Abstract 2767: Exploring ADAR1 dependencies in breast cancer brain-metastases

Abstract

Abstract Background: Adenosine deaminase acting on double-stranded RNA (ADAR1) is a recognized driver of epitranscriptomic (post-transcriptional) remodeling and tumor progression. Changes in amino acid sequence, mRNA splicing, and/or polyadenylation sites are only some of the adenosine-to-inosine (A-to-I) RNA editing effects. Under physiological conditions, ADAR1 activity prevents autoinflammation by inhibiting the accumulation of endogenous immunostimulatory double-stranded RNA and by suppressing the Z-RNA sensor ZBP1. Such mechanisms are exploited by cancer cells to desensitize tumor response to therapies, therefore augmenting aggressiveness. Approximately 10 to 20% of patients diagnosed with breast cancer (BC) will develop metastatic disease, which remains the leading cause of death in individuals with BC. We have hypothesized that ADAR1 and its interferon-inducible p150 isoform, play a pivotal role in promoting BC metastases since high levels of ADAR1 are associated with a worse prognosis in patients with high grade BC, especially in the triple-negative BC subgroup (TNBC), which is the most likely to develop brain metastases. Methods: We established a humanized mouse model of breast cancer brain metastases (BC-BrM) using neonatal intracerebroventricular inoculation of MDA-MD-231 TNBC cells and primary patient derived metastatic cells in Rag2−/−γc−/− mice. Before implantation, MDA-MD-231 cells were transduced with a nanoluc-GFP reporter for tracing ADAR1 enzymatic activity in the brain metastatic niche. Lentiviral shRNA knockdown vectors targeting ADAR1, combined with over-expression vectors of full-length ADAR1 or the p150 deleted isoform were adopted to detect editing changes in the metastatic model through RNA-sequencing of BC-BrM. Results: BrM derived from MDA-MD-231 implants display upregulation of ADAR1 p150 and activation of the WNT/β-catenin pathway compared to the non-implanted cell lines. Upon shRNA knockdown of ADAR1, decreased expression of BC stem cell markers was detected via FACS in MDA-MD-231 ADAR1 knocked-down versus control BC-BrM isolated cells. We are now exploring molecular pathways affected by ADAR1 loss/overexpression in establishing BrM. Future Directions: We have developed a biorepository of primary patient-derived metastatic breast cancer samples and have begun the process of tracking metastatic kinetics and ADAR1 activation with the ADAR1 reporter in an orthotopic mouse model. Overall, this study will provide new insights into the molecular role of ADAR1 deaminase activity in establishing and maintaining metastatic niches. Citation Format: Teresa Sposito, Emma E. Klacking, Antonio W. Ruiz, Jessica Pham, Catriona Jamieson. Exploring ADAR1 dependencies in breast cancer brain-metastases [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 2767.