Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 115, Issue 13, Pages 3249-3254Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1719190115
Keywords
IDO1; heme; cancer; kynurenine
Categories
Funding
- BMS, Inc.
- NIH [2R37 GM036298]
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For cancer cells to survive and proliferate, they must escape normal immune destruction. One mechanism by which this is accomplished is through immune suppression effected by up-regulation of indoleamine 2,3-dioxygenase (IDO1), a heme enzyme that catalyzes the oxidation of tryptophan to N-formylkynurenine. On deformylation, kynurenine and downstream metabolites suppress T cell function. The importance of this immunosuppressive mechanism has spurred intense interest in the development of clinical IDO1 inhibitors. Herein, we describe the mechanism by which a class of compounds effectively and specifically inhibits IDO1 by targeting its apoform. We show that the in vitro kinetics of inhibition coincide with an unusually high rate of intrinsic enzyme-heme dissociation, especially in the ferric form. X-ray crystal structures of the inhibitor-enzyme complexes show that heme is displaced from the enzyme and blocked from rebinding by these compounds. The results reveal that apo-IDO1 serves as a unique target for inhibition and that heme lability plays an important role in posttranslational regulation.
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