Abstract: MicroRNA-21 (miR-21) is a key regulator of gene expression involved in cancer progression and fibrosis. Its dysregulation promotes cell proliferation, resistance to apoptosis, Epithelial–Mesenchymal Transition (EMT), and Extracellular Matrix (ECM) remodeling, making it one of the most widely studied oncomiRs and fibromiRs. Evidence shows that miR-21 contributes to tumor growth, metastasis, and fibrosis by suppressing tumor suppressors such as PTEN and PDCD4 and activating pro-fibrotic pathways, including TGF-β signaling. Its consistent dysregulation highlights its potential as a biomarker for diagnosis, prognosis, and treatment monitoring. Several therapeutic strategies, such as antagomiRs, locked nucleic acids (LNAs), CRISPR-based inhibition, and nanoparticle- or viral-mediated delivery systems, have shown promising preclinical results. Despite advances, challenges remain in translating miR-21 inhibition to clinical use. Key limitations include off-target effects, delivery inefficiencies, and context-dependent variability in miR-21 function. These issues hinder the development of safe and effective miR-21-targeted therapies. MiR-21 plays a central role in cancer and fibrosis and offers significant potential as both a biomarker and therapeutic target. Future research should focus on precision-based approaches, next-generation gene-editing technologies, and improved preclinical models to optimize miR-21 inhibition for clinical application. This review compiles and evaluates current literature on miR-21 biogenesis, regulation, functional roles, and therapeutic targeting across various cancers and organ-specific fibrotic disorders.
Sharma et al. (Tue,) studied this question.