Abstract 1877: Measurement of cytosolic DNA sensing cGAS-STING pathway functional activity using in vitro phenotypic assay models
Authors: Sainathan Satheesh K. , Lipner Justin H. , Drake Jennifer I. , Epkins Brogan A. , Roux Brianna M. , King Alastair J. 
Published: June 2022

Innate immunity plays a vital role in detecting cytoplasmic nucleic acids resulting from viral infection or the presence of tumor cells. Cytosolic DNA is sensed by the cyclic-GMP-AMP synthase-stimulator of interferon genes (cGAS-STING) pathway, and in the case of tumors, activation of this pathway has potential to both positively and negatively modulate cancer development. Activation of the STING pathway is a key prerequisite for type I IFN production that is needed for either endogenous or treatment-induced cancer immune responses, and reduced cGAS-STING expression is associated with poorer survival of patients with lung adenocarcinoma, invasive breast ductal carcinoma, and gastric cancer. Intrinsic activation of the cGAS-STING pathway in the tumor microenvironment (TME) promotes cancer cell-intrinsic senescence and recruitment of immune cells, resulting in antitumor effects. For cancers that are difficult to treat and characterized by immune tolerance, combination therapies of STING agonists with immune checkpoint inhibitors represents a new paradigm in disease management. To date, only two early clinical trials of the STING agonist ADU-S100 in combination with checkpoint inhibitors are underway (NCT02675439 and NCT03172936). To progress clinical trials more rapidly and with better safety outcomes for patients with advanced treatment-refractory metastatic solid tumors or lymphomas, being able to reliably screen a variety of STING agonists in different types of in vitro cancer models is of paramount importance. We have previously reported a novel functional assay that is capable of demonstrating the potency level of different STING agonists, based on the IFNβ response in THP-1 monocytic leukemia cells. We further investigated the role of newly developed STING agonists and clinical compounds in phenotypic in vitro cancer cell and TME models to inform on oncotherapeutic development. STING-expressing cancer cell lines, chosen based on microarray mRNA expression, were treated with agonists and assayed for cGAS-STING activation status using a fully automated platform for high-content imaging. In vitro analysis demonstrated high phospho-STING activation at 4 hours. In the BioMAP® Oncology Colorectal TME model, STING activation increased IL-6 release and the effect on other primary immune and tissue remodeling biomarkers will be discussed. Preclinical studies indicate that STING agonists, used as adjuvants in combination with other agents or radiation therapy, suppress tumor progression, reduce cellular toxicity, and eliminate metastases in breast and pancreatic cancer models. Phenotypic assays that provide human, translational data early in discovery are a valuable tool to accelerate progress in this area.

Citation Format: Satheesh K. Sainathan, Justin H. Lipner, Jennifer I. Drake, Brogan A. Epkins, Brianna M. Roux, Alastair J. King. Measurement of cytosolic DNA sensing cGAS-STING pathway functional activity using in vitro phenotypic assay models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1877.