Interaction of the potent antitumoral compounds Casiopeinas® with blood serum and cellular bioligands

Casiopeinas® are among the few CuII compounds patented for their antitumor activity, but their mode of action has not been fully elucidated yet. One of them, Cas II-gly, is formed by 4,7-dimethyl-1,10-phenanthroline (Me2phen) and glycinato (Gly). In blood and cells, Cas II-gly can keep its identity or form mixed species with serum or cytosol bioligands (bL or cL) with composition CuII–Me2phen–bL/cL, CuII–Gly–bL/cL, or CuII–bL/cL. In this study, the binding of Cas II-gly with low molecular mass bioligands of blood serum (citric, L-lactic acid, and L-histidine) and cytosol (reduced glutathione (GSH), reduced nicotinamide adenine dinucleotide (NADH), adenosine triphosphate (ATP), and L-ascorbic acid) was examined through the application of instrumental (ElectroSpray Ionization-Mass Spectrometry and Electron Paramagnetic Resonance) and computational (Density Functional Theory) methods. The results indicated that mixed species CuII–Me2phen–bL/cL are formed, with the bioligands replacing glycinato. The formation of these adducts may participate in the copper transport toward the target organs and facilitate the cellular uptake or, in constrast, preclude it. In the systems with GSH, NADH and L-ascorbate, a redox reaction occurs with the partial oxidation of cL to the corresponding oxidized form (GSSG, NAD+ and dehydroascorbate) which interact with CuII. Formed CuI ion does not give complexation reactions with reduced or oxidized form of bioligands for its ‘soft’ character and low affinity for oxygen and nitrogen donors compared to CuII. However, CuI could promote Fenton-like reactions with production of reactive oxygen species (ROS) related to the antitumor activity of Casiopeinas®.