Tilorone suppresses TGF-β–driven fibroblast activation and restores BMP–Smad1/5/8 signaling: implications for laryngotracheal fibrosis

BACKGROUND: Laryngotracheal fibrosis is a rare but severe complication of prolonged intubation, leading to airway narrowing, respiratory distress, dysphonia, and, in advanced cases, life-threatening airway obstruction. Current treatments are primarily surgical, while pharmacologic approaches such as mitomycin C, corticosteroids, or 5-fluorouracil show inconsistent efficacy and potential toxicity. Thus, there remains a critical need for safe and effective antifibrotic therapies. Transforming growth factor-beta (TGF-β) is a key mediator of fibrosis, promoting fibroblast activation, migration, and expression of profibrotic markers such as alpha-smooth muscle actin (α-SMA). OBJECTIVES: This study aimed to evaluate the antifibrotic potential of tilorone dihydrochloride, a synthetic small molecule, in human respiratory fibroblasts in vitro. METHODS: Fibrotic alterations were assessed in human laryngotracheal fibrosis tissue samples. An in vitro model using MRC-5 human lung-derived fibroblasts was employed to investigate the effects of tilorone. Molecular analyses (RT-qPCR, immunocytochemistry, western blotting) quantified mRNA and protein expression of key signaling markers. Cell proliferation and viability were performed to evaluate potential cytotoxic effects of tilorone. Functional assays, including wound scratch and single-cell tracking, assessed fibroblast motility, and atomic force microscopy (AFM) measured extracellular matrix elasticity. RESULTS: Phosphorylation of Smad1/5/8, a key transcription factor in the bone morphogenetic protein (BMP) signaling, was reduced in both human laryngotracheal fibrosis tissue and TGF-β-treated MRC-5 fibroblasts. Tilorone treatment did not affect MRC-5 cell viability or proliferation but increased BMP2, BMP4, BMP7, and BMP14 (GDF5; Growth Differentiation Factor 5) mRNA expression, enhanced Smad1/5/8 phosphorylation, and suppressed TGF-β-induced Smad2/3 phosphorylation. Functionally, tilorone inhibited TGF-β-driven fibroblast migration and α-SMA expression, downregulated collagen I and III mRNA levels, and restored extracellular matrix elasticity, as confirmed by AFM. CONCLUSION: Tilorone counteracts TGF-β-mediated profibrotic signaling and restores BMP pathway activity in MRC-5 fibroblasts in vitro. These findings identify tilorone as a promising therapeutic candidate for fibrotic airway diseases such as laryngotracheal fibrosis.