Faculty Collaboration Database

Redox activation of Fe(III)-thiosemicarbazones and Fe(III)-bleomycin by thioredoxin reductase: specificity of enzymatic redox centers and analysis of reactive species formation by ESR spin trapping. Free Radic Biol Med 2013 Jul;60:183-94

Date

03/15/2013

Pubmed ID

23485585

Pubmed Central ID

PMC3654041

DOI

10.1016/j.freeradbiomed.2013.02.016

Scopus ID

2-s2.0-84875404357 (requires institutional sign-in at Scopus site)   26 Citations

Abstract

Thiosemicarbazones such as Triapine (Tp) and Dp44mT are tridentate iron (Fe) chelators that have well-documented antineoplastic activity. Although Fe-thiosemicarbazones can undergo redox cycling to generate reactive species that may have important roles in their cytotoxicity, there is only limited insight into specific cellular agents that can rapidly reduce Fe(III)-thiosemicarbazones and thereby promote their redox activity. Here we report that thioredoxin reductase-1 (TrxR1) and glutathione reductase (GR) have this activity and that there is considerable specificity to the interactions between specific redox centers in these enzymes and various Fe(III) complexes. Site-directed variants of TrxR1 demonstrate that the selenocysteine (Sec) of the enzyme is not required, whereas the C59 residue and the flavin have important roles. Although TrxR1 and GR have analogous C59/flavin motifs, TrxR is considerably faster than GR. For both enzymes, Fe(III)(Tp)2 is reduced faster than Fe(III)(Dp44mT)2. This reduction promotes redox cycling and the generation of hydroxyl radical (HO) in a peroxide-dependent manner, even with low-micromolar levels of Fe(Tp)2. TrxR also reduces Fe(III)-bleomycin and this activity is Sec-dependent. TrxR cannot reduce Fe(III)-EDTA at significant rates. Our findings are the first to demonstrate pro-oxidant reductive activation of Fe(III)-based antitumor thiosemicarbazones by interactions with specific enzyme species. The marked elevation of TrxR1 in many tumors could contribute to the selective tumor toxicity of these drugs by enhancing the redox activation of Fe(III)-thiosemicarbazones and the generation of reactive oxygen species such as HO.

Author List

Myers JM, Cheng Q, Antholine WE, Kalyanaraman B, Filipovska A, Arnér ES, Myers CR

Author

Balaraman Kalyanaraman PhD Professor in the Biophysics department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Antineoplastic Agents
Bleomycin
Glutathione Reductase
Humans
Hydroxyl Radical
Iron
Iron Chelating Agents
Oxidation-Reduction
Reactive Oxygen Species
Selenocysteine
Spin Trapping
Thioredoxin Reductase 1
Thiosemicarbazones