PROJECT SUMMARY Immune checkpoint blockade (ICB) therapy has shown great promise in cancer treatment recently. However, currently only a minority of patients could benefit from immune checkpoint therapy. Although the molecular mechanisms involved in the differential responses of cancer patients to immune checkpoint therapy remain unclear, a general consensus is that tumors with high mutational burden or tumors with inflammatory phenotypes are more likely to respond to immune checkpoint therapy due to the presence of higher numbers of anti-tumor T-cells. Thus it appears that the main challenge to improve immune checkpoint therapy is to manipulate the tumor microenvironment so it changes from a “cold” one with few anti-tumor T cells to a “hot” one with many anti-tumor T cells. As such methods and agents that can increase the inflammatory “hotness” of the tumor microenvironment are highly sought after. On the other hand, radiotherapy, which has been used to treat localized tumors, has been recently shown to activate immune signaling pathways. Those discoveries raise the tantalizing possibility that the efficacy of radiotherapy may be enhanced by manipulating the tumor immune microenvironment. In this project, we will examine the hypothesis that ATM inhibition is an effective approach to activate the cGAS/STING pathway by down-regulating mitochondria biogenesis to enable ICB therapy and boosts abscopal effect of radiotherapy. We will initially conduct experiments to determine if ATM inhibition could significantly enhance ICB therapy by use of CRISPR-mediated gene knockout of ATM (Aim 1). We will also attempt to define the downstream molecular mechanisms and factors that are involved ATM inhibition- mediated enhancement of ICB therapy (Aim 2). In addition, we will evaluate if a small molecule inhibitor of ATM could enhance ICB therapy and the systemic (i.e. abscopal) effects of radiotherapy in syngeneic mouse tumor models (Aim 3). Upon completion of the project, we hope we can gain significant insights into the roles of ATM in restraining activation of cellular innate immunity. Such understanding may facilitate the rapid development of novel approaches to enhance ICB therapy and radiotherapy.

PROJECT NARRATIVE In this project, we propose to examine a novel hypothesis that inhibition of the DNA double strand break response gene ATM can improve cancer immunotherapy and radiotherapy. If our hypothesis is proven correct, it will lead to better strategies for cancer therapy. Therefore, our study is highly relevant to public health.