Abstract 4484: Discovery of a potential first-in-class Za targeted small molecule inhibitor of ADAR1 p150 which demonstrates strong anti-tumor efficacy

Abstract Background: Adenosine deaminase, RNA specific (ADAR1), catalyzes the hydrolytic deamination of adenosine (A) to inosine (I) in double-stranded (ds) RNAs. ADAR1 has two isoforms: p110 in the nucleus and p150 in the cytoplasm. Both isoforms alter the coding and non-coding sections of self-dsRNA. The ADAR1 p150 isoform is expressed from an interferon (IFN)-response promoter and has a Z-DNA/Z-RNA binding domain at the N-terminus. ADAR1 has been implicated in promoting cell survival and resistance to immune response in several cancer types like multiple myeloma, breast, lung, liver, and skin cancer. Inhibition of ADAR1 p150 has the potential to enhance anti-tumor efficacy as monotherapy and in combination with other therapeutic modalities. The Zα domain of ADAR1 p150 provides exclusivity to p150 compared to the other isoforms. Herein, we outline the discovery of a potential first-in-class Zα targeted ADAR1 p150 inhibitor and degrader for cancer immunotherapy. Methods: AVA-ADR-001 was identified through a high throughput p110 knockout cell-based assay. The ability of AVA-ADR-001 to induce interferons was confirmed in various cell lines. The anti-tumor efficacy of AVA-ADR-001 was evaluated in B16F10 syngeneic melanoma mice model as monotherapy and in combination with anti-PD-1. PROTAC AVA-ADR-703 was used to demonstrate selective degradation of the ADAR1 p150 protein. Results: We have discovered AVA-ADR-001, a novel small molecule inhibitor of ADAR1 which significantly increases the IFN response in vitro in an MDA5-dependent manner. In vitro binding studies confirm that AVA-ADR-001 binds to the Zα domain of ADAR1 with low nM potency. AVA-ADR-001 demonstrates anti-tumor efficacy 1.5X superior to anti-PD1 ICB non-responsive tumor models. In addition, the AVA-ADR-001 monotherapy and combination groups showed a significant upregulation of numerous interferon-stimulated genes, including IFIH1, IFN-β, and CXCL-10. Finally, targeted protein degradation of ADAR1 p150 while sparing ADAR1 p110 was confirmed when cells were treated with AVA-ADR-703 with nM DC50, the PROTAC variant of AVA-ADR-001. Conclusions: To our knowledge, AVA-ADR-001 and AVA-ADR-703 are the first selective Zα-targeted small molecule inhibitor and degrader of ADAR1 p150 respectively to be disclosed. As a powerful and targeted first-in-class ADAR1 inhibitor, AVA-ADR-001 has demonstrated a strong induction of interferon (IFN) in a number of cancer cell lines and in vivo. AVA-ADR-001 has also demonstrated strong in vivo anti-tumor efficacy as monotherapy and in combination with anti-PD1. Furthermore, AVA-ADR-703 demonstrates selective and highly efficient degradation of ADAR1 p150 while sparing ADAR1 p110. Given that ADAR1 has a pro-metastatic and immune-suppressive role, AVA-ADR-001 and AVA-ADR-703 have significant potential to emerge as strong cancer immunotherapy candidates. Citation Format: Avijit Goswami, Sandeep Goyal, Kawaljit Singh, Princy Khurana, Barnali Deb, Aditya Kulkarni. Discovery of a potential first-in-class Za targeted small molecule inhibitor of ADAR1 p150 which demonstrates strong anti-tumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4484.