Dataset Information

Tumor Cell IDO Enhances Immune Suppression and Decreases Survival Independent of Tryptophan Metabolism in Glioblastoma.

ABSTRACT:

Purpose

Glioblastoma (GBM) is an incurable primary brain tumor that has not benefited from immunotherapy to date. More than 90% of GBM expresses the tryptophan (Trp) metabolic enzyme, indoleamine 2,3-dioxygenase 1 (IDO). This observation supported the historical hypothesis that IDO suppresses the antitumor immune response solely through a mechanism that requires intratumoral Trp depletion. However, recent findings led us to investigate the alternative hypothesis that IDO suppresses the anti-GBM immune response independent of its association with Trp metabolism.

Experimental design

IDO-deficient GBM cell lines reconstituted with IDO wild-type or IDO enzyme-null cDNA were created and validated in vitro and in vivo. Microarray analysis was conducted to search for genes that IDO regulates, followed by the analysis of human GBM cell lines, patient GBM and plasma, and The Cancer Genome Atlas (TCGA) database. Ex vivo cell coculture assays, syngeneic and humanized mouse GBM models, were used to test the alternative hypothesis.

Results

Nonenzymic tumor cell IDO activity decreased the survival of experimental animals and increased the expression of complement factor H (CFH) and its isoform, factor H like protein 1 (FHL-1) in human GBM. Tumor cell IDO increased CFH and FHL-1 expression independent of Trp metabolism. Increased intratumoral CFH and FHL-1 levels were associated with poorer survival among patients with glioma. Similar to IDO effects, GBM cell FHL-1 expression increased intratumoral regulatory T cells (Treg) and myeloid-derived suppressor cells while it decreased overall survival in mice with GBM.

Conclusions

Our study reveals a nonmetabolic IDO-mediated enhancement of CFH expression and provides a new therapeutic target for patients with GBM.

SUBMITTER: Zhai L

PROVIDER: S-EPMC8639612 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Abstract OBJECTIVE Glioblastoma (GBM) patients with high intratumoral IDO1 mRNA levels have an associated decrease in survival (Zhai et al., 2017; CCR). IDO1 is an immunosuppressive mediator that metabolizes tryptophan (Trp), and through its associated enzyme activity, has long been recognized to increase immunosuppressive CD4+CD25+FoxP3+ Tregs. Accordingly, we previously showed that the genetic knockdown of IDO1 in murine glioma cells, suppresses intratumoral Treg recruitment and increases animal subject survival. Unexpectedly, however, IDO1 knockdown has no effect on intratumoral Trp metabolism (Zhai et al., 2017; BBI). Further surprisingly, we recently demonstrated that, although IDO1 overexpression increases Treg levels in brain tumors, the pharmacological inhibition of IDO1 metabolism has no effect on Treg accumulation (Ladomersky et al., 2018; CCR). These novel data led us to question the requirement for IDO1 enzyme activity to regulate Tregs in malignant glioma. METHODS Lentiviral vectors encoding: (i) vector control-, (ii) wild-type (WT)-, or (iii) enzyme-null-IDO1, were created by site-directed mutagenesis in a plasmid containing WT, murine, IDO1-GFP cDNA. IDO1-deficient glioma cells from transgenic mice [(ERT2)GFAP→Cre;pTENfl/fl;p53fl/fl;Rbfl/fl;IDO1-/-] were transduced with the modified plasmids. RT-PCR, Western blotting and HPLC confirmed IDO1 expression and enzyme activity, in vitro. Syngeneic IDO1-/- mice were intracranially-engrafted with 2 × 105 modified glioma cells and studied for intratumoral Treg levels. RESULTS The substitution of IDO1 histidine 350, to an alanine (H350A), decreases IDO1 enzyme activity by 90%. Syngeneic mice with intracranial, IDO1 enzyme null (H350A) glioma, have similar intratumoral Treg levels as IDO1 WT glioma, at 25% and 26%, respectively, and is significantly increased as compared to the 5.8% Tregs in vector control glioma (P=0.015). CONCLUSIONS Our data challenge current dogma explaining how IDO1 causes Treg accumulation, and are in-line with the recent IDO1 enzyme inhibitor-focused Phase III clinical trial failure [NCT02752074]. We are now focused on revealing the mechanism underlying IDO1-mediated immunosuppression in malignant glioma.