Fig 2: PP, 4HPP and IL4I1 levels in pleural effusion samples of patients with stage IV non-small cell lung cancer. (A) PP and 4HPP levels in pleural effusion samples (n = 24). Horizontal lines indicate geometric means. (B) IL4I1 levels in pleural effusion of non-small cell lung cancer patients (n = 24) and ascites of high-grade serous ovarian cancer patients (n = 32). IL4I1 levels in four pleural effusion samples were below the lower limit of quantification (LLOQ). Geometric means are therefore not displayed. (C,D) Correlation between PP, 4HPP and IL4I1 levels in pleural effusion samples. Dashed lines indicate the LLOQ. Samples with an IL4I1 level below the LLOQ are shown at the LLOQ value. Results of Pearson’s correlation analyses are indicated in the graphs. 4HPP: 4-hydroxyphenylpyruvic acid; IL4I1: interleukin 4 induced 1; PP: phenylpyruvic acid; r: Pearson’s correlation rank coefficient.

Fig 3: Phe and Tyr metabolism in high-grade serous ovarian cancer patients and healthy donors. Amino acid and metabolite levels corresponding to (A) Phe and (B) Tyr metabolism as indirect measures of IL4I1 enzymatic activity in plasma of healthy donors (HD) (n = 30) and plasma and ascites of ovarian cancer patients (OC) (n = 24 and 32, respectively, with n = 22 overlapping patients). Levels of Phe, Tyr, PP and 4HPP were determined by LC-MS/MS analysis. Horizontal lines indicate geometric means. Repeated unpaired, two-tailed Kruskal–Wallis tests yielded significant results for comparison of Phe (p = 0.025) and Tyr levels (p = 0.011) between the groups. Results of Dunn’s post hoc tests are indicated in the graphs. For comparison of PP and 4HPP levels between the two groups, results of the Mann–Whitney U test are indicated in the graphs. (C,D) Correlation between PP, 4HPP and IL4I1 levels in ascites of ovarian cancer patients (n = 32). Results of Pearson’s correlation analyses are indicated in the graphs. Levels of IL4I1 were determined by ELISA. (E) PP, 4HPP and IL4I1 levels in ascites of patients with stage III (n = 22) and stage IV disease (n = 8). Samples of patients with stage IV disease are colored individually to allow for comparison between the graphs. Results of unpaired, two-tailed Mann–Whitney U tests are indicated in the graphs. #: levels of PP and 4HPP in plasma of healthy donors are influenced by sample processing conditions and should therefore not directly be compared to those of the other sample groups; 4HPP: 4-hydroxyphenylpyruvic acid; FIGO: International Federation of Gynecology and Obstetrics; IL4I1: interleukin 4 induced 1; Phe: l-phenylalanine; PP: phenylpyruvic acid; r: Pearson’s correlation rank coefficient; Tyr: l-tyrosine.

Fig 4: Overview of enzymatic reactions catalyzed by amino-acid metabolizing enzymes with known immunosuppressive properties in cancer. ARG1: arginase 1; GLS1: glutaminase 1; IDO1: indoleamine 2,3-dioxygenase 1; IL4I1: interleukin 4 induced 1; iNOS: inducible nitric oxide synthase; NFK: N-formylkynurenine; TDO: tryptophan 2,3-dioxygenase.