Abstract B030: Development and validation of a phenotypic screening platform for the identification of novel immuno-oncology targets
Authors: Rabolli Virginie , Martini Murielle , Scoumanne Ariane , Letellier Marie-Claire , Crosignani Stefano , Quéva Christophe , Detheux Michel , Swiercz Jakub M. , Cauwenberghs Sandra 
Published: November 2016

Abstract
iTeos Therapeutics developed a target discovery and drug repurposing platform based on phenotypic screening assays that mimic the immunosuppressive tumor microenvironment. Here, we present an immunosuppressive cell line/T cell co-culture assay that enables chemical and genomic screening. Multi-parameter readouts are combined to assess both T cell activity as well as tumor cell death. T cell activity is measured through high content imaging of cluster formation complemented with detection of INFγ secretion. Tumor cell death is assessed using a cytotoxicity assay. The current format of the assay (96-well) allows medium-throughput testing of up to 3,000 samples/screen.
As proof-of-concept we evaluated the assay for its ability to detect metabolic immune-oncology targets like indoleamine-2,3-dioxygenase 1 (IDO1). IDO1 is expressed in a wide range of cancers and mediates local T cell suppression through depletion of the essential amino acid tryptophan. The assay conditions were validated with an IDO1 inhibitor as positive control and subsequently scaled up for automation. A commercially available small molecule library [Selleck Bioactive Compound Library (cat number L1700), 1902 compounds] with a high percentage of clinically tested drugs was screened. The library was tested at two different concentrations (0.3 μM and 3 μM), with two independent T cell donors and spiked with IDO1 inhibitors as internal control. The combined analysis of T-cell activity and tumor killing led to the identification of 42 compounds with activity on multiple, potential immune suppressive pathways, including metabolism, epigenetics, autophagy, and TGFβ signaling.
This assay is also suitable for gene modulation strategy using shRNA or cDNA libraries enriched for genes expressed specifically in immune suppressive cells and tissues. Moreover the assay can be adapted to additional cell types such as MDSC or Treg, opening up opportunities for identification of novel immune suppressive targets.
In conclusion, this approach allows rapid identification of mechanisms and targets contributing to tumor resistance. Phenotypic screens allow higher confidence in the selection of targets with a potential for clinical translation.
[V.R., M.M., J.M.S., and S.C. contributed equally to this work.]
Citation Format: Virginie Rabolli, Murielle Martini, Ariane Scoumanne, Marie-Claire Letellier, Stefano Crosignani, Christophe Quéva, Michel Detheux, Jakub M. Swiercz, Sandra Cauwenberghs. Development and validation of a phenotypic screening platform for the identification of novel immuno-oncology targets [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr B030.