Abstract 2013: Extracellular vesicles transfer miR-181a to confer PARP inhibitor resistance and induce STING degradation in BRCA-mutated triple-negative breast and ovarian cancers cells
Authors: Bustos Matias A. , Yokoe Takamichi , Shoji Yoshiaki , Kobayashi Yuta , Mizuno Shodai , Murakami Tomohiro , Sekhar Sreeja C. , Knarr Matthew , Vasilev Steven A. , DiFeo Analisa , Drapkin Ronny , Hoon Dave S. 
Published: March 2024

Abstract
Background: Patients with BRCA-mutated breast cancer (BC), including triple-negative BC (TNBC), and ovarian cancer (OvCa) are treated with poly (ADP-ribose) polymerase inhibitors (PARPi). BC and OvCa tumors develop similar mechanisms of resistance to platinum-based agents and PARPi. This study aimed to identify microRNAs (miRs) inducing PARPi resistance in cancer cells that can be transferred by extracellular vesicles (EV).
Methods: Olaparib-resistant (OlaR) cell lines were analyzed for 2,083 miRs using HTG miRNA Whole Transcriptomic Analysis (WTA) and NGS. Functional assays were performed in BRCA1-mutated TNBC and OvCa cell lines. In-silico analysis were performed using TCGA, GTEx, CCLE, GDSC, and GEO databases.
Results: The miR-181 family (including miR-181a, p=0.001) was significantly upregulated in OlaR TNBC cell lines. High miR-181a levels occurred in tumor tissues of TNBC patients (p=0.001). miR-181a binds to the stimulator of interferon genes (STING) mRNA to promote STING mRNA degradation in OvCa. We hypothesized that miR-181a downregulates STING and downstream proinflammatory cytokines, to mediate PARPi resistance. miR-181a-overexpression induced olaparib resistance and STING downregulation in BRCA1-mutated TNBC cell lines. EV isolated from OlaR TNBC cell lines horizontally transferred miR-181a to non-resistant parental cell lines, which conferred PARPi-resistance and decreased STING. In clinical settings, STING levels were positively correlated with interferon gamma (IFNG) response scores (p=0.01). Low-IFNG response scores in HER2-negative BC patients showed a worse response to neoadjuvant treatment (p=0.001). Consistently, OlaR TNBC cell lines showed resistance to platinum-based drugs. OvCa cell lines resistant to cisplatin showed resistance to olaparib; but miR-181a knockout significantly improved olaparib sensitivity (p=0.001).
Conclusions: High levels of miR-181a decrease STING pathway, correlate with IFNG scores, drive PARPi and platinum-based drug resistance. Horizontal miR-181a EVs transfer can facilitate drug resistance in cells. The miR-181a-STING axis can be used for predicting PARPi responses in TNBC and OvCa tumors.
Citation Format: Matias A. Bustos, Takamichi Yokoe, Yoshiaki Shoji, Yuta Kobayashi, Shodai Mizuno, Tomohiro Murakami, Sreeja C. Sekhar, Matthew Knarr, Steven A. Vasilev, Analisa DiFeo, Ronny Drapkin, Dave S. Hoon. Extracellular vesicles transfer miR-181a to confer PARP inhibitor resistance and induce STING degradation in BRCA-mutated triple-negative breast and ovarian cancers cells [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 2013.