Abstract Anthracycline resistance represents a critical therapeutic challenge in breast cancer treatment, wherein alterations in tumor immune microenvironment and enhanced cellular resistance mechanisms facilitate chemoresistance progression. Transcriptome analysis of 142 HER2-negative breast cancer patients undergoing anthracycline-based chemotherapy revealed four distinct tumor-infiltrating cell subtypes, with subtype D exhibiting elevated M1 macrophage infiltration and superior prognostic outcomes. Differential expression analysis identified miR-222 as the predominantly upregulated microRNA in adriamycin-resistant cells, while Tandem Mass Tag mass spectrometry-based quantitative analysis elucidated PTEN as its direct target and FN1 as a crucial downstream mediator. Engineered extracellular vesicles (EVs) carrying miR-222 inhibitor reversed adriamycin resistance via PTEN/FN1 signaling modulation. Molecular docking analysis found specific PTEN-FN1 protein interactions characterized by stable hydrogen bonds at ARG142-ASP23 and ARG15-GLU95. In xenograft models, EVs-mediated delivery of miR-222 inhibitor significantly attenuated MCF-7/ADR tumor progression through miR-222 suppression and PTEN restoration, with concordant molecular alterations observed in serum derived EVs. Our findings establish a novel mechanism of EVs-mediated drug resistance through the microRNA-222/PTEN/FN1 axis and present engineered EVs as a promising therapeutic strategy for anthracycline resistance in breast cancer, while highlighting circulating EVs profiles as potential treatment monitoring biomarkers. Citation Format: W. Chen, Q. Shao, Z. Wang, B. Zhu, S. Yang. Engineered EVs-mediated miR-222 targeting PTEN/FN1 axis reverses anthracycline resistance in HER2-negative breast cancer abstract. In: Proceedings of the San Antonio Breast Cancer Symposium 2025; 2025 Dec 9-12; San Antonio, TX. Philadelphia (PA): AACR; Clin Cancer Res 2026;32(4 Suppl):Abstract nr PS2-11-17.
Chen et al. (2026) studied this question.