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

Abstract

Due to their significant biological activity, thiosemicarbazones (TSCs) are promising candidates for anticancer therapy. In part, the efficacy of TSCs is linked to their ability to chelate essential metal ions such as copper and iron. Triapine, the best-studied anticancer TSC, has been tested clinically with promising results in hematological diseases. During the last years, a novel subclass of TSCs with improved anticancer activity was found to induce paraptosis, a recently characterized form of cell death. The aim of this study was to identify structural and chemical properties associated with anticancer activity and paraptosis induction of TSCs.Results: When testing a panel of structurally related TSCs, compounds with nanomolar anticancer activity and paraptosis-inducing properties showed higher copper(II) complex solution stability and a slower reduction rate, which resulted in reduced redox activity. In contrast, TSCs with lower anticancer activity induced higher levels of superoxide that rapidly stimulated superoxide dismutase expression in treated cells, effectively protecting the cells from drug-induced redox stress.Innovation: Consequently, we hypothesize that in case of close Triapine derivatives, intracellular reduction leads to rapid dissociation of intracellularly formed copper complexes. In contrast, TSCs characterized by highly stable, slowly reducible copper(II) complexes are able to reach new intracellular targets such as the ER-resident protein disulfide isomerase. Conclusions:The additional modes of actions observed with highly active TSC derivatives are based on intracellular formation of stable copper complexes, offering a new approach to combat (drug-resistant) cancer cells.

Insight into the Anticancer Activity of Copper(II) 5-Methylenetrimethylammonium-Thiosemicarbazonates and Their Interaction with Organic Cation Transporters

“…On the contrary, significant spectral changes were detected with GSH as Figure 7a shows for complex 2 (and Supplementary Materials Figure S21a for 1). The first recorded spectrum after mixing the reactants showed several shifts of the absorbance bands most likely due to the formation of a ternary complex with GSH as reported for other TSC complexes [64,66,67]. Then a significant decrease of the absorbance was observed at λ max = 376 nm, while the absorbance value of the free proligand (λ max~3 29 nm) was increased, presumably due to decomposition of the generated copper(I) complex, which is unstable.…”

“…By looking at the structure of the two proligands (STSC and [H 2 L R ]Cl) a similar binding pattern is assumed in case of the complexes 1-4 studied in this work, even though different solution stability can be envisioned due to the presence of the [-NMe 3 ] + moiety, different N-terminal substitution and the type of solvent. DMSO is able to coordinate to copper(II) weakly, therefore, somewhat higher copper(II) complex stability is expected in the neat aqueous solution [64].…”

Cancer Cell Resistance Against the Clinically Investigated Thiosemicarbazone COTI-2 Is Based on Formation of Intracellular Copper Complex Glutathione Adducts and ABCC1-Mediated Efflux

“…Notably, copper(II) complexes of α- N -pyridyl thiosemicarbazones bearing an N,N,S – coordination mode are generally highly stable at physiological pH even at fairly low concentrations. 4 , 6 …”

“… 3 , 4 Also, the interaction with cellular copper ions has been associated with their mechanism of action, at least for a part of the known anticancer thiosemicarbazones. 5 , 6 …”

“… 8 , 9 Noteworthy, this thiosemicarbazone subclass is characterized by a higher copper(II) complex stability and additional modes of action such as induction of paraptotic cell death. 6 , 10 One of these thiosemicarbazones, namely, di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC; Scheme 1 ), entered a phase I clinical trial in 2016 (study number NCT02688101). 11 , 12 At the same time, another highly active but structurally more divergent thiosemicarbazone, 4-(pyridine-2-yl)- N -([(8 E )-5,6,7,8-tetrahydroquinolin-8-ylidene]amino)piperazine-1-carbothioamide, also known as COTI-2 ( Scheme 1 ), was developed by Cotinga Pharmaceuticals as a third-generation representative.…”