rapid discovery of modern drugs for treatment of cancer, microbial infections, and viral illnesses; these diseases are still among major global health concerns. To take inspiration from natural nucleases and also the therapeutic potential of metallopeptide antibiotics such as the bleomycin family, artificial metallonucleases with the ability of promoting DNA/RNA cleavage and eventually affecting cellular biological processes can be introduced as a new class of therapeutic candidates. Metal complexes can be considered as one of the main categories of artificial metalloscissors, which can prompt nucleic acid strand scission. Accordingly, biologists, inorganic chemists, and medicinal inorganic chemists worldwide have been designing, synthesizing and evaluating the biological properties of metal complexes as artificial metalloscissors. In this review, we try to highlight the recent studies conducted on the nuclease-like metalloscissors and their potential therapeutic applications. Under the light of the concurrent Covid-19 pandemic, the human need for new therapeutics was highlighted much more than ever before. The nuclease-like metalloscissors with the potential of RNA cleavage of invading viral pathogens hence deserve prime attention.

Synthesis, Characterization, and Cytotoxicity of Morpholine-Containing Ruthenium(II) p-Cymene Complexes

Morpholine motif is an important pharmacophore and, depending on the molecular design, may localize in cellular acidic vesicles. To understand the importance of the presence of pendant morpholine in a metal complex, six bidentate N,O-donor ligands with or without a pendant morpholine unit and their corresponding ruthenium(II) p-cymene complexes (1-6) are synthesized, purified, and structurally characterized by various analytical methods including X-ray diffraction. Complexes 2-4 crystallized in the P2₁/c space group, whereas 5 and 6 crystallized in the P1̅ space group. The solution stability studies using ¹H NMR support instantaneous hydrolysis of the native complexes to form monoaquated species in a solution of 3:7 (v/v) dimethyl sulfoxide-d₆ and 20 mM phosphate buffer (pH* 7.4, containing 4 mM NaCl). The monoaquated complexes are stable for at least up to 24 h. The complexes display excellent in vitro antiproliferative activity (IC₅₀ ca. 1-14 μM) in various cancer cell lines, viz., MDA-MB-231, MiaPaCa2, and Hep-G2. The presence of the pendant morpholine does not improve the dose efficacy, but rather, with 2-[[(2,6-dimethylphenyl)imino]methyl]phenol (HL1) and its pendant morpholine analogue (HL3) giving complexes 1 and 3, respectively, the antiproliferative activity was poorer with 3. MDA-MB-231 cells treated with the complexes show that the acidic vesicles remain acidic, but the population of acidic vesicles increases or decreases with time of exposure, as observed from the dispersed red puncta, depending on the complex used. The presence of the 2,6-disubstituted aniline and the naphthyl group seems to improve the antiproliferative dose. The complex treated MDA-MB-231 cells show that cathepsin D, which is otherwise present in the cytosolic lysosomes, translocates to the nucleus as a result of exposure to the complexes. Irrespective of the presence of a morpholine motif, the complexes do not activate caspase-3 to induce apoptosis and seem to favor the necrotic pathway of cell killing.