TY - JOUR T1 - The Potent and Novel Thiosemicarbazone Chelators, Dp44mT and Bp44mT, Affect Crucial Thiol Systems Required for Ribonucleotide Reductase Activity. JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.111.071324 SP - mol.111.071324 AU - Yu Yu AU - Yohan Suryo Rahmanto AU - Clare L Hawkins AU - Des R Richardson Y1 - 2011/01/01 UR - http://molpharm.aspetjournals.org/content/early/2011/03/09/mol.111.071324.abstract N2 - Di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT) possesses potent and selective anti-tumor activity. Its cytotoxicity has been attributed to iron chelation leading to inhibition of the iron-containing enzyme, ribonucleotide reductase (RR). Recently, thiosemicarbazone iron complexes were shown to be redox-active, although their effect on cellular anti-oxidant systems is unclear. Using a variety of anti-oxidants, we found only N-acetylcysteine significantly inhibited thiosemicarbazone-induced anti-proliferative 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<0.001) elevated oxidized trimeric thioredoxin levels to 213±5% (n=3) of the control. This was most likely due to a significant (p<0.01) decrease in thioredoxin reductase activity to 65±6% (n=4) of the control. Surprisingly, the non-redox-active chelator, desferrioxamine, increased thioredoxin oxidation to a lower extent (152±9%; n=3) and inhibited thioredoxin reductase activity (62±5%; n=4), but at a ten-fold higher concentration than thiosemicarbazones. In contrast, only the thiosemicarbazones significantly (p<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, while the NADPH/NADPtotal ratio was not reduced. This was important to consider since NADPH is required for thiol reduction. Thus, thiosemicarbazones could have an additional mechanism of RR inhibition via their effects on major thiol-containing systems. ER -