Gold(III) porphyrins: Synthesis and interaction with G-quadruplex DNA.

G-quadruplex nucleic acids (G4s) are RNA and DNA secondary structures involved in the regulation of multiple key biological processes. They can be found in telomeres, oncogene promoters, RNAs, but also in viral genomes. Due to their unique structural features, very distinct from the canonical duplexes or single-strands, G4s represent promising pharmacological targets for small molecules, namely G4-ligands. Gold(III) penta-cationic porphyrins, as specific G4 ligands, are able to inhibit HIV-1 infectivity and their antiviral activity correlates with their affinity for G4s. Up to now, one of the best antiviral compounds is meso-5,10,15,20-tetrakis[4-(N-methyl-pyridinium-2-yl)phenyl]porphyrinato gold(III) (1). Starting from this compound, we report a structure/affinity relationship study of gold(III) cationic porphyrins to find out the best porphyrin candidate for functionalization, in order to study the antiviral mechanism of action of these gold(III) porphyrins.

Novel 8-nitroquinolin-2(1H)-ones as NTR-bioactivated antikinetoplastid molecules: Synthesis, electrochemical and SAR study.

To study the antiparasitic 8-nitroquinolin-2(1H)-one pharmacophore, a series of 31 derivatives was synthesized in 1-5 steps and evaluated in vitro against both Leishmania infantum and Trypanosoma brucei brucei. In parallel, the reduction potential of all molecules was measured by cyclic voltammetry. Structure-activity relationships first indicated that antileishmanial activity depends on an intramolecular hydrogen bond (described by X-ray diffraction) between the lactam function and the nitro group, which is responsible for an important shift of the redox potential (+0.3 V in comparison with 8-nitroquinoline). With the assistance of computational chemistry, a set of derivatives presenting a large range of redox potentials (from -1.1 to -0.45 V) was designed and provided a list of suitable molecules to be synthesized and tested. This approach highlighted that, in this series, only substrates with a redox potential above -0.6 V display activity toward L. infantum. Nevertheless, such relation between redox potentials and in vitro antiparasitic activities was not observed in T. b. brucei. Compound 22 is a new hit compound in the series, displaying both antileishmanial and antitrypanosomal activity along with a low cytotoxicity on the human HepG2 cell line. Compound 22 is selectively bioactivated by the type 1 nitroreductases (NTR1) of L. donovani and T. brucei brucei. Moreover, despite being mutagenic in the Ames test, as most of nitroaromatic derivatives, compound 22 was not genotoxic in the comet assay. Preliminary in vitro pharmacokinetic parameters were finally determined and pointed out a good in vitro microsomal stability (half-life > 40 min) and a 92% binding to human albumin.

Copper transfer from Cu-Abeta to human serum albumin inhibits aggregation, radical production and reduces Abeta toxicity.

Amyloid-beta peptides (Abeta) and the protein human serum albumin (HSA) interact in vivo. They are both localised in the blood plasma and in the cerebrospinal fluid. Among other functions, HSA is involved in the transport of the essential metal copper. Complexes between Abeta and copper ions have been proposed to be an aberrant interaction implicated in the development of Alzheimer's disease, where Cu is involved in Abeta aggregation and production of reactive oxygen species (ROS). In the present work, we studied copper-exchange reaction between Abeta and HSA or the tetrapeptide DAHK (N-terminal Cu-binding domain of HSA) and the consequence of this exchange on Abeta-induced ROS production and cell toxicity. The following results were obtained: 1) HSA and DAHK removed Cu(II) from Abeta rapidly and stoichiometrically, 2) HSA and DAHK were able to decrease Cu-induced aggregation of Abeta, 3) HSA and DAHK suppressed the catalytic HO(.) production in vitro and ROS production in neuroblastoma cells generated by Cu-Abeta and ascorbate, 4) HSA and DAHK were able to rescue these cells from the toxicity of Cu-Abeta with ascorbate, 5) DAHK was more potent in ROS suppression and restoration of neuroblastoma cell viability than HSA, in correlation with an easier reduction of Cu(II)-HSA than Cu-DAHK by ascorbate, in vitro. Our data suggest that HSA is able to decrease aberrant Cu(II)-Abeta interaction. The repercussion of the competition between HSA and Abeta to bind Cu in the blood and brain and its relation to Alzheimer's disease are discussed.

Evidence that the principal CoII-binding site in human serum albumin is not at the N-terminus: implication on the albumin cobalt binding test for detecting myocardial ischemia.

Human serum albumin (HSA) is the most abundant protein in the blood plasma and is involved in the transport of metal ions. Four metal-binding sites with different specificities have been described in HSA: (i) the N-terminal site provided by Asp1, Ala2, and His3, (ii) the site at the reduced Cys34, (iii) site A, including His67 as a ligand, and (iv) the nonlocalized site B. HSA can bind CoII, and HSA was proposed to be involved in CoII transport. Recently, binding of CoII to HSA has attracted much interest due to the so-called albumin cobalt binding (ACB) test approved by the Food and Drug Administration for evaluation of myocardial ischemia. Although the binding of CoII to HSA is important, the binding of CoII to HSA is not well-characterized. Here the binding of CoII to HSA was studied under anaerobic conditions to prevent CoII oxidation. Electronic absorption, EPR, and NMR spectroscopies indicate three specific and well-separated binding sites for CoII in HSA. CoII ions in all three sites are in a high-spin state and coordinated in a distorted octahedral geometry. Competition experiments with CdII (known to bind to sites A and B) and CuII (known to bind to the N-terminal site) were used to identify the sites of binding of CoII to HSA. They revealed that the first two equivalents of CoII bind to sites A and B. Only the third may be bound to the N-terminal site. The repercussions of these results on the understanding of the ACB test and hence the myocardial ischemia are discussed.

Zinc(II) binds to the neuroprotective peptide humanin.

The abnormal accumulation of the peptide amyloid-beta in the form of senile (or amyloid) plaques is one of the hallmarks of Alzheimer's disease (AD). Zinc ions have been implicated in AD and plaques formation. Recently, the peptide humanin has been discovered. Humanin showed neuroprotective activity against amyloid-beta insults. Here the question investigated is if humanin could interact directly with Zn(II). It is shown that Zn(II) and its substitutes Cd(II)/Co(II) bind to humanin via a thiolate bond from the side chain of the single cysteine at position 8. The low intensity of the d-d bands of Co(II)-humanin indicated an octahedral coordination geometry. Titration experiments suggest that Zn(II) binds to humanin with an apparent affinity in the low muM range. This apparent Zn-binding affinity is in the same order as for amyloid-beta and glutathione and could thus be of physiological relevance.