Abstract 2306: CAR-T cell therapies targeting aspartyl β-hydroxylase (ASPH)
Authors: Thisted Thomas , Malhotra Kanam , Lebowitz Michael S. , Ghanbari Hossein 
Published: August 2019

Abstract
Aspartate β-hydroxylase (ASPH) is a unique cancer target that is expressed exclusively on the surface of cancer cells. It is a type II transmembrane protein predominantly expressed during embryogenesis where it promotes cell migration for organ development, but has very low expression in healthy adult tissue, and is localized to the intracellular compartment of the endoplasmic reticulum. However, re-expression and translocation to the tumor cell surface has been detected in more than 20 different types of cancers, with expression levels inversely correlated with disease prognosis. Promising phase I clinical trial results have been achieved with our ASPH-targeted vaccine, SNS-301, in the treatment of biochemical recurrence of prostate cancer (reported previously: Nordquist, et al. (2018) J Clin Oncol. 36, suppl; abstr e15166; Nordquist, et al. Annals of Oncology, 29, suppl_8, 1 October 2018, mdy279.404). This study demonstrated reductions in disease-specific biomarkers (i.e. PSA) which correlated to the breaking of immune self-tolerance as indicated by stimulation of both cellular and humoral ASPH-specific immune responses. Importantly the vaccine was well tolerated with minimal numbers of adverse events or off-target effects. Thus, ASPH represents a promising target for immunotherapeutic approaches to human cancers. Here we present studies that we have initiated towards the development of ASPH-targeted CAR (chimeric antigen receptor)-T cell therapies. A series of ASPH-targeting chimeric antigen receptor constructs have been produced which combine various ASPH-specific scFv domains and either the 4-1BB or CD28 co-stimulatory domains. The ASPH-specific scFv explored include several scFv that we previously isolated from a fully human non-immune scFv library displayed on the surface of yeast and targeted at different epitopes within the extracellular domain of ASPH as well as several affinity matured variations of these scFv (Yeung, et al. (2007) Human Antibodies 16, 163-76). All constructs were incorporated into a lentiviral vector which was used to transfect human CD4+ and CD8+ T-cells. CAR expression and affinities were determined by flow cytometry using a fluorescently labeled antigen. Cell killing efficacy and cytokine responses of the resulting CAR-T cells were observed in co-culture experiments with a series of ASPH-expressing human cancer cell lines allowing for the ranking of the CAR constructs in terms of overall extent of immune stimulation ex vivo. It is our expectation that the unique features of the ASPH tumor specific antigen will help overcome one of the major hurdles in T-cell therapy: the identification of antigens that permit effective targeting of tumors in the absence of non-tolerable and/or off-target toxicities to essential tissues and organs. Experiments to further characterize ASPH-targeted CAR-T cells are ongoing with the goal of moving these promising therapeutics into clinic.
Citation Format: Thomas Thisted, Kanam Malhotra, Michael S. Lebowitz, Hossein Ghanbari. CAR-T cell therapies targeting aspartyl β-hydroxylase (ASPH) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2306.