Noninvasive Assessment of Colitis Activity by Targeted Imaging of Neutrophil Elastase with [⁶⁸Ga]Ga-POL6014

Effective management of IBD necessitates ongoing evaluation of disease activity. Molecular imaging of neutrophil elastase (NE) could address this urgent need as it mechanistically targets the early event of intestinal inflammation. In this study, based on macrocyclic peptide POL6014, [⁶⁸Ga]Ga-POL6014 was developed for noninvasive assessment of colitis activity and treatment response through targeting of NE. [⁶⁸Ga]Ga-POL6014 exhibited high specificity and affinity for NE with the K_D of 14.81 nM and IC₅₀ of 3.02 nM. In PET imaging, [⁶⁸Ga]Ga-POL6014 could quickly visualize inflammation sites with colon uptake of 3.15 ± 0.63%ID/g and colon/muscle ratio of 4.92 ± 0.74 at 30 min p.i.. The specificity of [⁶⁸Ga]Ga-POL6014 was demonstrated by the dose-response blocking studies with POL6014. Furthermore, [⁶⁸Ga]Ga-POL6014 PET was used to evaluate treatment response to 5-ASA. The treatment significantly inhibited colon uptake of [⁶⁸Ga]Ga-POL6014 (1.71 ± 0.21 %ID/g), accompanied by a decrease in imaging contrast (2.81 ± 0.26). Immunofluorescence revealed the preservation of mucosal barrier integrity and a remarkable decrease in NE positive cells after 5-ASA treatment. Moreover, there were good correlations between PET quantification with NE expression and DAI score, indicating the reliability of [⁶⁸Ga]Ga-POL6014. Additionally, [⁶⁸Ga]Ga-POL6014 was widely distributed and cleared rapidly from nonspecific organs and blood pool, and was excreted through urinary system, suggesting its favorable pharmacokinetics. In conclusion, [⁶⁸Ga]Ga-POL6014 is a promising tracer that enables in vivo globally mapping of neutrophil-mediated inflammation in the entire gastrointestinal tract for early diagnosis, assessment of disease activity and evaluation of anti-inflammatory treatment response.