Background Interstitial lung disease (ILD) is one of the leading causes of death in systemic sclerosis (SSc). Since routine diagnostics such as CT and pulmonary function tests only detect impaired organ function and/or damage, there is an unmet need for the non-invasive diagnosis of ILD at earliest, possibly still reversible disease stages.
Objectives To assess nuclear imaging for the detection of SSc-ILD by using radiotracers specifically targeting integrin αvβ3 as a pathophysiologic key molecule of early inflammation-dependent fibrosis in the murine model of bleomycin-induced pulmonary fibrosis and in the multisystemic Fra-2 transgenic (tg) mouse model of SSc.
Methods Expression of integrin αvβ3 was analysed in lung sections from patients with SSc-ILD, idiopathic pulmonary fibrosis (IPF), healthy controls (n=5) as well as from bleomycin-treated mice, Fra-2 tg mice and respective controls (n=4) using immunohistochemistry. In vivo imaging was performed using 111In-DOTA-RGD radioconjugates specifically targeting integrin αvβ3. SPECT (single photon emission computed tomography) was performed using a small-animal SPECT/CT scanner (NanoSPECT/CT, Mediso). Animals were scanned at early disease time points to visualise inflammation-dependent pulmonary fibrosis. The pulmonary accumulation of the radiotracer was confirmed by ex vivo SPECT/CT, biodistribution, and autoradiography studies. Nonparametric non-related data were expressed as median(Q1,Q3). For statistical analysis, the Mann-Whitney U test was applied. P-values <0.05 were considered statistically significant.
Results In lung sections of patients with SSc-ILD and IPF, the expression of integrin αvβ3 was increased by 3.7-fold and 2.9-fold, respectively as compared to healthy controls (p<0.009, p<0.02). Lungs of bleomycin-treated and Fra-2 tg mice, but not of controls showed a significant increase in integrin αvβ3 expression (upregulation by 5.7-fold and 4.8-fold, respectively) as we have similarly observed in SSc-ILD and IPF patients (p<0.03 each, Fig. C). Integrin αvβ3 was primarily expressed on endothelial cells, inflammatory cells and myofibroblasts as indicated by sequential stainings with cell type-specific markers. Notably, at day 7 after intratracheal bleomycin installation, the peak of pulmonary inflammation, nuclear SPECT/CT with 111In-DOTA-RGD targeting integrin αvβ3, successfully visualised pulmonary inflammation and incipient fibrosis in the model of bleomycin-induced pulmonary fibrosis. Similarly, imaging of integrin αvβ3 in Fra-2 tg mice at 13 weeks of age, the starting point of pulmonary fibrosis, showed a higher pulmonary uptake of the radiotracer in Fra-2 tg mice than in controls (Fig. A). Ex vivo SPECT/CT of isolated lungs, biodistribution and autoradiography studies confirmed the in vivo results and validated the specific radiotracer uptake in lungs from bleomycin-challenged mice and Fra-2 tg mice as compared to controls (Fig. B).
Conclusions Our data provide the first evidence that targeting pathophysiologic key molecules using nuclear imaging methods for the visualization of inflammation-dependent fibrosis is a promising non-invasive approach for the early detection of lung involvement in SSc.
Disclosure of Interest J. Schniering Grant/research support from: Swiss National Science Foundation (S-85605–02–01), S. Haller Grant/research support from: Swiss National Science Foundation (S-85605–02–01), Z. Guo Grant/research support from: respective institution, C. Feghali-Bostwick Grant/research support from: respective institution, R. Schibli Grant/research support from: respective institution, O. Distler Grant/research support from: Bayer, Sanofi, Ergonex, Boehringer Ingelheim, Actelion, Pfizer, Consultant for: 4 D Science, Actelion, Active Biotec, Bayer, BiogenIdec, BMS, Boehringer Ingelheim, EpiPharm, Ergonex, espeRare foundation, Genentech/Roche, GSK, Inventiva, Lilly, medac, MedImmune, Pharmacyclics, Pfizer, Serodapharm, Sinoxa, C. Müller Grant/research support from: respective institution, B. Maurer Grant/research support from: respective institution