Granzyme B PET Imaging for Assessment of Disease Activity in Inflammatory Bowel Disease.

Developing a noninvasive imaging method to detect immune system activation with a high temporal resolution is key to improving inflammatory bowel disease (IBD) management. In this study, granzyme B (GZMB), typically released from cytotoxic T and natural killer cells, was targeted using PET with Ga-NOTA-GZP (where GZP is β-Ala-Gly-Gly-Ile-Glu-Phe-Asp-CHO) to detect early intestinal inflammation in murine models of colitis. Bioinformatic analysis was used to assess the potential of GZMB as a biomarker for detecting IBD and predicting response to treatment. Human active and quiescent Crohn disease and ulcerative colitis tissues were stained for GZMB. We used IL-10 mice treated with dextran sulfate sodium (DSS) as an IBD model, wild-type C57BL/6J mice as a control, and anti-tumor necrosis factor as therapy. We used a murine GZMB-binding peptide conjugated to a NOTA chelator (NOTA-GZP) labeled with Ga as the PET tracer. PET imaging was conducted at 1, 3, and 4 wk after colitis induction to evaluate temporal changes. Bioinformatic analysis showed that GZMB gene expression is significantly upregulated in human ulcerative colitis and Crohn disease compared with the noninflamed bowel by 2.98-fold and 1.92-fold, respectively; its expression is lower by 2.16-fold in treatment responders than in nonresponders. Immunofluorescence staining of human tissues demonstrated a significantly higher GZMB in patients with active than with quiescent IBD ( = 0.032).Ga-NOTA-GZP PET imaging showed significantly increased bowel uptake in IL-10 mice with DSS-induced colitis compared with vehicle-treated IL-10 mice (SUV, 0.75 vs. 0.24; < 0.001) and both vehicle- and DSS-treated wild-type mice (SUV, 0.26 and 0.37; < 0.001). In the IL-10 DSS-induced colitis model, the bowel PET probe uptake decreased in response to treatment with tumor necrosis factor-α (SUV, 0.32; < 0.001). There was a 4-fold increase in colonic uptake of Ga-NOTA-GZP in the colitis model compared with the control 1 wk after colitis induction. The uptake gradually decreased to approximately 2-fold by 4 wk after IBD induction; however, the inflamed bowel uptake remained significantly higher than control at all time points (week 4 SUV, 0.23 vs. 0.08; = 0.001). GZMB is a promising biomarker to detect active IBD and predict response to treatment. This study provides compelling evidence to translate GZMB PET for imaging IBD activity in clinical settings.