Abstract PO5-15-09: DNA damage induced necroptosis predicts response to radioimmunotherapy
Authors: Goddard Anna , Wang Qinhong , Cho Minguk , Lerner Lynn , Gupta Gaorav 
Published: May 2024

Abstract
Background: More than half of all cancer patients receive radiotherapy (RT) during their cancer experience. DNA damage induced by RT can initiate a pro-inflammatory immune response within the tumor microenvironment (TME), yet this response is not uniformly observed across all tumors. Mre11 is one of the first responders to double stranded breaks and coordinates the DNA damage response. Recent work in our lab reveals that Mre11 is required for cGAS mediated detection of cytoplasmic DNA, in turn activating STING to engage the type I interferon signaling pathway, downstream of which can activate ZBP1/RIPK3/MLKL mediated necroptosis. The purpose of this study is to determine if expression of the necroptotic pathway may predict whether breast tumors benefit from RT to overcome ICI resistance and induce systemic anti-tumor immunity in the form of an abscopal response. Methods: Four Trp53-/- Balb/c breast cancer syngeneic allograft models with low tumor mutational burden and resistance to dual ICI (anti-PD1 and anti-CTLA4, BioXcell) were used. Mice were implanted with bilateral tumors and randomly divided into four treatment cohorts: untreated, RT, ICI, or RT+ICI, where RT (8Gyx3) was administered to one tumor. Two lines exhibited abscopal responses to RT+ICI (i.e., “abscopal models”), whereas the other two did not (i.e., “non-abscopal models”). To identify gene expression patterns associated with abscopal responding breast tumors, we performed spatial transcriptomic analysis of tumors 10 days after initiating treatment using the GeoMx whole transcriptome assay targeting panCK+ tumor cells and tumor adjacent CD45+ immune cells (N &gt;5 for each treatment group and tumor type). Unsupervised hierarchical clustering was performed to identify gene expression patterns across areas of interest. Genes selectively induced by RT+ICI in abscopal models that were not induced in non-abscopal models were identified using two-tailed t-test and FDR correction for multiple testing (FDR&lt; 5%). DeSEQ2 and GSEA analysis were performed using publicly available mouse gene sets (Broad Institute). Results: The TME in untreated tumors in the abscopal models demonstrate upregulation in the B cell survival pathway and apoptotic pathways compared to untreated tumors in non-abscopal models. Hierarchical clustering of immune related genes in CD45+ segments of RT+ICI treated tumors exhibiting an abscopal response revealed a global shift in gene expression profiles after treatment. GSEA analysis of CD45+ segments from abscopal models shows that RT+ICI treatment results in enrichment of the interferon mediated signaling pathway including interferon alpha (p&lt; 0.0001), interferon beta (p&lt; 0.0001), type II interferon response (p&lt; 0.0001), and antigen processing and presentation (p&lt; 0.0001). In tumor cells of breast cancers demonstrating the abscopal response, Isg15 and Zbp1 are highly induced by RT+ICI. The necroptotic pathway, including Zbp1, Ripk3, and Mlkl, are significantly higher expressed in the panCK+ tumors known to demonstrate the abscopal response. Conclusion: Breast cancer models with an abscopal response to RT+ICI demonstrate higher expression of Isg15 and Zbp1, both of which are involved in secreted inflammatory signaling. The TME in these models have increased interferon signaling and antigen presentation in response to RT+ICI. The role of DNA damage induced necroptosis in generating an abscopal response in breast cancer warrants further investigation as a potential biomarker for response to RT+ICI combination therapy.
Citation Format: Anna Goddard, Qinhong Wang, Minguk Cho, Lynn Lerner, Gaorav Gupta. DNA damage induced necroptosis predicts response to radioimmunotherapy [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO5-15-09.