IDO1 and IDO2 are expressed in human tumors: levo- but not dextro-1-methyl tryptophan inhibits tryptophan catabolism |
| |
Authors: | Stefan Löb Alfred Königsrainer Derek Zieker Björn L D M Brücher Hans-Georg Rammensee Gerhard Opelz Peter Terness |
| |
Institution: | Department of General, Visceral and Transplant Surgery, University Hospital of Tübingen, Tübingen, Germany. stefan.loeb@med.uni-tuebingen.de |
| |
Abstract: | Objectives Indoleamine-2,3-Dioxygenase (IDO) is an immunosuppressive molecule inducible in various cells. In addition to classic IDO
(IDO1), a new variant, IDO2, has recently been described. When expressed in dendritic cells (DCs) or cancer cells, IDO was
thought to suppress the immune response to tumors. A novel therapeutic approach in cancer envisages inhibition of IDO with
1-methyl-tryptophan (1MT). The levo-isoform (l-1MT) blocks IDO1, whereas dextro-1MT (d-1MT), which is used in clinical trials, inhibits IDO2. Here we analyze IDO2 expression in human cancer cells and the impact
of both 1-MT isoforms on IDO activity.
Methods Surgically extirpated human primary tumors as well as human cancer cell lines were tested for IDO1 and IDO2 expression by
RT-PCR. IDO1 activity of Hela cells was blocked by transfection with IDO1-specific siRNA and analysed for tryptophan degradation
by RP-HPLC. The impact of d-1MT and l-1MT on IDO activity of Hela cells and protein isolates of human colon cancer were studied.
Results Human primary gastric, colon and renal cell carcinomas constitutively expressed both, IDO1 and IDO2 mRNA, whereas cancer cells
lines had to be induced to by Interferon-gamma (IFN-γ). Treatment of Hela cells with IDO1-specific siRNA resulted in complete
abrogation of tryptophan degradation. Only l-1MT, and not d-1MT, was able to block IDO activity in IFN-γ-treated Hela cells as well as in protein isolates of primary human colon cancer.
Conclusions Although IDO2 is expressed in human tumors, tryptophan degradation is entirely provided by IDO1. Importantly, d-1MT does not inhibit the IDO activity of malignant cells. If ongoing clinical studies show a therapeutic effect of d-1MT, this cannot be attributed to inhibition of IDO in tumor cells. |
| |
Keywords: | |
本文献已被 PubMed SpringerLink 等数据库收录! |
|