Stripping Immune Camouflage from Cancer Cells: Six Molecular Targeting Strategies Toward ADAR1 Inhibition
Background
Cancer cells are known to use adenosine deaminase acting on RNA 1 (ADAR1) as a shield to evade attacks from immune cells. In normal cells, ADAR1 performs base editing by converting adenosine to inosine in double-stranded RNA (dsRNA). This editing process is essential for preventing the misrecognition of self-generated dsRNA as exogenous viruses. It is a critical physiological mechanism that blocks excessive immune activation to protect cellular survival.
However, many cancer cells enhance this defense mechanism to avoid immune surveillance. Tumor cells with high dsRNA stress due to genomic instability show particularly high dependency on ADAR1 for survival. Blocking this protein's function activates immune sensors such as melanoma differentiation-associated protein 5 (MDA5) and protein kinase R (PKR), leading to a viral mimicry response where the cell is misidentified as infected and enters apoptosis. This mechanism has drawn attention as a key to transforming cold tumors, which resist immune cell infiltration, into hot tumors with active immune responses.
Key Findings
Recent research has classified six molecular targeting strategies for ADAR1 inhibition based on their mechanisms of action. First are nucleoside analogs such as 8-azanebularine, which bind to dsRNA and interfere with ADAR1 activity. Second are catalytic inhibitors that directly block the inosine conversion reaction by binding to the catalytic domain of the ADAR1 protein.
Third are Zα domain modulators. The ADAR1p150 isoform contains a unique Zα domain that binds to left-handed Z-RNA. Compounds such as AVA-ADR-001 block this domain to restore interferon signaling. Fourth are RNA substrate engagement inhibitors that physically prevent the protein from interacting with dsRNA. Fifth are indirect pathway regulators, such as those targeting splicing factor 3B (SF3B). Rebecsinib (17S-FD-895), a representative drug, suppresses ADAR1p150 expression and is currently in phase I clinical trials for acute myeloid leukemia. Sixth is proteolysis-targeting chimera (PROTAC) technology, which selectively degrades ADAR1p150 by recruiting E3 ligases, and Z-PROTAC development is ongoing.
Significance and Outlook
ADAR1 inhibition technology has emerged as a key to overcoming the limitations of immune-oncology therapies. Particularly in cold tumors that do not respond to immune checkpoint inhibitors, combining these drugs with ADAR1 inhibitors can remove the immune evasion barrier and maximize anti-cancer efficacy. It is expected to ignite anti-cancer immune responses and improve the response rates of existing immunotherapies.
However, challenges remain for clinical application. It is essential to clearly distinguish the selective inhibition of ADAR1 activity from its broader effects on RNA metabolism. Precision is required to minimize toxicities similar to autoimmune diseases while ensuring localized action. Establishing precise targeting technologies that reduce side effects on normal tissues and selectively target cancer cells is expected to be a prerequisite for practical implementation.
Adenosine deaminase acting on RNA 1 (ADAR1) is a critical regulator of innate immune signaling and a pan-cancer therapeutic target. Through catalyzing adenosine-to-inosine (A-to-I) editing and editing-independent mechanisms, ADAR1 suppresses activation of dsRNA sensing pathways, including protein kinase R (PKR), melanoma differentiation-associated protein 5 (MDA5), and oligodenylate-synthetase (OAS) signaling, that are critical for maintaining cellular tolerance to endogenous RNAs. In a subset of tumors characterized by elevated interferon-stimulated gene (ISG) expression and dsRNA stress, this function creates a dependency on ADAR1 for survival, establishing a therapeutic vulnerability that can be exploited to induce viral mimicry in cancer cells and enhance anti-tumor immune responses. Here, we review the emerging landscape of ADAR1 modulators, organizing reported compounds into mechanistic classes including nucleoside analogs, catalytic inhibitors, Zα domain modulators, RNA substrate engagement inhibitors, indirect pathway regulators, and PROTACs. We evaluate molecules within these classes with a focus on their mechanisms of action and experimental validation. We further discuss the challenges associated with distinguishing direct inhibition of ADAR1 activity from broader effects on RNA metabolism and innate immune activation. Finally, we highlight the therapeutic potential of ADAR1 targeting defined cancer subsets and examine combination strategies that leverage ADAR1 inhibition for improved sensitivity to current cancer therapeutics. Overall, this review outlines key considerations for the development of selective therapies targeting ADAR1.
This research provides a new milestone in the development of targeted therapies for solid tumors, an area with significant unmet medical needs. A specific application scenario involves designing combination therapies with immune checkpoint inhibitors and ADAR1 inhibitors. For example, pancreatic cancer patients who do not respond to immune checkpoint inhibitors could benefit from the addition of ADAR1 inhibitors to remove the immune evasion barrier. In such cases, the immune system can detect and attack the now-vulnerable cancer cells, reducing tumor size. From a pharmaceutical industry perspective, the Z-PROTAC platform, a targeted protein degradation technology, is expected to accelerate the discovery of customized drugs for refractory cancers. This research opens new therapeutic possibilities for both clinical practice and the drug development ecosystem.