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 ⁶⁸Ga-NOTA-GZP (where GZP is β-Ala–Gly–Gly–Ile–Glu–Phe–Asp–CHO) to detect early intestinal inflammation in murine models of colitis. Methods: 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 ⁶⁸Ga as the PET tracer. PET imaging was conducted at 1, 3, and 4 wk after colitis induction to evaluate temporal changes. Results: 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 (P = 0.032).⁶⁸Ga-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_mean, 0.75 vs. 0.24; P < 0.001) and both vehicle- and DSS-treated wild-type mice (SUV_mean, 0.26 and 0.37; P < 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_mean, 0.32; P < 0.001). There was a 4-fold increase in colonic uptake of ⁶⁸Ga-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_mean, 0.23 vs. 0.08; P = 0.001). Conclusion: 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.

开发一种无创成像方法以高时间分辨率检测免疫系统激活是改善炎症性肠病（IBD）管理的关键。在这项研究中，颗粒酶 B (GZMB) 通常由细胞毒性 T 细胞和自然杀伤细胞释放，使用 PET 和⁶⁸ Ga-NOTA-GZP（其中 GZP 是 β-Ala-Gly-Gly-Ile-Glu-Phe-Asp）进行靶向–CHO）检测小鼠结肠炎模型中的早期肠道炎症。方法：使用生物信息分析来评估 GZMB 作为检测 IBD 和预测治疗反应的生物标志物的潜力。对人类活动性和静止性克罗恩病和溃疡性结肠炎组织进行 GZMB 染色。我们使用用右旋糖酐硫酸钠 (DSS) 治疗的 IL-10 ^–/–小鼠作为 IBD 模型，野生型 C57BL/6J 小鼠作为对照，并使用抗肿瘤坏死因子作为治疗。我们使用与标记有⁶⁸ Ga 的 NOTA 螯合剂 (NOTA-GZP) 结合的鼠 GZMB 结合肽作为 PET 示踪剂。结肠炎诱导后 1、3 和 4 周进行 PET 成像以评估时间变化。结果：生物信息分析显示，与非炎症肠道相比，GZMB基因表达在人类溃疡性结肠炎和克罗恩病中显着上调，分别为2.98倍和1.92倍；其表达在治疗有反应者中比无反应者低 2.16 倍。人体组织的免疫荧光染色显示，活动性 IBD 患者的 GZMB 显着高于静止期 IBD（ P = 0.032）。⁶⁸ Ga-NOTA-GZP PET 成像显示，与媒介物治疗的 IL-10 ^–/–小鼠相比，患有 DSS 诱导结肠炎的 IL-10 ^–/–小鼠的肠道摄取显着增加（SUV_平均值，0.75 vs. 0.24； P < 0.001 ）以及媒介物和 DSS 处理的野生型小鼠（SUV_平均值，0.26 和 0.37； P < 0.001）。在 IL-10 ^–/– DSS 诱导的结肠炎模型中，肿瘤坏死因子 –α 治疗后肠道 PET 探针摄取减少（SUV_平均值，0.32； P < 0.001）。结肠炎诱导后 1 周，与对照相比，结肠炎模型中⁶⁸ Ga-NOTA-GZP 的结肠摄取增加了 4 倍。 IBD 诱导后 4 周，摄取量逐渐下降至约 2 倍；然而，在所有时间点，发炎肠道的摄取量仍然显着高于对照（第 4 周 SUV_平均值，0.23 vs. 0.08； P = 0.001）。结论： GZMB 是一种有前景的生物标志物，可用于检测活动性 IBD 并预测治疗反应。这项研究为将 GZMB PET 转化为临床环境中 IBD 活动成像提供了令人信服的证据。