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An adverse tumor-protective effect of IDO1 inhibition

ABSTRACT: Indoleamine 2, 3-dioxygenase 1 (IDO1) is a metabolic enzyme catalyzing the conversion of the essential amino acid tryptophan to kynurenine. It is induced by IFNg and its expression is linked to poor prognosis across various cancer types. T cells are particularly sensitive to IDO1-dependent tryptophan deprivation in the tumor microenvironment, leading to tumor immune resistance. Therefore, IDO1 inhibitors, such as epacadostat, have been developed, aiming to restore T cell antitumor activity. However, a recent phase III trial assessing the clinical benefit of epacadostat with the PD-1 antibody pembrolizumab in melanoma failed. This prompted us to study the role of IDO1, and the effect of its inhibition, on tumor cells that are under IFNg treatment and T cell attack. We showed that IDO1-mediated tryptophan depletion contributes to the anti-tumor effect of CD8 T cells. Thus, while epacadostat expectedly replenished tryptophan -the desired effect-, this led to adverse protection of melanoma cells from T cell-derived IFNg. RNA sequencing and ribosome profiling of (patient-derived) melanoma cell lines revealed that IFNg caused general protein translation shut down, which was reversed by IDO1 inhibition. Impaired translation was accompanied by an amino acid deprivation-dependent stress response driving ATF4high and MITFlow transcriptomic signatures, which was also observed in melanoma patient tumors. Downregulation of MITF in tumors and PDX- derived cell lines upon treatment was strongly predictive of response to response, to checkpoint blockade-treatment and IFNg, respectively. Conversely, MITF restoration in cultured tumor cells caused T cell resistance. These results highlight the critical role of tryptophan in the melanoma response to T cell-derived IFNg, uncovering an unexpected negative consequence of IDO1 inhibition.

ORGANISM(S): Homo sapiens

PROVIDER: GSE198460 | GEO | 2023/01/16

REPOSITORIES: GEO

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Project description:Many tumors escape by activating multiple cellular pathways that induce immunosuppression. One pivotal immune-suppressive mechanism is the production of tryptophan metabolites along the kynurenine pathway by IFNγ-induced IDO1 enzyme production 4-8. Phase III clinical trials using chemical inhibition of IDO1 in combination with PD1 pathway blockade, however, failed to improve melanoma treatment 9-12. This points at an incomplete understanding of the role of IDO1 and the consequent tryptophan degradation on mRNA translation and cancer progression. Here, we investigated the effects of prolonged IFNγ treatment on mRNA translation in melanoma cells by ribosome profiling. Surprisingly, we observed a massive accumulation of ribosomes ~20 amino acids downstream of tryptophan codons (termed here as W-Bumps) along with their expected stalling at the tryptophan codon itself. This indicated ribosomal bypass of the tryptophan codons in the absence of tryptophan. Detailed examination of W-Bumps position and its corresponding peptide sequences pinpointed towards ribosomal frameshifting events and their effects in the ribosome exit tunnel. In particular, W-Bumps strength was associated with the disorderedness level of potential out-of-frame peptides predicted downstream of tryptophan codons. Indeed, reporter assays demonstrated the induction of ribosomal frameshifting, and the generation of trans-frame proteins and their presentation at the cell surface after IFNγ treatment. Proteomics and immunopeptidomics analyses verified the production of IFNγ-induced trans-frame and out-of-frame aberrant peptides and their presentation on HLA class I molecules. Priming of naïve T cells from healthy donors with aberrant peptides resulted in identification of reactive, peptide-specific T cells. Altogether, our results suggest that IFNγ-induced IDO1-mediated tryptophan depletion plays a role in the immune recognition of melanoma cells by contributing to the diversity of the peptidome landscape, and by inducing the presentation of aberrant peptides.

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An adverse tumor-protective effect of IDO1 inhibition

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