Updates in the Clinical Development of Epacadostat and Other Indoleamine 2,3-Dioxygenase 1 Inhibitors (IDO1) for Human Cancers

Combination screen in multi-cell type tumor spheroids reveals interaction between aryl hydrocarbon receptor antagonists and E1 ubiquitin-activating enzyme inhibitor: Aryl-hydrocarbon receptor antagonist drug combinations

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that regulates genes of drug transporters and metabolic enzymes to detoxify small molecule xenobiotics. It has a complex role in cancer biology, influencing both the progression and suppression of tumors by modulating malignant properties of tumor cells and anti-tumor immunity, depending on the specific tumor type and developmental stage. This has led to the discovery and development of selective AhR modulators, including BAY 2416964 which is currently in clinical trials. To identify small molecule anticancer agents that might be combined with AhR antagonists for cancer therapy, a high-throughput combination screen was performed using multi-cell type tumor spheroids grown from malignant cells, endothelial cells, and mesenchymal stem cells. The AhR selective antagonists BAY 2416964, GNF351, and CH-223191 were tested individually and in combination with twenty-five small molecule anticancer agents. As single agents, BAY 2416964 and CH-223191 showed minimal activity, whereas GNF351 reduced the viability of some spheroid models at concentrations greater than 1 µM. The activity of most combinations aligned well with the single agent without apparent contributions from the AhR antagonist. All three AhR antagonists sensitized tumor spheroids to TAK-243, an E1 ubiquitin-activating enzyme inhibitor. These combinations were active in spheroids containing bladder, breast, ovary, kidney, pancreas, colon, and lung tumor cell lines. The AhR antagonists also potentiated pevonedistat, a selective inhibitor of the NEDD8-activating enzyme E1 regulatory subunit, in several tumor spheroid models. In contrast, the AhR antagonists did not enhance the cytotoxicity of the proteasome inhibitor bortezomib.

Pyroptosis and chemical classification of pyroptotic agents

Pyroptosis, as a lytic-inflammatory type of programmed cell death, has garnered considerable attention due to its role in cancer chemotherapy and many inflammatory diseases. This review will discuss the biochemical classification of pyroptotic inducers according to their chemical structure, pyroptotic mechanism, and cancer type of these targets. A structure-activity relationship study on pyroptotic inducers is revealed based on the surveyed pyroptotic inducer chemotherapeutics. The shared features in the chemical structures of current pyroptotic inducer agents were displayed, including an essential cyclic head, a vital linker, and a hydrophilic tail that is significant for π-π interactions and hydrogen bonding. The presented structural features will open the way to design new hybridized classes or scaffolds as potent pyroptotic inducers in the future, which may represent a solution to the apoptotic-resistance dilemma along with synergistic chemotherapeutic advantage.

Dual-targeted NAMPT inhibitors as a progressive strategy for cancer therapy

In mammals, nicotinamide phosphoribosyltransferase (NAMPT) is a crucial enzyme in the nicotinamide adenine dinucleotide (NAD+) synthesis pathway catalyzing the condensation of nicotinamide (NAM) with 5-phosphoribosyl-1-pyrophosphate (PRPP) to produce nicotinamide mononucleotide (NMN). Given the pivotal role of NAD+ in a range of cellular functions, including DNA synthesis, redox reactions, cytokine generation, metabolism, and aging, NAMPT has become a promising target for many diseases, notably cancer. Therefore, various NAMPT inhibitors have been reported and classified as first and second-generation based on their chemical structures and design strategies, dual-targeted being one. However, most NAMPT inhibitors suffer from several limitations, such as dose-dependent toxicity and poor pharmacokinetic properties. Consequently, there is no clinically approved NAMPT inhibitor. Hence, research on discovering more effective and less toxic dual-targeted NAMPT inhibitors with desirable pharmacokinetic properties has drawn attention recently. This review summarizes the previously reported dual-targeted NAMPT inhibitors, focusing on their design strategies and advantages over the single-targeted therapies.

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 epacadostat in patients with recurrent/metastatic head and neck squamous cell carcinoma (KEYNOTE-669/ECHO-304): a phase 3, randomized, open-label study

BACKGROUND

Advanced head and neck squamous cell carcinoma (HNSCC) has a poor prognosis, and new treatment options are needed. Combining immunotherapies with differing mechanisms of action may enhance clinical benefits compared with single-agent immunotherapy. Epacadostat, an indoleamine 2,3 dioxygenase 1 inhibitor, plus pembrolizumab, a PD-1 inhibitor, showed promising activity in advanced HNSCC in the phase 1/2 KEYNOTE-037/ECHO-202 trial.

METHODS

KEYNOTE-669/ECHO-304 is a randomized, open-label, phase 3 study evaluating the efficacy and safety of pembrolizumab plus epacadostat, pembrolizumab monotherapy, and the EXTREME regimen (cetuximab with a platinum [carboplatin or cisplatin] and 5-fluorouracil) in recurrent/metastatic (R/M) HNSCC. Participants had no prior systemic therapy for R/M HNSCC and were randomly assigned (2:1:2) to pembrolizumab 200 mg intravenously every 3 weeks plus epacadostat 100 mg orally twice daily, pembrolizumab monotherapy, or EXTREME. The primary endpoint was objective response rate (ORR; investigator assessment). Secondary endpoints were safety and tolerability. Change in serum kynurenine was an exploratory endpoint. Study enrollment was discontinued early as a strategic decision on May 2, 2018, and response assessment was discontinued after first on-study imaging assessment at week 9. Data cut-off was January 17, 2019.

RESULTS

Between December 1, 2017, and May 2, 2018, 89 patients were randomly allocated to pembrolizumab plus epacadostat (n = 35), pembrolizumab monotherapy (n = 19), or EXTREME (n = 35). ORR (95% CI) was 31% (17%-49%) for pembrolizumab plus epacadostat, 21% (6%-46%) for pembrolizumab monotherapy, and 34% (19%-52%) for EXTREME. Treatment-related adverse events (TRAEs) occurred in 82% (n = 28) of patients receiving pembrolizumab plus epacadostat, 63% (n = 12) receiving pembrolizumab monotherapy, and 100% (n = 34) receiving EXTREME. Grade 3-4 TRAEs occurred in 24% (n = 8) of patients receiving pembrolizumab plus epacadostat, 16% (n = 3) receiving pembrolizumab monotherapy, and 82% (n = 28) receiving EXTREME. No deaths occurred due to AEs. Pembrolizumab plus epacadostat treatment reduced kynurenine levels but not to that of healthy subjects.

CONCLUSIONS

Pembrolizumab plus epacadostat and pembrolizumab monotherapy provided a similar response rate to EXTREME and demonstrated a manageable safety profile in patients with R/M HNSCC.

TRIAL REGISTRATION

NCT03358472. Date of trial registration: November 30, 2017.

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.

Quantification and Profiling of Early and Late Differentiation Stage T Cells in Mantle Cell Lymphoma Reveals Immunotherapeutic Targets in Subsets of Patients

With the aim to advance the understanding of immune regulation in MCL and to identify targetable T-cell subsets, we set out to combine image analysis and spatial omic technology focused on both early and late differentiation stages of T cells. MCL patient tissue (n = 102) was explored using image analysis and GeoMx spatial omics profiling of 69 proteins and 1812 mRNAs. Tumor cells, T helper (TH) cells and cytotoxic (TC) cells of early (CD57-) and late (CD57+) differentiation stage were analyzed. An image analysis workflow was developed based on fine-tuned Cellpose models for cell segmentation and classification. TC and CD57+ subsets of T cells were enriched in tumor-rich compared to tumor-sparse regions. Tumor-sparse regions had a higher expression of several key immune suppressive proteins, tentatively controlling T-cell expansion in regions close to the tumor. We revealed that T cells in late differentiation stages (CD57+) are enriched among MCL infiltrating T cells and are predictive of an increased expression of immune suppressive markers. CD47, IDO1 and CTLA-4 were identified as potential targets for patients with T-cell-rich MCL TIME, while GITR might be a feasible target for MCL patients with sparse T-cell infiltration. In subgroups of patients with a high degree of CD57+ TC-cell infiltration, several immune checkpoint inhibitors, including TIGIT, PD-L1 and LAG3 were increased, emphasizing the immune-suppressive features of this highly differentiated T-cell subset not previously described in MCL.

Association of Indoleamine 2,3-Dioxygenase (IDO) Activity with Outcome after Cardiac Surgery in Adult Patients

Indoleamine 2,3-deoxygenase (IDO) plays an important role in the catabolism of the amino acid tryptophan. Tryptophan and its metabolites are key immune modulators. Increased IDO activity has been observed in various diseases and is associated with worse clinical outcomes. However, comprehensive research regarding its role in cardiac surgery remains limited. Therefore, we aimed to investigate perioperative changes in IDO activity and pathway metabolites, along with their impact on clinical outcomes in adult patients undergoing cardiac surgery. As an observational cohort study conducted at the Inselspital in Bern from January to December 2019, we retrospectively analyzed the data of prospectively collected biobank samples of patients undergoing cardiac surgery with the use of cardiopulmonary bypass. IDO pathway metabolite analysis was conducted by mass spectrometry. Perioperative dynamics were descriptively assessed and associated with pre-defined clinical outcome measures (30-day mortality, 1-year mortality, incidence of stroke and myocardial infarction, and length of hospital stay) through a multi-step exploratory regression analysis. A cohort of 192 adult patients undergoing cardiac surgery with the use of cardiopulmonary bypass were included (median age 67.0, IQR 60.0-73.0, 75.5% male). A significant perioperative decrease in the kynurenine/tryptophan (Kyn/Trp) ratio (-2.298, 95% CI -4.028 to -596, p = 0.009) and significant perioperative dynamics in the associated metabolites was observed. No association of perioperative changes in IDO activity and pathway metabolites with clinical outcomes was found. A significant decrease in the Kyn/Trp ratio among adult patients undergoing cardiac surgery indicates a perioperative downregulation of IDO, which stands in contrast to other pro-inflammatory conditions. Further studies are needed to investigate IDO in the setting of perioperative immunomodulation, which is a key driver of postoperative complications in cardiac surgery patients.

An Activatable Dual Polymer Nanosystem for Photoimmunotherapy and Metabolic Modulation of Deep-Seated Tumors

Nanomedicine in combination with immunotherapy has shown great potential in the cancer treatment, but phototherapeutic nanomaterials that specifically activate the immunopharmacological effects in deep tumors have rarely been developed due to limited laser penetration depth and tumor immune microenvironment. Herein, this work reports a newly synthesized semiconducting polymer (SP) grafted with imiquimod R837 and indoxmid encapsulated micelle (SPRIN-micelle) with strong absorption in the second near infrared window (NIR-II) that can relieve tumor immunosuppression and enhance the photothermal immunotherapy and catabolic modulation on tumors. Immune agonists (Imiquimod R837) and immunometabolic modulators (indoxmid) are covalently attached to NIR-II SP sensors via a glutathione (GSH) responsive self-immolation linker and then loaded into Pluronic F127 (F127) micelles by a temperature-sensitive critical micelle concentration (CMC)-switching method. Using this method, photothermal effect of SPRIN-micelles in deep-seated tumors can be activated, leading to effective tumor ablation and immunogenic cell death (ICD). Meanwhile, imiquimod and indoxmid are tracelessly released in response to the tumor microenvironment, resulting in dendritic cell (DC) maturation by imiquimod R837 and inhibition of both indoleamine 2,3-dioxygenase (IDO) activity and Treg cell expression by indoxmid. Ultimately, cytotoxic T-lymphocyte infiltration and tumor metastasis inhibition in deep solid tumors (9 mm) are achieved. In summary, this work demonstrates a new strategy for the combination of photothermal immunotherapy and metabolic modulation by developing a dual functional polymer system including activable SP and temperature-sensitive F127 for the treatment of deep solid tumors.

Identification and validation of tryptophan metabolism-related lncRNAs in lung adenocarcinoma prognosis and immune response

BACKGROUND

Tryptophan (Trp) is an essential amino acid. Increasing evidence suggests that tryptophan metabolism plays a complex role in immune escape from Lung adenocarcinoma (LUAD). However, the role of long non-coding RNAs (lncRNAs) in tryptophan metabolism remains to be investigated.

METHODS

This study uses The Cancer Genome Atlas (TCGA)-LUAD dataset as the training cohort, and several datasets from the Gene Expression Omnibus (GEO) database are merged into the validation cohort. Genes related to tryptophan metabolism were identified from the Molecular Signatures Database (MSigDB) database and further screened for lncRNAs with Trp-related expression. Subsequently, a prognostic signature of lncRNAs related to tryptophan metabolism was constructed using Cox regression analysis, (Least absolute shrinkage and selection operator regression) and LASSO analysis. The predictive performance of this risk score was validated by Kaplan-Meier (KM) survival analysis, (receiver operating characteristic) ROC curves, and nomograms. We also explored the differences in immune cell infiltration, immune cell function, tumor mutational load (TMB), tumor immune dysfunction and exclusion (TIDE), and anticancer drug sensitivity between high- and low-risk groups. Finally, we used real-time fluorescence quantitative PCR, CCK-8, colony formation, wound healing, transwell, flow cytometry, and nude mouse xenotransplantation models to elucidate the role of ZNF8-ERVK3-1 in LUAD.

RESULTS

We constructed 16 tryptophan metabolism-associated lncRNA prognostic models in LUAD patients. The risk score could be used as an independent prognostic indicator for the prognosis of LUAD patients. Kaplan-Meier survival analysis, ROC curves, and risk maps validated the prognostic value of the risk score. The high-risk and low-risk groups showed significant differences in phenotypes, such as the percentage of immune cell infiltration, immune cell function, gene mutation frequency, and anticancer drug sensitivity. In addition, patients with high-risk scores had higher TMB and TIDE scores compared to patients with low-risk scores. Finally, we found that ZNF8-ERVK3-1 was highly expressed in LUAD tissues and cell lines. A series of in vitro experiments showed that knockdown of ZNF8-ERVK3-1 inhibited cell proliferation, migration, and invasion, leading to cell cycle arrest in the G0/G1 phase and increased apoptosis. In vivo experiments with xenografts have shown that knocking down ZNF8-ERVK3-1 can significantly inhibit tumor size and tumor proliferation.

CONCLUSION

We constructed a new prognostic model for tryptophan metabolism-related lncRNA. The risk score was closely associated with common clinical features such as immune cell infiltration, immune-related function, TMB, and anticancer drug sensitivity. Knockdown of ZNF8-ERVK3-1 inhibited LUAD cell proliferation, migration, invasion, and G0/G1 phase blockade and promoted apoptosis.

Discovery of the sEH Inhibitor Epoxykynin as a Potent Kynurenine Pathway Modulator

Disease-related phenotypic assays enable unbiased discovery of novel bioactive small molecules and may provide novel insights into physiological systems and unprecedented molecular modes of action (MMOA). Herein, we report the identification and characterization of epoxykynin, a potent inhibitor of the soluble epoxide hydrolase (sEH). Epoxykynin was discovered by means of a cellular assay monitoring modulation of kynurenine (Kyn) levels in BxPC-3 cells upon stimulation with the cytokine interferon-γ (IFN-γ) and subsequent target identification employing affinity-based chemical proteomics. Increased Kyn levels are associated with immune suppression in the tumor microenvironment and, thus, the Kyn pathway and its key player indoleamine 2,3-dioxygenase 1 (IDO1) are appealing targets in immuno-oncology. However, targeting IDO1 directly has led to limited success in clinical investigations, demonstrating that alternative approaches to reduce Kyn levels are in high demand. We uncover a cross-talk between sEH and the Kyn pathway that may provide new opportunities to revert cancer-induced immune tolerance.

Targeting tumor-infiltrating tregs for improved antitumor responses

Immunotherapies have revolutionized the landscape of cancer treatment. Regulatory T cells (Tregs), as crucial components of the tumor immune environment, has great therapeutic potential. However, nonspecific inhibition of Tregs in therapies may not lead to enhanced antitumor responses, but could also trigger autoimmune reactions in patients, resulting in intolerable treatment side effects. Hence, the precision targeting and inhibition of tumor-infiltrating Tregs is of paramount importance. In this overview, we summarize the characteristics and subpopulations of Tregs within tumor microenvironment and their inhibitory mechanisms in antitumor responses. Furthermore, we discuss the current major strategies targeting regulatory T cells, weighing their advantages and limitations, and summarize representative clinical trials targeting Tregs in cancer treatment. We believe that developing therapies that specifically target and suppress tumor-infiltrating Tregs holds great promise for advancing immune-based therapies.

The Role of Tumor Metabolic Reprogramming in Tumor Immunity

The occurrence and development of tumors require the metabolic reprogramming of cancer cells, namely the alteration of flux in an autonomous manner via various metabolic pathways to meet increased bioenergetic and biosynthetic demands. Tumor cells consume large quantities of nutrients and produce related metabolites via their metabolism; this leads to the remodeling of the tumor microenvironment (TME) to better support tumor growth. During TME remodeling, the immune cell metabolism and antitumor immune activity are affected. This further leads to the escape of tumor cells from immune surveillance and therefore to abnormal proliferation. This review summarizes the regulatory functions associated with the abnormal biosynthesis and activity of metabolic signaling molecules during the process of tumor metabolic reprogramming. In addition, we provide a comprehensive description of the competition between immune cells and tumor cells for nutrients in the TME, as well as the metabolites required for tumor metabolism, the metabolic signaling pathways involved, and the functionality of the immune cells. Finally, we summarize current research targeted at the development of tumor immunotherapy. We aim to provide new concepts for future investigations of the mechanisms underlying the metabolic reprogramming of tumors and explore the association of these mechanisms with tumor immunity.

Targeting the aryl hydrocarbon receptor (AhR) with BAY 2416964: a selective small molecule inhibitor for cancer immunotherapy

BACKGROUND

The metabolism of tryptophan to kynurenines (KYN) by indoleamine-2,3-dioxygenase or tryptophan-2,3-dioxygenase is a key pathway of constitutive and adaptive tumor immune resistance. The immunosuppressive effects of KYN in the tumor microenvironment are predominantly mediated by the aryl hydrocarbon receptor (AhR), a cytosolic transcription factor that broadly suppresses immune cell function. Inhibition of AhR thus offers an antitumor therapy opportunity via restoration of immune system functions.

METHODS

The expression of AhR was evaluated in tissue microarrays of head and neck squamous cell carcinoma (HNSCC), non-small cell lung cancer (NSCLC) and colorectal cancer (CRC). A structure class of inhibitors that block AhR activation by exogenous and endogenous ligands was identified, and further optimized, using a cellular screening cascade. The antagonistic properties of the selected AhR inhibitor candidate BAY 2416964 were determined using transactivation assays. Nuclear translocation, target engagement and the effect of BAY 2416964 on agonist-induced AhR activation were assessed in human and mouse cancer cells. The immunostimulatory properties on gene and cytokine expression were examined in human immune cell subsets. The in vivo efficacy of BAY 2416964 was tested in the syngeneic ovalbumin-expressing B16F10 melanoma model in mice. Coculture of human H1299 NSCLC cells, primary peripheral blood mononuclear cells and fibroblasts mimicking the human stromal-tumor microenvironment was used to assess the effects of AhR inhibition on human immune cells. Furthermore, tumor spheroids cocultured with tumor antigen-specific MART-1 T cells were used to study the antigen-specific cytotoxic T cell responses. The data were analyzed statistically using linear models.

RESULTS

AhR expression was observed in tumor cells and tumor-infiltrating immune cells in HNSCC, NSCLC and CRC. BAY 2416964 potently and selectively inhibited AhR activation induced by either exogenous or endogenous AhR ligands. In vitro, BAY 2416964 restored immune cell function in human and mouse cells, and furthermore enhanced antigen-specific cytotoxic T cell responses and killing of tumor spheroids. In vivo, oral application with BAY 2416964 was well tolerated, induced a proinflammatory tumor microenvironment, and demonstrated antitumor efficacy in a syngeneic cancer model in mice.

CONCLUSIONS

These findings identify AhR inhibition as a novel therapeutic approach to overcome immune resistance in various types of cancers.

Interplay between Estrogen, Kynurenine, and AHR Pathways: An immunosuppressive axis with therapeutic potential for breast cancer treatment

Breast cancer is one of the most common malignancies among women worldwide. Estrogen exposure via endogenous and exogenous sources during a lifetime, together with environmental exposure to estrogenic compounds, represent the most significant risk factor for breast cancer development. As breast tumors establish, multiple pathways are deregulated. Among them is the aryl hydrocarbon receptor (AHR) signaling pathway. AHR, a ligand-activated transcription factor associated with the metabolism of polycyclic aromatic hydrocarbons and estrogens, is overexpressed in breast cancer. Furthermore, AHR and estrogen receptor (ER) cross-talk pathways have been observed. Additionally, the Tryptophan (Trp) catabolizing enzymes indolamine-2,3-dioxygenase (IDO) and tryptophan-2,3-dioxygenase (TDO) are overexpressed in breast cancer. IDO/TDO catalyzes the formation of Kynurenine (KYN) and other tryptophan-derived metabolites, which are ligands of AHR. Once KYN activates AHR, it stimulates the expression of the IDO enzyme, increases the level of KYN, and activates non-canonical pathways to control inflammation and immunosuppression in breast tumors. The interplay between E2, AHR, and IDO/TDO/KYN pathways and their impact on the immune system represents an immunosuppressive axis on breast cancer. The potential modulation of the immunosuppressive E2-AHR-IDO/TDO/KYN axis has aroused great expectations in oncotherapy. The present article will review the mechanisms implicated in generating the immunosuppressive axis E2-AHR-IDO/TDO/KYN in breast cancer and the current state of knowledge as a potential therapeutic target.

Unveiling the growing significance of metabolism in modulating immune cell function: exploring mechanisms and implications; a review

Immunometabolism has emerged as a rapidly growing field of research, holding significant promise for personalised medicine and precision immunotherapy. This review explores the intricate relationship between immune function and metabolic processes, emphasising their profound impact on various immune-related disorders. Understanding how metabolic dysregulation contributes to the pathogenesis of these disorders remains a critical research gap. Therefore, this review aims to bridge that gap by examining the key metabolic pathways involved and their specific implications in immune cell function. Key metabolic pathways, including glycolysis, mitochondrial metabolism, fatty acid metabolism, and amino acid metabolism, are discussed in the context of immune cell function. Dysregulation of these pathways can disrupt immune cell activation, differentiation, and overall function, contributing to disease pathogenesis. Understanding these metabolic alterations' molecular mechanisms is essential for developing targeted therapeutic interventions. The review also emphasises the importance of personalised medicine in immune-related disorders. The unique metabolic profiles of individuals can influence treatment outcomes, highlighting the need for tailored approaches. Integrating metabolic profiling into clinical practice can enhance treatment efficacy and improve patient outcomes. Investigating the clinical significance of immunometabolism in diverse disease contexts will facilitate the translation of research findings into clinical practice. Moreover, refining treatment strategies based on individual metabolic profiles will contribute to advancing precision immunotherapy.

RAIDS atlas of significant genetic and protein biomarkers in cervical cancer

Loss of function in epigenetic acting genes together with driver alterations in the PIK3CA pathway have been shown significantly associated with poor outcome in cervical squamous cell cancer. More recently, a CoxBoost analysis identified 16 gene alterations and 30 high level activated proteins to be of high interest, due to their association with either good or bad outcome, in the context of treatment received by chemoradiation. The objectives here were to review and confirm the significance of these molecular alterations as suggested by literature reports and to pinpoint alternate treatments options for poor-responders to chemoradiation.

Molecular Farming of Pembrolizumab and Nivolumab

Immune checkpoint inhibitors (ICIs) are a class of immunotherapy agents capable of alleviating the immunosuppressive effects exerted by tumorigenic cells. The programmed cell death protein 1 (PD-1)/programmed death-ligand 1 (PD-L1) immune checkpoint is one of the most ubiquitous checkpoints utilized by tumorigenic cells for immune evasion by inducing apoptosis and inhibiting the proliferation and cytokine production of T lymphocytes. Currently, the most frequently used ICIs targeting the PD-1/PD-L1 checkpoint include monoclonal antibodies (mAbs) pembrolizumab and nivolumab that bind to PD-1 on T lymphocytes and inhibit interaction with PD-L1 on tumorigenic cells. However, pembrolizumab and nivolumab are costly, and thus their accessibility is limited in low- and middle-income countries (LMICs). Therefore, it is essential to develop novel biomanufacturing platforms capable of reducing the cost of these two therapies. Molecular farming is one such platform utilizing plants for mAb production, and it has been demonstrated to be a rapid, low-cost, and scalable platform that can be potentially implemented in LMICs to diminish the exorbitant prices, ultimately leading to a significant reduction in cancer-related mortalities within these countries.

Intrinsic features of the cancer cell as drivers of immune checkpoint blockade response and refractoriness

Immune checkpoint blockade represents the latest revolution in cancer treatment by substantially increasing patients' lifetime and quality of life in multiple neoplastic pathologies. However, this new avenue of cancer management appeared extremely beneficial in a minority of cancer types and the sub-population of patients that would benefit from such therapies remain difficult to predict. In this review of the literature, we have summarized important knowledge linking cancer cell characteristics with the response to immunotherapy. Mostly focused on lung cancer, our objective was to illustrate how cancer cell diversity inside a well-defined pathology might explain sensitivity and refractoriness to immunotherapies. We first discuss how genomic instability, epigenetics and innate immune signaling could explain differences in the response to immune checkpoint blockers. Then, in a second part we detailed important notions suggesting that altered cancer cell metabolism, specific oncogenic signaling, tumor suppressor loss as well as tight control of the cGAS/STING pathway in the cancer cells can be associated with resistance to immune checkpoint blockade. At the end, we discussed recent evidences that could suggest that immune checkpoint blockade as first line therapy might shape the cancer cell clones diversity and give rise to the appearance of novel resistance mechanisms.

Targeting the tumor microenvironment by liposomal Epacadostat in combination with liposomal gp100 vaccine

Indoleamine-2,3-dioxygenase (IDO1) pathway has vital role in cancer immune escape and its upregulation leads to immunosuppressive environment which is associated with poor prognosis and progression in various cancers like melanoma. Previously, we showed the antitumoral efficacy of nanoliposomal form of Epacadostat (Lip-EPA), as an IDO1 inhibitor. Herein, we used Lip-EPA as a combination approach with liposomal gp100 (Lip-gp100) anti-cancer vaccine in melanoma model. Here, we showed that B16F10 tumor express IDO1 so using Lip-EPA will enhance the efficacy of vaccine therapy. The biodistribution of ICG-labelled liposomal form of EPA showed the remarkable accumulation of drug at tumor site. In an in vivo study, Lip-EPA enhanced the antitumor efficacy of Lip-gp100 in which the IDO mRNA expression was decreased (~ fourfold) in tumor samples. Also, we identified a significant increase in the number of infiltrated T lymphocytes (p < 0.0001) with enhanced in interferon gamma (IFN-γ) production (p < 0.0001). Additionally, Lip-EPA + Lip-gp100 significantly modulated intratumoral regulatory T cells which altogether resulted in the highest delay in tumor growth (TGD = 56.54%) and increased life span (ILS > 47.36%) in treated mice. Our study demonstrated that novel combination of Lip-EPA and Lip-gp100 was effective treatment with capability of being used in further clinical studies.

Addressing Natural Killer Cell Dysfunction and Plasticity in Cell-Based Cancer Therapeutics

Natural killer (NK) cells are cytotoxic group 1 innate lymphoid cells (ILC), known for their role as killers of stressed, cancerous, and virally infected cells. Beyond this cytotoxic function, NK cell subsets can influence broader immune responses through cytokine production and have been linked to central roles in non-immune processes, such as the regulation of vascular remodeling in pregnancy and cancer. Attempts to exploit the anti-tumor functions of NK cells have driven the development of various NK cell-based therapies, which have shown promise in both pre-clinical disease models and early clinical trials. However, certain elements of the tumor microenvironment, such as elevated transforming growth factor (TGF)-β, hypoxia, and indoalemine-2,3-dioxygenase (IDO), are known to suppress NK cell function, potentially limiting the longevity and activity of these approaches. Recent studies have also identified these factors as contributors to NK cell plasticity, defined by the conversion of classical cytotoxic NK cells into poorly cytotoxic, tissue-resident, or ILC1-like phenotypes. This review summarizes the current approaches for NK cell-based cancer therapies and examines the challenges presented by tumor-linked NK cell suppression and plasticity. Ongoing efforts to overcome these challenges are discussed, along with the potential utility of NK cell therapies to applications outside cancer.

Targeting tumor-associated macrophages for successful immunotherapy of ovarian carcinoma

Epithelial ovarian cancer (EOC) is among the top five causes of cancer-related death in women, largely reflecting early, prediagnosis dissemination of malignant cells to the peritoneum. Despite improvements in medical therapies, particularly with the implementation of novel drugs targeting homologous recombination deficiency, the survival rates of patients with EOC remain low. Unlike other neoplasms, EOC remains relatively insensitive to immune checkpoint inhibitors, which is correlated with a tumor microenvironment (TME) characterized by poor infiltration by immune cells and active immunosuppression dominated by immune components with tumor-promoting properties, especially tumor-associated macrophages (TAMs). In recent years, TAMs have attracted interest as potential therapeutic targets by seeking to reverse the immunosuppression in the TME and enhance the clinical efficacy of immunotherapy. Here, we review the key biological features of TAMs that affect tumor progression and their relevance as potential targets for treating EOC. We especially focus on the therapies that might modulate the recruitment, polarization, survival, and functional properties of TAMs in the TME of EOC that can be harnessed to develop superior combinatorial regimens with immunotherapy for the clinical care of patients with EOC.

Tumor-associated nonmyelinating Schwann cell-expressed PVT1 promotes pancreatic cancer kynurenine pathway and tumor immune exclusion

One of the major obstacles to treating pancreatic ductal adenocarcinoma (PDAC) is its immunoresistant microenvironment. The functional importance and molecular mechanisms of Schwann cells in PDAC remains largely elusive. We characterized the gene signature of tumor-associated nonmyelinating Schwann cells (TASc) in PDAC and indicated that the abundance of TASc was correlated with immune suppressive tumor microenvironment and the unfavorable outcome of patients with PDAC. Depletion of pancreatic-specific TASc promoted the tumorigenesis of PDAC tumors. TASc-expressed long noncoding RNA (lncRNA) plasmacytoma variant translocation 1 (PVT1) was triggered by the tumor cell-produced interleukin-6. Mechanistically, PVT1 modulated RAF proto-oncogene serine/threonine protein kinase-mediated phosphorylation of tryptophan 2,3-dioxygenase in TASc, facilitating its enzymatic activities in catalysis of tryptophan to kynurenine. Depletion of TASc-expressed PVT1 suppressed PDAC tumor growth. Furthermore, depletion of TASc using a small-molecule inhibitor effectively sensitized PDAC to immunotherapy, signifying the important roles of TASc in PDAC immune resistance.

Skin Cancer Pathobiology at a Glance: A Focus on Imaging Techniques and Their Potential for Improved Diagnosis and Surveillance in Clinical Cohorts

Early diagnosis is essential for completely eradicating skin cancer and maximizing patients' clinical benefits. Emerging optical imaging modalities such as reflectance confocal microscopy (RCM), optical coherence tomography (OCT), magnetic resonance imaging (MRI), near-infrared (NIR) bioimaging, positron emission tomography (PET), and their combinations provide non-invasive imaging data that may help in the early detection of cutaneous tumors and surgical planning. Hence, they seem appropriate for observing dynamic processes such as blood flow, immune cell activation, and tumor energy metabolism, which may be relevant for disease evolution. This review discusses the latest technological and methodological advances in imaging techniques that may be applied for skin cancer detection and monitoring. In the first instance, we will describe the principle and prospective clinical applications of the most commonly used imaging techniques, highlighting the challenges and opportunities of their implementation in the clinical setting. We will also highlight how imaging techniques may complement the molecular and histological approaches in sharpening the non-invasive skin characterization, laying the ground for more personalized approaches in skin cancer patients.

Strategies to overcome myeloid cell induced immune suppression in the tumor microenvironment

Cancer progression and metastasis due to tumor immune evasion and drug resistance is strongly associated with immune suppressive cellular responses, particularly in the case of metastatic tumors. The myeloid cell component plays a key role within the tumor microenvironment (TME) and disrupts both adaptive and innate immune cell responses leading to loss of tumor control. Therefore, strategies to eliminate or modulate the myeloid cell compartment of the TME are increasingly attractive to non-specifically increase anti-tumoral immunity and enhance existing immunotherapies. This review covers current strategies targeting myeloid suppressor cells in the TME to enhance anti-tumoral immunity, including strategies that target chemokine receptors to deplete selected immune suppressive myeloid cells and relieve the inhibition imposed on the effector arms of adaptive immunity. Remodeling the TME can in turn improve the activity of other immunotherapies such as checkpoint blockade and adoptive T cell therapies in immunologically "cold" tumors. When possible, in this review, we have provided evidence and outcomes from recent or current clinical trials evaluating the effectiveness of the specific strategies used to target myeloid cells in the TME. The review seeks to provide a broad overview of how myeloid cell targeting can become a key foundational approach to an overall strategy for improving tumor responses to immunotherapy.

Future directions in cancer immunotherapy with monoclonal antibodies

Introduction: Cancer immunotherapy with monoclonal antibodies (mAbs) has become a therapy with great potential nowadays. It is based on the affinity of antibodies to bind to specific molecules, thus inhibiting the growth and spread of cancer. There is a wide variety of mAbs with differentiated mechanisms and enormous clinical benefits. However, different immunotherapeutic alternatives have emerged due to their limitations, such as the long duration of organ toxicity and the inability to penetrate intracellularly. This mini-review will discuss the emerging alternatives of cancer immunotherapies based on mAbs.

Bispecific antibodies (BsAbs): Antibodies designed to bind to two epitopes of an antigen.

Antibody fragments: Fragments of the Fab region generated from the variable region of IgG and IgM and a scFv.

Antibody-drug conjugates (ADCs): Administration of mAbs and a toxin of high specificity for a tumour target.

Nanobodies (or nanocomponents): Small fragments of antibody heavy chain.

Intrabodies (or intracellular antibodies): Antibodies that are expressed intracellularly and synthesised inside cells by retroviral delivery systems.

Stereospecific and catalytic mAbs: Antibodies that recognise the 3D configurations of target molecules.

Combination immunotherapies: Therapies that combine cytokines with tumour-targeted mAbs.

Small molecule immunotherapeutics: Small molecule drugs that can stimulate intracellular pathways primarily involved in immune cell checkpoints and bind to mAb-like targets.

Conclusion: These new varieties of immunotherapy present significant advantages, but future research should continue to improve their efficacy and safety and identify new biomarkers.

Graphical abstract:

Druggable Metabolic Vulnerabilities Are Exposed and Masked during Progression to Castration Resistant Prostate Cancer

There is an urgent need for exploring new actionable targets other than androgen receptor to improve outcome from lethal castration-resistant prostate cancer. Tumor metabolism has reemerged as a hallmark of cancer that drives and supports oncogenesis. In this regard, it is important to understand the relationship between distinctive metabolic features, androgen receptor signaling, genetic drivers in prostate cancer, and the tumor microenvironment (symbiotic and competitive metabolic interactions) to identify metabolic vulnerabilities. We explore the links between metabolism and gene regulation, and thus the unique metabolic signatures that define the malignant phenotypes at given stages of prostate tumor progression. We also provide an overview of current metabolism-based pharmacological strategies to be developed or repurposed for metabolism-based therapeutics for castration-resistant prostate cancer.

Prediction of hepatocellular carcinoma prognosis and immunotherapeutic effects based on tryptophan metabolism-related genes

Background

L-tryptophan (Trp) metabolism involved in mediating tumour development and immune suppression. However, comprehensive analysis of the role of the Trp metabolism pathway is still a challenge.

Methods

We downloaded Trp metabolism-related genes’ expression data from different public databases, including TCGA, Gene Expression Omnibus (GEO) and Hepatocellular Carcinoma Database (HCCDB). And we identified two metabolic phenotypes using the ConsensusClusterPlus package. Univariate regression analysis and lasso Cox regression analysis were used to establish a risk model. CIBERSORT and Tracking of Indels by DEcomposition (TIDE) analyses were adopted to assess the infiltration abundance of immune cells and tumour immune escape.

Results

We identified two metabolic phenotypes, and patients in Cluster 2 (C2) had a better prognosis than those in Cluster 1 (C1). The distribution of clinical features between the metabolic phenotypes showed that patients in C1 tended to have higher T stage, stage, grade, and death probability than those of patients in C2. Additionally, we screened 739 differentially expressed genes (DEGs) between the C1 and C2. We generated a ten-gene risk model based on the DEGs, and the area under the curve (AUC) values of the risk model for predicting overall survival. Patients in the low-risk subgroup tended to have a significantly longer overall survival than that of those in the high-risk group. Moreover, univariate analysis indicated that the risk model was significantly correlated with overall survival. Multivariate analysis showed that the risk model remained an independent risk factor in hepatocellular carcinoma (p < 0.0001).

Conclusions

We identified two metabolic phenotypes based on genes of the Trp metabolism pathway, and we established a risk model that could be used for predicting prognosis and guiding immunotherapy in patients with hepatocellular carcinoma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02730-8.

Engineered DBCO+PD-1 Nanovesicles Carrying 1-MT for Cancer-Targeted Immunotherapy

Liver cancer cells evade immune surveillance and anticancer response through various pathways, including the programmed death-ligand 1 (PD-L1)/programmed death-1 (PD-1) immune checkpoint axis that exhausts CD8⁺ T cells. Inhibitors or antibodies of the PD-L1/PD-1 signaling axis are considered promising drugs for cancer immunotherapy and exhibit favorable clinical responses. However, adverse effects, immune tolerance, and delivery barriers of most patients limit the clinical application of PD-L1/PD-1 antibodies. Thus, it is critical to develop a novel delivery strategy to enhance anticancer immunotherapy. In this study, we bioengineered cell membrane-derived nanovesicles (NVs) presenting PD-1 proteins and dibenzocyclooctyne (DBCO) to encapsulate 1-methyltryptophan (1-MT) (DBCO+PD-1@1-MT NVs). DBCO can specifically interact with N-azidoacetylmannosamine-tetraacetylate (Ac₄ManN₃) labeled onto metabolic cells for targeted killing of cancers. We next explored the effects of DBCO+PD-1@1-MT NVs on anticancer Hepa1-6 cells in vitro and in vivo. Results showed that PD-1@1-MT NVs dramatically inhibited Hepa1-6 proliferation, promoted peripheral blood mononuclear cell (PBMC) expansion, and strengthened anticancer therapy via blockading the PD-1/PD-L1 immune checkpoint axis, owing to the 1-methyltryptophan (1-MT) enhancement of anticancer immunotherapy efficacy through suppressing the activity of indoleamine 2,3-dioxygenase (IDO). Thus, 1-MT was encapsulated into PD-1 NVs to synergistically enhance cancer immunotherapy. Results have shown that PD-1@1-MT NVs obviously attenuated tumor growth, promoting IFN-γ production, increasing the T cells infiltration in tumors and spleens, and improving the survival period of tumor-bearing mice compared to monotherapy. Therefore, we propose a promising delivery strategy of the combination of DBCO+PD-1 NVs and 1-MT for specific and effective cancer-targeted immunotherapy.

Identification of a Novel Pseudo-Natural Product Type IV IDO1 Inhibitor Chemotype

Natural product (NP)-inspired design principles provide invaluable guidance for bioactive compound discovery. Pseudo-natural products (PNPs) are de novo combinations of NP fragments to target biologically relevant chemical space not covered by NPs. We describe the design and synthesis of apoxidoles, a novel pseudo-NP class, whereby indole- and tetrahydropyridine fragments are linked in monopodal connectivity not found in nature. Apoxidoles are efficiently accessible by an enantioselective [4+2] annulation reaction. Biological evaluation revealed that apoxidoles define a new potent type IV inhibitor chemotype of indoleamine 2,3-dioxygenase 1 (IDO1), a heme-containing enzyme considered a target for the treatment of neurodegeneration, autoimmunity and cancer. Apoxidoles target apo-IDO1, prevent heme binding and induce unique amino acid positioning as revealed by crystal structure analysis. Novel type IV apo-IDO1 inhibitors are in high demand, and apoxidoles may provide new opportunities for chemical biology and medicinal chemistry research.

Engineered Hybrid Treg-Targeted Nanosomes Restrain Lung Immunosuppression by Inducing Intratumoral CD8+T Cell Immunity

Introduction

Tumor immunotherapy is a key therapeutic paradigm for the treatment of several malignancies. However, in metastatic lung cancer, classical immunotherapy regimes are ineffective due to regulatory T cell (Treg)-related immunosuppression and tumor relapse.

Materials

To address this issue, we designed specific biocompatible Treg-targeted nanocarriers (NCs) as a model of immune-based nanotherapy, in order to target Treg-related immunosuppression in the lung tumor microenvironment. This is achieved through the combination of Dasatinib and Epacadostat integrated into biodegradable nanosomes which can inhibit and reverse Treg-supporting immunosuppression. Flow cytometry and immunofluorescence analysis, PET/CT scan, PTT/PA imaging and the Balb/c tumor model were used to explore the anti-tumor effect of Treg-targeted NCs both in vitro and in vivo.

Results

Findings reveal that NC treatment triggered substantial tumor cell apoptosis and drastically decreased tumor volume followed by downregulation of Ki-67 antigen expression, respectively. Drug circulation time was also increased as shown by biodistribution analysis accompanied by greater accumulation in lung and peripheral tissues. Intratumoral Th1 cytokines’ expression was also increased, especially TNF-A, IL-12 by 42%, and IL-6 by 18% compared to PBS treatment. In addition, the presence of mature CD80⁺/CD86⁺dendritic cells (DCs) revealed T cell enrichment and a decline in MDSC infiltration and myeloid subsets. Interestingly, a significant decline of Gr/CD11b myeloid cell population in blood and tissue samples was also observed. This immune activation can be attributed to the enhanced PTT efficiency and tumor targeting ability of the nanospheres which under near infrared (NIR) exposure can prompt highly efficient tumor ablation. We also demonstrated their therapeutic efficacy against 4T1 metastatic breast cancer model. Additionally, the photothermal therapy in combination with PD-L1 checkpoint blockade therapy exerted long-term tumor control over both primary and distant tumors.

Discussion

Overall, our findings present a novel nano-enabled platform for the inhibition of Treg-dependent immunosuppression in NSCLC and provide a novel nanotherapeutic strategy for the treatment of metastatic neoplasia.

USP14 promotes tryptophan metabolism and immune suppression by stabilizing IDO1 in colorectal cancer

Indoleamine 2,3 dioxygenase 1 (IDO1) is an attractive target for cancer immunotherapy. However, IDO1 inhibitors have shown disappointing therapeutic efficacy in clinical trials, mainly because of the activation of the aryl hydrocarbon receptor (AhR). Here, we show a post-transcriptional regulatory mechanism of IDO1 regulated by a proteasome-associated deubiquitinating enzyme, USP14, in colorectal cancer (CRC). Overexpression of USP14 promotes tryptophan metabolism and T-cell dysfunction by stabilizing the IDO1 protein. Knockdown of USP14 or pharmacological targeting of USP14 decreases IDO1 expression, reverses suppression of cytotoxic T cells, and increases responsiveness to anti-PD-1 in a MC38 syngeneic mouse model. Importantly, suppression of USP14 has no effects on AhR activation induced by the IDO1 inhibitor. These findings highlight a relevant role of USP14 in post-translational regulation of IDO1 and in the suppression of antitumor immunity, suggesting that inhibition of USP14 may represent a promising strategy for CRC immunotherapy.

Targeting Indoleamine Dioxygenase and Tryptophan Dioxygenase in Cancer Immunotherapy: Clinical Progress and Challenges

Indoleamine 2.3-dioxygenases (IDO1/2) and tryptophan 2.3-dioxygenase (TDO) are the initial and rate-limiting enzymes in tryptophan metabolism, which play an essential role in mediating immunosuppression in tumor microenvironment. Accumulating evidence has indicated that both IDO1 and TDO are highly expressed in many malignant tumors, and their expression is generally associated with reduced tumor-infiltrating immune cells, increased regulatory T-cell infiltration, as well as cancer progression and poor prognosis for malignancies. A large number of IDO1 and TDO inhibitors have been screened or synthesized in the last two decades. Thus far, at least 12 antagonists targeting IDO1 and TDO have advanced to clinical trials. In this account, we conducted a comprehensive review of the development of IDO1 and TDO inhibitors in cancer immunotherapy, particularly their clinical research progress, and presented the current challenges and corresponding solutions.

Connections between metabolism and epigenetics: mechanisms and novel anti-cancer strategy

Cancer cells undergo metabolic adaptations to sustain their growth and proliferation under several stress conditions thereby displaying metabolic plasticity. Epigenetic modification is known to occur at the DNA, histone, and RNA level, which can alter chromatin state. For almost a century, our focus in cancer biology is dominated by oncogenic mutations. Until recently, the connection between metabolism and epigenetics in a reciprocal manner was spotlighted. Explicitly, several metabolites serve as substrates and co-factors of epigenetic enzymes to carry out post-translational modifications of DNA and histone. Genetic mutations in metabolic enzymes facilitate the production of oncometabolites that ultimately impact epigenetics. Numerous evidences also indicate epigenome is sensitive to cancer metabolism. Conversely, epigenetic dysfunction is certified to alter metabolic enzymes leading to tumorigenesis. Further, the bidirectional relationship between epigenetics and metabolism can impact directly and indirectly on immune microenvironment, which might create a new avenue for drug discovery. Here we summarize the effects of metabolism reprogramming on epigenetic modification, and vice versa; and the latest advances in targeting metabolism-epigenetic crosstalk. We also discuss the principles linking cancer metabolism, epigenetics and immunity, and seek optimal immunotherapy-based combinations.

IDO1 plays a tumor-promoting role via MDM2-mediated suppression of the p53 pathway in diffuse large B-cell lymphoma

With the intensive therapeutic strategies, diffuse large B-cell lymphoma (DLBCL) is still a fatal disease due to its progressive characteristics. Indoleamine 2,3-dioxygenase 1 (IDO1) is a key regulator that catalyzes the commitment step of the kynurenine pathway in the immune system, its aberrant activation may contribute to malignant cell escape eradication. However, the role of IDO1 in DLBCL progression remains elusive. Our study showed IDO1 expression was upregulated in DLBCL and was associated with a poor prognosis and low overall survival. Inhibition of IDO1 suppressed DLBCL cell proliferation in vitro and impeded xenograft tumorigenesis in vivo. RNA-seq analyses revealed MDM2 was downregulated while TP53 was upregulated in IDO1 inhibition OCI-Ly10 cells. Mechanistically, IDO1 inhibition decreased the expression of MDM2, a major negative regulator of p53, and restored p53 expression in OCI-Ly3 and OCI-Ly10 cells, resulting in cell cycle arrest and apoptosis. IDO1 inhibition induced cell apoptosis coupled with PUMA and BAX upregulation, as well as BCL2 and BCL-XL downregulation. In addition, p21, a p53 transcriptional target, was upregulated in cell cycle arrest. Taken together, this study revealed IDO1 is essential for the proliferation of DLBCL cells and may be a potential therapeutic target for the treatment of DLBCL.

Novel 1,2,3-Triazole Erlotinib Derivatives as Potent IDO1 Inhibitors: Design, Drug-Target Interactions Prediction, Synthesis, Biological Evaluation, Molecular Docking and ADME Properties Studies

Indoleamine 2,3-dioxygenase 1 (IDO1) plays a predominant role in cancer immunotherapy which catalyzes the initial and rate limiting steps of the kynurenine pathway as a key enzyme. To explore novel IDO1 inhibitors, five derivatives of erlotinib-linked 1,2,3-triazole compounds were designed by using a structure-based drug design strategy. Drug-target interactions (DTI) were predicted by DeePurpose, an easy-to-use deep learning library that contains more than 50 algorithms. The DTI prediction results suggested that the designed molecules have potential inhibitory activities for IDO1. Chemical syntheses and bioassays showed that the compounds exhibited remarkable inhibitory activities against IDO1, among them, compound e was the most potent with an IC₅₀ value of 0.32 ± 0.07 μM in the Hela cell assay. The docking model and ADME analysis exhibited that the effective interactions of these compounds with heme iron and better drug-likeness ensured the IDO1 inhibitory activities. The studies suggested that compound e was a novel and interesting IDO1 inhibitor for further development.

Dual-responsive nano-prodrug micelles for MRI-guided tumor PDT and immune synergistic therapy

Micelles as nanocarriers not only offer new opportunities for early diagnosis and treatment of malignant cancers but also encounter numerous barriers in the path of efficient delivery of drugs to diseased areas in the body. To address these issues, we developed a pH/GSH responsive nano-prodrug micelle (NLG919/PGA-Cys-PPA@Gd) with a high drug-loading ratio and controlled drug release performance for MRI-guided tumor photodynamic therapy (PDT) and immune synergistic therapy. Under normal conditions, theranostic nanomicelles remained stable and in a photo-quenched state. Upon accumulation in the tumor site, however, the micelles demonstrated tumor microenvironment (TME) triggered photoactive formed-PPA (a photosensitizer) and NLG919 (an indoleamine 2,3-dioxygenase (IDO) inhibitor) release because the amide bonds of PGA-Cys-PPA and the disulfide linkage of Cys were sensitive to pH and GSH, respectively. More importantly, these micelles could avoid the undesired PPA leakage in blood circulation due to the conjugation between PPA and polymers. Furthermore, the obtained micelles could also enhance the contrast of T₁-weighted MRI of tumors by virtue of their high relaxivity (r₁ = 29.85 mM^-1 s^-1). In vitro and in vivo results illustrated that the micelles had good biocompatibility and biosafety. On the basis of the efficient drug delivery strategies in PDT and IDO pathway inhibition, this intelligent dual-drug delivery system could serve as an effective approach for MRI guided combination therapy of cancer.

An Update to Hallmarks of Cancer

In the last decade, there has been remarkable progress in research toward understanding and refining the hallmarks of cancer. In this review, we propose a new hallmark - "pro-survival autophagy." The importance of pro-survival autophagy is well established in tumorigenesis, as it is related to multiple steps in cancer progression and vital for some cancers. Autophagy is a potential anti-cancer therapeutic target. For this reason, autophagy is a good candidate as a new hallmark of cancer. We describe two enabling characteristics that play a major role in enabling cells to acquire the hallmarks of cancer - "tumor-promoting microenvironment and macroenvironment" and "cancer epigenetics, genome instability and mutation." We also discuss the recent updates, therapeutic and prognostic implications of the eight hallmarks of cancer described by Hanahan et al. in 2011. Understanding these hallmarks and enabling characteristics is key not only to developing new ways to treat cancer efficiently but also to exploring options to overcome cancer resistance to treatment.

Potential of Ferritin-Based Platforms for Tumor Immunotherapy

Ferritin is an iron storage protein that plays a key role in iron homeostasis and cellular antioxidant activity. Ferritin has many advantages as a tumor immunotherapy platform, including a small particle size that allows for penetration into tumor-draining lymph nodes or tumor tissue, a unique structure consisting of 24 self-assembled subunits, cavities that can encapsulate drugs, natural targeting functions, and a modifiable outer surface. In this review, we summarize related research applying ferritin as a tumor immune vaccine or a nanocarrier for immunomodulator drugs based on different targeting mechanisms (including dendritic cells, tumor-associated macrophages, tumor-associated fibroblasts, and tumor cells). In addition, a ferritin-based tumor vaccine expected to protect against a wide range of coronaviruses by targeting multiple variants of SARS-CoV-2 has entered phase I clinical trials, and its efficacy is described in this review. Although ferritin is already on the road to transformation, there are still many difficulties to overcome. Therefore, three barriers (drug loading, modification sites, and animal models) are also discussed in this paper. Notwithstanding, the ferritin-based nanoplatform has great potential for tumor immunotherapy, with greater possibility of clinical transformation.

The Role of Kynurenines Produced by Indolamine-2,3-Dioxygenase 1 in Sepsis

BACKGROUND

The enzyme indolamine-2,3-dioxygenase 1 (IDO1) is the rate-limiting enzyme of the kynurenine (KYN) pathway and metabolizes the essential amino acid tryptophan to KYNs. The depletion of tryptophan and the generation of KYNs were shown to be involved in the global downregulation of the immune system during the later stages of sepsis, also referred to as sepsis-associated immunosuppression.

SUMMARY

The generation of KYNs by IDO1 leads to a depletion of effector T cells, including increased rate of apoptosis, decreased ability of T-cell proliferation and activation, and the generation of FoxP3+ regulatory T cells. Furthermore, KYN was shown a potent vasorelaxant during inflammation-induced hypotension. Experimental studies in murine sepsis models and in humans show promising data for using the activation of IDO1 both as a prognostic marker and potential drug target in sepsis.

Influence of the Metabolism on Myeloid Cell Functions in Cancers: Clinical Perspectives

Tumor metabolism plays a crucial role in sustaining tumorigenesis. There have been increasing reports regarding the role of tumor metabolism in the control of immune cell functions, generating a potent immunosuppressive contexture that can lead to immune escape. The metabolic reprogramming of tumor cells and the immune escape are two major hallmarks of cancer, with several instances of crosstalk between them. In this paper, we review the effects of tumor metabolism on immune cells, focusing on myeloid cells due to their important role in tumorigenesis and immunosuppression from the early stages of the disease. We also discuss ways to target this specific crosstalk in cancer patients.

Myricetin inhibits interferon-γ-induced PD-L1 and IDO1 expression in lung cancer cells

Programmed death ligand-1 (PD-L1) and indoleamine 2, 3-dioxygenase 1 (IDO1) are immune checkpoints induced by interferon-γ (IFN-γ) in the tumor microenvironment, leading to immune escape of tumors. Myricetin (MY) is a flavonoid distributed in many edible and medicinal plants. In this study, MY was identified to inhibit IFN-γ-induced PD-L1 expression in human lung cancer cells. It also reduced the expression of IDO1 and the production of kynurenine which is the product catalyzed by IDO1, while didn't show obvious effect on the expression of major histocompatibility complex-I (MHC-I), a crucial molecule for antigen presentation. In addition, the function of T cells was evaluated using a co-culture system consist of lung cancer cells and the Jurkat-PD-1 T cell line overexpressing PD-1. MY restored the survival, proliferation, CD69 expression and interleukin-2 (IL-2) secretion of Jurkat-PD-1 T cells suppressed by IFN-γ-treated lung cancer cells. Mechanistically, IFN-γ up-regulated PD-L1 and IDO1 at the transcriptional level through the JAK-STAT-IRF1 axis, which was targeted and inhibited by MY. Together, our research revealed a new mechanism of MY mediated anti-tumor activity and highlighted the potential implications of MY in tumor immunotherapy.

Disturbed lipid and amino acid metabolisms in COVID-19 patients

The Coronavirus disease 2019 (COVID-19) pandemic is overwhelming the healthcare systems. Identification of systemic reactions underlying COVID-19 will lead to new biomarkers and therapeutic targets for monitoring and early intervention in this viral infection. We performed targeted metabolomics covering up to 630 metabolites within several key metabolic pathways in plasma samples of 20 hospitalized COVID-19 patients and 37 matched controls. Plasma metabolic signatures specifically differentiated severe COVID-19 from control patients. The identified metabolic signatures indicated distinct alterations in both lipid and amino acid metabolisms in COVID-19 compared to control patient plasma. Systems biology-based analyses identified sphingolipid, tryptophan, tyrosine, glutamine, arginine, and arachidonic acid metabolism as mostly impacted pathways in COVID-19 patients. Notably, gamma-aminobutyric acid (GABA) was significantly reduced in COVID-19 patients and GABA plasma levels allowed for stratification of COVID-19 patients with high sensitivity and specificity. The data reveal large metabolic disturbances in COVID-19 patients and suggest use of GABA as potential biomarker and therapeutic target for the infection.

The cytotoxic effects of indoleamine 2, 3-dioxygenase inhibitors on triple negative breast cancer cells upon tumor necrosis factor α stimulation

Context

Overexpressed indoleamine 2,3-dioxygenase (IDO) has been observed in many types of cancer and plays an essential role in the tumor microenvironment through immune cells function.

Aims

In our study, the therapeutic potentials of two different IDO inhibitors (Epacadostat [EPA] and 1-methyl-L-tryptophan [L-1MT]) in triple-negative breast cancer (TNBC) cells were assessed with and without tumor necrosis factor-α (TNF-α) stimulation.

Materials and Methods

The anticancer activity of EPA and L-1MT alone and in combination with TNF-α was analyzed by WST-1, annexin V, cell cycle analysis, and acridine orange/ethidium bromide staining. In addition, the relationship between IDO1 and programmed death-ligand 1 (PD-L1) expressions in TNBC cells upon treatment with IDO inhibitors was evaluated by reverse transcription-polymerase chain reaction analysis.

Statistical Analysis Used

SPSS 22.0 was conducted for statistical analysis. The one-way analysis of variance with Tukey's multiple comparison test was performed for multiple groups. Independent (unpaired) t -test was used for the comparison of two groups.

Results

EPA and L-1MT alone significantly suppressed the TNBC cell viability through the induction of apoptotic cell death and G0/G1 arrest (P < 0.05). TNF-α alone induced the overexpression of IDO1 and PD-L1 in TNBC cells compared with MCF-10A control cells. However, IDO inhibitors significantly inhibited overexpressed IDO1 mRNA levels. Furthermore, EPA alone and co-treated with TNF-α suppressed the mRNA level of PD-L1 in TNBC cells. Therefore, TNF-α stimulation enhanced the therapeutic effects of IDO inhibitors on TNBC.

Conclusions

Our findings showed that the efficacy of IDO inhibitors was mediated by pro-inflammatory cytokine. However, different molecular signaling pathways are associated with pro-inflammatory cytokines production, and the expression of IDO1 and PD-L1 calls for further investigations.

Barriers to Immunotherapy in Ovarian Cancer: Metabolic, Genomic, and Immune Perturbations in the Tumour Microenvironment

A lack of explicit early clinical signs and effective screening measures mean that ovarian cancer (OC) often presents as advanced, incurable disease. While conventional treatment combines maximal cytoreductive surgery and platinum-based chemotherapy, patients frequently develop chemoresistance and disease recurrence. The clinical application of immune checkpoint blockade (ICB) aims to restore anti-cancer T-cell function in the tumour microenvironment (TME). Disappointingly, even though tumour infiltrating lymphocytes are associated with superior survival in OC, ICB has offered limited therapeutic benefits. Herein, we discuss specific TME features that prevent ICB from reaching its full potential, focussing in particular on the challenges created by immune, genomic and metabolic alterations. We explore both recent and current therapeutic strategies aiming to overcome these hurdles, including the synergistic effect of combination treatments with immune-based strategies and review the status quo of current clinical trials aiming to maximise the success of immunotherapy in OC.

Discovery of IDO1 inhibitors containing a decahydroquinoline, decahydro-1,6-naphthyridine, or octahydro-1H-pyrrolo[3,2-c]pyridine scaffold

A series of IDO1 inhibitors containing a decahydroquinoline, decahydro-1,6-naphthyridine, or octahydro-1H-pyrrolo[3,2-c]pyridine scaffold were identified with good cellular and human whole blood activity against IDO1. These inhibitors contain multiple chiral centers and all diastereomers were separated. The absolute stereochemistry of each isomers were not determined. Compounds 15 and 27 stood out as leads due to their good cellular as well as human whole blood IDO1 inhibition activity, low unbound clearance, and reasonable mean residence time in rat cassette PK studies.

Harnessing Metabolic Reprogramming to Improve Cancer Immunotherapy

Immune escape is one of the hallmarks of cancer. While metabolic reprogramming provides survival advantage to tumor cancer cells, accumulating data also suggest such metabolic rewiring directly affects the activation, differentiation and function of immune cells, particularly in the tumor microenvironment. Understanding how metabolic reprogramming affects both tumor and immune cells, as well as their interplay, is therefore critical to better modulate tumor immune microenvironment in the era of cancer immunotherapy. In this review, we discuss alterations in several essential metabolic pathways in both tumor and key immune cells, provide evidence on their dynamic interaction, and propose innovative strategies to improve cancer immunotherapy via the modulation of metabolic pathways.

Cisplatin Resistance and Redox-Metabolic Vulnerability: A Second Alteration

The development of drug resistance in tumors is a major obstacle to effective cancer chemotherapy and represents one of the most significant complications to improving long-term patient outcomes. Despite early positive responsiveness to platinum-based chemotherapy, the majority of lung cancer patients develop resistance. The development of a new combination therapy targeting cisplatin-resistant (CR) tumors may mark a major improvement as salvage therapy in these patients. The recent resurgence in research into cellular metabolism has again confirmed that cancer cells utilize aerobic glycolysis ("the Warburg effect") to produce energy. Hence, this observation still remains a characteristic hallmark of altered metabolism in certain cancer cells. However, recent evidence promotes another concept wherein some tumors that acquire resistance to cisplatin undergo further metabolic alterations that increase tumor reliance on oxidative metabolism (OXMET) instead of glycolysis. Our review focuses on molecular changes that occur in tumors due to the relationship between metabolic demands and the importance of NAD+ in redox (ROS) metabolism and the crosstalk between PARP-1 (Poly (ADP ribose) polymerase-1) and SIRTs (sirtuins) in CR tumors. Finally, we discuss a role for the tumor metabolites of the kynurenine pathway (tryptophan catabolism) as effectors of immune cells in the tumor microenvironment during acquisition of resistance in CR cells. Understanding these concepts will form the basis for future targeting of CR cells by exploiting redox-metabolic changes and their consequences on immune cells in the tumor microenvironment as a new approach to improve overall therapeutic outcomes and survival in patients who fail cisplatin.

Radiation in Combination With Targeted Agents and Immunotherapies for Pediatric Central Nervous System Tumors - Progress, Opportunities, and Challenges

Pediatric brain tumors are the most common solid tumors in children and represent a heterogenous group of diagnoses. While some are treatable with current standard of care, relapsed/refractory disease is common and some high-risk diagnoses remain incurable. A growing number of therapy options are under development for treatment of CNS tumors, including targeted therapies that disrupt key tumor promoting processes and immunotherapies that promote anti-tumor immune function. While these therapies hold promise, it is likely that single agent treatments will not be sufficient for most high-risk patients and combination strategies will be necessary. Given the central role for radiotherapy for many pediatric CNS tumors, we review current strategies that combine radiation with targeted therapies or immunotherapies. To promote the ongoing development of rational combination treatments, we highlight 1) mechanistic connections between molecular drivers of tumorigenesis and radiation response, 2) ways in which molecular alterations in tumor cells shape the immune microenvironment, and 3) how radiotherapy affects the host immune system. In addition to discussing strategies to maximize efficacy, we review principles that inform safety of combination therapies.