Abstract 2865: IL4I1, IDO1 and other amino acid-metabolizing enzymes in high-grade serous ovarian cancer
Authors: Grobben Yvonne , Ouden Judith E. den , Aguado Cristina , van Altena Anne M. , Kraneveld Aletta D. , Zaman Guido J. 
Published: June 2023

Abstract
Ovarian cancer is among the most lethal malignancies in women, and breakthrough immunotherapies including anti-PD-1/PD-L1 and anti-CTLA4 have thus far not been able to significantly ameliorate patient outcomes. In various tumor types, amino acid-metabolizing enzymes such as indoleamine 2,3-dioxygenase 1 (IDO1) and arginase 1 (ARG1) have been found to be among the culprits responsible for generation of an immunosuppressive tumor microenvironment. More recently, interleukin 4 induced 1 (IL4I1) was put forward as a promising anticancer drug target, whereas its expression may also contribute to resistance against IDO1 inhibition. Similar to IDO1, IL4I1 can metabolize tryptophan (Trp) resulting in the formation of AhR agonists, although phenylalanine (Phe) and tyrosine (Tyr) are also major substrates of IL4I1.
Plasma and ascites (i.e., peritoneal fluid buildup) were collected from advanced-stage high-grade serous ovarian cancer (HGSOC) patients to determine whether aberrant metabolism by amino acid-metabolizing enzymes occurs in these patients and to evaluate ascites as a potential source of biomarkers related to these enzymes. Activity of the enzymes was indirectly determined through measurement of relevant amino acids and metabolites by targeted metabolomics using LC-MS/MS, while levels of secreted IL4I1 were determined by ELISA. Amino acid, metabolite and enzyme concentrations were compared to healthy control subjects and were examined for correlations with clinicopathological characteristics and clinical outcomes. Pleural effusions from non-small cell lung cancer patients were included to evaluate whether the results could be extended towards another type of cancer-related fluid buildup.
Metabolism of Trp was significantly elevated in HGSOC patients compared to control subjects, likely attributable to increased IDO1 expression. Kynurenine (Kyn) levels and Kyn/Trp ratios were higher in ascites compared to plasma samples, demonstrating the value of utilizing this fluid for biomarker detection. Whereas elevated metabolism of Trp by IL4I1 could not be detected in the patients, high levels of Phe- and Tyr-derived metabolites associated with IL4I1 activity were found in their ascites. Levels of these metabolites significantly correlated with the concentration of IL4I1. Moreover, enhanced metabolism of Phe and Tyr correlated with disease stage, suggesting a role for IL4I1 in HGSOC progression. Elevated levels of IL4I1-associated metabolites were also found in the pleural effusions of a subset of non-small cell lung cancer patients, demonstrating that enhanced IL4I1 activity is not limited to ovarian cancer ascites.
In conclusion, our results suggest that IL4I1 may be involved in HGSOC progression, indicating this enzyme as a potential therapeutic target. The levels of IL4I1- and IDO1-generated metabolites in ascites may additionally serve as valuable diagnostic or predictive biomarkers.
Citation Format: Yvonne Grobben, Judith E. den Ouden, Cristina Aguado, Anne M. van Altena, Aletta D. Kraneveld, Guido J. Zaman. IL4I1, IDO1 and other amino acid-metabolizing enzymes in high-grade serous ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2865.