Imaging\nPulmonary Fibrosis and Treatment Efficacy\nIn Vivo with Autotaxin-Specific PET Ligand [<sup>18</sup>F]ATX-1905

Idiopathic\npulmonary fibrosis (IPF) is a fatal disease characterized\nby unpredictable progression and limited therapeutic options. Current\ndiagnosis relies on high resolution computed tomography (HRCT), which\nmay not adequately capture early signs of deterioration. The enzyme\nautotaxin (ATX) emerges as a prominently expressed extracellular secretory\nenzyme in the lungs of IPF patients. The objective of this study was\nto evaluate the effectiveness of <sup>18</sup>F-labeled ATX-targeted\ntracer [<sup>18</sup>F]­ATX-1905, in comparison with [<sup>18</sup>F]­FDG, for early fibrosis diagnosis, disease evolution monitoring,\nand treatment efficacy assessment in bleomycin-induced pulmonary fibrosis\n(BPF) models. To assess treatment efficacy, mice were treated with\ntwo commonly used drugs for IPF, pirfenidone or nintedanib, from Day\n9 to Day 23 postbleomycin administration. Lung tissue assessments\nencompassed inflammation severity via H&E staining, and Ashcroft\nscoring via Masson staining, alongside quantification of ATX expression\nthrough ELISA. Positron emission tomography (PET) imaging employing\n[<sup>18</sup>F]­FDG and [<sup>18</sup>F]­ATX-1905 tracked disease progression\npre- and post-treatment. The extent of pulmonary fibrosis corresponded\nto changes in ATX expression levels in the BPF mouse model. Notably,\n[<sup>18</sup>F]­ATX-1905 exhibited elevated uptake in BPF lungs during\nthe progression of the disease, particularly evident at the early\nstage (Day 9). This uptake was inhibited by an ATX inhibitor, PF-8380,\nunderscoring the specificity of the radiotracer. Conversely, [<sup>18</sup>F]­FDG uptake, peaking at Day 15, decreased subsequently,\nlikely reflective of diminished inflammation. A 2-week treatment regimen\nusing either pirfenidone or nintedanib resulted in notable reductions\nof ATX expression levels and fibrosis degrees within lung tissues,\nbased on ELISA and Masson staining, as evidenced by PET imaging with\n[<sup>18</sup>F]­ATX-1905. [<sup>18</sup>F]­FDG uptake also decreased\nfollowing the treatment period. Additionally, PET/CT imaging extended\nto a nonhuman primate (NHP) BPF model. The uptake of [<sup>18</sup>F]­ATX-1905 (SUV<sub>max</sub> = 2.2) was significantly higher than\nthat of [<sup>18</sup>F]­FDG (SUV<sub>max</sub> = 0.7) in fibrotic\nlung tissue. Using our novel ATX-specific radiotracer [<sup>18</sup>F]­ATX-1905 and PET/CT imaging, we demonstrated excellent ability\nin early fibrosis detection, disease monitoring, and treatment assessment\nwithin lungs of the BPF mouse models. [<sup>18</sup>F]­ATX-1905 displayed\nremarkable specificity for ATX expression and high sensitivity for\nATX alterations, suggesting its potential for monitoring varying ATX\nexpression in lungs of IPF patients.