Dual Role of Glutathione as a Reducing Agent and Cu-Ligand Governs the ROS Production by Anticancer Cu-Thiosemicarbazone Complexes.

α-Pyridyl thiosemicarbazones (TSC) such as Triapine (3AP) and Dp44mT are a promising class of anticancer agents. Contrary to Triapine, Dp44mT showed a pronounced synergism with CuII, which may be due to the generation of reactive oxygen species (ROS) by Dp44mT-bound CuII ions. However, in the intracellular environment, CuII complexes have to cope with glutathione (GSH), a relevant CuII reductant and CuI-chelator. Here, aiming at rationalizing the different biological activity of Triapine and Dp44mT, we first evaluated the ROS production by their CuII-complexes in the presence of GSH, showing that CuII-Dp44mT is a better catalyst than CuII-3AP. Furthermore, we performed density functional theory (DFT) calculations, which suggest that a different hard/soft character of the complexes could account for their different reactivity with GSH.

Copper-Catalyzed Glutathione Oxidation is Accelerated by the Anticancer Thiosemicarbazone Dp44mT and Further Boosted at Lower pH.

Glutathione (GSH) is the most abundant thiol in mammalian cells and plays a crucial role in maintaining redox cellular homeostasis. The thiols of two GSH molecules can be oxidized to the disulfide GSSG. The cytosolic GSH/GSSG ratio is very high (>100), and its reduction can lead to apoptosis or necrosis, which are of interest in cancer research. CuII ions are very efficient oxidants of thiols, but with an excess of GSH, CuIn(GS)m clusters are formed, in which CuI is very slowly reoxidized by O2 at pH 7.4 and even more slowly at lower pH. Here, the aerobic oxidation of GSH by CuII was investigated at different pH values in the presence of the anticancer thiosemicarbazone Dp44mT, which accumulates in lysosomes and induces lysosomal membrane permeabilization in a Cu-dependent manner. The results showed that CuII-Dp44mT catalyzes GSH oxidation faster than CuII alone at pH 7.4 and hence accelerates the production of very reactive hydroxyl radicals. Moreover, GSH oxidation and hydroxyl radical production by CuII-Dp44mT were accelerated at the acidic pH found in lysosomes. To decipher this unusually faster thiol oxidation at lower pH, density functional theory (DFT) calculations, electrochemical and spectroscopic studies were performed. The results suggest that the acceleration is due to the protonation of CuII-Dp44mT on the hydrazinic nitrogen, which favors the rate-limiting reduction step without subsequent dissociation of the CuI intermediate. Furthermore, preliminary biological studies in cell culture using the proton pump inhibitor bafilomycin A1 indicated that the lysosomal pH plays a role in the activity of CuII-Dp44mT.

A Boron-Containing Compound Acting on Multiple Targets Against Alzheimer's Disease. Insights from Ab Initio and Molecular Dynamics Simulations.

Given the multifactorial nature and pathogenesis of Alzheimer's disease, therapeutic strategies are addressed to combine the benefits of every single-target drug into a sole molecule. Quantum mechanics and molecular dynamics (MD) methods were employed here to investigate the multitarget action of a boron-containing compound against Alzheimer's disease. The antioxidant activity as a radical scavenger and metal chelator was explored by means of density functional theory. The most plausible radical scavenger mechanisms, which are hydrogen transfer, radical adduct formation, and single-electron transfer in aqueous and lipid environments, were fully examined. Metal chelation ability was investigated by considering the complexation of Cu(II) ion, one of the metals that in excess can even catalyze the ß-amyloid (Aß) aggregation. The most probable complexes in the physiological environment were identified by considering both the stabilization energy and the shift of the λmax induced by the complexation. The excellent capability to counteract Aß aggregation was explored by performing MD simulations on protein-ligand adducts, and the activity was compared with that of curcumin, chosen as a reference.

Sequestering Ability of a Synthetic Chelating Agent towards Copper(II) and Iron(III): A Detailed Theoretical and Experimental Analysis.

In the continuous effort to identify selective chelators towards bioavailable and toxic metal ions, the potential selectivity of a novel N,O chelating ligand, recently synthesized and claimed to be able to bind to Cu(II) ions forming stable complexes while leaving unaltered the level of essential metal ions, was scrutinized using a combined theoretical and experimental approach. A multistep synthetic procedure was used to synthesize the ligand, whose chelating properties along with the stability of the complexes formed binding Cu(II) and, for comparison, Fe(III) ions were evaluated using potentiometric measurements and UV-Vis spectroscopy. DFT analysis allowed to disclose the structural characteristics of the formed complexes. In the plethora of all the possible structures, a selection of the most reliable ones was achieved by means of a stringent comparison between experimental and simulated UV-Vis spectra. The outcomes of the present investigation demonstrate that the Cu(II) sequestering ability of the ligand is smaller than that towards Fe(III). The strategy used here should allow to check the propensity of ligands in selectively binding metal ions.