Noninvasive Detection of Experimental Colitis Using Folate Receptor-β-Targeted PET Imaging in Mice

Purpose Positron emission tomography (PET) is a promising noninvasive technique for detecting and monitoring inflammatory bowel disease (IBD). In IBD pathogenesis, activated macrophages – marked by overexpression of folate receptor beta (FR-β) – play a key role. Leveraging this target, folate-based PET tracers have been developed to visualize macrophage-driven inflammation. This study evaluated the feasibility of FR-β-binding aluminum-fluoride-18-labeled 1,4,7-triazacyclononane-1,4,7-triacetic acid conjugated folate ([ ¹⁸ F]FOL) PET/computed tomography (CT) for detecting intestinal inflammation in a murine model of acute colitis. Procedures Acute colitis was induced in female and male C57BL/6NCrl mice via 2.5% dextran sodium sulfate (DSS) in drinking water for 6 days, followed by recovery. Healthy age- and sex-matched mice served as controls. Mice underwent whole-body [ ¹⁸ F]FOL PET/CT imaging followed by ex vivo biodistribution analysis. Intestinal tissues were further analyzed by digital autoradiography and immunohistochemical staining for FR-β and Mac-3, a marker of macrophages. 2-Deoxy-2-[ ¹⁸ F]fluoro- D -glucose ([ ¹⁸ F]FDG) PET/CT was performed to evaluate metabolic activity in the gastrointestinal tract. Results DSS-treated mice developed significant clinical signs of colitis, including weight loss and increased disease activity scores. PET/CT and ex vivo analyses revealed significantly higher [ ¹⁸ F]FOL uptake in the distal colon of DSS-treated mice compared to controls. Autoradiography and immunohistochemistry confirmed the presence of inflamed regions with increased Mac-3 in the distal colon. However, only a subset of Mac-3-positive macrophages expressed FR-β. Quantitative analysis demonstrated a correlation between tracer uptake and Mac-3 staining intensity. Conclusions [ ¹⁸ F]FOL PET/CT regions enriched with activated macrophages in DSS-induced colitis, although quantitative uptake in the colon was variable. The elevated splenic uptake and strong histological correlation suggest that FR-β-targeted PET imaging can reflect systemic macrophage activation in acute IBD. These findings support the continued investigation of [ ¹⁸ F]FOL in chronic inflammation models and its translational potential for imaging macrophage-driven pathology in IBD.