Discovery and Characterisation of Dual Inhibitors of Tryptophan 2,3-Dioxygenase (TDO2) and Indoleamine 2,3-Dioxygenase 1 (IDO1) Using Virtual Screening

Implications of Kynurenine Pathway Metabolism for the Immune System, Hypothalamic-Pituitary-Adrenal Axis, and Neurotransmission in Alcohol Use Disorder

In recent years, there has been a marked increase in interest in the role of the kynurenine pathway (KP) in mechanisms associated with addictive behavior. Numerous reports implicate KP metabolism in influencing the immune system, hypothalamic-pituitary-adrenal (HPA) axis, and neurotransmission, which underlie the behavioral patterns characteristic of addiction. An in-depth analysis of the results of these new studies highlights interesting patterns of relationships, and approaching alcohol use disorder (AUD) from a broader neuroendocrine-immune system perspective may be crucial to better understanding this complex phenomenon. In this review, we provide an up-to-date summary of information indicating the relationship between AUD and the KP, both in terms of changes in the activity of this pathway and modulation of this pathway as a possible pharmacological approach for the treatment of AUD.

Restoration of p53 functions by suppression of mortalin-p53 sequestration: an emerging target in cancer therapy

Functional inactivation of wild-type p53 is a major trait of cancerous cells. In many cases, such inactivation occurs by either TP53 gene mutations or due to overexpression of p53 binding partners. This review focuses on an overexpressed p53 binding partner called mortalin, a mitochondrial heat shock protein that sequesters both wild-type and mutant p53 in malignant cells due to changes in subcellular localization. Clinical evidence suggests a drastic depletion of the overall survival time of cancer patients with high mortalin expression. Therefore, mortalin-p53 sequestration inhibitors could be game changers in improving overall survival rates. This review explores the consequences of mortalin overexpression and challenges, status and strategies for accelerating drug discovery to suppress mortalin-p53 sequestration.

Indoleamine 2,3-Dioxygenase as a Therapeutic Target for Alzheimer's Disease and Geriatric Depression

Neuroimmune-triggered neuroinflammation of the central nervous system is emerging as an important aetiopathogenic factor for multiple neurological disorders, including depression, dementia, Alzheimer's disease, multiple sclerosis and others. Tryptophan metabolism via the kynurenic pathway, which is initiated by the indoleamine-2,3-dioxygenase (IDO-1) enzyme, is a key regulator of the neuroimmune system and its associated neuroinflammatory effects. As discussed in this review, targeting the production of immunopathic and potentially neurotoxic kynurenine metabolites by inhibitory downregulation of IDO-1 may prove a viable target against inflammation-induced neurological conditions, particularly depression and dementia.

Pancancer Analysis of Revealed TDO2 as a Biomarker of Prognosis and Immunotherapy

Background

Tryptophan 2,3-dioxygenase (TDO) encoded by TDO2, a rate-limiting enzyme in the kynurenine pathway, catabolizes tryptophan to kynurenine, evades immune surveillance, and promotes tumor growth. Although accumulating evidence suggests a crucial role of TDO2 during tumor formation and development, systematic evaluation of TDO2 across human cancers has rarely been reported.

Methods

To shed more light on the role of TDO2 in human cancer, we explored the expression profiles of TDO2 and identified its prognostic value in pancancer analysis through TCGA, CCLE, and GTEx databases. We further utilized TCGA data to evaluate the association between TDO2 and tumor immunological features, such as mismatch repair (MMR), tumor immune infiltration, immune checkpoint-related genes, tumor mutational burden (TMB), microsatellite instability (MSI), and DNA methyltransferase (DNMT).

Results

TDO2 exhibited different expression levels in various cancer cell lines. Frequently, TDO2 was detected to be highly expressed in the majority of cancers. In addition, high TDO2 expression was correlated with an unfavorable prognosis for patients in KIRP, LGG, TGCT, and UVM. Moreover, high TDO2 expression level positively correlated with higher immune infiltration, especially dendritic cells. Additionally, there is a close relationship between TDO2 and immune checkpoint-related gene markers, such as LAIR1, CD276, NRP1, CD80, and CD86. Finally, correlation analysis has demonstrated a high-correlation between TDO2 and TMB, MSI, MMR, and DNMT of multiple cancer types.

Conclusion

Therefore, our results suggest that TDO2 can function as a potential prognostic biomarker due to its role in tumor immunity regulation.

Dual-target inhibitors of indoleamine 2, 3 dioxygenase 1 (Ido1): A promising direction in cancer immunotherapy

Indoleamine 2, 3-dioxygenase 1 (IDO1) is a rate-limiting enzyme that catalyzes the kynurenine (Kyn) pathway of tryptophan metabolism in the first step, and the kynurenine pathway plays a fundamental role in immunosuppression in the tumor microenvironment. Therefore, researchers are vigorously developing IDO1 inhibitors, hoping to apply them to cancer immunotherapy. Nowadays, there have been 11 kinds of IDO1 inhibitors entering clinical trials, among which many inhibitors have shown good tumor inhibitory effect in phase I/II clinical trials. But the phase III study of the most promising IDO1 inhibitor compound 29 (Epacadostat) failed in 2018, which may be caused by the compensation effect offered by tryptophan 2,3-dioxygenase (TDO), the mismatched drug combination strategies, or other reasons. Luckily, dual-target inhibitors show great potential and advantages in solving these problems. In recent years, many studies have linked IDO1 to popular targets and selected many IDO1 dual-target inhibitors through pharmacophore fusion strategy and library construction, which enhance the tumor inhibitory effect and reduce side effects. Currently, three kinds of IDO1/TDO dual-target inhibitors have entered clinical trials, and extensive studies have been developing on IDO1 dual-target inhibitors. In this review, we summarize the IDO1 dual-target inhibitors developed in recent years and focus on the structure optimization process, structure-activity relationship, and the efficacy of in vitro and in vivo experiments, shedding a light on the pivotal significance of IDO1 dual-target inhibitors in the treatment of cancer, providing inspiration for the development of new IDO1 dual-target inhibitors.

Development of a cancer cells self‑activating and miR‑125a‑5p expressing poly‑pharmacological nanodrug for cancer treatment

Cancer cells can acquire resistance to targeted therapeutic agents when the designated targets or their downstream signaling molecules develop protein conformational or activity changes. There is an increasing interest in developing poly-pharmacologic anticancer agents to target multiple oncoproteins or signaling pathways in cancer cells. The microRNA 125a-5p (miR-125a-5p) is a tumor suppressor, and its expression has frequently been downregulated in tumors. By contrast, the anti-apoptotic molecule BIRC5/SURVIVIN is highly expressed in tumors but not in the differentiated normal tissues. In the present study, the development of a BIRC5 gene promoter-driven, miR-125a-5p expressing, poly-L-lysine-conjugated magnetite iron poly-pharmacologic nanodrug (pL-MNP-pSur-125a) was reported. The cancer cells self-activating property and the anticancer effects of this nanodrug were examined in both the multidrug efflux protein ABCB1/MDR1-expressing/-non-expressing cancer cells in vitro and in vivo. It was demonstrated that pL-MNP-pSur-125a decreased the expression of ERBB2/HER2, HDAC5, BIRC5, and SP1, which are hot therapeutic targets for cancer in vitro. Notably, pL-MNP-pSur-125a also downregulated the expression of TDO2 in the human KB cervical carcinoma cells. PL-MNP-pSur-125a decreased the viability of various BIRC5-expressing cancer cells, regardless of the tissue origin or the expression of ABCB1, but not of the human BIRC5-non-expressing HMEC-1 endothelial cells. In vivo, pL-MNP-pSur-125a exhibited potent antitumor growth effects, but without inducing liver toxicity, in various zebrafish human-ABCB1-expressing and ABCB1-non-expressing tumor xenograft models. In conclusion, pL-MNP-pSur-125a is an easy-to-prepare and a promising poly-pharmacological anticancer nanodrug that has the potential to manage numerous malignancies, particularly for patients with BIRC5/ABCB1-related drug resistance after prolonged chemotherapeutic treatments.

Reversing an Oncogenic Epithelial-to-Mesenchymal Transition Program in Breast Cancer Reveals Actionable Immune Suppressive Pathways

Approval of checkpoint inhibitors for treatment of metastatic triple negative breast cancer (mTNBC) has opened the door for the use of immunotherapies against this disease. However, not all patients with mTNBC respond to current immunotherapy approaches such as checkpoint inhibitors. Recent evidence demonstrates that TNBC metastases are more immune suppressed than primary tumors, suggesting that combination or additional immunotherapy strategies may be required to activate an anti-tumor immune attack at metastatic sites. To identify other immune suppressive mechanisms utilized by mTNBC, our group and others manipulated oncogenic epithelial-to-mesenchymal transition (EMT) programs in TNBC models to reveal differences between this breast cancer subtype and its more epithelial counterpart. This review will discuss how EMT modulation revealed several mechanisms, including tumor cell metabolism, cytokine milieu and secretion of additional immune modulators, by which mTNBC cells may suppress both the innate and adaptive anti-tumor immune responses. Many of these pathways/proteins are under preclinical or clinical investigation as therapeutic targets in mTNBC and other advanced cancers to enhance their response to chemotherapy and/or checkpoint inhibitors.

Parallel discovery of selective and dual inhibitors of tryptophan dioxygenases IDO1 and TDO2 with a newly-modified enzymatic assay

The expression of tryptophan catabolising enzyme indoleamine 2,3-dioxygenase 1 (IDO1) or tryptophan 2,3-dioxygenase 2 (TDO2) in cancers is associated with suppressed immunity and poor patient prognosis. Results from human clinical trials of IDO1 inhibitors have been disappointing. There is now a strong interest in the development of TDO2-selective or dual IDO1/TDO2 inhibitors that may surpass IDO1 inhibitors by providing broader efficacy and blocking constitutively-expressed hepatic TDO2. To expedite the discovery of novel TDO2-specific and dual inhibitors, an assay that enabled the efficient and accurate measurement of the inhibitory activity of compounds against both IDO1 and TDO2 enzymes, concurrently in the same experiment was established to screen 5,682 compounds that included the National Cancer Institute Diversity set 5, for inhibition of IDO1 and TDO2 activity. This screen identified 82 compounds that inhibited either IDO1, TDO2 or both enzymes > 50% at 20 µM. Thirty Pan Assay Interference compounds were removed from the list and the IC₅₀ of the remaining 52 compounds against IDO1 and TDO2 was subsequently determined using the newly-developed concurrent assay. Ten compounds were confirmed as dual IDO1/TDO2 inhibitors having IC₅₀ values under 50 µM against both enzymes and within 2-fold of each other. Six compounds with IC₅₀ values between 1.39 and 8.41 µM were identified as potential TDO2-selective leads. The use of this concurrent protocol is anticipated to expedite the discovery of novel leads for dual and selective inhibitors against IDO1 and or TDO2 and speed the evaluation of novel analogues that will ensue.

Development of Indoleamine 2,3-Dioxygenase 1 Inhibitors for Cancer Therapy and Beyond: A Recent Perspective

Indoleamine 2,3-dioxygenase 1 (IDO1) has received increasing attention due to its immunosuppressive function in connection with various diseases, including cancer. A recent increase in the understanding of IDO1 has significantly contributed to the discovery of numerous novel inhibitors, but the latest clinical outcomes raised questions and have indicated a future direction of IDO1 inhibition for therapeutic approaches. Herein, we present a comprehensive review of IDO1, discussing the latest advances in understanding the IDO1 structure and mechanism, an overview of recent IDO1 inhibitor discoveries and potential therapeutic applications to provide helpful information for medicinal chemists investigating IDO1 inhibitors.

Indoleamine and tryptophan 2,3-dioxygenases as important future therapeutic targets

Conversion of tryptophan to N-formylkynurenine is the first and rate-limiting step of the tryptophan metabolic pathway (i.e., the kynurenine pathway). This conversion is catalyzed by three enzyme isoforms: indoleamine 2,3-dioxygenase 1 (IDO1), indoleamine 2,3-dioxygenase 2 (IDO2), and tryptophan 2,3-dioxygenase (TDO). As this pathway generates numerous metabolites that are involved in various pathological conditions, IDOs and TDO represent important targets for therapeutic intervention. This pathway has especially drawn attention due to its importance in tumor resistance. Over the last decade, a large number of IDO and TDO inhibitors have been developed, many of which have entered clinical trials. Here, detailed structural comparisons of these three enzymes (with emphasis on their active sites), their involvement in cellular signaling, and their role(s) in pathological conditions are discussed. Furthermore, the most important recent inhibitors described in papers and patents and involved in clinical trials are reviewed, with a focus on both selective and multiple inhibitors. A short overview of the biochemical and cellular assays used for inhibitory potency evaluation is also presented. This review summarizes recent advances on IDO and TDO as potential drug targets, and provides the key features and perspectives for further research and development of potent inhibitors of the kynurenine pathway.

Different effects of tryptophan 2,3-dioxygenase inhibition on SK-Mel-28 and HCT-8 cancer cell lines

Purpose

Indoleamine 2,3-dioxygenase-1 (IDO1) and more recently, tryptophan 2,3-dioxygenase (TDO), are tryptophan-catabolizing enzymes with immunoregulatory properties in cancer. IDO1 is more expressed than TDO in many tumours including melanomas; however, IDO inhibitors did not give expected results in clinical trials, highlighting the need to consider TDO. We aimed to characterize both TDO expression and function in a melanoma cell line, named SK-Mel-28, with the purpose to compare it with a colon cancer cell line, HCT-8, and with a human endothelial cell line (HUVEC).

Methods

TDO expression was assessed as real time-PCR and western blot, for mRNA and protein expression, respectively. While cell proliferation was assessed as cell duplication, cell apoptosis and cell cycle were analysed by means of flow cytometry.

Results

SK-Mel-28 cells showed higher TDO levels compared to HCT-8 and to HUVEC cells. A selective TDO inhibitor, 680C91, significantly impaired cell proliferation in a concentration-dependent manner, by inducing cell arrest during the G2 phase for SK-Mel-28 and HUVEC cells, while an early apoptosis was increasing in HCT-8 cells. No toxic effects were observed. These data demonstrated that TDO is highly expressed in SK-Mel-28 cells and may be involved in the regulation of their proliferation.

Conclusion

TDO may directly modulate cancer cell function rather than immune suppression and can be considered as a target for melanoma progression together with IDO1.

New Insights from Crystallographic Data: Diversity of Structural Motifs and Molecular Recognition Properties between Groups of IDO1 Structures

A large number of crystallographic structures of IDO1 in different ligand-bound and -unbound states have been disclosed over the last decade. Yet, only a few of them have been exploited for structure-based drug design (SBDD) campaigns. In this study, we analyzed the structural motifs and molecular-recognition properties of three groups of IDO1 structures: 1) structures containing the heme group and inhibitors in the catalytic site; 2) heme-free structures of IDO1; 3) substrate-bound structures of IDO1. The results suggest that unrelated conformations of the enzyme have been solved with different ligand-induced changes of secondary motifs that localize even in regions remote from the catalytic site. Moreover, the study identified an uncharted region of molecular-recognition space covered by IDO1 binding sites that could guide the selection of diverse structures for additional SBDD studies aimed at the identification of novel lead compounds with differentiated chemical scaffolds.