Optimization of Therapeutic modRNA Delivery to the Lung for Prevention of Pulmonary Fibrosis

Background/Objectives: Pulmonary fibrosis is a progressive and fatal disease characterized by excessive extracellular matrix deposition and irreversible lung remodeling. Although modified mRNA (modRNA) therapeutics offer a promising strategy for regulating disease-driving pathways, effective pulmonary delivery remains challenging due to the inherent liver tropism of conventional lipid nanoparticles (LNPs). This study aimed to establish an optimized platform for lung-selective modRNA delivery and therapeutic screening for pulmonary fibrosis. Methods: A panel of charge-modified LNP formulations was evaluated in vivo for pulmonary tropism following systemic administration of luciferase (Luc) modRNA. Administration routes, biodistribution in healthy and bleomycin (BLM)-induced fibrotic lungs, and endogenous microRNA (miRNA)-mediated de-targeting strategies were assessed. Candidate antifibrotic modRNAs targeting the transforming growth factor-beta (TGF-β) signaling pathway were subsequently evaluated in normal human lung fibroblasts (NHLFs). Results: Among the formulations tested, 50% DOTAP MC3 LNPs demonstrated the most favorable balance of pulmonary transfection, physicochemical properties, and limited off-target expression. Intravenous (IV) administration achieved robust lung expression with a superior safety profile compared with intratracheal (IT) delivery. Importantly, pulmonary biodistribution was preserved in BLM-induced fibrotic lungs despite extensive tissue remodeling. Incorporation of miR-122 recognition sites further enhanced selectivity, resulting in 94.5% of total transgene expression being localized to the lungs while substantially reducing residual hepatic expression. In vitro screening identified dominant-negative TGF-β receptor II (DNTGFBR2) modRNA as a potent inhibitor of TGF-β-induced fibrotic activation, significantly suppressing α-SMA and CTGF expression. Conclusions: These findings establish a comprehensive platform for pulmonary modRNA therapeutic development by integrating lung-selective LNP engineering, optimal systemic delivery, miRNA-mediated de-targeting, and therapeutic payload screening. This strategy provides a foundation for the development of targeted RNA therapies for pulmonary fibrosis and other organ-specific diseases.