Targeting dsRNA sensing and ADAR1 in melanoma

PROJECT SUMMARY: Over the past decade the development of immune checkpoint blockade (ICB) in melanoma and other tumor types has transformed the treatment options available for many patients with cancer. However, within melanoma only approximately half of patients experience a durable response to treatment, with worse results

in most other tumor types. We and others have identified strategies to enhance anti-tumor immunity and sensitize non-responsive murine melanoma tumors to ICB by targeting dsRNA pattern recognition receptors (PRRs). These strategies include the agonism of the dsRNA sensor RIG-I and the loss of Adenosine

Deaminase Acting on dsRNA (ADAR1). We showed that ADAR1 is an innate inhibitory checkpoint in tumor cells that limits anti-cancer immunity, and that targeting it therapeutically can trigger multiple dsRNA PRRs to sensitize tumors to immunotherapy. Both RIG-I agonism and targeting ADAR1 resulted in enhanced cytokine

release in murine tumor microenvironments and improved the recruitment and control of tumors by T cells. In recent work we have uncovered evidence that co-targeting multiple dsRNA sensing pathways induces cooperative effects and enhances anti-tumor immunity compared with targeting single sensors. However,

several gaps in knowledge limit the translation of these strategies into effective therapies for patients. These include: i) defining the optimal therapeutic strategy for targeting dsRNA PRRs; ii) understanding mechanisms by which dsRNA sensing in tumors programs immune cell function; and iii) identifying the patients most likely

to respond to dsRNA-targeting therapeutics. To test the effects of dsRNA PRR stimulation on patient tumor and immune samples ex vivo, we developed a novel perturbational single cell RNA sequencing approach. Applying this strategy, we found that dsRNA stimulation of patient tumor and immune cells induces distinct T

cell programs of activation and survival and that these approaches may be most effective in tumors with high pre-treatment levels of interferon signaling and adenosine-to-inosine dsRNA editing. In Aim 1 of this proposal, we will test the hypothesis that co-targeting ADAR1 and RIG-I enhances the activation, proliferation and

function of anti-tumor T cells. We will explore mechanisms of this finding in mouse models including the increased recruitment, activation and cross-presentation of tumor antigens by dendritic cells. In Aim 2 we will seek to identify the tumor determinants of therapeutic response to targeting ADAR1 and uncover insights that

will facilitate the development of small molecule and nucleic acid therapeutics. If successful, the work described in this proposal will help define the rules by which tumors and T cells respond to dsRNA stimulation and advance the development of dsRNA-targeting strategies for melanoma and other tumors.