Immune Checkpoint Inhibition Overcomes ADCP-Induced Immunosuppression by Macrophages.

Antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) critically contribute to the efficacy of anti-tumor therapeutic antibodies. We report here an unexpected finding that macrophages after ADCP inhibit NK cell-mediated ADCC and T cell-mediated cytotoxicity in breast cancers and lymphomas. Mechanistically, AIM2 is recruited to the phagosomes by FcγR signaling following ADCP and activated by sensing the phagocytosed tumor DNAs through the disrupted phagosomal membrane, which subsequently upregulates PD-L1 and IDO and causes immunosuppression. Combined treatment with anti-HER2 antibody and inhibitors of PD-L1 and IDO enhances anti-tumor immunity and anti-HER2 therapeutic efficacy in mouse models. Furthermore, neoadjuvant trastuzumab therapy significantly upregulates PD-L1 and IDO in the tumor-associated macrophages (TAMs) of HER2+ breast cancer patients, correlating with poor trastuzumab response. Collectively, our findings unveil a deleterious role of ADCP macrophages in cancer immunosuppression and suggest that therapeutic antibody plus immune checkpoint blockade may provide synergistic effects in cancer treatment.

Indoleamine 2,3-dioxygenase 1 activation in mature cDC1 promotes tolerogenic education of inflammatory cDC2 via metabolic communication.

Conventional dendritic cells (cDCs), cDC1 and cDC2, act both to initiate immunity and maintain self-tolerance. The tryptophan metabolic enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is used by cDCs in maintaining tolerance, but its role in different subsets remains unclear. At homeostasis, only mature CCR7+ cDC1 expressed IDO1 that was dependent on IRF8. Lipopolysaccharide treatment induced maturation and IDO1-dependent tolerogenic activity in isolated immature cDC1, but not isolated cDC2. However, both human and mouse cDC2 could induce IDO1 and acquire tolerogenic function when co-cultured with mature cDC1 through the action of cDC1-derived l-kynurenine. Accordingly, cDC1-specific inactivation of IDO1 in vivo exacerbated disease in experimental autoimmune encephalomyelitis. This study identifies a previously unrecognized metabolic communication in which IDO1-expressing cDC1 cells extend their immunoregulatory capacity to the cDC2 subset through their production of tryptophan metabolite l-kynurenine. This metabolic axis represents a potential therapeutic target in treating autoimmune demyelinating diseases.

Indoleamine 2,3-dioxygenase 1 is essential for sustaining durable antibody responses.

Humoral immunity is essential for protection against pathogens, emphasized by the prevention of 2-3 million deaths worldwide annually by childhood immunizations. Long-term protective immunity is dependent on the continual production of neutralizing antibodies by the subset of long-lived plasma cells (LLPCs). LLPCs are not intrinsically long-lived, but require interaction with LLPC niche stromal cells for survival. However, it remains unclear which and how these interactions sustain LLPC survival and long-term humoral immunity. We now have found that the immunosuppressive enzyme indoleamine 2,3- dioxygenase 1 (IDO1) is required to sustain antibody responses and LLPC survival. Activation of IDO1 occurs upon the engagement of CD80/CD86 on the niche dendritic cells by CD28 on LLPC. Kynurenine, the product of IDO1 catabolism, activates the aryl hydrocarbon receptor in LLPC, reinforcing CD28 expression and survival signaling. These findings expand the immune function of IDO1 and uncover a novel pathway for sustaining LLPC survival and humoral immunity.

Inhibition of the BTK-IDO-mTOR axis promotes differentiation of monocyte-lineage dendritic cells and enhances anti-tumor T cell immunity.

Monocytic-lineage inflammatory Ly6c+CD103+ dendritic cells (DCs) promote antitumor immunity, but these DCs are infrequent in tumors, even upon chemotherapy. Here, we examined how targeting pathways that inhibit the differentiation of inflammatory myeloid cells affect antitumor immunity. Pharmacologic inhibition of Bruton's tyrosine kinase (BTK) and the tryptophan-degrading enzyme indoleamine 2,3-dioxygenase (IDO) or deletion of Btk or Ido1 allowed robust differentiation of inflammatory Ly6c+CD103+ DCs during chemotherapy, promoting antitumor T cell responses and inhibiting tumor growth. Immature Ly6c+c-kit+ precursor cells had epigenetic profiles similar to conventional DC precursors; deletion of Btk or Ido1 promoted differentiation of these cells. Mechanistically, a BTK-IDO axis inhibited a tryptophan-sensitive differentiation pathway driven by GATOR2 and mTORC1, and disruption of the GATOR2 in monocyte-lineage precursors prevented differentiation into inflammatory DCs in vivo. IDO-expressing DCs and monocytic cells were present across a range of human tumors. Thus, a BTK-IDO axis represses differentiation of inflammatory DCs during chemotherapy, with implications for targeted therapies.

Kynurenine importation by SLC7A11 propagates anti-ferroptotic signaling.

IDO1 oxidizes tryptophan (TRP) to generate kynurenine (KYN), the substrate for 1-carbon and NAD metabolism, and is implicated in pro-cancer pathophysiology and infection biology. However, the mechanistic relationships between IDO1 in amino acid depletion versus product generation have remained a longstanding mystery. We found an unrecognized link between IDO1 and cell survival mediated by KYN that serves as the source for molecules that inhibit ferroptotic cell death. We show that this effect requires KYN export from IDO1-expressing cells, which is then available for non-IDO1-expressing cells via SLC7A11, the central transporter involved in ferroptosis suppression. Whether inside the "producer" IDO1+ cell or the "receiver" cell, KYN is converted into downstream metabolites, suppressing ferroptosis by ROS scavenging and activating an NRF2-dependent, AHR-independent cell-protective pathway, including SLC7A11, propagating anti-ferroptotic signaling. IDO1, therefore, controls a multi-pronged protection pathway from ferroptotic cell death, underscoring the need to re-evaluate the use of IDO1 inhibitors in cancer treatment.

Immune-regulated IDO1-dependent tryptophan metabolism is source of one-carbon units for pancreatic cancer and stellate cells.

Cancer cells adapt their metabolism to support elevated energetic and anabolic demands of proliferation. Folate-dependent one-carbon metabolism is a critical metabolic process underpinning cellular proliferation supplying carbons for the synthesis of nucleotides incorporated into DNA and RNA. Recent research has focused on the nutrients that supply one-carbons to the folate cycle, particularly serine. Tryptophan is a theoretical source of one-carbon units through metabolism by IDO1, an enzyme intensively investigated in the context of tumor immune evasion. Using in vitro and in vivo pancreatic cancer models, we show that IDO1 expression is highly context dependent, influenced by attachment-independent growth and the canonical activator IFNγ. In IDO1-expressing cancer cells, tryptophan is a bona fide one-carbon donor for purine nucleotide synthesis in vitro and in vivo. Furthermore, we show that cancer cells release tryptophan-derived formate, which can be used by pancreatic stellate cells to support purine nucleotide synthesis.

A Relay Pathway between Arginine and Tryptophan Metabolism Confers Immunosuppressive Properties on Dendritic Cells.

Arginase 1 (Arg1) and indoleamine 2,3-dioxygenase 1 (IDO1) are immunoregulatory enzymes catalyzing the degradation of l-arginine and l-tryptophan, respectively, resulting in local amino acid deprivation. In addition, unlike Arg1, IDO1 is also endowed with non-enzymatic signaling activity in dendritic cells (DCs). Despite considerable knowledge of their individual biology, no integrated functions of Arg1 and IDO1 have been reported yet. We found that IDO1 phosphorylation and consequent activation of IDO1 signaling in DCs was strictly dependent on prior expression of Arg1 and Arg1-dependent production of polyamines. Polyamines, either produced by DCs or released by bystander Arg1+ myeloid-derived suppressor cells, conditioned DCs toward an IDO1-dependent, immunosuppressive phenotype via activation of the Src kinase, which has IDO1-phosphorylating activity. Thus our data indicate that Arg1 and IDO1 are linked by an entwined pathway in immunometabolism and that their joint modulation could represent an important target for effective immunotherapy in several disease settings.

IDO1 promotes CSFV replication by mediating tryptophan metabolism to inhibit NF-κB signaling.

Tryptophan metabolism plays a crucial role in facilitating various cellular processes essential for maintaining normal cellular function. Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the conversion of tryptophan (Trp) into kynurenine (Kyn), thereby initiating the degradation of Trp. The resulting Kyn metabolites have been implicated in the modulation of immune responses. Currently, the role of IDO1-mediated tryptophan metabolism in the process of viral infection remains relatively unknown. In this study, we discovered that classical swine fever virus (CSFV) infection of PK-15 cells can induce the expression of IDO1, thereby promoting tryptophan metabolism. IDO1 can negatively regulate the NF-κB signaling by mediating tryptophan metabolism, thereby facilitating CSFV replication. We found that silencing the IDO1 gene enhances the expression of IFN-α, IFN-ß, and IL-6 by activating the NF-κB signaling pathway. Furthermore, our observations indicate that both silencing the IDO1 gene and administering exogenous tryptophan can inhibit CSFV replication by counteracting the cellular autophagy induced by Rapamycin. This study reveals a novel mechanism of IDO1-mediated tryptophan metabolism in CSFV infection, providing new insights and a theoretical basis for the treatment and control of CSFV.IMPORTANCEIt is well known that due to the widespread use of vaccines, the prevalence of classical swine fever (CSF) is shifting towards atypical and invisible infections. CSF can disrupt host metabolism, leading to persistent immune suppression in the host and causing significant harm when co-infected with other diseases. Changes in the host's metabolic profiles, such as increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, can also influence virus replication. Mammals utilize various pathways to modulate immune responses through amino acid utilization, including increased catabolic metabolism of amino acids and the production of immunoregulatory metabolites and their derivatives, thereby limiting viral replication. Therefore, this study proposes that targeting the modulation of tryptophan metabolism may represent an effective approach to control the progression of CSF.

Single-cell RNA-sequencing of human eosinophils in allergic inflammation in the esophagus.

BACKGROUND: Eosinophils are elusive cells involved in allergic inflammation. Single-cell RNA-sequencing (scRNA-seq) is an emerging approach to deeply characterize cellular properties, heterogeneity, and functionality. OBJECTIVES: We sought to comprehensively characterize the transcriptome and biological functions of human eosinophils at a site of severe allergic inflammation in the esophagus (ie, eosinophilic esophagitis [EoE]). METHODS: We employed a gravity-based scRNA-seq methodology to sequence blood eosinophils from patients with EoE and control individuals compared to a reanalyzed public scRNA-seq dataset of human esophageal eosinophils of EoE patients. We used flow cytometry, immunostaining, and a stimulation assay to verify mRNA findings. RESULTS: In total, scRNA-seq was obtained from 586 eosinophils (188 from blood [n = 6 individuals] and 398 from esophagus [n = 6 individuals]). The esophageal eosinophils were composed of a population of activated eosinophils (enriched in 659 genes compared with peripheral blood-associated eosinophils) and a small population of eosinophils resembling peripheral blood eosinophils (enriched in 62 genes compared with esophageal eosinophils). Esophageal eosinophils expressed genes involved in sensing and responding to diverse stimuli, most notably IFN-γ, IL-10, histamine and leukotrienes, and succinate. Esophageal eosinophils were most distinguished from other esophageal populations by gene expression of the receptors CCR3, HRH4, SUCNR1, and VSTM1; transcription factors CEBPE, OLIG1, and OLIG2; protease PRSS33; and the hallmark eosinophil gene CLC. A web of bidirectional eosinophil interactions with other esophageal populations was derived. Comparing esophageal eosinophils and mast cells revealed that esophageal eosinophils expressed genes involved in DNAX-activation protein-12 (also known as TYROBP) interactions, IgG receptor-triggered events, immunoregulation, and IL-10 signaling. CONCLUSIONS: In EoE, esophageal eosinophils exist as 2 populations, a minority population resembling blood eosinophils and the other population characterized by high de novo transcription of diverse sensing receptors and inflammatory mediators readying them to potentially intersect with diverse cell types.

Effects of E2 on the IDO1-mediated metabolic KYN pathway in OVX female mice.

The aim of this study was to investigate the role of 17ß-estradiol (E2)-mediated oestrogen receptor (ER) in modulating the depressive-like behaviours of ovariectomy (OVX) mice and the associated mechanisms. E2 was administrated in OVX mice. The behaviour and physiological changes of OVX mice including immobility time in tail suspension test (TST) and forced swimming test (FST), levels of serum E2, inflammatory mediators, oxidative stress factors, indoleamine2,3-dioxygenase 1 (IDO1) and the neurotransmitters mediated by IDO1 activation were then recorded. Cell injury models established by lipopolysaccharide (LPS) or H2O2 stimulation in HT22 and BV2 cells were employed to further explore the mechanisms of E2's function. E2 treatment improved OVX-induced increase of immobility time in FST and TST. Meanwhile, E2 ameliorated the changes of inflammatory factors (NF-κB, TNF-α and IL-6), IDO1, IDO1-mediated TRP/KYN pathway and oxidative stress factors (iNOS, MDA, GSH and SOD) in the hippocampus of OVX mice. Interestingly, ERß inhibitor abolished E2's inhibitory effects on the inflammation and IDO1-mediated TRP/KYN pathway; ERß inhibitor also abolished E2's anti-oxidative stress effect. In cell experiments, ERß small interfering RNA (siRNA) pretreatment reversed E2's anti-inflammatory effect on LPS-treated HT22 and BV2 cells and E2's inhibitory effect on IDO1 expression in LPS-treated BV2 cells. ERß siRNA pretreatment also reversed E2's anti-oxidation effect on H2O2-treated HT22 cells. E2 exert the antidepressant function in OVX mice via ERß-modulated suppression of NF-κB-mediated inflammatory pathway, oxidative stress factors and IDO1-mediated TRP/KYN pathway in the hippocampus.

Indoleamine dioxygenase and tryptophan dioxygenase activities are regulated through control of cell heme allocation by nitric oxide.

Indoleamine-2, 3-dioxygenase (IDO1) and Tryptophan-2, 3-dioxygenase (TDO) catalyze the conversion of L-tryptophan to N-formyl-kynurenine and thus play primary roles in metabolism, inflammation, and tumor immune surveillance. Because their activities depend on their heme contents, which vary in biological settings and go up or down in a dynamic manner, we studied how their heme levels may be impacted by nitric oxide (NO) in mammalian cells. We utilized cells expressing TDO or IDO1 either naturally or via transfection and determined their activities, heme contents, and expression levels as a function of NO exposure. We found NO has a bimodal effect: a narrow range of low NO exposure promoted cells to allocate heme into the heme-free TDO and IDO1 populations and consequently boosted their heme contents and activities 4- to 6-fold, while beyond this range the NO exposure transitioned to have a negative impact on their heme contents and activities. NO did not alter dioxygenase protein expression levels, and its bimodal impact was observed when NO was released by a chemical donor or was generated naturally by immune-stimulated macrophage cells. NO-driven heme allocations to IDO1 and TDO required participation of a GAPDH-heme complex and for IDO1 required chaperone Hsp90 activity. Thus, cells can up- or downregulate their IDO1 and TDO activities through a bimodal control of heme allocation by NO. This mechanism has important biomedical implications and helps explain why the IDO1 and TDO activities in animals go up and down in response to immune stimulation.

IL4i1 and IDO1: Oxidases that control a tryptophan metabolic nexus in cancer.

Regulated tryptophan metabolism by immune cells has been associated with the promotion of tolerance and poor outcomes in cancer. The main focus of research has centered on local tryptophan depletion by IDO1, an intracellular heme-dependent oxidase that converts tryptophan to formyl-kynurenine. This is the first step of a complex pathway supplying metabolites for de novo NAD+ biosynthesis, 1-carbon metabolism, and a myriad of kynurenine derivatives of which several act as agonists of the arylhydrocarbon receptor (AhR). Thus, cells that express IDO1 deplete tryptophan while generating downstream metabolites. We now know that another enzyme, the secreted L-amino acid oxidase IL4i1 also generates bioactive metabolites from tryptophan. In tumor microenvironments, IL4i1 and IDO1 have overlapping expression patterns, especially in myeloid cells, suggesting the two enzymes control a network of tryptophan-specific metabolic events. New findings about IL4i1 and IDO1 have shown that both enzymes generate a suite of metabolites that suppress oxidative cell death ferroptosis. Thus, within inflammatory environments, IL4i1 and IDO1 simultaneously control essential amino acid depletion, AhR activation, suppression of ferroptosis, and biosynthesis of key metabolic intermediates. Here, we summarize the recent advances in this field, focusing on IDO1 and IL4i1 in cancer. We speculate that while inhibition of IDO1 remains a viable adjuvant therapy for solid tumors, the overlapping effects of IL4i1 must be accounted for, as potentially both enzymes may need to be inhibited at the same time to produce positive effects in cancer therapy.

Pathomic model based on histopathological features and machine learning to predict IDO1 status and its association with breast cancer prognosis.

PURPOSE: To establish a pathomic model using histopathological image features for predicting indoleamine 2,3-dioxygenase 1 (IDO1) status and its relationship with overall survival (OS) in breast cancer. METHODS: A pathomic model was constructed using machine learning and histopathological images obtained from The Cancer Genome Atlas database to predict IDO1 expression. The model performance was evaluated based on the area under the curve, calibration curve, and decision curve analysis (DCA). Prediction scores (PSes) were generated from the model and applied to divide the patients into two groups. Survival outcomes, gene set enrichment, immune microenvironment, and tumor mutations were assessed between the two groups. RESULTS: Survival analysis followed by multivariate correction revealed that high IDO1 is a protective factor for OS. Further, the model was calibrated, and it exhibited good discrimination. Additionally, the DCA showed that the proposed model provided a good clinical net benefit. The Kaplan-Meier analysis revealed a positive correlation between high PS and improved OS. Univariate and multivariate Cox regression analyses demonstrated that PS is an independent protective factor for OS. Moreover, differentially expressed genes were enriched in various essential biological processes, including extracellular matrix receptor interaction, angiogenesis, transforming growth factor ß signaling, epithelial mesenchymal transition, cell junction, tryptophan metabolism, and heme metabolic processes. PS was positively correlated with M1 macrophages, CD8 + T cells, T follicular helper cells, and tumor mutational burden. CONCLUSION: These results indicate the potential ability of the proposed pathomic model to predict IDO1 status and the OS of breast cancer patients.

Expression and Prognostic Significance of LAG-3, TIGIT, VISTA, and IDO1 in Endometrial Serous Carcinoma.

Endometrial serous carcinoma (ESC) is an uncommon, aggressive type of endometrial cancer. While immune checkpoint blockade has emerged as a promising treatment option for endometrial carcinomas, research on the expression of immune checkpoints that could serve as prospective immunotherapy targets in ESC is limited. We examined the prevalence and prognostic value of lymphocyte-activation gene 3 (LAG-3), T-cell immunoglobulin and ITIM domain (TIGIT), V-domain immunoglobulin (Ig) suppressor of T-cell activation (VISTA), and indoleamine 2,3-dioxygenase 1 (IOD1) in 94 cases of ESC and correlated their expression with CD8+ and FOXP3+ tumor-infiltrating lymphocytes (TILs). We observed a positive correlation among LAG-3, TIGIT, and VISTA expressed on immune cells, and among these markers and CD8+ and FOXP3+ TIL densities. In Kaplan-Meier survival analysis, tumors with high levels of LAG-3 and TIGIT expression had better progression-free survival (PFS) and overall survival (OS) than those with lower levels of expression (LAG-3: PFS, P = .03, OS, P = .04; TIGIT: PFS, P = .01, OS, P = .009). In multivariate analysis, only high TIGIT expression was of independent prognostic value for better OS. VISTA expression in immune or tumor cells, and IDO1 expression in tumor cells, did not show a significant association with survival. Our data indicate that LAG-3, TIGIT, and VISTA immune checkpoints have roles in the microenvironment of ESC, and their expression patterns highlight the complex interactions among the different components of this system. High levels of these markers, together with high CD8+ TIL, suggest the potential immunogenicity of a subset of these tumors. Further studies are needed to elucidate the roles of various immune components in the ESC microenvironment and their association with intrinsic tumor properties.

Kynurenine in IDO1high cancer cell-derived extracellular vesicles promotes angiogenesis by inducing endothelial mitophagy in ovarian cancer.

BACKGROUND: Mitophagy, a prominent cellular homeostasis process, has been implicated in modulating endothelial cell function. Emerging evidence suggests that extracellular vesicles (EVs) participate in intercellular communication, which could modulate tumor angiogenesis, a hallmark of ovarian cancer (OC) progression. However, the underlying mechanisms through how EVs regulate endothelial mitophagy associated with tumor angiogenesis during OC development remain obscure. METHODS: The effect of cancer cell-derived EVs on endothelial mitophagy and its correlation with tumor angiogenesis and OC development were explored by in vitro and in vivo experiments. Multi-omics integration analysis was employed to identify potential regulatory mechanisms of cancer cell-derived EVs on endothelial mitophagy, which is involved in tumor angiogenesis associated with OC development. These insights were then further corroborated through additional experiments. An orthotopic OC mouse model was constructed to assess the antiangiogenic and therapeutic potential of the Indoleamine 2,3 dioxygenase-1 (IDO1) inhibitor. RESULTS: Cancer cell-derived EVs promoted tumor angiogenesis via the activation of endothelial mitophagy, contributing to the growth and metastasis of OC. The aberrantly high expression of IDO1 mediated abnormal tryptophan metabolism in cancer cells and promoted the secretion of L-kynurenine (L-kyn)-enriched EVs, with associated high levels of L-kyn in EVs isolated from both the tumor tissues and patient plasma in OC. EVs derived from IDO1high ovarian cancer cells elevated nicotinamide adenine dinucleotide (NAD +) levels in endothelial cells via delivering L-kyn. Besides, IDO1high ovarian cancer cell-derived EVs upregulated sirt3 expression in endothelial cells by increasing acetylation modification. These findings are crucial for promoting endothelial mitophagy correlated with tumor angiogenesis. Notably, both endothelial mitophagy and tumor angiogenesis could be suppressed by the IDO1 inhibitor in the orthotopic OC mouse model. CONCLUSIONS: Together, our findings unveil a mechanism of mitophagy in OC angiogenesis and indicate the clinical relevance of EV enriched L-kyn as a potential biomarker for tumorigenesis and progression. Additionally, IDO1 inhibitors might become an alternative option for OC adjuvant therapy.

Type-II IFN inhibits SARS-CoV-2 replication in human lung epithelial cells and ex vivo human lung tissues through indoleamine 2,3-dioxygenase-mediated pathways.

Interferons (IFNs) are critical for immune defense against pathogens. While type-I and -III IFNs have been reported to inhibit SARS-CoV-2 replication, the antiviral effect and mechanism of type-II IFN against SARS-CoV-2 remain largely unknown. Here, we evaluate the antiviral activity of type-II IFN (IFNγ) using human lung epithelial cells (Calu3) and ex vivo human lung tissues. In this study, we found that IFNγ suppresses SARS-CoV-2 replication in both Calu3 cells and ex vivo human lung tissues. Moreover, IFNγ treatment does not significantly modulate the expression of SARS-CoV-2 entry-related factors and induces a similar level of pro-inflammatory response in human lung tissues when compared with IFNß treatment. Mechanistically, we show that overexpression of indoleamine 2,3-dioxygenase 1 (IDO1), which is most profoundly induced by IFNγ, substantially restricts the replication of ancestral SARS-CoV-2 and the Alpha and Delta variants. Meanwhile, loss-of-function study reveals that IDO1 knockdown restores SARS-CoV-2 replication restricted by IFNγ in Calu3 cells. We further found that the treatment of l-tryptophan, a substrate of IDO1, partially rescues the IFNγ-mediated inhibitory effect on SARS-CoV-2 replication in both Calu3 cells and ex vivo human lung tissues. Collectively, these results suggest that type-II IFN potently inhibits SARS-CoV-2 replication through IDO1-mediated antiviral response.

AT-0174, a novel dual IDO1/TDO2 enzyme inhibitor, synergises with temozolomide to improve survival in an orthotopic mouse model of glioblastoma.

BACKGROUND: Glioblastoma is an aggressive brain cancer, usually of unknown etiology, and with a very poor prognosis. Survival from diagnosis averages only 3 months if left untreated and this only increases to 12-15 months upon treatment. Treatment options are currently limited and typically comprise radiotherapy plus a course of the DNA-alkylating chemotherapeutic temozolomide. Unfortunately, the disease invariably relapses after several months of treatment with temozolomide, due to the development of resistance to the drug. Increased local tryptophan metabolism is a feature of many solid malignant tumours through increased expression of tryptophan metabolising enzymes. Glioblastomas are notable for featuring increased expression of the tryptophan catabolizing enzymes indole-2,3-dioxygenase-1 (IDO1), and especially tryptophan-2,3-dioxygenase-2 (TDO2). Increased IDO1 and TDO2 activity is known to suppress the cytotoxic T cell response to tumour cells, and this has led to the proposal that the IDO1 and TDO2 enzymes represent promising immuno-oncology targets. In addition to immune modulation, however, recent studies have also identified the activity of these enzymes is important in the development of resistance to chemotherapeutic agents. METHODS: In the current study, the efficacy of a novel dual inhibitor of IDO1 and TDO2, AT-0174, was assessed in an orthotopic mouse model of glioblastoma. C57BL/6J mice were stereotaxically implanted with GL261(luc2) cells into the striatum and then administered either vehicle control, temozolomide (8 mg/kg IP; five 8-day cycles of treatment every 2 days), AT-0174 (120 mg/kg/day PO) or both temozolomide + AT-0174, all given from day 7 after implantation. RESULTS: Temozolomide decreased tumour growth and improved median survival but increased the infiltration of CD4+ Tregs. AT-0174 had no significant effect on tumour growth or survival when given alone, but provided clear synergy in combination with temozolomide, further decreasing tumour growth and significantly improving survival, as well as elevating CD8+ T cell expression and decreasing CD4+ Treg infiltration. CONCLUSION: AT-0174 exhibited an ideal profile for adjunct treatment of glioblastomas with the first-line chemotherapeutic drug temozolomide to prevent development of CD4+ Treg-mediated chemoresistance.

Epacadostat plus pembrolizumab versus placebo plus pembrolizumab for advanced urothelial carcinoma: results from the randomized phase III ECHO-303/KEYNOTE-698 study.

BACKGROUND: Indoleamine 2,3-dioxygenase 1 (IDO1) levels correlate with poor outcomes in urothelial carcinoma (UC). IDO1 and programmed death-ligand 1 (PD-L1) are often co-expressed. Epacadostat is a potent and highly selective inhibitor of IDO1. In a subgroup analysis of patients with advanced UC participating in a phase I/II study, epacadostat-pembrolizumab treatment produced an objective response rate (ORR) of 35%. METHODS: ECHO-303/KEYNOTE-698 was a double-blinded, randomized phase III study of adults with metastatic or unresectable locally advanced UC with recurrence or progression following first-line platinum-based chemotherapy. Participants were randomized to epacadostat 100 mg twice daily (BID) plus pembrolizumab or placebo plus pembrolizumab until completion of 35 pembrolizumab infusions, disease progression, or unacceptable toxicity. The primary endpoint was investigator-assessed ORR per Response Evaluation Criteria in Solid Tumors version 1.1. RESULTS: Target enrollment was 648 patients; enrollment was halted early based on efficacy results from the phase III ECHO-301/KEYNOTE-252 study in metastatic melanoma. Forty-two patients were randomized to each treatment arm. Median duration of follow-up was 62 days in each arm. The investigator-assessed ORR (unconfirmed) was 26.2% (95% CI 16.35-48.11) for epacadostat plus pembrolizumab and 11.9% (95% CI 4.67-29.50) for placebo plus pembrolizumab. Two complete responses were reported, both in the placebo-plus-pembrolizumab arm. Circulating kynurenine levels increased from C1D1 to C2D1 in the placebo-plus-pembrolizumab arm and numerically decreased in the epacadostat-plus-pembrolizumab arm. The safety profile of epacadostat plus pembrolizumab was similar to that of pembrolizumab monotherapy, although a numerically greater proportion of patients in the combination vs. control arm experienced treatment-related grade ≥ 3 adverse events (16.7% vs. 7.3%). One patient in each arm died due to cardiovascular events, which were not deemed drug-related. No new safety concerns were identified for either agent. CONCLUSIONS: Epacadostat plus pembrolizumab demonstrated anti-tumor activity and was generally tolerable as second-line treatment of patients with unresectable locally advanced or recurrent/progressive metastatic UC. Epacadostat 100 mg BID, when administered with pembrolizumab, did not normalize circulating kynurenine in most patients. Further study of combined IDO1/PD-L1 inhibition in this patient population, particularly with epacadostat doses that result in durable normalization of circulating kynurenine, may be warranted. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03374488. Registered 12/15/2017.

A randomized, open-label, phase 3 trial of pembrolizumab plus epacadostat versus sunitinib or pazopanib as first-line treatment for metastatic renal cell carcinoma (KEYNOTE-679/ECHO-302).

BACKGROUND: Immunotherapy-based combinations have emerged as standard therapies for patients with metastatic renal cell carcinoma (mRCC). Pembrolizumab, a PD-1 inhibitor, combined with epacadostat, an indoleamine 2,3-deoxygenase 1 selective inhibitor, demonstrated promising antitumor activity in a phase 1 study in advanced solid tumors, including mRCC. METHODS: KEYNOTE-679/ECHO-302 was a randomized, open-label, parallel-group, multicenter, phase 3 study (NCT03260894) that compared pembrolizumab plus epacadostat with sunitinib or pazopanib as first-line treatment for mRCC. Eligible patients had histologically confirmed locally advanced or metastatic clear cell RCC and had not received systemic therapy. Patients were randomly assigned 1:1 to pembrolizumab 200 mg IV every 3 weeks plus epacadostat 100 mg orally twice daily versus sunitinib 50 mg orally once daily (4 weeks on treatment followed by 2 weeks off treatment) or pazopanib 800 mg orally once daily. Original dual primary end points were progression-free survival and overall survival. Enrollment was stopped when a phase 3 study in melanoma of pembrolizumab plus epacadostat compared with pembrolizumab monotherapy did not meet its primary end point. This protocol was amended, and primary end point was changed to investigator-assessed objective response rate (ORR) per RECIST 1.1. RESULTS: One-hundred-twenty-nine patients were randomly assigned to receive pembrolizumab plus epacadostat (n = 64) or sunitinib/pazopanib (n = 65). Median (range) follow-up, defined as time from randomization to data cutoff, was 10.3 months (2.2-14.3) and 10.3 months (2.7-13.8) in the pembrolizumab plus epacadostat and sunitinib/pazopanib arms, respectively. ORRs were similar between pembrolizumab plus epacadostat (31.3% [95% CI 20.2-44.1] and sunitinib/pazopanib (29.2% [18.6-41.8]). Grade 3-5 treatment-related adverse events occurred in 34.4% and 42.9% of patients in the pembrolizumab plus epacadostat and sunitinib/pazopanib arms, respectively. One patient in the sunitinib/pazopanib arm died of septic shock (not treatment-related). Circulating kynurenine levels decreased in the pembrolizumab plus epacadostat arm, but not to levels observed in healthy subjects. CONCLUSIONS: ORRs were similar between pembrolizumab plus epacadostat and sunitinib/pazopanib as first-line treatment in patients with mRCC. Safety and tolerability appeared similar between treatment arms; no new safety concerns were identified. Antitumor responses observed in patients with RCC receiving pembrolizumab plus epacadostat may be driven primarily by pembrolizumab. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov; NCT03260894 .

Pembrolizumab plus either epacadostat or placebo for cisplatin-ineligible urothelial carcinoma: results from the ECHO-307/KEYNOTE-672 study.

BACKGROUND: Indoleamine 2,3- dioxygenase 1 (IDO1) is an immunosuppressive enzyme that has been correlated with shorter disease-specific survival in patients with urothelial carcinoma (UC). IDO1 may counteract the antitumor effects of immune checkpoint inhibitors. Epacadostat is a potent and highly selective inhibitor of IDO1. In the phase I/II ECHO-202/KEYNOTE-037 study, epacadostat plus pembrolizumab resulted in a preliminary objective response rate (ORR) of 35% in a cohort of patients with advanced UC. METHODS: ECHO-307/KEYNOTE-672 was a double-blinded, randomized, phase III study. Eligible adults had confirmed locally advanced/unresectable or metastatic UC of the urinary tract and were ineligible to receive cisplatin-based chemotherapy. Participants were randomly assigned (1:1) to receive epacadostat (100 mg twice daily) plus pembrolizumab (200 mg every 3 weeks) or placebo plus pembrolizumab for up to 35 pembrolizumab infusions. The primary endpoint was investigator-assessed ORR per Response Evaluation Criteria in Solid Tumors (version 1.1). RESULTS: A total of 93 patients were randomized (epacadostat plus pembrolizumab, n = 44; placebo plus pembrolizumab, n = 49). Enrollment was stopped early due to emerging data from the phase III ECHO-301/KEYNOTE-252 study. The median duration of follow-up was 64 days in both arms. Based on all available data at cutoff, ORR (unconfirmed) was 31.8% (95% CI, 22.46-55.24%) for epacadostat plus pembrolizumab and 24.5% (95% CI, 15.33-43.67%) for placebo plus pembrolizumab. Circulating kynurenine levels numerically increased from C1D1 to C2D1 in the placebo-plus-pembrolizumab arm and decreased in the epacadostat-plus-pembrolizumab arm. Epacadostat-plus-pembrolizumab combination treatment was well tolerated with a safety profile similar to the placebo arm. Treatment discontinuations due to treatment-related adverse events were more frequent with epacadostat (11.6% vs. 4.1%). CONCLUSIONS: Treatment with epacadostat plus pembrolizumab resulted in a similar ORR and safety profile as placebo plus pembrolizumab in cisplatin-ineligible patients with previously untreated locally advanced/unresectable or metastatic UC. At a dose of 100 mg twice daily, epacadostat did not appear to completely normalize circulating kynurenine levels when administered with pembrolizumab. Larger studies with longer follow-up and possibly testing higher doses of epacadostat, potentially in different therapy settings, may be warranted. TRIAL REGISTRATION: ClinicalTrials.gov identifier: NCT03361865, retrospectively registered December 5, 2017.