成纤维细胞活化蛋白（FAP）是一种潜在的肿瘤诊断和治疗靶点，因为它仅在大多数实体肿瘤基质中癌相关成纤维细胞的细胞膜上选择性表达。本研究的目的是开发一种99mTc标记的成纤维细胞活化蛋白抑制剂（FAPI）探针，评估其在裸鼠中的成像效果，并进一步探索对健康志愿者的生物分布和对肿瘤患者的摄取。设计并合成了一种含有d-脯氨酸的FAPI衍生物配体（DP-FAPI）作为连接物，并通过试剂盒配制得到了稳定的亲水性99mTc标记复合物（[99mTc]Tc-DP-FAPI）。在转染了FAP的HT-1080细胞（FAP-HT-1080）中进行了体外细胞摄取和饱和结合检测。在携带U87 MG肿瘤的BALB/c裸鼠中进行了生物分布表征和微型单光子发射计算机体层摄影（SPECT）成像。此外，对四名健康志愿者和三名胃肠道肿瘤患者进行了首次人体应用。体外实验表明，[99mTc]Tc-DP-FAPI的纳摩尔级Kd值表明其对FAP具有显着的高靶亲和力。生物分布和微型SPECT成像研究表明，[99mTc]Tc-DP-FAPI表现出高吸收量和高肿瘤/非靶向比率。在四名健康志愿者中计算出[99mTc]Tc-DP-FAPI的有效剂量约为<5 mSv。在三名胃肠道肿瘤患者中，[99mTc]Tc-DP-FAPI定量SPECT/ CT显示了高且可靠的摄取量。[99mTc]Tc-DP-FAPI在体外表现出对FAP的高选择性和亲和力。动物和临床研究证实了[99mTc]Tc-DP-FAPI在原发性肿瘤成像方面的安全性和有效性，揭示了该探针的潜在临床应用价值。

Fibroblast activation protein (FAP) is a potential target for tumor diagnosis and treatment because it is selectively expressed on the cell membrane of cancer-associated fibroblasts in most solid tumor stroma. The aim of this study was to develop a 99mTc-labeled fibroblast activation protein inhibitor (FAPI) tracer, evaluate its imaging efficacy in nude mice, and further explore its biodistribution in healthy volunteers and uptake in tumor patients. An FAPI-derived ligand (DP-FAPI) containing d-proline was designed and synthesized as a linker, and a stable hydrophilic 99mTc-labeled complex ([99mTc]Tc-DP-FAPI) was obtained by kit formulation. In vitro cellular uptake and saturation binding assays were performed in FAP-transfected HT-1080 cells (FAP-HT-1080). The biodistribution was characterized, and micro-single-photon emission computed tomography (SPECT) imaging was performed in BALB/c nude mice bearing U87 MG tumors. Furthermore, a first-in-man application was performed in four healthy volunteers and three patients with gastrointestinal tumors. In vitro, the nanomolar Kd values of [99mTc]Tc-DP-FAPI indicated that it had significantly high target affinity for FAP. Biodistribution and micro-SPECT imaging studies showed that [99mTc]Tc-DP-FAPI exhibited high uptake and high tumor-to-nontargeted ratios. The calculated effective dose for [99mTc]Tc-DP-FAPI was approximately <5 mSv in four healthy volunteers. In three patients with gastrointestinal tumors, [99mTc]Tc-DP-FAPI quantitative SPECT/CT revealed high and reliable uptake. [99mTc]Tc-DP-FAPI exhibited high selectivity and affinity for FAP in vitro. The safety and effectiveness of [99mTc]Tc-DP-FAPI in primary tumor imaging have been confirmed by animal and clinical studies, revealing the potential clinical application value of this tracer.