Abstract 3786: In vivo miR-449b mimic-based nanotherapy suppresses growth and progression of triple-negative breast cancer

Abstract Triple-negative breast cancer (TNBC) comprises 15-20% of breast cancers and is associated with an aggressive course and the highest mortality rate in all breast cancer subtypes owing to high rates of early metastasis recurrence, and a low response to adjuvant chemotherapy. Currently, there is no effective targeted therapy strategy for TNBC due to significant genetic heterogeneity and a lack of defined molecular targets. Recent evidence from our and other laboratories revealed that non-coding RNAs such as tumor suppressor microRNAs (miRNAs) are dysregulated in cancer cells by regulating the expression of target genes (mRNAs) that are involved in critical cellular processes such as cell cycle, proliferation, differentiation, and migration/invasion, drug resistance, and tumor growth. Analyzing the TCGA-patient database, we recently found that reduced miR-449b expression was associated with significantly shorter survival in TNBC patients (n=56 patients with high expression, n=41 patients with low expression, p=0.0011). Our studies revealed that miR449b expression is reduced in TNBC cell lines and its ectopic expression using commercially available transfection reagent inhibited TNBC cell proliferation, migration, and invasion. Since in vivo delivery of miRNA therapeutics has been challenging, we developed magnetic nanoparticles for miR-449b delivery which inhibited in vitro cell proliferation, invasion, and migration. To elucidate molecular mechanisms underlying miR-449b-induced tumor suppressive effects, we investigated potential targets of miR449b using several target prediction algorithms and found that miR-449b has binding sites in the 3'-UTR of the proto-oncogene, eukaryotic elongation factor-2 kinase (eEF2K) gene. We demonstrated eEF2K expression is highly upregulated in TNBC cell lines and eEF2K expression correlates with shorter overall survival in patients with TNBC. More importantly, eEF2K expression was markedly inhibited after ectopic expression of miR-449b in TNBC cells. TNBC cells were also treated with siRNAs specific for eEF2K which led to reduced cell growth and invasion/migration, recapitulating the effects of miR-449b expression Furthermore, in vivo administration of miR-449b-loaded magnetic nanoparticles (0.6 mg/kg once a week in TNBC orthotopic xenograft models (MDA-MB-231) in mice resulted in significant inhibition of eEF2K and tumor growth. Additionally, magnetic nanoparticles-miR-449b treatment in mice did not cause detectable side effects. These findings suggest that miR-449b functions as a tumor suppressor by targeting eEF2K-mediated oncogenic signaling leading to the tumor growth and progression of TNBC. Taken together, our study suggests that the miR-449 nanotherapy using magnetic nanoparticles may be a promising therapeutic strategy that provides a safe and effective antitumor efficacy against TNBC. Citation Format: Goknur Kara, Bulent Ozpolat. In vivo miR-449b mimic-based nanotherapy suppresses growth and progression of triple-negative breast cancer. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3786.