Marília I.F. Barbosa

In Vitro and In Vivo Activities of Ruthenium(II) Phosphine/Diimine/Picolinate Complexes (SCAR) against Mycobacterium tuberculosis

Rifampicin, discovered more than 50 years ago, represents the last novel class of antibiotics introduced for the first-line treatment of tuberculosis. Drugs in this class form part of a 6-month regimen that is ineffective against MDR and XDR TB, and incompatible with many antiretroviral drugs. Investments in R&D strategies have increased substantially in the last decades. However, the number of new drugs approved by drug regulatory agencies worldwide does not increase correspondingly. Ruthenium complexes (SCAR) have been tested in our laboratory and showed promising activity against Mycobacterium tuberculosis. These complexes showed up to 150 times higher activity against MTB than its organic molecule without the metal (free ligand), with low cytotoxicity and high selectivity. In this study, promising results inspired us to seek a better understanding of the biological activity of these complexes. The in vitro biological results obtained with the SCAR compounds were extremely promising, comparable to or better than those for first-line drugs and drugs in development. Moreover, SCAR 1 and 4, which presented low acute toxicity, were assessed by Ames test, and results demonstrated absence of mutagenicity.

Nitro/nitrosyl ruthenium complexes are potent and selective anti-Trypanosoma cruzi agents causing autophagy and necrotic parasite death

ABSTRACT cis-[RuCl(NO2)(dppb)(5,5′-mebipy)] (complex 1), cis-[Ru(NO2)2(dppb)(5,5′-mebipy)] (complex 2), ct-[RuCl(NO)(dppb)(5,5′-mebipy)](PF6)2 (complex 3), and cc-[RuCl(NO)(dppb)(5,5′-mebipy)](PF6)2 (complex 4), where 5,5′-mebipy is 5,5′-dimethyl-2,2′-bipyridine and dppb is 1,4-bis(diphenylphosphino)butane, were synthesized and characterized. The structure of complex 2 was determined by X-ray crystallography. These complexes exhibited a higher anti-Trypanosoma cruzi activity than benznidazole, the current antiparasitic drug. Complex 3 was the most potent, displaying a 50% effective concentration (EC50) of 2.1 ± 0.6 μM against trypomastigotes and a 50% inhibitory concentration (IC50) of 1.3 ± 0.2 μM against amastigotes, while it displayed a 50% cytotoxic concentration (CC50) of 51.4 ± 0.2 μM in macrophages. It was observed that the nitrosyl complex 3, but not its analog lacking the nitrosyl group, releases nitric oxide into parasite cells. This release has a diminished effect on the trypanosomal protease cruzain but induces substantial parasite autophagy, which is followed by a series of irreversible morphological impairments to the parasites and finally results in cell death by necrosis. In infected mice, orally administered complex 3 (five times at a dose of 75 μmol/kg of body weight) reduced blood parasitemia and increased the survival rate of the mice. Combination index analysis of complex 3 indicated that its in vitro activity against trypomastigotes is synergic with benznidazole. In addition, drug combination enhanced efficacy in infected mice, suggesting that ruthenium-nitrosyl complexes are potential constituents for drug combinations.

Structural isomerism of Ru(II)-carbonyl complexes: synthesis, characterization and their antitrypanosomal activities

New complexes with the general formula [RuCl(CO)(dppb)(diimine)]PF6, [dppb = 1,4-bis(diphenylphosphino)butane; diimine = 2,2′-bipyridine (bipy) or 1,10-phenanthroline (phen)], were prepared. Thus, the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 (1), ct-[RuCl(CO)(dppb)(phen)]PF6 (2), tc-[RuCl(CO)(dppb)(bipy)]PF6 (3), tc-[RuCl(CO)(dppb)(phen)]PF6 (4), cc-[RuCl(CO)(dppb)(bipy)]PF6 (5) and cc-[RuCl(CO)(dppb)(phen)]PF6 (6) were obtained and characterized. In this case, the first letter in the prefixes indicates the position of CO with respect to the chlorido ligand and the second one is related to the phosphorus atoms. The compositions of the complexes were confirmed by analytical techniques and an octahedral environment around the ruthenium was confirmed by single-crystal X-ray diffraction of the complexes ct-[RuCl(CO)(dppb)(bipy)]PF6 and cc-[RuCl(CO)(dppb)(phen)]PF6. The oxidation potentials of the complexes were determined by cyclic voltammetry and it was found that they vary according to the CO position in the complexes. In order to obtain information on the stability of the ct, tc and cc-[RuCl(CO)(dppb)(bipy)]PF6 (1), (3) and (5) isomers, computational studies were carried out, and they showed large differences between the HOMO/LUMO energies. As monitored by 13C NMR, the stability of the complexes with respect to CO displacement, for at least 72 h, in DMSO-d6 solution, is independent of the CO position in the complexes. Pharmacological evaluation of the complexes against the Trypanosoma cruzi parasite revealed the structure–activity relationships, showing that the presence and position of the CO ligand in the complexes are relevant for the antiparasitic activity of the compounds. The most active compound, the tc-[RuCl(CO)(dppb)(bipy)]PF6 isomer, presented potent antiparasitic activity, which was achieved by causing oxidative stress followed by parasite cell death through necrosis. Thus, the findings presented here demonstrate that the use of a carbonyl ligand provides stability and pharmacological properties to ruthenium/diphosphine/diimine complexes.

[Ru(pipe)(dppb)(bipy)]PF6: A novel ruthenium complex that effectively inhibits ERK activation and cyclin D1 expression in A549 cells

Lung cancer is the most frequent type of cancer worldwide. In Brazil, only 14% of the patients diagnosed with lung cancer survived 5years in the last decades. Although improvements in the therapeutic approach, it is relevant to identify new chemotherapeutic agents. In this framework, ruthenium metal compounds emerge as a promising alternative to platinum-based compounds once they displayed lower cytotoxicity and more selectivity for tumor cells. The present study aimed to evaluate the antitumor potential of innovative ruthenium(II) complex, [Ru(pipe)(dppb)(bipy)]PF6 (PIPE) on A549 cells, which is derived from non-small cell lung cancer. Results demonstrated that PIPE effectively reduced the viability and proliferation rate of A549 cells. When PIPE was used at 9μM there was increase in G0/G1 cell population with concomitant reduction in frequency of cells in S-phase, indicating cell cycle arrest in G1/S transition. Antiproliferative activity of PIPE was associated to its ability of reducing cyclin D1 expression and ERK phosphorylation levels. Cytotoxic activity of PIPE on A549 cells was observed when PIPE was used at 18μM, which was associated to its ability of inducing apoptosis by intrinsic pathway. Taken together, the data demonstrated that PIPE is a promising antitumor agent and further in vivo studies should be performed.

A novel platinum complex containing a piplartine derivative exhibits enhanced cytotoxicity, causes oxidative stress and triggers apoptotic cell death by ERK/p38 pathway in human acute promyelocytic leukemia HL-60 cells

Piplartine (piperlongumine) is a plant-derived compound found in some Piper species that became a novel potential antineoplastic agent. In the present study, we synthesized a novel platinum complex containing a piplartine derivative cis-[PtCl(PIP-OH)(PPh3)2]PF6 (where, PIP-OH = piplartine demethylated derivative; and PPh3 = triphenylphosphine) with enhanced cytotoxicity in different cancer cells, and investigated its apoptotic action in human promyelocytic leukemia HL-60 cells. The structure of PIP-OH ligand was characterized by X-ray crystallographic analysis and the resulting platinum complex was characterized by infrared, molar conductance measurements, elemental analysis and NMR experiments. We found that the complex is more potent than piplartine in a panel of cancer cell lines. Apoptotic cell morphology, increased internucleosomal DNA fragmentation, without cell membrane permeability, loss of the mitochondrial transmembrane potential, increased phosphatidylserine externalization and caspase-3 activation were observed in complex-treated HL-60 cells. Treatment with the complex also caused a marked increase in the production of reactive oxygen species (ROS), and the pretreatment with N-acetyl-L-cysteine, an antioxidant, reduced the complex-induced apoptosis, indicating activation of ROS-mediated apoptosis pathway. Important, pretreatment with a p38 MAPK inhibitor (PD 169316) and MEK inhibitor (U-0126), known to inhibit ERK1/2 activation, also prevented the complex-induced apoptosis. The complex did not induce DNA intercalation in cell-free DNA assays. In conclusion, the complex exhibits more potent cytotoxicity than piplartine in a panel of different cancer cells and triggers ROS/ERK/p38-mediated apoptosis in HL-60 cells.

CCDC 1522481: Experimental Crystal Structure Determination

Related Article: Murillo C. Ribeiro, Rodrigo S. Correa, Marilia I.F. Barbosa, Fabio G. Delolo, Javier Ellena, Andre L. Bogado, Alzir A. Batista|2017|Polyhedron|137|311|doi:10.1016/j.poly.2017.08.013