Tryptophan Metabolism Contributes to Radiation-Induced Immune Checkpoint Reactivation in Glioblastoma

Abstract

Immune checkpoint inhibitors designed to revert tumor-induced immunosuppression have emerged as potent anticancer therapies. Tryptophan metabolism represents an immune checkpoint, and targeting this pathway's rate-limiting enzyme IDO1 is actively being investigated clinically. Here, we studied the intermediary metabolism of tryptophan metabolism in glioblastoma and evaluated the activity of the IDO1 inhibitor GDC-0919, both alone and in combination with radiation (RT). LC/GC-MS and expression profiling was performed for metabolomic and genomic analyses of patient-derived glioma. Immunocompetent mice were injected orthotopically with genetically engineered murine glioma cells and treated with GDC-0919 alone or combined with RT. Flow cytometry was performed on isolated tumors to determine immune consequences of individual treatments. Integrated cross-platform analyses coupling global metabolomic and gene expression profiling identified aberrant tryptophan metabolism as a metabolic node specific to the mesenchymal and classical subtypes of glioblastoma. GDC-0919 demonstrated potent inhibition of this node and effectively crossed the blood-brain barrier. Although GDC-0919 as a single agent did not demonstrate antitumor activity, it had a strong potential for enhancing RT response in glioblastoma, which was further augmented with a hypofractionated regimen. RT response in glioblastoma involves immune stimulation, reflected by increases in activated and cytotoxic T cells, which was balanced by immune checkpoint reactivation, reflected by an increase in IDO1 expression and regulatory T cells (Treg). GDC-0919 mitigated RT-induced Tregs and enhanced T-cell activation. Tryptophan metabolism represents a metabolic node in glioblastoma, and combining RT with IDO1 inhibition enhances therapeutic response by mitigating RT-induced immunosuppression. .

Integrative cross-platform analyses identify enhanced heterotrophy as a metabolic hallmark in glioblastoma

“…Cysteine and tryptophan metabolism also have established roles in a variety of malignancies, including glioblastoma. 32,33 Our studies reinforce the clear importance that aberrant amino acid metabolism plays in gliomagenesis, with numerous amino acids contributing to diverse metabolic functions enriched in glioblastoma. This included intermediates of serine, glutathione, cysteine, tryptophan, and urea metabolism that have been implicated in many oncogenic roles, including energy production, maintenance of redox balance, protein and nucleotide synthesis, anaplerosis, and immune modulation.…”

Both IDO1 and TDO contribute to the malignancy of gliomas via the Kyn–AhR–AQP4 signaling pathway

“…50 Although IDO1 inhibitors have not demonstrated antitumor activity as single agents in orthotopic glioma animals, a unique synergy when combined with radiotherapy, temozolomide, or anti-programmed cell death protein 1 antibody has been noted. [28][29][30][51][52][53] TDO inhibitors have not been tested in glioma animals. In this study, RY103, an IDO1/TDO dual inhibitor, showed excellent therapeutic efficacy via downregulating the IDO1/TDO-Kyn-AhR-AQP4 signal pathway in GL261 orthotopic glioma mice.…”

Immunosuppressive IDO in Cancer: Mechanisms of Action, Animal Models, and Targeting Strategies

“…Considering the work by our group and others in repeatedly demonstrating the remarkable pathogenic influence of IDO in subjects with GBM, the elucidation of its role and multi-variate functions may provide a path for enhancing the effectiveness of cancer immunotherapy against malignant glioma in the future. IDO mRNA is highly expressed in ≥90% of GBM patients presenting with wild-type isocitrate dehydrogenase (wtIDH) and while not normally expressed, is inducible among a majority of human GBM cell lines after exposure to proinflammatory cytokines (23,66,(107)(108)(109)(110). While TDO expression is expressed at an even higher mRNA level than IDO in patient-resected GBM (33,(109)(110)(111), IDO2 levels are negligible or undetectable at the mRNA level (65), despite an IHC-focused study suggesting high IDO2 protein levels in GBM (n = 52) (109); the latter of which likely reflects conclusions based on non-specific antibody immunostaining.…”

“…long after surgical resection of the tumor which may reflect a treatment-related effect rather than due to the malignancy itself. A recent study by Kesarwani et al provided additional insights into metabolomic profiling of newly diagnosed GBM (n = 80) and lower grade gliomas (LGG, n = 28) demonstrating that, GBM patients have increased intratumoral Trp and Kyn levels, but decreased KA as compared to LGG patients (110). Interestingly, Trp and Kyn accumulation was specific to classical and mesenchymal GBM subtypes, whereas KA accumulation was only evident in the proneural subtype.…”