Abstract B11: Antagonist of cIAP1/2 and XIAP induces immunogenic cell death and alters antigen-processing machinery in preclinical head and neck cancer models
Authors: Ye Wenda , Gunti Sreenivasulu , Van Waes Carter , Schmitt Nicole C. 
Published: September 2020

Abstract
Background/Rationale: The Cancer Genome Atlas (TCGA) analysis of head and neck squamous cell carcinomas (HNSCCs) has revealed common alterations in the Tumor Necrosis Factor (TNF) Receptor signaling pathway, with 30% overexpressing genes encoding for Fas-Associated Death Domain (FADD) and/or cellular Inhibitor of Apoptosis Proteins 1/2 (cIAP1/2). We have previously shown that ASTX660, an antagonist of cIAP1/2 and XIAP, sensitizes murine oral cancer (MOC) cells to TNFα and also demonstrates synergistic antitumor activity when used in combination with radiation therapy (XRT) and PD-1 immune checkpoint blockade, leading to tumor growth delay or eradication in a syngeneic mouse model (Xiao et al., OncoImmunology 2018). These combination treatments also enhanced the number and function of CD8+ T cells and dendritic cells. However, the immune effects of IAP antagonists at the tumor cell level are still unknown. We hypothesized that ASTX660 enhances immune-based killing of tumor cells through induction of immunogenic cell death (ICD) and upregulation of antigen-processing machinery (APM) components.
Methods/Results: We performed ICD vaccination experiments in two syngeneic mouse models of HNSCC. We vaccinated mice with MOC1 cells killed by XRT, mitoxantrone (MTX), ASTX660 + TNFα or the combination of ASTX660 + TNFα + XRT in the left flank. One week later we rechallenged with live MOC1 cells in the right flank and monitored subsequent tumor formation/growth. Positive controls XRT and MTX, known ICD inducers, resulted in tumor rejection rates of 40% and 20%, respectively. Cells treated with ASTX660 + TNFα demonstrated growth of tumors at the vaccination site on the left flank, but 90% rejection when rechallenged with viable cells on the right. Combination vaccination group ASTX660 + TNFα + XRT showed 100% tumor rejection with no vaccination site growth. Similar results were obtained with the MEER (HPV-positive) mouse model. To test our hypothesis that ASTX660 upregulates APM components, we analyzed expression of intracellular APM components by flow cytometry in human HNSCC cell lines (UMSCC-46, -11B, and -74A) treated with interferon gamma (positive control), ASTX660 alone, TNFα alone, or ASTX660 + TNFα. Changes in APM components were variable among cell lines treated with ASTX660 + TNFα, though HLA-A,B,C was consistently upregulated.
Conclusions/Future Directions: Our results demonstrate that ASTX660 induces ICD and upregulates APM components, providing a mechanism contributing to synergism between IAP antagonists with XRT as an effective treatment modality for HNSCC. Furthermore, with a significantly more favorable drug toxicity profile than cisplatin, combination treatment with ASTX660 + XRT may be a potential replacement for traditional chemoradiation in HNSCC.
Citation Format: Wenda Ye, Sreenivasulu Gunti, Carter Van Waes, Nicole C. Schmitt. Antagonist of cIAP1/2 and XIAP induces immunogenic cell death and alters antigen-processing machinery in preclinical head and neck cancer models [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr B11.