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

Abstract

COTI-2 is a novel anticancer thiosemicarbazone in phase I clinical trial. However, the effects of metal complexation (a main characteristic of thiosemicarbazones) and acquired resistance mechanisms are widely unknown. Therefore, in this study, the copper and iron complexes of COTI-2 were synthesized and evaluated for their anticancer activity and impact on drug resistance in comparison to metal-free thiosemicarbazones. Investigations using Triapine-resistant SW480/Tria and newly established COTI-2-resistant SW480/Coti cells revealed distinct structure–activity relationships. SW480/Coti cells were found to overexpress ABCC1, and COTI-2 being a substrate for this efflux pump. This was unexpected, as ABCC1 has strong selectivity for glutathione adducts. The recognition by ABCC1 could be explained by the reduction kinetics of a ternary Cu-COTI-2 complex with glutathione. Thus, only thiosemicarbazones forming stable, nonreducible copper(II)-glutathione adducts are recognized and, in turn, effluxed by ABCC1. This reveals a crucial connection between copper complex chemistry, glutathione interaction, and the resistance profile of clinically relevant thiosemicarbazones.

Modulation of Intracellular Copper Levels as the Mechanism of Action of Anticancer Copper Complexes: Clinical Relevance

“…In contrast to NSC319726, COTI-2 did not affect intracellular Zn accumulation in HNSCC-mutant TP 53 cells, indicating that its mechanism of action might be independent of Zn chelation [ 267 ]. The activity of COTI-2 was significantly potentiated by coordination to a Cu(II) center and decreased upon coordination to a Fe(II) center, suggesting that Cu plays an important role in the mechanism of action of COTI-2 [ 271 ]. Recently it was revealed that resistant profile of both COTI-2 and its Cu(II) complex was governed by GSH-dependent ABCC1 efflux pump [ 271 ].…”

“…The activity of COTI-2 was significantly potentiated by coordination to a Cu(II) center and decreased upon coordination to a Fe(II) center, suggesting that Cu plays an important role in the mechanism of action of COTI-2 [ 271 ]. Recently it was revealed that resistant profile of both COTI-2 and its Cu(II) complex was governed by GSH-dependent ABCC1 efflux pump [ 271 ]. It was shown that COTI-2/Cu complex formed stable and non-reducible adduct with GSH, which was recognized by ABCC1 and pumped out of the COTI-2-resistant cancer cells [ 271 ].…”

“…Recently it was revealed that resistant profile of both COTI-2 and its Cu(II) complex was governed by GSH-dependent ABCC1 efflux pump [ 271 ]. It was shown that COTI-2/Cu complex formed stable and non-reducible adduct with GSH, which was recognized by ABCC1 and pumped out of the COTI-2-resistant cancer cells [ 271 ]. These findings are crucial for understanding potential resistance mechanisms in cancer patients.…”

Exploring the Monoterpene Indole Alkaloid Scaffold for Reversing P-Glycoprotein-Mediated Multidrug Resistance in Cancer

“…As can be observed in Table 3, the semicarbazone derivatives (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32) were much less active, having significant FAR values only at 2 µM. As with azine derivatives, compounds sharing aromatic substituents (25-32) showed higher activity (FAR values = 3.20-8.77) than those with aliphatic moieties (22)(23)(24).…”

“…The monoterpene indole alkaloid of the corynanthe-type [18], dregamine (1), was previously isolated, in a large amount, from the alkaloid fraction of the methanol extract of Tabernaemontana elegans roots [13]. As mentioned above, dregamine (1) derivatives were reported as promising MDR reversers [13][14][15], prompting us to carry out new chemical modifications to obtain 19 azines (3-21) and 11 semicarbazone (22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32) derivatives.…”