Document Detail

Mechanistic studies of semicarbazone triapine targeting human ribonucleotide reductase in vitro and in mammalian cells: tyrosyl radical quenching not involving reactive oxygen species.
MedLine Citation:
PMID:  22915594     Owner:  NLM     Status:  MEDLINE    
Triapine® (3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP)) is a drug in Phase II trials. One of its established cellular targets is the β(2) subunit of ribonucleotide reductase that requires a diferric-tyrosyl-radical [(Fe(III)(2)-Y·)(Fe(III)(2))] cofactor for de novo DNA biosynthesis. Several mechanisms for 3-AP inhibition of β(2) have been proposed; one involves direct iron chelation from β(2), whereas a second involves Y· destruction by reactive oxygen species formed in situ in the presence of O(2) and reductant by Fe(II)-(3-AP). Inactivation of β(2) can thus arise from cofactor destruction by loss of iron or Y·. In vitro kinetic data on the rates of (55)Fe and Y· loss from [((55)Fe(III)(2)-Y·)((55)Fe(III)(2))]-β(2) under aerobic and anaerobic conditions reveal that Y· loss alone is sufficient for rapid β(2) inactivation. Oxyblot(TM) and mass spectrometric analyses of trypsin-digested inhibited β(2), and lack of Y· loss from H(2)O(2) and O(2)(•) treatment together preclude reactive oxygen species involvement in Y· loss. Three mammalian cell lines treated with 5 μm 3-AP reveal Y· loss and β(2) inactivation within 30-min of 3-AP-exposure, analyzed by whole-cell EPR and lysate assays, respectively. Selective degradation of apo- over [(Fe(III)(2)-Y·)(Fe(III)(2))]-β(2) in lysates, similar iron-content in β(2) immunoprecipitated from 3-AP-treated and untreated [(55)Fe]-prelabeled cells, and prolonged (12 h) stability of the inhibited β(2) are most consistent with Y· loss being the predominant mode of inhibition, with β(2) remaining iron-loaded and stable. A model consistent with in vitro and cell-based biochemical studies is presented in which Fe(II)-(3-AP), which can be cycled with reductant, directly reduces Y· of the [(Fe(III)(2)-Y·)(Fe(III)(2))] cofactor of β(2).
Yimon Aye; Marcus J C Long; JoAnne Stubbe
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Publication Detail:
Type:  Journal Article; Research Support, N.I.H., Extramural; Research Support, Non-U.S. Gov't     Date:  2012-08-22
Journal Detail:
Title:  The Journal of biological chemistry     Volume:  287     ISSN:  1083-351X     ISO Abbreviation:  J. Biol. Chem.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-15     Completed Date:  2012-12-31     Revised Date:  2013-10-17    
Medline Journal Info:
Nlm Unique ID:  2985121R     Medline TA:  J Biol Chem     Country:  United States    
Other Details:
Languages:  eng     Pagination:  35768-78     Citation Subset:  IM    
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
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MeSH Terms
COS Cells
Cercopithecus aethiops
Enzyme Stability
Hydrogen Peroxide / metabolism*
Iron / metabolism*
K562 Cells
NIH 3T3 Cells
Protein Subunits / genetics,  metabolism*
Pyridines / pharmacology*
Ribonucleotide Reductases / genetics,  metabolism*
Superoxides / metabolism*
Thiosemicarbazones / pharmacology*
Grant Support
GM29595/GM/NIGMS NIH HHS; R01 GM029595/GM/NIGMS NIH HHS; //Howard Hughes Medical Institute
Reg. No./Substance:
0/Protein Subunits; 0/Pyridines; 0/Thiosemicarbazones; 11062-77-4/Superoxides; 143621-35-6/3-aminopyridine-2-carboxaldehyde thiosemicarbazone; 7439-89-6/Iron; 7722-84-1/Hydrogen Peroxide; EC 1.17.4.-/Ribonucleotide Reductases

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