Immunosuppressive Kynurenine Research Articles

The First Human Application of an F-18-Labeled Tryptophan Analog for PET Imaging of Cancer.

Preclinical studies showed the tryptophan analog PET radiotracer 1-(2-18F-fluoroethyl)-L-tryptophan (18F-FETrp) to accumulate in various tumors, including gliomas, and being metabolized via the immunosuppressive kynurenine pathway. In this first-in-human study, we tested the use 18F-FETrp-PET in patients with neuroendocrine and brain tumors. We applied dynamic brain imaging in patients with gliomas (n = 2) and multi-pass 3D whole-body PET scans in patients with neuroendocrine tumors (n =4). Semiquantitative analysis of organ and tumor tracer uptake was performed using standardized uptake values (SUVs). In addition, organ dosimetry was performed based on extracted time-activity curves and the OLINDA software. Neuroendocrine tumors showed an early peak (10-min post-injection) followed by washout. Both gliomas showed prolonged 18F-FETrp accumulation plateauing around 40 min and showing heterogeneous uptake including non-enhancing tumor regions. Biodistribution showed moderate liver uptake and fast clearance of radioactivity into the urinary bladder; the estimated effective doses were similar to other 18F-labeled radioligands. The study provides proof-of-principle data for the safety and potential clinical value of 18F-FETrp-PET for molecular imaging of human gliomas.

Glutamine metabolism inhibition has dual immunomodulatory and antibacterial activities against Mycobacterium tuberculosis

As one of the most successful human pathogens, Mycobacterium tuberculosis (Mtb) has evolved a diverse array of determinants to subvert host immunity and alter host metabolic patterns. However, the mechanisms of pathogen interference with host metabolism remain poorly understood. Here we show that a glutamine metabolism antagonist, JHU083, inhibits Mtb proliferation in vitro and in vivo. JHU083-treated mice exhibit weight gain, improved survival, a 2.5 log lower lung bacillary burden at 35 days post-infection, and reduced lung pathology. JHU083 treatment also initiates earlier T-cell recruitment, increased proinflammatory myeloid cell infiltration, and a reduced frequency of immunosuppressive myeloid cells when compared to uninfected and rifampin-treated controls. Metabolomic analysis of lungs from JHU083-treated Mtb-infected mice reveals citrulline accumulation, suggesting elevated nitric oxide (NO) synthesis, and lowered levels of quinolinic acid which is derived from the immunosuppressive metabolite kynurenine. JHU083-treated macrophages also produce more NO potentiating their antibacterial activity. When tested in an immunocompromised mouse model of Mtb infection, JHU083 loses its therapeutic efficacy suggesting the drug’s host-directed effects are likely to be predominant. Collectively, these data reveal that JHU083-mediated glutamine metabolism inhibition results in dual antibacterial and host-directed activity against tuberculosis.

The immunomodulatory role of IDO1-Kynurenine-NAD+ pathway in switching cold tumor microenvironment in PDAC.

Pancreatic ductal adenocarcinoma (PDAC) is the most common exocrine tumor of the pancreas characterized by late diagnosis, adverse overall 5-year survival, a higher propensity for metastatic disease, and lack of efficacy of systemic therapy options. These adverse outcomes can be partly attributed to complex tumor microenvironment (TME). Over the past decade, immunotherapy has revolutionized the management of certain cancers; thus far, the immunologically 'non-inflamed' tumor microenvironment in PDACs has proven to be challenging. Indolamine 2,3-dioxygenase 1 (IDO1) is the rate-limiting enzyme in the catabolic pathway of L-Tryptophan, an essential amino acid, that gives rise to the immunosuppressive metabolite Kynurenine. IDO1, Indolamine 2,3-dioxygenase 2 (IDO2), and Tryptophan 2,3-dioxygenase (TDO) are the key enzymes in the tryptophan catabolic pathway but we focus on the role of the predominant enzyme form IDO1 in this review. Nicotinamide phosphoribosyl transferase (iNAMPT) regulates the intracellular concentration of NAD and is upregulated in the tumor. In light of the potential role of IDO1 as a driver of hostile TME in PDAC and NAD+ as a key coenzyme in anti-tumor immune response, this review urges focus on extensive research and initiation of clinical trials using IDO1 and NAMPT inhibitors in pancreatic cancer in the future.

Tryptophanase Expressed by Salmonella Halts Breast Cancer Cell Growth In Vitro and Inhibits Production of Immunosuppressive Kynurenine.

Tryptophan is an essential amino acid required for tumor cell growth and is also the precursor to kynurenine, an immunosuppressive molecule that plays a role in limiting anticancer immunity. Tryptophanase (TNase) is an enzyme expressed by different bacterial species that converts tryptophan into indole, pyruvate and ammonia, but is absent in the Salmonella strain VNP20009 that has been used as a therapeutic delivery vector. We cloned the Escherichia coli TNase operon tnaCAB into the VNP20009 (VNP20009-tnaCAB), and were able to detect linear production of indole over time, using Kovács reagent. In order to conduct further experiments using the whole bacteria, we added the antibiotic gentamicin to stop bacterial replication. Using a fixed number of bacteria, we found that there was no significant effect of gentamicin on stationary phase VNP20009-tnaCAB upon their ability to convert tryptophan to indole over time. We developed a procedure to extract indole from media while retaining tryptophan, and were able to measure tryptophan spectrophotometrically after exposure to gentamicin-inactivated whole bacterial cells. Using the tryptophan concentration equivalent to that present in DMEM cell culture media, a fixed number of bacteria were able to deplete 93.9% of the tryptophan in the culture media in 4 h. In VNP20009-tnaCAB depleted tissue culture media, MDA-MB-468 triple negative breast cancer cells were unable to divide, while those treated with media exposed only to VNP20009 continued cell division. Re-addition of tryptophan to conditioned culture media restored tumor cell growth. Treatment of tumor cells with molar equivalents of the TNase products indole, pyruvate and ammonia only caused a slight increase in tumor cell growth. Using an ELISA assay, we confirmed that TNase depletion of tryptophan also limits the production of immunosuppressive kynurenine in IFNγ-stimulated MDA-MB-468 cancer cells. Our results demonstrate that Salmonella VNP20009 expressing TNase has improved potential to stop tumor cell growth and reverse immunosuppression.

Abstract 1849: Superiority of dual IDO1/TDO2 inhibition versus IDO1 selective inhibition in reducing immunosuppressive KYN levels in tumors co-expressing IDO1 and TDO2

Abstract Indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO2) catalyze the oxidation of L-Tryptophan (TRP) leading to the formation of immunosuppressive kynurenine (KYN) pathway metabolites. According to TCGA, a substantial fraction of different tumor types expresses both IDO1 and TDO2. In 82 tumor samples (GBM, hepatocellular carcinoma, NSCLC, and ovarian cancer) analyzed for IDO1/TDO2 RNA expression (RNA sequencing) and TRP metabolite content (LC-MS/MS), we found TDO2 highly expressed in hepatocellular carcinoma and to lower levels in NSCLC and ovarian cancer. IDO1 was found to be expressed in NSCLC and ovarian cancer but at higher levels and its expression was correlating with KYN levels. Immunosuppressive properties of KYN and downstream metabolites are mediated through T cell apoptosis and regulatory T cell (Treg) induction. In our hands, KYN at concentrations ≥ 50uM was shown to be immunosuppressive, notably inducing T cell apoptosis. According to our and published data, such high KYN concentrations (≥ 50uM) can be found in a subset of human tumors. As outlined, both IDO1 and TDO2 can contribute to high KYN levels in tumors. Hence, dual IDO1/TDO2 inhibition should be superior in decreasing tumor KYN levels and levering immunosuppression as compared to IDO1 selective inhibition. In this regard, we have generated potent dual IDO1/TDO2 inhibitors inhibiting IDO1 and TDO2 enzyme activity in cellular assays in vitro. To prove the concept of superiority in vivo, we established a dual IDO1/TDO2 expressing human tumor model (LOVO+IFNg) in the mouse and showed that the oral administration of a dual IDO1/TDO2 inhibitor as compared to an IDO1 selective inhibitor showed enhanced KYN/TRP modulation in the tumor. Lead compounds with favorable drug-like properties are currently investigated for pre-clinical development. Citation Format: Carina Lotz-Jenne, Sylvaine Cren, Christoph Joesch, Sabine Ackerknecht, Jennifer Brandes, Claire Moebs, Dominik Hartl, Felix Hartrampf, Philippe Guerry, Julien Pothier, Alexia Chavanton-Arpel. Superiority of dual IDO1/TDO2 inhibition versus IDO1 selective inhibition in reducing immunosuppressive KYN levels in tumors co-expressing IDO1 and TDO2 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1849.

Indoleamine 2,3-Dioxygenase 1: A Promising Therapeutic Target in Malignant Tumor.

Tumorigenesis is a complex multifactorial and multistep process in which tumors can utilize a diverse repertoire of immunosuppressive mechanisms to evade host immune attacks. The degradation of tryptophan into immunosuppressive kynurenine is considered an important immunosuppressive mechanism in the tumor microenvironment. There are three enzymes, namely, tryptophan 2,3-dioxygenase (TDO), indoleamine 2,3-dioxygenase 1 (IDO1), and indoleamine 2,3-dioxygenase 2 (IDO2), involved in the metabolism of tryptophan. IDO1 has a wider distribution and higher activity in catalyzing tryptophan than the other two; therefore, it has been studied most extensively. IDO1 is a cytosolic monomeric, heme-containing enzyme, which is now considered an authentic immune regulator and represents one of the promising drug targets for tumor immunotherapy. Collectively, this review highlights the regulation of IDO1 gene expression and the ambivalent mechanisms of IDO1 on the antitumoral immune response. Further, new therapeutic targets via the regulation of IDO1 are discussed. A comprehensive analysis of the expression and biological function of IDO1 can help us to understand the therapeutic strategies of the inhibitors targeting IDO1 in malignant tumors.

Preclinical Characterization of Linrodostat Mesylate, a Novel, Potent, and Selective Oral Indoleamine 2,3-Dioxygenase 1 Inhibitor.

Tumors can exploit the indoleamine 2,3-dioxygenase 1 (IDO1) pathway to create an immunosuppressive microenvironment. Activated IDO1 metabolizes tryptophan into immunosuppressive kynurenine, leading to suppressed effector T-cell (Teff) proliferation, allowing for tumor escape from host immune surveillance. IDO1 inhibition counteracts this immunosuppressive tumor microenvironment and may improve cancer outcomes, particularly when combined with other immunotherapies. Linrodostat mesylate (linrodostat) is a potent, selective oral IDO1 inhibitor that occupies the heme cofactor-binding site to prevent further IDO1 activation and is currently in multiple clinical trials for treatment of patients with advanced cancers. Here, we assess the in vitro potency, in vivo pharmacodynamic (PD) activity, and preclinical pharmacokinetics (PKs) of linrodostat. Linrodostat exhibited potent cellular activity, suppressing kynurenine production in HEK293 cells overexpressing human IDO1 and HeLa cells stimulated with IFNγ, with no activity against tryptophan 2,3-dioxygenase or murine indoleamine 2,3-dioxygenase 2 detected. Linrodostat restored T-cell proliferation in a mixed-lymphocyte reaction of T cells and allogeneic IDO1-expressing dendritic cells. In vivo, linrodostat reduced kynurenine levels in human tumor xenograft models, exhibiting significant PD activity. Linrodostat demonstrated a PK/PD relationship in the xenograft model, preclinical species, and samples from patients with advanced cancers, with high oral bioavailability in preclinical species and low to moderate systemic clearance. Our data demonstrate that linrodostat potently and specifically inhibits IDO1 to block an immunosuppressive mechanism that could be responsible for tumor escape from host immune surveillance with favorable PK/PD characteristics that support clinical development.

Tryptophan: A Rheostat of Cancer Immune Escape Mediated by Immunosuppressive Enzymes IDO1 and TDO.

Blockade of the immunosuppressive tryptophan catabolism mediated by indoleamine 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase (TDO) holds enormous promise for sensitising cancer patients to immune checkpoint blockade. Yet, only IDO1 inhibitors had entered clinical trials so far, and those agents have generated disappointing clinical results. Improved understanding of molecular mechanisms involved in the immune-regulatory function of the tryptophan catabolism is likely to optimise therapeutic strategies to block this pathway. The immunosuppressive role of tryptophan metabolite kynurenine is becoming increasingly clear, but it remains a mystery if tryptophan exerts functions beyond serving as a precursor for kynurenine. Here we hypothesise that tryptophan acts as a rheostat of kynurenine-mediated immunosuppression by competing with kynurenine for entry into immune T-cells through the amino acid transporter called System L. This hypothesis stems from the observations that elevated tryptophan levels in TDO-knockout mice relieve immunosuppression instigated by IDO1, and that the vacancy of System L transporter modulates kynurenine entry into CD4+ T-cells. This hypothesis has two potential therapeutic implications. Firstly, potent TDO inhibitors are expected to indirectly inhibit IDO1 hence development of TDO-selective inhibitors appears advantageous compared to IDO1-selective and dual IDO1/TDO inhibitors. Secondly, oral supplementation with System L substrates such as leucine represents a novel potential therapeutic modality to restrain the immunosuppressive kynurenine and restore anti-tumour immunity.

Activatable Polymer Nanoenzymes for Photodynamic Immunometabolic Cancer Therapy.

Tumor immunometabolism contributes substantially to tumor proliferation and immune cell activity, and thus plays a crucial role in the efficacy of cancer immunotherapy. Modulation of immunometabolism to boost cancer immunotherapy is mostly based on small-molecule inhibitors, which often encounter the issues of off-target adverse effects, drug resistance, and unsustainable response. In contrast, enzymatic therapeutics can potentially bypass these limitations but has been less exploited. Herein, an organic polymer nanoenzyme (SPNK) with near-infrared (NIR) photoactivatable immunotherapeutic effects is reported for photodynamic immunometabolic therapy. SPNK is composed of a semiconducting polymer core conjugated with kynureninase (KYNase) via PEGylated singlet oxygen (1 O2 ) cleavable linker. Upon NIR photoirradiation, SPNK generates 1 O2 not only to exert photodynamic effect to induce the immunogenic cell death of cancer, but also to unleash KYNase and trigger its activity to degrade the immunosuppressive kynurenine (Kyn). Such a combinational effect mediated by SPNK promotes the proliferation and infiltration of effector T cells, enhances systemic antitumor T cell immunity, and ultimately permits inhibition of both primary and distant tumors in living mice. Therefore, this study provides a promising photodynamic approach toward remotely controlled enzymatic immunomodulation for improved anticancer therapy.

Oxaliplatin-/NLG919 prodrugs-constructed liposomes for effective chemo-immunotherapy of colorectal cancer

High expression of indoleamine 2,3-dioxygenase 1 (IDO1) is a major cause of tumor induced immunosuppression, and appears to be associated with poor prognosis in human colorectal cancer and some others. In this study, we construct a bifunctional liposome by self-assembly of oxaliplatin-prodrug (Oxa(IV)) conjugated phospholipid and alkylated NLG919 (aNLG), an IDO1 inhibitor, together with other commercial lipids. The obtained aNLG/Oxa(IV)-Lip can not only release cytotoxic oxaliplatin inside the reductive cytosol to trigger immunogenic cell death (ICD) of cancer cells, but also efficiently retard the degradation of tryptophan to immunosuppressive kynurenine via the NLG919 mediated inhibition of IDO1. Moreover, in vivo pharmacokinetic studies indicate that such aNLG/Oxa(IV)-Lip has a long blood circulation time, thereby enables highly-efficient passive tumor homing. Upon tumor accumulation, such aNLG/Oxa(IV)-Lip presents superior synergistic antitumor efficacies to both subcutaneous and orthotopic CT26 tumors, ascribing to significantly primed anti-tumor immunity of enhanced intratumoral infiltration of CD8+ T cells, scretion of cytotoxic cytokines and downregulation of immunosuppressive regulatory T cells. This work highlights that such bifunctional aNLG/Oxa(IV)-Lip is a potent candidate for future clinical translation owing to its excellent biocompatibility and high therapeutic efficacy.

P110 Identification of the tryptophan metabolite 3-hydroxyanthranilic acid as a novel tool for the differentiation of Crohn’s disease phenotypes

Abstract Background The widely varying therapeutic response of patients with inflammatory bowel disease (IBD) continues to raise question regarding the unclarified heterogeneity of disease pathomechanisms. While biomarkers for the differentiation of Crohn’s disease (CD) vs. ulcerative colitis (UC) have been suggested, specific markers for a subclassification of CD phenotypes are still rare. Since an altered signature of the tryptophan metabolism is associated with chronic inflammatory disease, we sought to characterise potential biomarkers focusing on the downstream metabolites of kynurenine metabolism. The widely varying therapeutic response of patients with inflammatory bowel disease (IBD) continues to raise question regarding the unclarified heterogeneity of disease pathomechanisms. While biomarkers for the differentiation of Crohn’s disease (CD) vs. ulcerative colitis (UC) have been suggested, specific markers for a subclassification of CD phenotypes are still rare. Since an altered signature of the tryptophan metabolism is associated with chronic inflammatory disease, we sought to characterise potential biomarkers focusing on the downstream metabolites of kynurenine metabolism. Methods Using immunohistochemical staining, we analysed and compared the mucosal tryptophan immune metabolism in biotic samples from patients with UC (n = 11), CD (n = 11) and healthy control (n = 12). Localisation-specific quantification of immune cell infiltration, tryptophan-metabolizing enzyme expression and mucosal tryptophan downstream metabolite levels was performed. Results As expected, we found generally increased immune cell infiltrates in the tissue of all patients with IBD. However, in patients with CD, significant differences were found between regulatory T-cell markers in the ileum compared with the colon. In line with this finding, we identified kynureninase as a modulator of immunosuppressive kynurenine levels specifically in the ileum of patients with CD. Correspondingly, significantly elevated levels of the kynurenine metabolite 3-hydroxyanthranilic acid were detected in CD ileum samples. Conclusion Highlighting the heterogeneity of the different phenotypes of CD, we identified 3-hydroxyanthranilic acid as a potential mucosal biomarker allowing the localisation-specific differentiation of ileum or colon inflammation in patients with CD. Moreover, we characterised the kynurenine-degrading enzyme kynureninase as a modulator of immunosuppression and chronic inflammation with potential therapeutic relevance.

Chemoresistance was correlated with elevated expression and activity of indoleamine 2,3-dioxygenase in breast cancer.

Indoleamine 2,3-dioxygenase (IDO) catalyses degradation of the essential amino acid tryptophan leading to the production of immunosuppressive kynurenine and tryptophan exhausting. IDO expression and activity contribute to aggressive tumor growth, inferior therapeutic gain and poor prognosis. The aim of this study was to explore the association between chemoresistance and IDO expression, activity in breast cancer METHODS: Immunohistochemistry was applied for evaluating IDO expression in biopsy tissues. Serum IDO activity was examined via High-performance liquid chromatography (HPLC). Western blots (WB), HPLC and Real-time PCR (RT-PCR) were used to analyze IDO protein, IDO enzyme activity and IDO gene expression in original and paclitaxel-resistant cells respectively. Logistic regression and survival analysis were applied to explore the association between chemoresistance and IDO expression, activity in breast cancer. IDO expression in tumor tissues was associated with serum IDO activity (P = 0.004). Both IDO expression in tumor and serum activity were associated with clinical tumor stage, node stage and estrogen receptor (ER) status (all P < 0.05); clinical response and pathologic complete response (pCR) to NAC were both related to IDO expression and activity prior NAC (all P < 0.05). Multivariate analysis showed IDO activity before NAC was the only independent factor affected pCR (P = 0.032). ROC curves showed that the IDO expression and activity had discriminative ability for predicting the clinical response and pCR. In the prognostic analysis, patients with high IDO expression had significantly impaired overall survival (5year survival rate: 53.57% vs 80.00%) and progression-free survival (5year survival rate: 46.43% vs 72.00%, P = 0.031 and P = 0.046). In vitro, significantly increased IDO protein, IDO mRNA expression and IDO enzyme activity in paclitaxel-resistant cells were demonstrated in comparing of sensitive cells. IDO expression and activity associated with advanced breast cancer, poor response to neoadjuvant chemotherapy and prognosis. IDO expression and activity were significantly increased in paclitaxel-resistant breast cancer cells.

A highly efficient modality to block the degradation of tryptophan for cancer immunotherapy: locked nucleic acid-modified antisense oligonucleotides to inhibit human indoleamine 2,3-dioxygenase 1/tryptophan 2,3-dioxygenase expression.

Tumors can utilize a diverse repertoire of immunosuppressive mechanisms to evade attack by the immune system. Despite promising success with blockade of immune checkpoints like PD-1 the majority of patients does not respond to current immunotherapies. The degradation of tryptophan into immunosuppressive kynurenine is an important immunosuppressive pathway. Recent attempts to target the key enzymes of this pathway-IDO1 and TDO2-have so far failed to show therapeutic benefit in the clinic, potentially caused by insufficient target engagement. We, therefore, sought to add an alternative, highly efficient approach to block the degradation of tryptophan by inhibiting the expression of IDO1 and TDO2 using locked nucleic acid (LNA)-modified antisense oligonucleotides (ASOs). We show that LNA-modified ASOs can profoundly inhibit the expression of IDO1 and TDO2 in cancer cells in vitro without using a transfection reagent with IC50 values in the sub-micromolar range. We furthermore measured kynurenine production by ASO-treated cancer cells in vitro and observed potently reduced kynurenine levels. Accordingly, inhibiting IDO1 expression in cancer cells in an in vitro system leads to increased proliferation of activated T cells in coculture. We furthermore show that combined treatment of cancer cells in vitro with IDO1-specific ASOs and small molecule inhibitors can reduce the production of kynurenine by cancer cells in a synergistic manner. In conclusion, we propose that a combination of LNA-modified ASOs and small molecule inhibitors should be considered as a strategy for efficient blockade of the degradation of tryptophan into kynurenine in cancer immunotherapy.

Abstract CT011: First-in-human Phase I study of M4112, the first dual inhibitor of indoleamine 2,3-dioxygenase-1 and tryptophan 2,3-dioxygenase 2, in patients with advanced solid malignancies

Abstract BACKGROUND: Indoleamine 2,3-dioxygenase 1 (IDO1) and the related enzyme tryptophan 2,3-dioxygenase 2 (TDO2) are enzymes that mediate the rate limiting step in the metabolism of tryptophan (Trp) into the immunosuppressive metabolite kynurenine (Kyn). The accumulation of Kyn suppresses effector T and activates suppressor T regs generating an immune suppressive environment and escape mechanism for anti-PD-L1/anti-PD-1 agents. While both enzymes are upregulated in various tumors, the expression of IDO1 and TDO2 in human cancers is distinct and not overlapping, suggesting that the use of dual inhibitor should provide an enhanced anti-tumor effect. This is a first in human Phase I study investigating the safety, PK, pharmacodynamic effect and preliminary clinical activity of M4112, a highly selective dual IDO1/TDO2 inhibitor. PATIENTS AND METHODS: Patients with advanced solid malignancies were treated with M4112 (100, 200, 400, 600, or 800mg twice daily [BID] oral). The dose-escalation evaluated patients in 28-day cycles. Treatment was continued until disease progression, or unacceptable toxicity. RESULTS: 15 patients were enrolled. One dose-limiting toxicity (DLT) occurred at 800 mg BID (grade 3, rash, with fever and hypotension). The adverse events regardless of causality in &amp;gt;20% of patients were fatigue, nausea, rash, cough, CK increase, vomiting, diarrhea and decreased appetite. Exposure for 100mg and 200mg doses were proportional, with greater than proportional increase in exposure observed at 400mg and 600mg but less than proportional increase at 800mg. The observed Cmin (C1D15) at doses ≥ 400mg BID was above the IC50 based on animal studies. M4112 treatment resulted in dose-dependent IDO1 inhibition in ex vivo stimulated blood with approximately &amp;gt;90% IDO1 activity inhibited throughout the dosing period at 800mg BID. In contrast, M4112 did not show sustained reduction of plasma Kyn levels up to 800mg BID: 12-35% decrease in plasma Kyn levels were observed on C1D1 up to 6h post dosing, that returned to or exceeded baseline values on C1D15. Consistent with preclinical findings, the plasma Trp increased during C1D1 at dose levels ≥200mg, suggesting liver TDO2 inhibition responsible for this increase. There were no objective responses, however in 7 of 15 cancer patients time until documented progressive disease was ≥16 weeks. These are preliminary data. CONCLUSIONS: M4112 was generally well tolerated, with stable disease as best response. M4112 achieved &amp;gt;90% IDO1 inhibition in ex vivo stimulated blood assay. Unlike IDO1 specific inhibitors, ex vivo IDO1 inhibition did not translate into plasma Kyn reduction following M4112 treatment. This is the first report of a dual inhibition of IDO1 and TDO2 showing acceptable safety profile and prolonged time to progression in cancer patients. Further investigation is warranted. Citation Format: Kyriakos Papadopoulos, Paul Eder, Sarina A. Piha-Paul, Claude Gimmi, Elizabeth Hussey, Sen Zhang, Lu Li, Christina Habermehl, Aung Naing. First-in-human Phase I study of M4112, the first dual inhibitor of indoleamine 2,3-dioxygenase-1 and tryptophan 2,3-dioxygenase 2, in patients with advanced solid malignancies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr CT011.

Abstract 1288: Blocking tumor-associated immune suppression with BAY-218, a novel, selective aryl hydrocarbon receptor (AhR) inhibitor

Abstract Tumor cells co-opt multiple pathways in order to evade attack by infiltrating immune cells. One such mechanism is the upregulation of indole-2,3-dioxygenase (IDO1) and/or tryptophan-2,3-dioxygenase (TDO2), both of which are first-step, rate-limiting enzymes degrading tryptophan to the immunosuppressive metabolites kynurenine (KYN) and kynurenic acid (KA). KYN and KA bind and activate the aryl hydrocarbon receptor (AhR), which is expressed in many cell types and is well known for its immunosuppressive effects. Targeting of the AhR with an inhibitor may therefore provide a novel immunotherapeutic approach for enhancing anti-tumoral immune responses and treating cancer. Here we describe the identification and functional immune characterization of BAY-218, a novel, selective and potent AhR small molecule inhibitor. Mechanistically, BAY-218 inhibited AhR nuclear translocation, dioxin response element (DRE)-luciferase reporter expression and AhR-regulated target gene expression induced by both exogenous and endogenous AhR ligands. In vitro, BAY-218 rescued TNFα production from KA-suppressed LPS-treated primary human monocytes. Furthermore, BAY-218 enhanced T cell cytokine production in a human mixed lymphocyte reaction (MLR) and a mouse antigen-specific bone-marrow-derived dendritic cell (BMDC)-OT-I T cell co-culture. In the MLR, BAY-218 increased anti-PD1 antibody-mediated IL-2 and IFNγ secretion, while an IDO inhibitor did not, indicating that BAY-218 is able to block AhR activation mediated by ligands outside of the IDO-KYN pathway. In vivo, BAY-218 enhanced anti-tumoral immune responses and reduced tumor growth in the syngeneic mouse tumor models CT26 and B16-OVA. FACS analysis of leukocytes infiltrating B16-OVA tumors demonstrated that administration of BAY-218 increased the frequency of tumor-infiltrating CD8+ T cells and NK cells while decreasing GR1+ myeloid cells and CD206+M2 macrophages. Furthermore, BAY-218 enhanced therapeutic efficacy of an anti-PD-L1 antibody in the CT26 model. In summary, AhR inhibition with BAY-218 stimulates pro-inflammatory monocyte and T cell responses in vitro and drives anti-tumor immune responses, resulting in decreased tumor growth, in vivo. Thus, inhibiting AhR represents a novel immunotherapeutic approach for blocking AhR-mediated tumor-associated immunosuppression. Citation Format: Ilona Gutcher, Christina Kober, Lars Roese, Julian Roewe, Norbert Schmees, Florian Prinz, Matyas Gorjanacz, Ulrike Roehn, Benjamin Bader, Horst Irlbacher, Detlef Stoeckigt, Rafael Carretero, Katharina Sahm, Iris Oezen, Hilmar Weinmann, Ingo V. Hartung, Bertolt Kreft, Michael Platten. Blocking tumor-associated immune suppression with BAY-218, a novel, selective aryl hydrocarbon receptor (AhR) inhibitor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1288.

Reversal of Triple-Negative Breast Cancer EMT by miR-200c Decreases Tryptophan Catabolism and a Program of Immunosuppression.

Tryptophan-2,3-dioxygenase (TDO2), a rate-limiting enzyme in the tryptophan catabolism pathway, is induced in triple-negative breast cancer (TNBC) by inflammatory signals and anchorage-independent conditions. TNBCs express extremely low levels of the miR-200 family compared with estrogen receptor-positive (ER+) breast cancer. In normal epithelial cells and ER+ breast cancers and cell lines, high levels of the family member miR-200c serve to target and repress genes involved in epithelial-to-mesenchymal transition (EMT). To identify mechanism(s) that permit TNBC to express TDO2 and other proteins not expressed in the more well-differentiated ER+ breast cancers, miRNA-200c was restored in TNBC cell lines. The data demonstrate that miR-200c targeted TDO2 directly resulting in reduced production of the immunosuppressive metabolite kynurenine. Furthermore, in addition to reversing a classic EMT signature, miR-200c repressed many genes encoding immunosuppressive factors including CD274/CD273, HMOX-1, and GDF15. Restoration of miR-200c revealed a mechanism, whereby TNBC hijacks a gene expression program reminiscent of that used by trophoblasts to suppress the maternal immune system to ensure fetal tolerance during pregnancy. IMPLICATIONS: Knowledge of the regulation of tumor-derived immunosuppressive factors will facilitate development of novel therapeutic strategies that complement current immunotherapy to reduce mortality for patients with TNBC.

Abstract 3757: Targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine

Abstract The tryptophan/kynurenine pathway has been clinically validated in several tumor types with small-molecule IDO1 inhibitors in combination with checkpoint inhibition. Indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1) and tryptophan 2,3-dioxygenase 2 (TDO2) are upregulated in a number of tumor types, metabolizing tryptophan to form immunosuppressive kynurenine. We are developing Kynureninase (Kynase), a kynurenine depleting enzyme, to treat IDO1 and TDO2 positive tumors. The human Kynase has been successfully engineered to vastly increase catalytic activity and stability toward kynurenine over the wild type enzyme. In mice, Kynase achieved prolonged Kynurenine degradation (≥5 days) in plasma and tumor draining lymph node (TDLN), leading to anti-tumor activity as a single agent and in combination with check point inhibitors in mouse syngeneic tumor models. Kynase demonstrated superior tumor growth inhibition and survival benefit relative to a leading IDO1 inhibitor epacadostat in these models. The effects of Kynase on a number of immune cell types, both in vitro and in vivo, are being investigated. Human Kynase has also shown a favorable PK profile and kynurenine degradation in non-human primates, and Kynase variants are now moving toward development candidate selection for treatment of cancers where both IDO/TDO pathways play a significant immunosuppressive role. Citation Format: Silvia Coma, Jill Cavanaugh, James Nolan, Jeremy Tchaicha, Karen McGovern, Everett Stone, Candice Lamb, Christos Karamitros, John Blazek, Kendra Garrison, George Georgiou, Mark Manfredi, Xiaoyan Michelle Zhang. Targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3757.

Aminoisoxazoles as Potent Inhibitors of Tryptophan 2,3-Dioxygenase 2 (TDO2).

Tryptophan 2,3-dioxygenase 2 (TDO2) catalyzes the conversion of tryptophan to the immunosuppressive metabolite kynurenine. TDO2 overexpression has been observed in a number of cancers; therefore, TDO inhibition may be a useful therapeutic intervention for cancers. We identified an aminoisoxazole series as potent TDO2 inhibitors from a high-throughput screen (HTS). An extensive medicinal chemistry effort revealed that both the amino group and the isoxazole moiety are important for TDO2 inhibitory activity. Computational modeling yielded a binding hypothesis and provided insight into the observed structure-activity relationships. The optimized compound 21 is a potent TDO2 inhibitor with modest selectivity over indolamine 2,3-dioxygenase 1 (IDO1) and with improved human whole blood stability.

Abstract 5570: A novel approach to targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine

Abstract Checkpoint inhibitors have become the cornerstone for new innovation in immune-based oncology therapy. Several orthogonal immune pathways are currently being investigated to relieve suppression or boost activity of the innate and adaptive immune system. The IDO immune-metabolism pathway was recently clinically validated in melanoma in combination with checkpoint inhibition. This opens up a new approach to relieving suppressive mediators and lends credence to the tumor microenvironment containing small molecule metabolites that induce immune tolerance. Both indoleamine-pyrrole 2,3-dioxygenase 1 (IDO1) and Tryptophan 2,3-dioxygenase (TDO) enzymes metabolize tryptophan, forming Kynurenine which binds the aryl hydrocarbon receptor (AHR) in multiple innate and adaptive immune cell types causing a net immunosuppressive effect. Both enzymes are upregulated across many tumor types, however, only the IDO1 enzyme has thus far been addressed in the clinic with small molecule inhibitors. We have postulated that enzyme-mediated depletion of Kynurenine into safe and immunologically inert metabolites can alleviate tumor immunosuppression. We have cloned and characterized several bacterial Kynureninases (KYNase) which preferentially degrade Kynurenine with a &amp;gt;1,000 higher kcat/KM as opposed to mammalian enzymes that cleave 3-OH Kynurenine. We show that PEGylated bacterial KYNases can deplete Kynurenine produced by IDO1+, TDO+ and IDO1/TDO+ dual positive human cancer cells whereas, the IDO1 inhibitor epacadostat or TDO inhibitor 680C91 only selectively inhibited Kyn production in IDO1+ or TDO+ cells respectively. In vivo, a single subcutaneous dose of KYNase in B16F10 tumor-bearing mice was able to deplete Kynurenine in both the plasma and tumors and increase effector T-cells in the tumor. KYNase demonstrated significant tumor growth inhibition and survival benefit either as a single agent or in combination with checkpoint inhibitors (anti-PD1 or anti-CTLA4) in B16F10, CT26 and 4T1 models. Interestingly, KYNase combined with anti-PD1, showed greater efficacy than epacadostat / anti-PD1 combination in CT26 tumor bearing mice. A pharmacologically optimized human KYNase is currently moving toward clinical development for the treatment of cancers where both IDO/TDO pathways play a significant immunosuppressive role through kynurenine production. Citation Format: Michelle Zhang, Everett Stone, Todd A. Triplett, Kendra Triplett, Candice Lamb, Christos S. Karamitros, John Blazek, George Georgiou, Mark G. Manfredi. A novel approach to targeting the IDO/TDO pathway through degradation of the immunosuppressive metabolite kynurenine [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5570. doi:10.1158/1538-7445.AM2017-5570

Mesenchymal Stem Cells Promote Metastasis of Lung Cancer Cells by Downregulating Systemic Antitumor Immune Response

Since majority of systemically administered mesenchymal stem cells (MSCs) become entrapped within the lungs, we used metastatic model of lung cancer, induced by intravenous injection of Lewis lung cancer 1 (LLC1) cells, to investigate the molecular mechanisms involved in MSC-mediated modulation of metastasis. MSCs significantly augmented lung cancer metastasis, attenuate concentrations of proinflammatory cytokines (TNF-α, IL-17), and increase levels of immunosuppressive IL-10, nitric oxide, and kynurenine in sera of LLC1-treated mice. MSCs profoundly reduced infiltration of macrophages, TNF-α-producing dendritic cells (DCs), TNF-α-, and IL-17-producing CD4+ T cells but increased IL-10-producing CD4+ T lymphocytes in the lungs of tumor-bearing animals. The total number of lung-infiltrated, cytotoxic FasL, perforin-expressing, TNF-α-, and IL-17-producing CD8+ T lymphocytes, and NKG2D-expressing natural killer (NK) cells was significantly reduced in LLC1 + MSC-treated mice. Cytotoxicity of NK cells was suppressed by MSC-conditioned medium. This phenomenon was abrogated by the inhibitors of inducible nitric oxide synthase (iNOS) and indoleamine 2,3-dioxygenase (IDO), suggesting the importance of iNOS and IDO for MSC-mediated suppression of antitumor cytotoxicity of NK cells. This study provides the evidence that MSCs promote lung cancer metastasis by suppressing antitumor immune response raising concerns regarding safety of MSC-based therapy in patients who have genetic susceptibility for malignant diseases.