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

Transforming growth factor beta activation by the alpha v beta 6 integrin is central to the pathogenesis of idiopathic pulmonary fibrosis. Expression of the alpha v beta 6 integrin is increased in fibrotic lung tissue and is a promising therapeutic target for treatment of the disease. Currently, measurement of alpha v beta 6 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 alpha v beta 6 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 In-111-labeled alpha v beta 6-specific (diethylenetriamine pentaacetate-tetra [DTPA]-A20FMDV2) or control (DTPA-A20FMDVran) peptide by nanoSPECT/CT imaging. Development of fibrosis was assessed by lung hydroxyproline content, and alpha v beta 6 protein and itgb6 messenger RNA were measured in the lungs. Results: Maximal binding of In-111-labeled A20FMDV2 peptide to alpha v beta 6 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 alpha v beta 6-blocking antibodies. Levels of In-111-labeled A20FMDV2 peptide correlated positively with hydroxyproline, alpha v beta 6 protein, and itgb6 messenger RNA levels. Conclusion: We have developed a highly sensitive, quantifiable, and noninvasive technique for measuring alpha v beta 6 integrin levels within the lung. Measurement of alpha v beta 6 integrins by SPECT/CT scanning has the potential for use in stratifying therapy for patients with pulmonary fibrosis.