Fibroblast activation protein (FAP) has become an attractive target for diagnosis and therapy, and a series of FAP inhibitor (FAPI)–based radiotracers has been developed and had excellent performance for diagnosis outcomes in clinical applications. Yet, their fast clearance and insufficient tumor retention have hampered their further clinical application in cancer treatment. In this study, we developed 2 albumin binder–conjugated FAPI radiotracers, TEFAPI-06 and TEFAPI-07. They were derived from FAPI-04 and were optimized by conjugating 2 types of well-studied albumin binders, 4-(p-iodophenyl) butyric acid moiety (TEFAPI-06) and truncated Evans blue moiety (TEFAPI-07), to try to overcome the above limitations at the expense of prolonging the blood circulation. Methods: TEFAPI-06 and TEFAPI-07 were synthesized and labeled with ⁶⁸Ga, ⁸⁶Y, and ¹⁷⁷Lu successfully. A series of cell assays was performed to identify the binding affinity and FAP specificity in vitro. PET imaging, SPECT imaging, and biodistribution studies were performed to evaluate the pharmacokinetics in pancreatic cancer patient–derived xenograft (PDX) animal models. The cancer treatment efficacy of ¹⁷⁷Lu-TEFAPI-06 and ¹⁷⁷Lu-TEFAPI-07 were evaluated in pancreatic cancer PDX–bearing mice. Results: The binding affinities (dissociation constants) to FAP of ⁶⁸Ga-TEFAPI-06 and ⁶⁸Ga-TEFAPI-07 were 10.16 ± 2.56 nM and 7.81 ± 2.28 nM, respectively, which were comparable with that of ⁶⁸Ga-FAPI-04. Comparative PET imaging of HT-1080-FAP and HT-1080 tumor–bearing mice and a blocking study showed the FAP-targeting ability in vivo of these 2 tracers. Compared with ¹⁷⁷Lu-FAPI-04, PET imaging, SPECT imaging, and biodistribution studies of TEFAPI-06 and TEFAPI-07 demonstrated their remarkably enhanced tumor accumulation and retention, respectively. Notable tumor growth inhibition by ¹⁷⁷Lu-TEFAPI-06 and ¹⁷⁷Lu-TEFAPI-07 were observed, whereas the control group and the group treated by ¹⁷⁷Lu-FAPI-04 showed a slight therapeutic effect. Conclusion: Two albumin binder–conjugated FAPI radiopharmaceuticals have been developed and evaluated in vitro and in vivo. Significantly improved tumor uptake and retention were observed, compared with the original FAPI tracer. Both ¹⁷⁷Lu-TEFAPI-06 and ¹⁷⁷Lu-TEFAPI-07 showed remarkable growth inhibition of PDX tumors, whereas the side effects were almost negligible, demonstrating that these radiopharmaceuticals are promising for further clinical translational studies.

成纤维细胞激活蛋白（FAP）已成为诊断和治疗的一个有吸引力的靶点，一系列基于FAP抑制剂（FAPI）的放射性示踪剂已被开发出来，并在临床应用中具有优异的诊断结果。然而，它们的快速清除和肿瘤保留不足阻碍了它们在癌症治疗中的进一步临床应用。在这项研究中，我们开发了 2 种白蛋白结合剂结合的 FAPI 放射性示踪剂：TEFAPI-06 和 TEFAPI-07。它们源自 FAPI-04，并通过缀合 2 种经过充分研究的白蛋白结合物、4-(对碘苯基)丁酸部分 (TEFAPI-06) 和截短的伊文思蓝部分 (TEFAPI-07) 进行优化，以尝试克服上述限制的代价是延长血液循环。方法：合成TEFAPI-06和TEFAPI-07，并成功进行⁶⁸ Ga、 ⁸⁶ Y、 ¹⁷⁷ Lu标记。进行了一系列细胞测定，以确定体外结合亲和力和 FAP 特异性。进行 PET 成像、SPECT 成像和生物分布研究，以评估胰腺癌患者异种移植 (PDX) 动物模型中的药代动力学。在携带 PDX 的胰腺癌小鼠中评估了¹⁷⁷ Lu-TEFAPI-06 和¹⁷⁷ Lu-TEFAPI-07 的癌症治疗功效。结果： ⁶⁸ Ga-TEFAPI-06和⁶⁸ Ga-TEFAPI-07与FAP的结合亲和力（解离常数）分别为10.16±2.56 nM和7.81±2.28 nM，与⁶⁸ Ga-FAPI-04相当。 。 HT-1080-FAP 和 HT-1080 荷瘤小鼠的对比 PET 成像和阻断研究显示了这 2 种示踪剂的体内 FAP 靶向能力。 与¹⁷⁷ Lu-FAPI-04相比，TEFAPI-06和TEFAPI-07的PET成像、SPECT成像和生物分布研究分别证明它们显着增强了肿瘤积累和保留。观察到¹⁷⁷ Lu-TEFAPI-06和¹⁷⁷ Lu-TEFAPI-07显着抑制肿瘤生长，而对照组和¹⁷⁷ Lu-FAPI-04处理组显示出轻微的治疗效果。结论：已经开发出两种白蛋白结合剂结合的 FAPI 放射性药物，并进行了体外和体内评估。与原始 FAPI 示踪剂相比，观察到肿瘤摄取和保留显着改善。 ¹⁷⁷ Lu-TEFAPI-06和¹⁷⁷ Lu-TEFAPI-07均表现出对PDX肿瘤的显着生长抑制作用，而副作用几乎可以忽略不计，表明这些放射性药物有望用于进一步的临床转化研究。