Preclinical SPECT/CT Imaging of αvβ6 Integrins for Molecular Stratification of Idiopathic Pulmonary Fibrosis

Transforming growth factor b activation by the avb6 integrin is central to the pathogenesis of idiopathic pulmonary fibrosis. Expression of the avb6 integrin is increased in fibrotic lung tissue and is a promising therapeutic target for treatment of the disease. Currently, measurement of avb6 integrin levels in the lung requires immunohistochemical analysis of biopsy samples. This procedure is clinically impractical for many patients with pulmonary fibrosis, and a noninvasive strategy for measuring avb6 integrin levels in the lungs is urgently required to facilitate monitoring of disease progression and therapeutic responses. Methods: Using a murine model of bleomycin-induced lung injury, we assessed the binding of intravenously administered 111In-labeled avb6-specific (diethylenetriamine pentaacetate-tetra [DTPA]-A20FMDV2) or control (DTPAA20FMDVran) peptide by nanoSPECT/CT imaging. Development of fibrosis was assessed by lung hydroxyproline content, and avb6 protein and itgb6 messenger RNA were measured in the lungs. Results: Maximal binding of 111In-labeled A20FMDV2 peptide to avb6 integrins was detected in the lungs 1 h after intravenous administration. No significant binding was detected in mice injected with control peptide. Integrin binding was increased in the lungs of bleomycin-, compared with saline-, exposed mice and was attenuated by pretreatment with avb6-blocking antibodies. Levels of 111 In-labeled A20FMDV2 peptide correlated positively with hydroxyproline, avb6 protein, and itgb6 messenger RNA levels. Conclusion: We have developed a highly sensitive, quantifiable, and noninvasive technique for measuring avb6 integrin levels within the lung. Measurement of avb6 integrins by SPECT/CT scanning has the potential for use in stratifying therapy for patients with pulmonary fibrosis.