1334 AVA-ADR-001 supresses tumor growth and induces anti-tumor immunity by selectively inhibiting ADAR1 p150

Abstract Adenosine deaminase acting on RNA (ADAR1) catalyzes the hydrolytic deamination of adenosine (A) to inosine (I) in double-stranded RNA (dsRNA). There are 2 isoforms of ADAR1 (p110 in the nucleus; p150 in cytoplasm) and both modify self dsRNA in coding and non-coding regions. The ADAR1 p150 isoform is expressed from an interferon (IFN)-responsive promoter and has a Z-DNA/Z-RNA binding domain at the N-terminus. Previous reports have provided a strong rationale for the development of ADAR1 p150 inhibitors for cancer immunotherapy. Here, we describe AVA-ADR-001, a potential first-in-class small molecule inhibitor of ADAR1 p150 targeting the Zα domain. AVA-ADR-001 binds specifically to the Zα domain of ADAR1 p150 as confirmed by fluorescence spectroscopy and showed significant interferon induction in THP1 macrophages, which have high ADAR1 p150 expression compared with monocytes. Proteomics and transcriptomics analysis revealed significant upregulation of interferon signaling upon treatment with AVA-ADR − 001. Interestingly, activation of interferon signaling resulted in AVA-ADR-001 induced cell killing in ADAR1-independent cell lines. In addition, treatment with AVA-ADR − 001 resulted in significant activation of PKR, which may explain the decreased cell proliferation. Finally, AVA-ADR-001 showed superior anti-tumor efficacy compared to anti-PD1 in an in vivo tumor efficacy study and has a moderately synergistic effect when combined. Overall, this study reveals that ADAR1 p150 inhibition by AVA-ADR-001 exerts a multipronged impact on anti-tumor efficacy mediated by immune cells, accumulation of interferons and activation of PKR, resulting in protein translation inhibition and cell proliferation arrest.