Revisiting the thiosemicarbazonecopper(II) reaction with glutathione. Activity against colorectal carcinoma cell lines

Abstract

Thiosemicarbazones (TSCs), and their copper derivatives, have been extensively studied mainly due to the potential applications as antitumor compounds. A part of the biological activity of the TSC-Cu complexes rests on their reactivity against cell reductants, as glutathione (GSH). The present paper describes the structure of the [Cu(PTSC)(ONO)] compound (1) (HPTSC=pyridine-2-carbaldehyde thiosemicarbazone) and its spectroscopic and magnetic properties. ESI studies performed on the reaction of GSH with 1 and the analogous [{Cu(PTSC*)(ONO)}] derivative (2, HPTSC*=pyridine-2-carbaldehyde 4N-methylthiosemicarbazone) show the absence of peaks related with TSC-Cu-GSH species. However GSH-Cu ones are detected, in good agreement with the release of Cu ions after reduction in the experimental conditions. The reactivity of 1 and 2 with cytochrome c and myoglobin and their activities against HT-29 and SW-480 colon carcinoma cell lines are compared with those shown by the free HPTSC and HPTSC* ligands.

High Copper Complex Stability and Slow Reduction Kinetics as Key Parameters for Improved Activity, Paraptosis Induction, and Impact on Drug-Resistant Cells of Anticancer Thiosemicarbazones

“…When we investigated the role of redox activity, opposing to the current theory of activation by reduction (16,20,27), nanomolar-active TSCs were characterized by copper(II) complexes with higher stability and less efficient reduction by reducing agents. This observation is in line with other studies such as from Garcia-Tojal et al, and from Santoro et al who both found slower reduction by GSH in the case of the copper(II) complex of Dp44mT, as compared to the copper(II) complexes of Triapine and FTSC/PTSC (11,44). Moreover, for both Triapine as well as FTSC, reduction of the copper(II) complex resulted in efficient binding of the copper(I) ion to GSH leaving a metal-free ligand able to interact with other metal ions such as iron or zinc (44).…”

“…In good agreement with the literature (11), no time-dependent spectral changes were observed in the case of AA which suggests that these metal complexes cannot be reduced by AA under the applied conditions (see Suppl. Figure 5).…”

“…Significantly, for all of these effects, the interactions with (intracellular) copper pools leading to formation of redox-active copper complexes were suggested to be crucial (16,19,34). Thus, it was proposed that copper complexes induce ROS (superoxide) by redox reaction with intracellular reductants, a mechanism also referred to as "activation by reduction" (11,34,36,44,49). Accordingly, a strong synergism between the metal-free ligand and free copper salts has been repeatedly reported for nanomolar-active TSCs (19,28,49).…”

“…Accordingly, a strong synergism between the metal-free ligand and free copper salts has been repeatedly reported for nanomolar-active TSCs (19,28,49). However, the experiments supporting the ROS model were often performed either with preformed copper(II) complexes (11,34) or by preincubation of the ligands with high levels of extracellular copper (28,36,49). In contrast, in many cases, incubation with the metal-free ligands alone did not induce global ROS detectable for example by the DCF-DA stain (13,28,34).…”

“…However, the role of other metals (especially copper), metalloenzymes and metal-interacting proteins is gaining more attention (16,22). For example, the ability of copper(II)-TSC complexes to undergo redox cycling in the presence of reducing agents, with production of reactive oxygen species (ROS) (a process also called "activation by reduction" ( 22)), and the disruption of the cellular thiol redox homeostasis is increasingly discussed as relevant contributions to TSC activity (11,23,27,44). Furthermore, the interaction with copper ions has been recently suggested to be involved in collateral sensitivity of P-glycoprotein (P-gp, ABCB1)-overexpressing multidrug-resistant cancer cells to the nanomolar-active TSC di-2-pyridylketone 4,4-dimethyl-3-thiosemicarbazone (Dp44mT) (21).…”