Mononuclear η6-arene ruthenium(II) complexes with pyrazolyl-pyridazine ligands: synthesis, CT-DNA binding, reactivity towards glutathione, and cytotoxicity.

Organometallic η6-arene ruthenium(II) complexes with 3-chloro-6-(1H-pyrazol-1-yl)pyridazine (Ru1, Ru2, and Ru5) and 3-chloro-6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridazine (Ru3-4) N,N' heterocyclic and η6-arene (cymene (Ru1-4) or toluene (Ru 5)) have been synthesized. The ruthenium(II) complexes have common "three-legged piano-stool" pseudo-octahedral structures known for half-sandwich complexes. Evolution of their UV-Visible absorption spectra in PBS buffer or DMSO over 24 h confirmed their good solvolysis stability. Titrations of the complexes with the calf thymus DNA (CT-DNA) were monitored using UV-Visible absorption and fluorescence spectroscopies. The complexes interact moderately with CT-DNA and their binding constants are in the order of 104 M-1. Competitive binding of the complexes to a DNA-Hoechst 33,258 depicted competitive displacement of Hoechst from DNA's minor grooves. These complexes bind to glutathione forming GSH-adducts through S coordination by replacement of a halide, with the iodo-analogues having higher binding constants than the chloro-complexes. Cyclic voltammograms of the complexes exhibited one electron-transfer quasi-reversible process. Trends in the molecular docking data of Ru1-5/DNA were similar to those for DNA binding constants. Of the five, only Ru1, Ru3 and Ru5 showed some activity (moderate) against the MCF-7 breast cancer cells with IC50 values in the range of 59.2-39.9 for which Ru5 was the most active. However, the more difficult-to-treat cell line, MDA-MB 231 cell was recalcitrant to the treatment by these complexes.

Selective Targeting of Regulated Rhabdomyosarcoma Cells by Trinuclear Ruthenium(II)-Arene Complexes.

The use of benzimidazole-based trinuclear ruthenium(II)-arene complexes (1-3) to selectively target the rare cancer rhabdomyosarcoma is reported. Preliminary cytotoxic evaluations of the ruthenium complexes in an eight-cancer cell line panel revealed enhanced, selective cytotoxicity toward rhabdomyosarcoma cells (RMS). The trinuclear complex 1 was noted to show superior short- and long-term cytotoxicity in RMS cell lines and enhanced selectivity relative to cisplatin. Remarkably, 1 inhibits the migration of metastatic RMS cells and maintains superior activity in a 3D multicellular spheroid model in comparison to that of the clinically used cisplatin. Mechanistic insights reveal that 1 effectively induces genomic DNA damage, initiates autophagy, and prompts the intrinsic and extrinsic apoptotic pathways in RMS cells. To the best of our knowledge, 1 is the first trinuclear ruthenium(II) arene complex to selectively kill RMS cells in 2D and 3D cell cultures.

Trinuclear ruthenium(II) polypyridyl complexes: Evaluation as photosensitizers for enhanced cervical cancer treatment.

Trinuclear ruthenium(II) polypyridyl complexes anchored to benzimidazole-triazine / trisamine scaffolds were investigated as photosensitizers for photodynamic therapy. The trinuclear complexes were noted to produce a significant amount of singlet oxygen in both DMF and aqueous media, are photostable and show appreciable emission quantum yields (ɸem). In our experimental setting, despite the moderate phototoxic activity in the HeLa cervical cancer cell line, the phototoxic indices (PI) of the trinuclear complexes are superior relative to the PIs of a clinically approved photosensitizer, Photofrin®, and the pro-drug 5-aminolevulinic acid (PI: >7 relative to PI: >1 and PI: 4.4 for 5-aminolevulinic acid and Photofrin®, respectively). Furthermore, the ruthenium complexes were noted to show appreciable long-term cytotoxicity upon light irradiation in HeLa cells in a concentration-dependent manner. Consequently, this long-term activity of the ruthenium(II) polypyridyl complexes embodies their ability to reduce the probability of the recurrence of cervical cancer. Taken together, this presents a strong motivation for the development of polymetallic complexes as anticancer agents.

Aminoquinoline-based Re(I) tricarbonyl complexes: Insights into their antiproliferative activity and mechanisms of action.

In an effort to develop new potent anticancer agents, two Schiff base rhenium(I) tricarbonyl complexes, containing the ubiquitous aminoquinoline scaffold, were synthesized. Both aminoquinoline ligands and Re(I) complexes showed adequate stability over a 48-h incubation period. Furthermore, the cytotoxic activity of the precursor ligands and rhenium(I) complexes were evaluated against the hormone-dependent MCF-7 and hormone-independent triple negative MDA-MB-231 breast cancer cell lines. Inclusion of the [Re(CO)3Cl]+ entity significantly enhanced the cytotoxicity of the aminoquinoline Schiff base ligands against the tested cancer cell lines. Remarkably, the incorporation of the Schiff-base iminoquinolyl entity notably enhanced the cytotoxic activity of the Re(I) complexes, in comparison with the iminopyridyl entity. Notably, the quinolyl-substituted complex showed up to three-fold higher activity than cisplatin against breast cancer cell lines, underpinning the significance of the quinoline pharmacophore in rational drug design. In addition, the most active Re(I) complex showed better selectivity towards the breast cancer cells over non-tumorigenic FG-0 cells. Western blotting revealed that the complexes increased levels of γH2AX, a key DNA damage response protein. Moreover, apoptosis was confirmed in both cell lines due to the detection of cleaved PARP. The complexes show favourable binding affinities towards both calf thymus DNA (CT-DNA), and bovine serum albumin (BSA), and the order of their interactions align with their cytotoxic effects. The in silico molecular simulations of the complexes were also performed with CT-DNA and BSA targets.

Synthesis and antiproliferative activity of benzimidazole-based, trinuclear neutral cyclometallated and cationic, N

A series of 2-phenyl and 2-pyridyl tris-benzimidazole ligands was reacted with the [Ru(p-cymene)Cl2]2 dimer to yield the corresponding neutral cyclometallated and cationic organoruthenium(ii) complexes. All of the synthesized compounds were characterized using an array of spectroscopic and analytical techniques, including 1H, 13C nuclear magnetic resonance (NMR), infrared spectroscopy and mass spectrometry. The trinuclear compounds were screened for their cytotoxicy against the MCF-7 breast cancer cell line and the triple negative MDA-MB-231 breast cancer cell line at concentrations of 10 and 20 µM. Overall, the 2-pyridyl ligands 10 and 11, and their corresponding trinuclear complexes [16][PF6]3 and [17][PF6]3, show the most promising activity as these compounds significantly reduce the percentage cell survival of MCF-7 and MDA-MB-231 breast cancer cell lines at the aforementioned fixed concentrations. It was observed that 10 and [16][PF6]3 show potency greater than that of cisplatin against the MCF-7 breast cancer cell line, and [17][PF6]3 shows potency comparable to that of cisplatin against the MCF-7 cell line. Additionally, the synthesized compounds were observed to have relatively low cytotoxicty towards MCF-12A breast epithelial cells and relatively higher selectivity towards MCF-7 breast cancer cells compared to cisplatin.

Structure-activity relationship studies of antiplasmodial cyclometallated ruthenium(II), rhodium(III) and iridium(III) complexes of 2-phenylbenzimidazoles.

Benzimidazoles, such as albendazole, thiabendazole and omeprazole have antiplasmodial activity against Plasmodium falciparum and are widely used as scaffolds for metal-based drug research. Incorporating substituents with various lipophilic and electronic properties can influence trans-membrane interactions and concomitantly improve the biological activity. To study structure-activity relationships, a series of 2-phenylbenzimidazoles and their corresponding Ru(II), Ir(III) and Rh(III) cyclometallated complexes were synthesised and evaluated for antiplasmodial activity against the chloroquine-sensitive (NF54) strain of the human malaria parasite Plasmodium falciparum. Selected metal complexes were further screened against the multidrug-resistant (K1) strain. In general, the 2-phenylbenzimidazole ligands showed weak antiplasmodial activities (IC50 ∼ 17.66-22.32 µM) while an enhancement of antiplasmodial activity was observed upon coordination of the ligands with either ruthenium, iridium or rhodium. The new cyclometallated complexes were found to be active against both parasite strains, with IC50 values in the low to submicromolar range (0.12-5.17 µM). In addition, the metal complexes have relatively low cytotoxicity against mammalian Chinese Hamster Ovarian (CHO) cells.