Abstract
RATIONALE: α(v) integrins, key regulators of transforming growth factor-β activation and fibrogenesis in in vivo models of pulmonary fibrosis, are expressed on abnormal epithelial cells (α(v)β(6)) and fibroblasts (α(v)β(1)) in fibrotic lungs. OBJECTIVES: We evaluated multiple α(v) integrin inhibition strategies to assess which most effectively reduced fibrogenesis in explanted lung tissue from patients with idiopathic pulmonary fibrosis. METHODS: Selective α(v)β(6) and α(v)β(1), dual α(v)β(6)/α(v)β(1), and multi-α(v) integrin inhibitors were characterized for potency, selectivity, and functional activity by ligand binding, cell adhesion, and transforming growth factor-β cell activation assays. Precision-cut lung slices generated from lung explants from patients with idiopathic pulmonary fibrosis or bleomycin-challenged mouse lungs were treated with integrin inhibitors or standard-of-care drugs (nintedanib or pirfenidone) and analyzed for changes in fibrotic gene expression or TGF-β signaling. Bleomycin-challenged mice treated with dual α(v)β(6)/α(v)β(1) integrin inhibitor, PLN-74809, were assessed for changes in pulmonary collagen deposition and Smad3 phosphorylation. MEASUREMENTS AND MAIN RESULTS: Inhibition of integrins α(v)β(6) and α(v)β(1) was additive in reducing type I collagen gene expression in explanted lung tissue slices from patients with idiopathic pulmonary fibrosis. These data were replicated in fibrotic mouse lung tissue, with no added benefit observed from inhibition of additional α(v) integrins. Antifibrotic efficacy of dual α(v)β(6)/α(v)β(1) integrin inhibitor PLN-74809 was confirmed in vivo, where dose-dependent inhibition of pulmonary Smad3 phosphorylation and collagen deposition was observed. PLN-74809 also, more potently, reduced collagen gene expression in fibrotic human and mouse lung slices than clinically relevant concentrations of nintedanib or pirfenidone. CONCLUSIONS: In the fibrotic lung, dual inhibition of integrins α(v)β(6) and α(v)β(1) offers the optimal approach for blocking fibrogenesis resulting from integrin-mediated activation of transforming growth factor-β.