Abstract A044: A precision medicine platform to predict the clinical response to chemo- and immunotherapy for epithelial ovarian cancer
Authors: Zaman Guido J.R. , Ouden Judith E. den , Dylus Jelle , Doornmalen Antoon M. van , Mulder Winfried R. , Vu-Pham Diep , Gerwen Suzanne J.C. van , Uitdehaag Joost C.M. , Buijsman Rogier C. , Massuger Leon F. , Altena Anne M. van 
Published: March 2020

Abstract
Introduction: Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy. First-line therapy in advanced EOC is surgery in combination with platinum-based chemotherapy and paclitaxel. 15-20% of patients do not respond and in 80% of advanced cases, the disease recurs within three years. 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. Currently, the only approved companion diagnostic is BRCA gene mutations for PARP inhibitors. More diagnostic assays to predict the clinical response to chemo- or immunotherapies are needed. We have developed a biomarker discovery platform using ascites of ovarian cancer patients. Experimental procedures Ascites was gathered from patients by punction or during debulking surgery. Cells were collected by centrifugation and characterized by flow cytometry using specific antibodies. Genomic DNA was sequenced using Illumina cancer gene panels. Gene expression was analyzed by quantitative PCR (qPCR). Cellular activity of the tryptophan metabolizing enzymes IDO1 and TDO was measured with NFK Green [1]. Levels of L-tryptophan and its metabolite L-kynurenine in ascites fluid and blood were determined with LC-MS/MS. In vitro data were related to tumor histopathology and clinical response data. Results: Low passage cell samples from twenty patients were profiled for sensitivity to various cytotoxic agents and targeted anti-cancer therapies in cell proliferation assays. In parallel the mutation status of fifty cancer genes including BRCA1 and 2 was assessed by DNA sequencing. The expression of genes implicated in resistance to chemotherapy (CCNE1, ABCB1) or immunotherapy (PD-L1, IDO1, TDO) was determined with qPCR. The immune status of ascites was analyzed by measuring the relative proportion of different immune cell populations, i.e., cytotoxic and regulatory T cells, monocytes, dendritic and natural killer cells. The expression of the immune suppressive markers PD-L1, IDO1 and TDO was related to the immune cell composition of the ascites, kynurenine-tryptophan ratio, and clinical response data. A tumor cell sample derived from a patient with low grade serous ovarian cancer (LGSOC) was heterozygous for an oncogenic NRAS mutation and was much more sensitive to MEK inhibitors than other samples not harboring the mutation. The cells also expressed IDO1 and high levels of PD-L1 at the cell surface. Two other samples derived from high grade serous ovarian cancer (HGSOC) expressed high PD-L1 and one also IDO1. Several HGSOC samples expressed TDO. One HGSOC sample showed high expression of the ABCB1 gene, encoding the multidrug transporter P-glycoprotein. The sample was relatively resistant to paclitaxel, a known substrate of P-glycoprotein Conclusion: Our study shows that in vitro drug sensitivity assays with primary patient samples can be used to confirm or identify predictive drug response biomarkers. In an ongoing study, in which hundred patients with HGSOC will be included, the in vitro drug response of tumor cells from ascites to first-line cytotoxic anti-cancer agents will be determined and compared to the clinical response of patients bearing specific genomic biomarkers. [1] Seegers et al. (2014) J Biomol Screen 19, 1266-1272
Citation Format: Guido J.R. Zaman, Judith E. den Ouden, Jelle Dylus, Antoon M. van Doornmalen, Winfried R. Mulder, Diep Vu-Pham, Suzanne J.C. van Gerwen, Joost C.M. Uitdehaag, Rogier C. Buijsman, Leon F. Massuger, Anne M. van Altena. A precision medicine platform to predict the clinical response to chemo- and immunotherapy for epithelial ovarian cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference on Molecular Targets and Cancer Therapeutics; 2019 Oct 26-30; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2019;18(12 Suppl):Abstract nr A044. doi:10.1158/1535-7163.TARG-19-A044