Abstract 5551: Potent oral ERAP1 inhibitors modify the immunopeptidome in vivo and are novel immunotherapy agents
Authors: Ware Jamie , McIntyre Patrick , Clark Kristopher , Tong Carmen , Shiers Jason , Lori Elisa , de Almeida Camila , Reeves Emma , Leonard Henry , Remtulla Alihussein , Ford Michael , Ternette Nicola , Poynton Fergus , James Edd , Young Lesley , Quibell Martin , Joyce Peter I. 
Published: September 2020

Abstract
Immune checkpoint therapy has changed the cancer treatment paradigm, however the majority of patients respond poorly to T cell checkpoint blockade alone. Emerging evidence suggests factors that increase the diversity of the immunopeptidome such as high tumor mutation burden and HLA-I evolutionary divergence (HED), improve clinical response to checkpoint blockade providing an impetus to develop strategies that increase the presentation of cancer associated antigens to the immune system. Endoplasmic reticulum aminopeptidase 1 (ERAP1) is an aminopeptidase that trims peptides loaded into classical and nonclassical MHC molecules. Human genome-wide association studies have identified single nucleotide polymorphisms within ERAP1 that are associated with immune-related diseases, such as ankylosing spondylitis, providing human genetic validation for ERAP1's role in human disease and antigen presentation. Furthermore, in mice, genetic ablation, reduction or pharmacological inhibition of ERAP1 changes the immune repertoire, creating novel antigens with improved immunogenicity that lead to the generation of productive CD8 T cell responses and tumor growth inhibition in various syngeneic models. We have generated and profiled highly potent, species cross reactive and selective ERAP1 inhibitors through a suite of in vitro and in vivo assays to develop these as novel immunotherapy agents. In vitro CETSA measurements show potent cellular target engagement that correlates with in vitro SPR and enzyme potency. Using the model antigen SIINFEKL and Class I MHC expression as key pharmacodynamic measurements, we demonstrate Class I modulation in vitro and in vivo in line with published data from ERAP1 knockout mice. These assays are being used to elucidate the kinetics and temporal dynamics of the antigen change to optimise dosing schedules for in vivo studies. Implementation of our immunopeptidomics pipeline has demonstrated treatment with ERAP1 inhibitors both generate novel antigens in vitro and in vivo and lead to profound and consistent increased overall immunopeptidome length in mouse and human cells. To establish the functional consequence of these changes, we developed a human primary T cell immunogenicity platform. The immunogenic potential of these novel cancer associated antigens has been confirmed by the ability to stimulate IFNγ production in naïve T cells and suggests responses to these antigens could reinvigorate anti-tumor responses. Extensive assessment of mouse and human CD8 T cells responses is ongoing, in order to characterise and select Grey Wolf Therapeutics' first lead ERAP1 inhibitor for use as monotherapy or in combination with other immunotherapies such as checkpoint blockade.
Citation Format: Jamie Ware, Patrick McIntyre, Kristopher Clark, Carmen Tong, Jason Shiers, Elisa Lori, Camila de Almeida, Emma Reeves, Henry Leonard, Alihussein Remtulla, Michael Ford, Nicola Ternette, Fergus Poynton, Edd James, Lesley Young, Martin Quibell, Peter I. Joyce. Potent oral ERAP1 inhibitors modify the immunopeptidome in vivo and are novel immunotherapy agents [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 5551.