Abstract

Epithelial ovarian cancer (EOC) is the most lethal gynecologic malignancy. First-line therapy 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 tools to predict the clinical response to chemo- or immunotherapies are needed. This poster presentation is on the development of a biomarker discovery platform using ascites of ovarian cancer patients.

Ascites was gathered from patients by punction or during debulking surgery. Cells were collected by centrifugation and characterized by flow cytometry using tumor cell, immune cell and fibroblast surface markers. Low passage tumor 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 and BRCA1 and BRCA2 was assessed by DNA sequencing. The expression of genes implicated in resistance to chemotherapy (CCNE1, ABCB1) or immunotherapy (PD-L1, IDO1, TDO2) was determined with quantitative real-time PCR. 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.

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.