Immunobiochemical pathways of neopterin formation and tryptophan breakdown via indoleamine 2,3-dioxygenase correlate with circulating tumor cells in ovarian cancer patients- A study of the OVCAD consortium

Tryptophan metabolism in health and disease

Tryptophan (Trp) metabolism primarily involves the kynurenine, 5-hydroxytryptamine, and indole pathways. A variety of bioactive compounds produced via Trp metabolism can regulate various physiological functions, including inflammation, metabolism, immune responses, and neurological function. Emerging evidence supports an intimate relationship between Trp metabolism disorder and diseases. The levels or ratios of Trp metabolites are significantly associated with many clinical features. Additionally, studies have shown that disease progression can be controlled by modulating Trp metabolism. Indoleamine-2,3-dioxygenase, Trp-2,3-dioxygenase, kynurenine-3-monooxygenase, and Trp hydroxylase are the rate-limiting enzymes that are critical for Trp metabolism. These key regulatory enzymes can be targeted for treating several diseases, including tumors. These findings provide novel insights into the treatment of diseases. In this review, we have summarized the recent research progress on the role of Trp metabolites in health and disease along with their clinical applications.

Amino Acid-Metabolizing Enzymes in Advanced High-Grade Serous Ovarian Cancer Patients: Value of Ascites as Biomarker Source and Role for IL4I1 and IDO1

The molecular mechanisms contributing to immune suppression in ovarian cancer are not well understood, hampering the successful application of immunotherapy. Amino acid-metabolizing enzymes are known to contribute to the immune-hostile environment of various tumors through depletion of amino acids and production of immunosuppressive metabolites. We aimed to collectively evaluate the activity of these enzymes in high-grade serous ovarian cancer patients by performing targeted metabolomics on plasma and ascites samples. Whereas no indication was found for enhanced l-arginine or l-glutamine metabolism by immunosuppressive enzymes in ovarian cancer patients, metabolism of l-tryptophan by indoleamine 2,3-dioxygenase 1 (IDO1) was significantly elevated compared to healthy controls. Moreover, high levels of l-phenylalanine- and l-tyrosine-derived metabolites associated with interleukin 4 induced 1 (IL4I1) activity were found in ovarian cancer ascites samples. While l-tryptophan is a major substrate of both IDO1 and IL4I1, only its enhanced conversion into l-kynurenine by IDO1 could be detected, despite the observed activity of IL4I1 on its other substrates. In ascites of ovarian cancer patients, metabolite levels were higher compared to those in plasma, demonstrating the value of utilizing this fluid for biomarker identification. Finally, elevated metabolism of l-phenylalanine and l-tyrosine by IL4I1 correlated with disease stage, pointing towards a potential role for IL4I1 in ovarian cancer progression.

Platinum-resistant ovarian cancer: From drug resistance mechanisms to liquid biopsy-based biomarkers for disease management

Resistance to platinum-based chemotherapy is a major clinical challenge in ovarian cancer, contributing to the high mortality-to-incidence ratio. Management of the platinum-resistant disease has been difficult due to diverse underlying molecular mechanisms. Over the past several years, research has revealed several novel molecular targets that are being explored as biomarkers for treatment planning and monitoring of response. The therapeutic landscape of ovarian cancer is also rapidly evolving, and alternative therapies are becoming available for the recurrent platinum-resistant disease. This review provides a snapshot of platinum resistance mechanisms and discusses liquid-based biomarkers and their potential utility in effective management of platinum-resistant ovarian cancer.

Association of a Combined Cancer Exhaustion Score with Circulating Tumor Cells and Outcome in Ovarian Cancer-A Study of the OVCAD Consortium

We investigated the prognostic role of systemic characteristics for cancer exhaustion and the presence of circulating tumor cells (CTCs) in primary epithelial ovarian cancer (EOC) patients. We included 185 patients in this multicenter study with a median follow-up time of 10.25 years. Albumin, c-reactive protein (CRP) and the kynurenine to tryptophan ratio (Kyn/Trp) as well as the CTC-related marker cyclophilin C (PPIC) were obtained before primary therapy and were correlated to the respective clinical and outcome data. The information provided by albumin and Kyn/Trp was integrated in a combined score for cancer exhaustion (CCES). A high CCES characterized by hypoalbuminemia and a high Kyn/Trp was associated with both decreased overall and progression-free survival, independent from other known prognostic factors in a multivariable analysis. The presence of PPIC-positive CTCs was significantly associated with a high CCES, highlighting that the interplay between the systemic microenvironment and CTCs should be considered in "liquid biopsy" biomarker assessment.

Comparison of preoperative serum neopterin, periostin, indoleamine 2,3-dioxygenase, YKL-40, and tenascin-C levels with current tumor markers for early-stage endometrial cancer

OBJECTIVE

To compare the predictive value of serum levels of neopterin, periostin, YKL-40, tenascin-C (TNC), and indoleamine 2,3-dioxygenase (IDO) with current tumor markers for the primary diagnosis of early-stage endometrial cancer.

METHODS

A prospective cross-sectional study was conducted between January 2020 and November 2020. A total of 59 patients (38 women newly diagnosed with early-stage endometrial cancer [study group] and 21 women with benign endometrial pathologies [control group]) were enrolled. Blood samples were collected prior to surgery and underwent immunoassay analysis.

RESULTS

Carcinoembryonic antigen (CEA), periostin, and IDO levels were significantly higher in the study group than the control group (P = 0.008, P = 0.034, and P = 0.003, respectively). Receiver operating characteristic curve analysis revealed that IDO, periostin, and CEA were good predictors of early-stage endometrial cancer (AUC = 0.733, 95% CI, 0.602-0.840, P < 0.002; AUC = 0.668, 95% CI, 0.533-0.785, P = 0.018; and AUC = 0.709, 95% CI, 0.576-0.820, P = 0.002, respectively). Correlation analysis revealed no significant correlation of any biomarker with age or body mass index in either the control or study group.

CONCLUSION

Serum CEA, periostin, and IDO levels were significantly higher in women with endometrial cancer than in those without cancer. These results may help identify new markers for diagnosing endometrial cancer.

Inflammation-Induced Tryptophan Breakdown is Related With Anemia, Fatigue, and Depression in Cancer

Many patients with cancer suffer from anemia, depression, and an impaired quality of life (QoL). These patients often also show decreased plasma tryptophan levels and increased kynurenine concentrations in parallel with elevated concentrations of Th1 type immune activation marker neopterin. In the course of anti-tumor immune response, the pro-inflammatory cytokine interferon gamma (IFN-γ) induces both, the enzyme indoleamine 2,3-dioxygenase (IDO) to degrade tryptophan and the enzyme GTP-cyclohydrolase I to form neopterin. High neopterin concentrations as well as an increased kynurenine to tryptophan ratio (Kyn/Trp) in the blood of cancer patients are predictive for a worse outcome. Inflammation-mediated tryptophan catabolism along the kynurenine pathway is related to fatigue and anemia as well as to depression and a decreased QoL in patients with solid tumors. In fact, enhanced tryptophan breakdown might greatly contribute to the development of anemia, fatigue, and depression in cancer patients. IDO activation and stimulation of the kynurenine pathway exert immune regulatory mechanisms, which may impair anti-tumor immune responses. In addition, tumor cells can degrade tryptophan to weaken immune responses directed against them. High IDO expression in the tumor tissue is associated with a poor prognosis of patients. The efficiency of IDO-inhibitors to inhibit cancer progression is currently tested in combination with established chemotherapies and with immune checkpoint inhibitors. Inflammation-mediated tryptophan catabolism and its possible influence on the development and persistence of anemia, fatigue, and depression in cancer patients are discussed.

Liquid biopsy in ovarian cancer

Ovarian cancer has the worst survival rate because it is typically diagnosed at advanced stage. Despite treatment, the disease commonly recurs due to chemo-resistance. Liquid biopsy, based on minimally invasive blood tests, has the advantage of following tumor evolution in real time, offering novel insights on cancer prevention and treatment. Circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating cell-free microRNAs (cfmiRNAs) and circulating exosomes represent the major components of liquid biopsy. In this chapter, we provide an overview of recent research on CTCs, ctDNA, cfmiRNAs and exosomes in ovarian cancer. We also focus on the clinical value of liquid biopsy in early diagnosis, prognosis, treatment response, as well as screening in the general population.

Comprehensive analysis of mRNA-level and miRNA-level subpathway activities for identifying robust ovarian cancer prognostic signatures

Ovarian cancer (OvCa) causes the highest mortality among all gynaecologic cancers. A large number of mRNA‐ or miRNA‐based signatures were identified for OvCa patient prognosis. However, the comprehensive analysis of function‐level prognostic signatures is currently not considered in OvCa. In the present study, we respectively inferred subpathway activities from mRNA and miRNA levels based on high‐throughput expression profiles and reconstructed subpathways. Firstly, the activities of two tumour pathways were calculated and the difference between normal and tumour samples were analysed using multiple tumour types. Then, we calculated subpathway activities for OvCa based on the expression profiles from both mRNA and miRNA levels. Furthermore, based on these subpathway activity matrices, we performed bootstrap analysis to obtain sub‐training sets and utilized univariate method to identify robust OvCa prognostic subpathways. A comprehensive comparison of subpathway results between these two levels was performed. As a result, we observed subpathway mutual exclusion trend between the levels of mRNA and miRNA, which indicated the necessary of combining mRNA‐miRNA levels. Finally, by using ICGC data as testing sets, we utilized two strategies to verify survival predictive power of the mRNA‐miRNA combined subpathway signatures and performed comparisons with results from individual levels. It was confirmed that our framework displayed application to identify robust and efficient prognostic signatures for OvCa, and the combined signatures indeed exhibited advantages over individual ones. In the study, we took a step forward in relevant novel integrated functional signatures for OvCa prognosis.

Liquid biopsy in ovarian cancer: the potential of circulating miRNAs and exosomes

Ovarian cancer still remains the most lethal female cancer, since in most cases it is diagnosed at an advanced stage. Usually after completion of primary treatment chemoresistance occurs, and recurrent disease is finally observed. Liquid biopsy, based on minimally invasive and serial blood tests, has the advantage of following tumor evolution in real time, offering novel insights on precision medicine. Circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating cell-free microRNAs (cfmiRNAs) and circulating exosomes represent the major components of liquid biopsy analysis. Liquid biopsy has been already implemented in ovarian cancer, and most studies so far are mainly focused on CTCs and ctDNA. This review is mainly focused on the clinical potential of circulating miRNAs and exosomes as a source of liquid biopsy biomarkers in ovarian cancer diagnosis, prognosis, and response to treatment.