Abstract 5604: High TDO and IDO1 expression in ovarian cancer-associated cells isolated from malignant ascites
Authors: van Riel Wilhelmina , van Doornmalen Antoon , Mulder Winfried , Vu Diep , Dylus Jelle , den Ouden Judith , van Altena Anne , Buijsman Rogier , Zaman Guido 
Published: September 2020

Abstract
In epithelial ovarian cancer (EOC), 15-20% of tumors do not respond to first-line chemotherapy, consisting of platinum-based therapy plus paclitaxel, and in recurrences the response rate is even lower. PARP inhibitors synergize with platinum therapy and have been approved for platinum sensitive EOC. Clinical trials with immunotherapies, such as PD-1/PD-L1 blockade, have so far not been successful. There is a great need of novel therapies with improved long term treatment outcome, as well as diagnostic tools and biomarkers to predict chemotherapy response in the clinic. We have used malignant ascites collected from patients with EOC, to identify new biomarkers of chemotherapy response and to support small molecule drug discovery programs on the tryptophan metabolizing enzymes TDO and IDO1 with clinically relevant assays. Modulation of TDO or IDO1 activity with small molecule inhibitors decreases anti-tumor immune response by inducing T cell anergy. Ascites was gathered from eighteen patients with advanced stage EOC. Cells were isolated by centrifugation and tumor cells were separated from immune cells by overnight adherence to tissue culture plates. Both cell fractions were characterized for the expression of immune and cancer cell markers by flow cytometry and/or quantitative PCR. TDO and IDO1 activity was determined using a functional assay and small molecule inhibitors. All samples expressed CA125 or HE4, or both ovarian cancer markers. Flow cytometry analysis of eleven adherent cell samples with anti-EpCAM or CA125 confirmed their EOC origin. Five of six samples showed high cell surface expression of PD-L1. Adherent cell samples were cultured over 2 - 3 passages and further characterized for TDO and IDO1 expression and activity. All cultured cell samples stained negative for immune cell markers (CD45) and only a small fraction (less than 10%) stained positive for a fibroblast marker. Two samples out of eighteen showed high IDO1 gene expression. However, only after stimulation with IFNγ, the tryptophan metabolizing activity in these samples was detectable, and could be inhibited with selective IDO1 inhibitors. In contrast, four samples expressed relatively high TDO and detectable endogenous tryptophan metabolizing activity, which could be inhibited by selective TDO inhibitors. The immune cell composition of the ascites, the expression and activity of TDO, IDO1 and PD-L1 were related to the clinical outcome of the patients from which the ascites was derived.
Citation Format: Wilhelmina van Riel, Antoon van Doornmalen, Winfried Mulder, Diep Vu, Jelle Dylus, Judith den Ouden, Anne van Altena, Rogier Buijsman, Guido Zaman. High TDO and IDO1 expression in ovarian cancer-associated cells isolated from malignant ascites [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5604.