Abstract 1773: Tumor cell-intrinsic STING pathway activation leads to robust induction of Type III Interferons and contributes to the anti-tumor activity elicited by STING agonism
Authors: Cetinbas Naniye Malli , Monnell Travis , Catcott Kalli , Lee Winnie , Shaw Pamela , Slocum Kelly , Avocetien Kenneth , Bentley Keith , Clardy Susan , Jones Brian , Kelleher Eoin , Mosher Rebecca , Thomas Joshua D. , Toader Dorin , Duvall Jeremy , Bukhalid Raghida A. , Damelin Marc , Lowinger Timothy B. 
Published: July 2021

Abstract
STING pathway plays a critical role in inducing anti-tumor immunity by upregulating Type 1 Interferon (IFN) and IFN-stimulated genes within the tumor microenvironment in response to cytosolic nucleic acid ligands. Therefore, the STING pathway agonism has emerged as a potential therapeutic mechanism to stimulate an anti-tumor innate immune response. Intratumorally injected free STING-agonists that are currently being evaluated in the clinic by others have shown limited effects in non-injected lesions. Antibody-drug conjugates (ADCs) constitute a proven therapeutic modality that enables tumor-targeted drug delivery with systemic administration. We have previously demonstrated that the tumor cell-intrinsic STING pathway is activated in the presence of cues from immune cells and contributes to the anti-tumor activity of tumor cell-targeted Immunosynthen STING-agonist ADCs, in which a STING-agonist payload is conjugated to a tumor cell-targeting antibody. Here we investigated the nature of the STING pathway activation in tumor cells and its contribution to the anti-tumor activity elicited by STING agonism. Leveraging ADCs with a wild type (wt) or mutant Fc (deficient in Fcγ receptor -FcγR- binding), we delivered a STING-agonist simultaneously to tumor-resident immune and cancer cells or only to cancer cells through FcγR-mediated and/or tumor antigen-mediated ADC internalization. We utilized these ADCs in in vivo human tumor xenograft models and STING wt or knock out (ko) cancer cell:immune cell co-cultures and evaluated gene expression, cytokine production, and anti-tumor activities induced by STING-agonist ADCs. Surprisingly, Nanostring analysis of the human tumor xenografts from mice treated with tumor cell-targeted STING-agonist ADCs revealed human tumor cell-specific activation of Type III IFNs. In human cancer cell:immune cell co-cultures, treatment with tumor cell-targeted STING-agonist ADCs also led to marked upregulation of Type III IFNs, which was significantly reduced in STING ko cancer cell:immune cell co-cultures, suggesting that the cancer cells may contribute majority of the Type III IFNs downstream of STING pathway activation. Blocking Type III IFNs with neutralizing antibodies in cancer cell:immune cell co-cultures inhibited the production of key cytokines, including Type I IFN, and nearly abolished tumor cell-killing in response to STING-agonist ADC treatment, indicating that the Type III IFNs play an important role in the anti-tumor activity induced by STING activation. These studies reveal a previously underappreciated mechanism of STING agonist anti-tumor activity. The ability of tumor cell-targeted STING-agonist ADCs to activate STING in both tumor cells and in tumor-resident immune cells may represent a significant therapeutic advantage of an Immunosynthen ADC approach to STING agonism.
Citation Format: Naniye Malli Cetinbas, Travis Monnell, Kalli Catcott, Winnie Lee, Pamela Shaw, Kelly Slocum, Kenneth Avocetien, Keith Bentley, Susan Clardy, Brian Jones, Eoin Kelleher, Rebecca Mosher, Joshua D. Thomas, Dorin Toader, Jeremy Duvall, Raghida A. Bukhalid, Marc Damelin, Timothy B. Lowinger. Tumor cell-intrinsic STING pathway activation leads to robust induction of Type III Interferons and contributes to the anti-tumor activity elicited by STING agonism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1773.