Imaging Pulmonary Fibrosis and Treatment Efficacy In Vivo with Autotaxin-Specific PET Ligand [¹⁸F]ATX-1905

Idiopathic pulmonary fibrosis (IPF) is a fatal disease characterized by unpredictable progression and limited therapeutic options. Current diagnosis relies on high resolution computed tomography (HRCT), which may not adequately capture early signs of deterioration. The enzyme autotaxin (ATX) emerges as a prominently expressed extracellular secretory enzyme in the lungs of IPF patients. The objective of this study was to evaluate the effectiveness of ¹⁸F-labeled ATX-targeted tracer [¹⁸F]ATX-1905, in comparison with [¹⁸F]FDG, for early fibrosis diagnosis, disease evolution monitoring, and treatment efficacy assessment in bleomycin-induced pulmonary fibrosis (BPF) models. To assess treatment efficacy, mice were treated with two commonly used drugs for IPF, pirfenidone or nintedanib, from Day 9 to Day 23 postbleomycin administration. Lung tissue assessments encompassed inflammation severity via H&E staining, and Ashcroft scoring via Masson staining, alongside quantification of ATX expression through ELISA. Positron emission tomography (PET) imaging employing [¹⁸F]FDG and [¹⁸F]ATX-1905 tracked disease progression pre- and post-treatment. The extent of pulmonary fibrosis corresponded to changes in ATX expression levels in the BPF mouse model. Notably, [¹⁸F]ATX-1905 exhibited elevated uptake in BPF lungs during the progression of the disease, particularly evident at the early stage (Day 9). This uptake was inhibited by an ATX inhibitor, PF-8380, underscoring the specificity of the radiotracer. Conversely, [¹⁸F]FDG uptake, peaking at Day 15, decreased subsequently, likely reflective of diminished inflammation. A 2-week treatment regimen using either pirfenidone or nintedanib resulted in notable reductions of ATX expression levels and fibrosis degrees within lung tissues, based on ELISA and Masson staining, as evidenced by PET imaging with [¹⁸F]ATX-1905. [¹⁸F]FDG uptake also decreased following the treatment period. Additionally, PET/CT imaging extended to a nonhuman primate (NHP) BPF model. The uptake of [¹⁸F]ATX-1905 (SUV_max = 2.2) was significantly higher than that of [¹⁸F]FDG (SUV_max = 0.7) in fibrotic lung tissue. Using our novel ATX-specific radiotracer [¹⁸F]ATX-1905 and PET/CT imaging, we demonstrated excellent ability in early fibrosis detection, disease monitoring, and treatment assessment within lungs of the BPF mouse models. [¹⁸F]ATX-1905 displayed remarkable specificity for ATX expression and high sensitivity for ATX alterations, suggesting its potential for monitoring varying ATX expression in lungs of IPF patients.