Exploiting exo and endo furan-maleimide Diels-Alder linkages for the functionalization of organoruthenium complexes.

Diels-Alder cycloadditions involving furans and maleimides are extensively used in organic chemistry and materials synthesis. Given the promising advances of organoruthenium complexes in therapy, we explored the possibility of exploiting such Diels-Alder linkages as a mean to modulate their biological properties.

Sodium Tetraphenylborate Displays Selective Bactericidal Activity against Neisseria meningitidis and N. gonorrhoeae and Is Effective at Reducing Bacterial Infection Load.

Neisseria meningitidis and Neisseria gonorrhoeae, two highly related species that might have emerged from a common commensal ancestor, constitute major human threats. Vaccines are available to prevent N. meningitidis infection, whereas there are only a limited number of antibiotics available for N. gonorrhoeae Unfortunately, some strains of these species are rapidly evolving and capable of escaping human interventions. Thus, it is now urgent to develop new avenues to fight these bacteria. This study reports that a boron-based salt, sodium tetraphenylborate (NaBPh4), displays high bactericidal activity and remarkable specificity against N. meningitidis and N. gonorrhoeae Other closely related commensal species such as Neisseria lactamica, which is found in the normal flora of healthy individuals, were found to be less affected even at 5-fold higher doses of NaBPh4 This specificity was further observed when much lower sensitivity was found for more distant Neisseriaceae species (such as Neisseria elongata or Kingella oralis) and completely unrelated species. Significant boron uptake by N. meningitidis cells was observed after incubation with 5 µM NaBPh4, as measured by inductively coupled plasma mass spectrometry, suggesting that this drug candidate's target(s) could be located intracellularly or within the cell envelope. Furthermore, mutants with slightly decreased susceptibility displayed alterations in genes coding for cell envelope elements, which reduced their virulence in an animal model of infection. Finally, a single dose of NaBPh4 resulted in a significant reduction in bacterial burden in a mouse model of N. meningitidis bacteremia. Although numerous boron-containing species were previously reported for their complex biological activities, the observation of this narrow selectivity is unprecedented and of potential importance from a therapeutic standpoint.

Cu-catalyzed click conjugation of cobalamin to a BODIPY-based fluorophore: A versatile tool to explore the cellular biology of vitamin B12.

The Cu-catalyzed click conjugation of an azide-functionalized vitamin B12 (cobalamin) and an alkyne-labeled 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) led to the formation of a highly stable fluorescent BODIPY-labeled vitamin B12 (λex/λem = 495/508 nm). The formation of what has been identified as an iodine adduct of the conjugate was also observed as a side-product during this reaction and could be removed using HPLC. BODIPY-labeled vitamin B12 was characterized by NMR and HR-ESI-MS. In vitro studies on wild-type human fibroblasts indicated that BODIPY-labeled vitamin B12 could internalize in a manner similar to that of untagged vitamin B12. ATP-binding cassette sub-family D member 4 (ABCD4) is a lysosomal localized transporter required to export vitamin B12 from the lysosomal lumen to the cytosol. Mutations in this transporter result in the accumulation of vitamin B12 in lysosomes. In human fibroblasts harbouring a mutation in ABCD4, BODIPY-labeled vitamin B12 accumulated in the lumen of lysosomes. Our data suggests the potential use of BODIPY-labeled vitamin B12 to investigate the intracellular behavior of the vitamin in the context of disorders related to the abnormal cellular utilization of the vitamin. Moreover, results presented here demonstrate that click chemistry could be exploited for the conjugation of vitamin B12 to various other fluorophores.

Synthesis and biological assessment of a ruthenium(II) cyclopentadienyl complex in breast cancer cells and on the development of zebrafish embryos.

Ruthenium-based complexes currently attract great attention as they hold promise to replace platinum-based drugs as a first line cancer treatment. Whereas ruthenium arene complexes are some of the most studied species for their potential anticancer properties, other types of ruthenium complexes have been overlooked for this purpose. Here, we report the synthesis and characterization of Ru(II) cyclopentadienyl (Cp), Ru(II) cyclooctadienyl (COD) and Ru(III) complexes bearing anastrozole or letrozole ligands, third-generation aromatase inhibitors currently used for the treatment of estrogen receptor positive (ER +) breast cancer. Among these complexes, Ru(II)Cp 2 was the only one that displayed a high stability in DMSO and in cell culture media and consequently, the only complex for which the in vitro and in vivo biological activities were investigated. Unlike anastrozole alone, complex 2 was considerably cytotoxic in vitro (IC50 values < 1 µM) in human ER + breast cancer (T47D and MCF7), triple negative breast cancer (TNBC) (MBA-MB-231), and in adrenocortical carcinoma (H295R) cells. Theoretical (docking simulation) and experimental (aromatase catalytic activity) studies suggested that an interaction between 2 and the aromatase enzyme was not likely to occur and that the bulkiness of the PPh3 ligands could be an important factor preventing the complex to reach the active site of the enzyme. Exposure of zebrafish embryos to complex 2 at concentrations around its in vitro cytotoxicity IC50 value (0.1-1 µM) did not lead to noticeable signs of toxicity over 96 h, making it a suitable candidate for further in vivo investigations. This study confirms the potential of Ru(II)Cp complexes for breast cancer therapy, more specifically against TNBCs that are usually not responsive to currently used chemotherapeutic agents.

Organoruthenium(II) Complexes Bearing an Aromatase Inhibitor: Synthesis, Characterization, in Vitro Biological Activity and in Vivo Toxicity in Zebrafish Embryos.

Third-generation aromatase inhibitors such as anastrozole (ATZ) and letrozole (LTZ) are widely used to treat estrogen receptor-positive ER+ breast cancers in postmenopausal women. Investigating their ability to coordinate metals could lead to the emergence of a new category of anticancer drug candidates with a broader spectrum of pharmacological activities. In this study, a series of ruthenium (II) arene complexes bearing the aromatase inhibitor anastrozole was synthesized and characterized. Among these complexes, [Ru(η 6 -C6H6)(PPh3)(η 1 -ATZ)Cl]BPh4 (3) was found to be the most stable in cell culture media, to lead to the highest cellular uptake and in vitro cytotoxicity in two ER+ human breast cancer cell lines (MCF7 and T47D), and to induce a decrease in aromatase activity in H295R cells. Exposure of zebrafish embryos to complex 3 (12.5 µM) did not lead to noticeable signs of toxicity over 96 h, making it a suitable candidate for further in vivo investigations.

Synthesis, characterization and biological evaluation of cationic organoruthenium(ii) fluorene complexes: influence of the nature of the counteranion.

In this study, five ruthenium arene complexes with fluorene-bearing N,N-(1) and N,O-(2) donor Schiff base ligands were synthesized and fully characterized. Cationic ruthenium complexes 3[X], ([Ru(η6-C6H6)(Cl)(fluorene-N[double bond, length as m-dash]CH-pyridine)][X] (where X = BF4, PF6, BPh4), were obtained by reacting ligand 1 with [Ru(η6-C6H6)Cl2]2 in the presence of NH4X salts, whereas neutral complex 4, Ru(η6-C6H6)(Cl)(fluorene-N[double bond, length as m-dash]CH-naphtholate), was isolated by reacting ligand 2 with the same precursor. It was possible to obtain a cationic version of the latter, 5[BF4], by reacting 4 with AgBF4 in the presence of pyridine. All compounds were fully characterized by NMR and HR-ESI-MS whereas some of them were also analyzed by single crystal X-ray analysis. Their in vitro antiproliferative activity was also assessed in human breast cancer cell lines, notably MCF-7 and T47D. Complex 4 and its cationic counterpart 5[BF4] were found to be the most cytotoxic compounds of the series (IC50 = 6.2-16.2 µM) and displayed higher antiproliferative activities than cisplatin in both cell lines. It was found that 5[BF4] undergoes a ligand exchange reaction and readily converts to 4 in the presence of 0.1 M NaCl, explaining the similarity in their observed cytotoxicities. Whereas 3[BF4] and 3[PF6] were found inactive at the tested concentrations, 3[BPh4] displayed a considerable cytotoxicity (IC50 = 16.7-27.8 µM). Notably, 3[BPh4], 4 (and 5[BF4]) were active against T47D, a cisplatin resistant cell line. Interestingly, 4 (16.4 µM) was found to be less cytotoxic than 3[BPh4] and cisplatin (6.6 and 7.9 µM, respectively) in breast healthy cells (MCF-12A). However, in comparison to 4 and cisplatin (at 10 µM), a lower in vivo toxicity was observed for complex 3[BPh4] on the development of zebrafish (Danio rerio) embryos.

Anticancer Activity and Catalytic Potential of Ruthenium(II)-Arene Complexes with N,O-Donor Ligands.

The special ability of organometallic complexes to catalyze various transformations might offer new effective mechanisms for the treatment of cancer. Studies that report both the biological properties and the ability of metallic complexes to promote therapeutically relevant catalytic reactions are limited. Herein, we report the anticancer activity and catalytic potential of some ruthenium(II)-arene complexes bearing bidentate Schiff base ligands (2a and 2b) and their reduced analogues (5a and 5b, respectively). In comparison to their Schiff base counterparts 2a and 2b, we demonstrate that amine complexes 5a and 5b display (i) a higher in vitro antiproliferative activity on different human cancer cell lines, (ii) a lower rate of hydrolysis, and (iii) an improved initial catalytic rate for the reduction of NAD+ to NADH. In contrast to their imine analogues 2a and 2b, we also show that amine complexes 5a and 5b induce the generation of intracellular reactive oxygen species (ROS) in MCF-7 breast cancer cells. Our results highlight the impact that a simple ligand modification such as the reduction of an imine moiety can have on both the catalytic and biological activities of metal complexes. Moreover, the ruthenium complexes reported here display some antiproliferative activity against T47D breast cancer cells, known for their cis-platin resistance.