Pathogenetic Interplay Between IL-6 and Tryptophan Metabolism in an Experimental Model of Obesity.

Obesity is a metabolic disease characterized by a state of chronic, low-grade inflammation and dominated by pro-inflammatory cytokines such as IL-6. Indoleamine 2,3-dioxygenase 1 (IDO1) is an enzyme that catalyzes the first step in the kynurenine pathway by transforming l-tryptophan (Trp) into l-kynurenine (Kyn), a metabolite endowed with anti-inflammatory and immunoregulatory effects. In dendritic cells, IL-6 induces IDO1 proteasomal degradation and shuts down IDO1-mediated immunosuppressive effects. In tumor cells, IL-6 upregulates IDO1 expression and favors tumor immune escape mechanisms. To investigate the role of IDO1 and its possible relationship with IL-6 in obesity, we induced the disease by feeding mice with a high fat diet (HFD). Mice on a standard diet were used as control. Experimental obesity was associated with high IDO1 expression and Kyn levels in the stromal vascular fraction of visceral white adipose tissue (SVF WAT). IDO1-deficient mice on HFD gained less weight and were less insulin resistant as compared to wild type counterparts. Administration of tocilizumab (TCZ), an IL-6 receptor (IL-6R) antagonist, to mice on HFD significantly reduced weight gain, controlled adipose tissue hypertrophy, increased insulin sensitivity, and induced a better glucose tolerance. TCZ also induced a dramatic inhibition of IDO1 expression and Kyn production in the SVF WAT. Thus our data indicated that the IL-6/IDO1 axis may play a pathogenetic role in a chronic, low-grade inflammation condition, and, perhaps most importantly, IL-6R blockade may be considered a valid option for obesity treatment.

Tracking Hidden Binding Pockets Along the Molecular Recognition Path of l-Trp to Indoleamine 2,3-Dioxygenase 1.

Indoleamine 2,3-dioxygenase 1 (IDO1) catalyzes the oxidative cleavage of l-Tryptophan (l-Trp) to yield N-formyl-kynurenine in the first and rate limiting step of the kynurenine pathway. Bioactive metabolites, involved in the regulation of important immunological responses and neurological processes, are then produced by downstream enzymes along the pathway. Inhibitors of IDO1 are being designed and developed as therapeutic agents for immuno-oncology. In this work, we investigated the molecular recognition path of l-Trp to IDO1, integrating biophysical methods with supervised molecular dynamics (suMD) and mutagenesis experiments. Results allowed disclosing for the first time high and low dissociation constants of l-Trp to IDO1, and the presence of a metastable interaction site located at the upper part of a channel whose borders are defined by the EF-loop and the C-terminal part of the JK-loop. Collectively, our results provide new clues for the design of next-generation IDO1 ligands.

Assessment of TILs, IDO-1, and PD-L1 in resected non-small cell lung cancer: an immunohistochemical study with clinicopathological and prognostic implications.

Several cancers, especially non-small cell lung cancer (NSCLC), are able to escape the immunosurveillance of tumor-infiltrating lymphocytes (TILs); among the molecules involved, the indoleamine 2,3-dioxygenase 1 (IDO-1) and the programmed cell death ligand-1 (PD-L1) play a crucial role. These aspects are of great interest in the current immunotherapeutic era, therefore the current study analyses the TILs, IDO-1, and PD-L1 interactions and their correlations with clinicopathological parameters and prognosis in NSCLC. One hundred ninety-three NSCLC surgical specimens, formalin-fixed, and paraffin-embedded were assessed for TILs density, TILs localization, IDO-1 (clone 4.16H1), and PD-L1 (clone E1L3N) immunohistochemical expressions. This data was correlated with clinicopathological parameters, disease free, and overall survivals. IDO-1 and PD-L1 high expressions were related to the solid pattern of adenocarcinomas (respectively p = 0.036 and p = 0.026); high PD-L1 expression was correlated with squamous histotype (p = 0.048). IDO-1 overexpression correlated with former smokers (p = 0.041), higher adenocarcinoma stages (p = 0.039), and with both higher TILs density and PD-L1 expression (respectively p = 0.025 and p = 0.0003). A better prognosis was associated with TILs intratumoral or mixed localizations (p = 0.029). TILs localization affects NSCLC prognosis; the higher expression of IDO-1 and PD-L1 in poorly differentiated and more aggressive lung adenocarcinomas, as well as the correlation between high PD-L1 expression and squamous cell histotype, confirm the more efficient immunoescaping of these NSCLC subgroups.

Urinary l-kynurenine quantification and selective extraction through a molecularly imprinted solid-phase extraction device.

l-Kynurenine is an endogenous metabolite generated by the catabolic pathway of l-tryptophan and it could be a potential biomarker to test the efficacy of several checkpoint inhibitors that have already reached the clinical trials in the antitumor therapy. Thus, a molecularly imprinted polymer specific for the recognition of this metabolite was synthesized and used as innovative system in solid-phase extraction technique for the specific extraction and quantification of l-kynurenine in human urine. The off-line system was firstly tested on l-kynurenine standard solutions, allowing recoveries up to 97.7% (relative standard deviation = 2.2%) and then applied to fortified and deproteinated human urine samples, where a recovery of 84.1% (relative standard deviation = 3.1%) was obtained. The method was validated and it revealed a good linearity in the range of 0.157-20 µg/mL (r2  = 0.9992). The optimized procedure demonstrated a good feasibility on biological samples, allowing a ready quantification of l-kynurenine in the human urine, where the metabolite was found at a very low concentration (0.80 µg/mL). The extraction system developed could attract attention of pharmaceutical industries for l-kynurenine production as potential drug in the treatment of autoimmune disorders through its extraction and purification from biological matrixes.

Fragment-based approach to identify IDO1 inhibitor building blocks.

Indoleamine 2,3-dioxygenase 1 (IDO1) is attracting a great deal of interest as drug target in immune-oncology being highly expressed in cancer cells and participating to the tumor immune-editing process. Although several classes of IDO1 inhibitors have been reported in literature and patent applications, only few compounds have proved optimal pharmacological profile in preclinical studies to be advanced in clinical trials. Accordingly, the quest for novel structural classes of IDO1 inhibitors is still open. In this paper, we report a fragment-based screening campaign that combines Water-LOGSY NMR experiments and microscale thermophoresis approach to identify fragments that may be helpful for the development of novel IDO1 inhibitors as therapeutic agents in immune-oncology disorders.

Modulation of natriuretic peptide receptors in human adipose tissue: molecular mechanisms behind the "natriuretic handicap" in morbidly obese patients.

The B-type natriuretic peptide (BNP) hormone plays a crucial role in the regulation of cardiovascular and energy homeostasis. Obesity is associated with low circulating levels of BNP, a condition known as "natriuretic handicap." Recent evidences suggest an altered expression of BNP receptors-both the signaling natriuretic peptide receptors (NPR)-A and the clearance NPR-C receptor-in adipose tissue (AT) as one of the putative causes of natriuretic handicap. The current study aims at clarifying the molecular mechanisms behind the natriuretic handicap, focusing on NPR modulation in the AT of obese and control subjects. The study enrolled 34 obese and 20 control subjects undergoing bariatric or abdominal surgery, respectively. The main clinical and biochemical parameters, including circulating BNP, were assessed. In visceral (VAT) and subcutaneous AT (SAT) samples, collected during surgery, the adipocytes and stromal vascular fraction (SVF) expression of NPR-A and NPR-C and the SVF secretion of interleukin 6 (IL-6) were determined. Both VAT and SAT from obese patients expressed a lower NPR-A/NPR-C ratio in adipocytes and the SVF secreted a higher level of IL-6, compared with the controls. Moreover, NPR-A/NPR-C ratio expressed by VAT and SAT adipocytes negatively correlated with body mass index, insulin, the Homeostasis Model Assessment of Insulin resistance, and IL-6 secreted by SVF, and the expression of the clearance receptor NPR-C, in both the VAT and SAT adipocytes, showed a negative correlation with circulating BNP. Overall, insulin resistance/hyperinsulinemia and AT inflammation (ie, high level of IL-6) are the major determinants of the lower NPR-A/NPR-C ratio in adipocytes, thus contributing to the natriuretic handicap in obese subjects.

The Proteasome Inhibitor Bortezomib Controls Indoleamine 2,3-Dioxygenase 1 Breakdown and Restores Immune Regulation in Autoimmune Diabetes.

Bortezomib (BTZ) is a first-in-class proteasome inhibitor approved for the therapy of multiple myeloma that also displays unique regulatory activities on immune cells. The enzyme indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan metabolizing enzyme exerting potent immunoregulatory effects when expressed in dendritic cells (DCs), the most potent antigen-presenting cells capable of promoting either immunity or tolerance. We previously demonstrated that, in inflammatory conditions, IDO1 is subjected to proteasomal degradation in DCs, turning these cells from immunoregulatory to immunostimulatory. In non-obese diabetic (NOD) mice, an experimental model of autoimmune diabetes, we also identified an IDO1 defect such that the DCs do not develop tolerance toward pancreatic islet autoantigens. We found that BTZ rescues IDO1 protein expression in vitro in a particular subset of DCs, i.e., plasmacytoid DCs (pDCs) from NOD mice. When administered in vivo to prediabetic mice, the drug prevented diabetes onset through IDO1- and pDC-dependent mechanisms. Although the drug showed no therapeutic activity when administered alone to overtly diabetic mice, its combination with otherwise suboptimal dosages of autoimmune-preventive anti-CD3 antibody resulted in disease reversal in 70% diabetic mice, a therapeutic effect similar to that afforded by full-dosage anti-CD3. Thus, our data indicate a potential for BTZ in the immunotherapy of autoimmune diabetes and further underline the importance of IDO1-mediated immune regulation in such disease.