The fibronectin-targeting PEG-FUD imaging probe shows enhanced uptake during fibrogenesis in experimental lung fibrosis

Progressive forms of interstitial lung diseases, including idiopathic pulmonary fibrosis (IPF), are deadly disorders lacking non-invasive biomarkers for assessment of early disease activity, which presents a major obstacle in disease management. Excessive extracellular matrix (ECM) deposition is a hallmark of these disorders, with fibronectin being an abundant ECM glycoprotein that is highly upregulated in early fibrosis and serves as a scaffold for the deposition of other matrix proteins. Due to its role in active fibrosis, we are targeting fibronectin as a biomarker of early lung fibrosis disease activity via the PEGylated fibronectin-binding polypeptide (PEG-FUD). In this work, we demonstrate the binding of PEG-FUD to the fibrotic lung throughout the course of bleomycin-induced murine model of pulmonary fibrosis. We first analyzed the binding of radiolabeled PEG-FUD following direct incubation to precision cut lung slices from mice at different stages of experimental lung fibrosis. Then, we administered fluorescently labeled PEG-FUD subcutaneously to mice over the course of bleomycin-induced pulmonary fibrosis and assessed peptide uptake 24 h later through ex vivo tissue imaging. Using both methods, we found that peptide targeting to the fibrotic lung is increased during the fibrogenic phase of the single dose bleomycin lung fibrosis model (days 7 and 14 post-bleomycin). At these timepoints we found a correlative relationship between peptide uptake and fibrotic burden. These data suggest that PEG-FUD targets fibronectin associated with active fibrogenesis in this model, making it a promising candidate for a clinically translatable molecular imaging probe to non-invasively determine pulmonary fibrosis disease activity, enabling accelerated therapeutic decision-making.