IDO2 is critical for IDO1-mediated T-cell regulation and exerts a non-redundant function in inflammation

The exploitation of enzyme-based cancer immunotherapy

Cancer immunotherapy utilizes the immune system and its wide-ranging components to deliver anti-tumor responses. In immune escape mechanisms, tumor microenvironment-associated soluble factors and cell surface-bound molecules are mainly accountable for the dysfunctional activity of tumor-specific CD8⁺ T cells, natural killer (NK) cells, tumor associated macrophages (TAMs) and stromal cells. The myeloid-derived suppressor cells (MDSCs) and Foxp3⁺ regulatory T cells (Tregs), are also key tumor-promoting immune cells. These potent immunosuppressive networks avert tumor rejection at various stages, affecting immunotherapies' outcomes. Numerous clinical trials have elucidated that disruption of immunosuppression could be achieved via checkpoint inhibitors. Another approach utilizes enzymes that can restore the body's potential to counter cancer by triggering the immune system inhibited by the tumor microenvironment. These immunotherapeutic enzymes can catalyze an immunostimulatory signal and modulate the tumor microenvironment via effector molecules. Herein, we have discussed the immuno-metabolic roles of various enzymes like ATP-dephosphorylating ectoenzymes, inducible Nitric Oxide Synthase, phenylamine, tryptophan, and arginine catabolizing enzymes in cancer immunotherapy. Understanding the detailed molecular mechanisms of the enzymes involved in modulating the tumor microenvironment may help find new opportunities for cancer therapeutics.

Indoleamine 2,3-dioxygenase 2 immunohistochemical expression in medullary thyroid carcinoma: implications in prognosis and immunomodulatory effects

BACKGROUND

The linkage between IDO2 expression and cancer progression is still unclear, particularly in medullary thyroid carcinoma (MTC). Our purpose is to unveil the potential correlations between IDO2 status, clinical-pathological parameters, patients' prognosis, and the possible immunomodulatory functions in MTC.

METHODS

Immunohistochemical expression levels of IDO2 were evaluated in the resected MTC surgical specimens and corresponding lymph nodes. CD4 + T cell infiltration was also evaluated by immunohistochemical analysis in the MTC tissues. The association of the IDO2 expression level with clinicopathologic characteristics, overall survival (OS)/recurrence-free survival (RFS), and CD4 + T cell infiltration were retrospectively investigated.

RESULTS

High expression of IDO2 is closely associated with more aggressive clinicopathological features, such as multifocality, ETE, a higher pT stage and especially a higher pN stage. Moreover, a significant difference in RFS was observed between the IDO2-high and IDO2-low groups. IDO2 expression of lymph node tissues was significantly related to the metastasis status. Furthermore, we found that IDO2 expression is negatively correlated with CD4 + T cell infiltrations in MTC tissues.

CONCLUSION

The expression level of IDO2 is associated with aggressive characteristics and is predictive of poor prognosis in patients with MTC. Also, an interesting observation is that IDO2 involvement in MTC showed a moderate sexual dimorphism, of which female patients tend to be more affected by IDO2 status. Moreover, our results showed the potential immunomodulatory functions of IDO2. The close relationship between IDO2 and CD4 + T cell infiltration in the MTC microenvironment, together with its potential prognostic implications, makes it possible for IDO2 to serve as an alternative drug target in cancer immunotherapy and as a new prognostic tool.

Investigating the effects of IDO1, PTGS2, and TGF-β1 overexpression on immunomodulatory properties of hTERT-MSCs and their extracellular vesicles

The therapeutic potential of mesenchymal stem cells (MSCs) is out of the question. Yet, recent drawbacks have resulted in a strategic shift towards the application of MSC-derived cell-free products such as extracellular vesicles (EVs). Recent reports revealed that functional properties of MSCs, including EV secretion patterns, correlate with microenvironmental cues. These findings highlight the urgent need for defining the optimal circumstances for EV preparation. Considering the limitations of primary cells, we employed immortalized cells as an alternative source to prepare therapeutically sufficient EV numbers. Herein, the effects of different conditional environments are explored on human TERT-immortalized MSCs (hTERT-MSCs). The latter were transduced to overexpress IDO1, PTGS2, and TGF-β1 transgenes either alone or in combination, and their immunomodulatory properties were analyzed thereafter. Likewise, EVs derived from these various MSCs were extensively characterized. hTERT-MSCs-IDO1 exerted superior inhibitory effects on lymphocytes, significantly more than hTERT-MSCs-IFN-γ. As such, IDO1 overexpression promoted the immunomodulatory properties of such enriched EVs. Considering the limitations of cell therapy like tumor formation and possible immune responses in the host, the results presented herein might be considered as a feasible model for the induction of immunomodulation in off-the-shelf and cell-free therapeutics, especially for autoimmune diseases.

The ups, downs and new trends of IDO1 inhibitors

Cancer immunotherapy has become an emerging driving force in the development of innovative strategies to fight against cancer. Despite the significant clinical benefits that many cancer patients have gained, the generally average response rate of ~ 20% is far behind the expectation for immune checkpoint inhibitors (ICIs). Combination of ICIs with indoleamine 2,3-dioxygenase-1 (IDO1) inhibitors is considered as an alternative solution and has proved effective in tremendous preclinical studies. However, the failure of phase III ECHO-301/KEYNOTE-252 trial seriously dampened the enthusiasm on the rationality of IDO1-targeting strategy. Fortunately, in spite of the ups and downs in the developmental journey of IDO1 inhibitors, multiple new approaches have been proposed to bridge the gap between lab to the clinic. Here, we review the recent advances in the development of small molecule inhibitors targeting IDO1 especially the new trend of IDO1 inhibitors after ECHO-301 clinical trials, including dual or pan-inhibitors targeting IDO1 and TDO or IDO2, apo-IDO1 inhibitors, IDO1 PROTACs, as well as other IDO1 inhibitors.

The emerging roles of IDO2 in cancer and its potential as a therapeutic target

During the past decades, tryptophan metabolism disorder was discovered to play a vital and complex role in the development of cancer. Indoleamine 2,3-dioxygenase 2 (IDO2) is one of the initial and rate-limiting enzymes of the kynurenine pathway of tryptophan catabolism. Increasing evidence indicates that IDO2 is upregulated in some tumors and plays a role in the development of cancer. In spite of the growing body of research, few reviews focused on the role of IDO2 in cancer. Here, we review the emerging knowledge on the roles of IDO2 in cancer and its potential as a therapeutic target. Firstly, the main biological features and regulatory mechanisms are reviewed, after which we focus on the expression and roles of IDO2 in cancer. Finally, we discuss the potential of IDO2 as a therapeutic target for cancer treatment.

Deletion of indoleamine 2,3 dioxygenase (Ido)1 but not Ido2 exacerbates disease symptoms of MOG35-55-induced experimental autoimmune encephalomyelitis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system (CNS) with pathological features of inflammation, demyelination, and neurodegeneration. Several lines of evidence suggest that the enzymes indoleamine 2,3-dioxygenase (Ido)1 and/or Ido2 influences susceptibility to autoimmune diseases. Deletion of Ido1 exacerbates experimental autoimmune encephalomyelitis (EAE) an animal model of MS. However, no data exist on the role of Ido2 in the pathogenesis of EAE. We investigated whether deletion of Ido2 affected the pathogenesis of EAE. Temporal expression of interferon gamma (Ifng), Ido1 variants, Ido2 variants, as well as genes encoding enzymes of the kynurenine pathway in the spleen and spinal cord of C57BL/6 mice with or without EAE were determined by RT-qPCR. Moreover, EAE was induced in C57BL/6, two Ido1 knockout strains (Ido1KO and Ido1TK) and one Ido2 knockout mouse strain (Ido2-/-) and disease monitored by clinical scores and weight change. Performance on the rotarod was performed on days 0, 5, 10 and 15 post induction. The extent of demyelination in the spinal cord was determined after staining with Oil red O. The development of EAE altered gene expression in both the spleen and spinal cord. Deletion of Ido1 exacerbated the clinical symptoms of EAE. In stark contrast, EAE in Ido2-/- mice did not differ clinically or histologically from control mice. These results confirm a protective role for Ido1, on the pathogenesis of MOG35-55-induced EAE in C57BL/6J mice.