The interactions of the ruthenium(II)-cymene complexes with lysozyme and cytochrome c

Anticancer organometallic half-sandwich complexes of estrone-derived (N,N) donor ligands with enhanced aqueous solubility

Four steroidal derivatives (L1-4) bearing an (N,N) metal-chelating subunit on the D-ring, in addition to the organometallic [M(arene)(N,N)Cl]Cl complexes of L1,2 were synthesized and characterized, in which M(arene) is Rh(III)(η5-C5Me5) or Ir(III)(η5-C5Me5) or Ru(II)(η6-p-cymene). The solution chemical properties of both the estrone-based ligands and selected complexes were investigated by spectroscopic methods. At pH = 7.4, the ligands are predominantly positively charged, moderately lipophilic (logD7.4 = +0.6 - +3.2), and exhibit low-to-medium micromolar solubility (S7.4 = 9-543 μM) and are more hydrophilic than estrone; however, complexation improved the aqueous solubility of the obtained organometallics. The Rh(η5-C5Me5) and Ru(η6-p-cymene) complexes of L1 demonstrated high stability in solution (<1 % bidentate ligand dissociation at pH 7.4 for 48 h), forming a higher fraction of mixed hydroxido species [M(arene)(N,N)(OH)]+ in the case of the Ru complexes. Both coordination and intermolecular interactions of the organometallic complexes with human serum albumin were observed. The ligands and their complexes were tested in human cancer cell lines to investigate their in vitro anticancer activity. Studies in Colo-205 and MCF-7 cells revealed the moderate-to-strong cytotoxicity of the ligands (IC50 = 5-50 μM) with limited selectivity toward cancer cells over the non-cancerous CCD-19Lu fibroblast cell line. Complexation increased the cytotoxicity, especially for Rh(III)(η5-C5Me5) and Ir(III)(η5-C5Me5) complexes in the MCF-7 cell line compared to the ligands.

Delineating the binding site of a series of gold(III) Schiff base chelates on HSA via experimentation and in silico methods

Human serum albumin (HSA) is crucial for drug transport, influencing pharmacokinetics and pharmacological activity. While drug binding to HSA is well-studied, precise identification of primary binding sites remains underexplored. Since unbound drug fractions impact distribution and receptor-site concentration, understanding HSA interactions is essential for evaluating pharmacokinetics and toxicity. This study presents a systematic workflow integrating fluorescence quenching, circular dichroism, and ligand-binding thermodynamics to map ligand binding on HSA. Using patented Schiff base Au (III) chelates, we validate our approach with experimental data, molecular dynamics simulations, and QM/MM TD-DFT methods. Results indicate all three chelates preferentially bind Sudlow's site I, with affinities following AuL3 > AuL1 > AuL1, with logka values ranging from 4.73 to 5.03. Thermodynamic analysis suggests endothermic, hydrophobic-driven binding. Competitive site displacement assays confirm these findings. Overall, our results highlight HSA's potential as a transporter for metal-based therapeutics and demonstrate the efficacy of our workflow in accurately determining drug-binding sites.

Not All Binding Sites Are Equal: Site Determination and Folding State Analysis of Gas-Phase Protein-Metallodrug Adducts

Modern approaches in metallodrug research focus on compounds that bind protein targets rather than DNA. However, the identification of protein targets and binding sites is challenging. Using intact mass spectrometry and proteomics, we investigated the binding of the antimetastatic agent RAPTA-C to the model proteins ubiquitin, cytochrome c, lysozyme, and myoglobin. Binding to cytochrome c and lysozyme was negligible. However, ubiquitin bound up to three Ru moieties, two of which were localized at Met1 and His68 as [Ru(cym)], and [Ru(cym)] or [Ru(cym)(PTA)] adducts, respectively. Myoglobin bound up to four [Ru(cym)(PTA)] moieties and five sites were identified at His24, His36, His64, His81/82 and His113. Collision-induced unfolding (CIU) studies via ion-mobility mass spectrometry allowed measuring protein folding as a function of collisional activation. CIU of protein-RAPTA-C adducts showed binding of [Ru(cym)] to Met1 caused a significant compaction of ubiquitin, likely from N-terminal S-Ru-N chelation, while binding of [Ru(cym)(PTA)] to His residues of ubiquitin or myoglobin induced a smaller effect. Interestingly, the folded state of ubiquitin formed by His functionalization was more stable than Met1 metalation. The data suggests that selective metalation of amino acids at different positions on the protein impacts the conformation and potentially the biological activity of anticancer compounds.

Organometallic Ru(II), Rh(III) and Re(I) complexes of sterane-based bidentate ligands: synthesis, solution speciation, interaction with biomolecules and anticancer activity

In this study, we present the synthesis, characterization and in vitro cytotoxicity of six organometallic [Ru(II)(η6-p-cymene)(N,N)Cl]Cl, [Rh(III)(η5-C5Me5)(N,N)Cl]Cl and [Re(I)(CO)3(N,N)Cl] complexes, in which the (N,N) ligands are sterane-based 2,2'-bipyridine derivatives (4-Me-bpy-St-OH, 4-Ph-bpy-St-OH). The solution chemical behavior of the ligands and the complexes was explored by UV-visible spectrophotometry and 1H NMR spectroscopy. The ligands and their Re(I) complexes are neutral at pH = 7.40; this contributes to their highly lipophilic character (log D7.40 > +3). The Ru(II) and Rh(III) half-sandwich complexes are much more hydrophilic, and this property is greatly affected by the actual chloride ion content of the medium. The half-sandwich Ru and Rh complexes are highly stable in 30% (v/v) DMSO/water (<5% dissociation at pH = 7.40); this is further increased in water. The Rh(III)(η5-C5Me5) complexes were characterized by higher water/chloride exchange and pKa constants compared to their Ru(II)(η6-p-cymene) counterparts. The Re(I)(CO)3 complexes are also stable in solution over a wide pH range (2-12) without the release of the bidentate ligand; only the chlorido co-ligand can be replaced with OH- at higher pH values. A comprehensive discussion of the binding affinity of the half-sandwich Ru(II) and Rh(III) complexes toward human serum albumin and calf-thymus DNA is also provided. The Ru(II)(η6-p-cymene) complexes interact with human serum albumin via intermolecular forces, while for the Rh(III)(η5-C5Me5) complexes the coordinative binding mode is suggested as well. They are also able to interact with calf-thymus DNA, most likely via the coordination of the guanine nitrogen. The Ru(II)(η6-p-cymene) complexes were found to be the most promising among the tested compounds as they exhibited moderate-to-strong cytotoxic activity (IC50 = 3-11 μM) in LNCaP as well as in PC3 prostate cells in an androgen receptor-independent manner. They were also significantly cytotoxic in breast and colon adenocarcinoma cancer cell lines and showed good selectivity for cancer cells.

Pharmacological assessment of Ru(II) complex with GidA protein- A novel topoisomerase II inhibitor towards cancer therapeutics

The interactions of ruthenium(II) complex with Glucose inhibited division protein A (GidA protein) was studied through various spectroscopic techniques with the ultimate goal of preparing adducts with good selectivity for cancer cells. In all the cases, formation of a tight metal-protein conjugate was observed. The influence of pH, reducing agents and chelators on the formation of adduct was analysed by UV- visible spectroscopy. While there was no effect on the addition of sodium ascorbate, some alterations on some selected bands were seen on the UV-visible spectra on the addition of EDTA. The adduct was stable in the pH range of 5-8. Addition of ruthenium(II) complex effectively quenched the intrinsic fluorescence of GidA and it occurred through static quenching. The effect of ruthenium(II) complex on the conformation of GidA has been examined by analyzing CD spectrum. Though, there was some conformational changes observed in the presence of ruthenium(II) complex, α- helix in the secondary structure of GidA retained its identity. Molecular docking of ruthenium(II) complex with GidA also indicated that GidA docks through hydrophobic interaction. The stable semisynthetic complex (ruthenium(II) complex with GidA) was checked for topoisomerase II inhibition. Relaxation and decatenation assay proved topoisomerase II inhibition of semisynthetic complex.Communicated by Ramaswamy H. Sarma.

Critical factors affecting the albumin binding of half-sandwich Ru(ii) and Rh(iii) complexes of 8-hydroxyquinolines and oligopyridines

There is significant interest today in the interaction of half-sandwich anticancer organometallic complexes with proteins. It is considered as a crucial factor in the transport and mode of action of these compounds; thus it can affect their overall pharmacological and toxicological profiles. Albumin binding of high stability Ru(ii)(η⁶-p-cymene) and Rh(iii)(η⁵-C₅Me₅) complexes formed with 8-hydroxyquinoline, its 5-chloro-7-((proline-1-yl)methyl) substituted derivative, 2,2'-bipyridine and 1,10-phenanthroline is discussed herein. The interaction with human serum albumin in terms of kinetic aspects, binding strength and possible binding sites was studied in detail by means of various methods such as ¹H NMR spectroscopy, UV-visible spectrophotometry, steady-state and time-resolved fluorometry, ultrafiltration and capillary zone electrophoresis. Ru(ii)(η⁶-p-cymene)(2,2'-bipyridine) and Ru(ii)(η⁶-p-cymene)(1,10-phenanthroline) complexes do not bind to the protein measurably, most probably due to kinetic reasons. However, other complexes bind significantly to albumin with fairly different kinetics to albumin. The binding affinity towards hydrophobic binding pockets shows correlation with lipophilicity along with the actual charge of the respective complexes. The studied complexes preserve their original structure upon interaction with albumin. Formation constants computed for the binding of these metal complexes to histidine-containing model oligopeptides demonstrated significant ternary complex formation, pointing out the importance of histidine coordination in the binding of these types of complexes.

Modulation of Diverse Procoagulant Venom Activities by Combinations of Platinoid Compounds

Procoagulant snake venoms have been inhibited by the ruthenium containing compounds CORM-2 and RuCl₃ separately, presumably by interacting with critical histidine or other sulfur-containing amino acids on key venom enzymes. However, combinations of these and other platinoid containing compounds could potentially increase, decrease or not affect the procoagulant enzyme function of venom. Thus, the purpose of this investigation was to determine if formulations of platinoid compounds could inhibit venom procoagulant activity and if the formulated compounds interacted to enhance inhibition. Using a human plasma coagulation kinetic model to assess venom activity, six diverse venoms were exposed to various combinations and concentrations of CORM-2, CORM-3, RuCl₃ and carboplatin (a platinum containing compound), with changes in venom activity determined with thrombelastography. The combinations of CORM-2 or CORM-3 with RuCl₃ were found to enhance inhibition significantly, but not in all venoms nor to the same extent. In sharp contrast, carboplatin-antagonized CORM-2 mediated the inhibition of venom activity. These preliminary results support the concept that platinoid compounds may inhibit venom enzymatic activity at the same or different molecular sites and may antagonize inhibition at the same or different sites. Further investigation is warranted to determine if platinoid formulations may serve as potential antivenoms.