Effects of 1-methyltryptophan stereoisomers on IDO2 enzyme activity and IDO2-mediated arrest of human T cell proliferation

Cancer Immunol Immunother. 2012 Nov;61(11):2013-20. doi: 10.1007/s00262-012-1265-x. Epub 2012 Apr 22.

Abstract

IDO2 is a newly discovered enzyme with 43 % similarity to classical IDO (IDO1) protein and shares the same critical catalytic residues. IDO1 catalyzes the initial and rate-limiting step in the degradation of tryptophan and is a key enzyme in mediating tumor immune tolerance via arrest of T cell proliferation. The role of IDO2 in human T cell immunity remains controversial. Here, we demonstrate that similar to IDO1, IDO2 also degrades tryptophan into kynurenine and is inhibited more efficiently by Levo-1-methyl tryptophan (L-1MT), an IDO1 competitive inhibitor, than by dextro-methyl tryptophan (D-1MT). Although IDO2 enzyme activity is weaker than IDO1, it is less sensitive to 1-MT inhibition than IDO1. Moreover, our results indicate that human CD4(+) and CD8(+) T cell proliferation was inhibited by IDO2, but both L-1MT and D-1MT could not reverse IDO2-mediated arrest of cell proliferation, even at high concentrations. These data indicate that IDO2 is an inhibitory mechanism in human T cell proliferation and support efforts to develop more effective IDO1 and IDO2 inhibitors in order to overcome IDO-mediated immune tolerance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • CD4-Positive T-Lymphocytes / drug effects*
  • CD8-Positive T-Lymphocytes / drug effects*
  • Cells, Cultured
  • Humans
  • Indoleamine-Pyrrole 2,3,-Dioxygenase / antagonists & inhibitors*
  • Kynurenine / biosynthesis
  • Lymphocyte Activation / drug effects*
  • Stereoisomerism
  • Tryptophan / analogs & derivatives*
  • Tryptophan / chemistry
  • Tryptophan / pharmacology

Substances

  • IDO1 protein, human
  • IDO2 protein, human
  • Indoleamine-Pyrrole 2,3,-Dioxygenase
  • Kynurenine
  • Tryptophan
  • 1-methyltryptophan