Abstract 3810: Targeting the ADAR1/PKR pathway in <i>TP53</i>-mutant acute myeloid leukemia

Abstract TP53-mutated (TP53-Mut) acute myeloid leukemia (AML) is a highly aggressive subtype with poor prognosis and limited treatment options. Using the Cancer Dependency Map (DepMap), we identified therapeutic vulnerabilities unique to TP53-Mut AML compared to TP53-WT AML. As expected, TP53-WT cells were dependent on MDM2, validating our approach. In TP53-Mut cells, ADAR1, IPPK, PRKRA, and USP18 emerged as top vulnerabilities. Of note, ADAR1 dependency scores were positively correlated with IPPK (r=0.56), PRKRA (r=0.50), and USP18 (r=0.53). Furthermore, ADAR1 was a central node connecting all other identified TP53-mut AML dependencies. A network analysis revealed EIF2AK2 (PKR) expression as a marker of sensitivity to PRKRA, USP18 and ADAR1 dependencies. PKR activation is a marker of response to ADAR1 loss suggesting that the ADAR1-PKR pathway plays a pivotal role in TP53-Mut AML biology. Loss of ADAR1 was validated as a dependency in TP53-Mut AML cells both in vitro and in vivo. ADAR1 catalyzes adenosine-to-inosine (A-to-I) RNA editing. Its loss causes dsRNA accumulation, triggering interferon (IFN) signaling and PKR activation, leading to translational inhibition and cell death. Consistent with ADAR1 biology, a genome-wide CRISPR screen in TP53-KO MV4-11 AML cells revealed that knockout of IFN pathway activators (e.g., IRF9, STAT2, and IFNAR1) and knockout of PKR, conferred resistance to ADAR1 loss. Of note, our screen identified the knockout of USP18, PRKRA, and IPPK as sensitizers to ADAR1 loss, validating our initial network analysis. Combined knockout of ADAR1 with USP18 or PRKRA enhanced PKR activation, driving lethality in TP53-Mut AML cells. Given the lack of commercially available ADAR1 inhibitors, we explored alternative methods to activate PKR. Through a drug repurposing screen, we identified FDA-approved small molecules that unexpectedly activate PKR and synergize with ADAR1 knockout, significantly reducing TP53-Mut AML proliferation. Co-treatment with interferon-beta (IFNβ), which activates PKR and mimics ADAR1 knockout, and PKR-activating molecules yielded pronounced anti-proliferative effects in TP53-Mut AML cells and a TP53-Mut patient-derived xenograft (PDX) model cultured short-term in vitro. In conclusion, we have established that TP53-Mut AML cells rely on the ADAR1-PKR pathway for survival. Our findings revealed a novel therapeutic opportunity combining FDA-approved agents and offering a promising strategy for the treatment of TP53-Mut AML, addressing a critical unmet need in treating this aggressive leukemia subtype. Citation Format: Yara Rodriguez, Gabriela Alexe, Audrey Taillon, Mariya Atanasova, Paige Stocker, Haley Curtis, Allen Thayakumar, Lucy Merickel, Silvi Salhotra, Kieren Marini, Olasunkanmi Olaoye, Constanze Scheider, Oivin Guicherit, Kimberly Stegmaier. Targeting the ADAR1/PKR pathway in TP53-mutant acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3810.