The Potent and Novel Thiosemicarbazone Chelators Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone and 2-Benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone Affect Crucial Thiol Systems Required for Ribonucleotide Reductase Activity

Abstract

Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone possesses potent and selective antitumor activity. Its cytotoxicity has been attributed to iron chelation leading to inhibition of the ironcontaining enzyme ribonucleotide reductase (RR). Thiosemicarbazone iron complexes have been shown to be redox-active, although their effect on cellular antioxidant systems is unclear. Using a variety of antioxidants, we found that only N-acetylcysteine significantly inhibited thiosemicarbazone-induced antiproliferative activity. Thus, we examined the effects of thiosemicarbazones on major thiol-containing systems considering their key involvement in providing reducing equivalents for RR. Thiosemicarbazones significantly (p Ͻ 0.001) elevated oxidized trimeric thioredoxin levels to 213 Ϯ 5% (n ϭ 3) of the control. This was most likely due to a significant (p Ͻ 0.01) decrease in thioredoxin reductase activity to 65 Ϯ 6% (n ϭ 4) of the control. We were surprised to find that the non-redox-active chelator desferrioxamine increased thioredoxin oxidation to a lower extent (152 Ϯ 9%; n ϭ 3) and inhibited thioredoxin reductase activity (62 Ϯ 5%; n ϭ 4), but at a 10-fold higher concentration than thiosemicarbazones. In contrast, only the thiosemicarbazones significantly (p Ͻ 0.05) reduced the glutathione/oxidized-glutathione ratio and the activity of glutaredoxin that requires glutathione as a reductant. All chelators significantly decreased RR activity, whereas the NADPH/ NADP total ratio was not reduced. This was important to consider because NADPH is required for thiol reduction. Thus, thiosemicarbazones could have an additional mechanism of RR inhibition via their effects on major thiol-containing systems.

The Iron Chelators Dp44mT and DFO Inhibit TGF-β-induced Epithelial-Mesenchymal Transition via Up-Regulation of N-Myc Downstream-regulated Gene 1 (NDRG1)

“…The other major mechanism of thiosemicarbazone activity is mediated through the redox cycling of their iron and copper complexes (17), causing cell death and apoptosis through targeting lysosome integrity (18) and oxidizing glutathione and the sulfhydryl groups of proteins involved in reducing systems (19).…”

The Iron Chelator, Deferasirox, as a Novel Strategy for Cancer Treatment: Oral Activity Against Human Lung Tumor Xenografts and Molecular Mechanism of Action

“…More recently, chelators from these classes, namely, Dp44mT and 2-benzoylpyridine-4,4-dimethyl-3-thiosemicarbazone (Bp44mT), were shown to have an additional mechanism of ribonucleotide reductase inhibition via their effects on major thiol-containing systems (Yu et al, 2011b). Additionally, these ligands modulate the expression of a variety of proteins involved in cell cycle control, such as members of the cyclin family and cyclindependent kinases (Yu et al, 2007).…”

Cellular Uptake of the Antitumor Agent Dp44mT Occurs via a Carrier/Receptor-Mediated Mechanism

“…Furthermore, Dp44mT increases the expression of the potent metastasis suppressor, N-myc downstream-regulated gene 1 (Le and Kovacevic et al, 2011). Due to its ability to deplete cellular Fe (Yuan et al, 2004), Dp44mT causes cell cycle arrest at the G 1 /S phase (Noulsri et al, 2009;Rao et al, 2009) and inhibits the activity of the Fe-dependent enzyme ribonucleotide reductase, impeding cellular DNA synthesis and proliferation (Yu et al, 2011). Interestingly, Dp44mT was observed to accumulate within lysosomes, where it forms redoxactive copper (Cu) complexes that induce oxidative damage and lysosomal permeabilization .…”