淋巴细胞激活基因3（LAG-3）被认为是下一代免疫检查点和免疫治疗的有前途的预后生物标志物。与程序性细胞死亡蛋白 1/程序性死亡配体 1 和细胞毒性 T 淋巴细胞抗原 4 抑制剂一样，正电子发射断层扫描 (PET) 成像策略可以有利于 LAG-3 相关治疗的临床决策的制定。在本研究中，我们开发并验证了 68Ga 标记的环肽示踪剂，用于实验室到临床研究中 LAG-3 表达的 PET 成像。一系列 LAG-3 靶向环肽经过 68GaCl3 修饰和放射性标记，并评估了它们的亲和力以及体外和体内的特异性、生物分布、药代动力学和辐射剂量测定。此外，构建hu-PBL-SCID (PBL)小鼠模型以验证[68Ga]Ga-CC09-1使用纵向PET成像绘制LAG-3淋巴细胞浸润图的能力。最后，[68Ga]Ga-CC09-1 被转化为首次人体研究，以评估其安全性、生物分布和 LAG-3 表达成像的潜力。采用一系列靶向 LAG-3 的环肽作为先导化合物设计和开发 68Ga 标记的 PET 示踪剂。体外结合测定显示[68Ga]Ga-CC09-1在中国仓鼠卵巢-人LAG-3细胞和外周血单核细胞中具有更高的亲和力和特异性。体内PET成像显示[68Ga]Ga-CC09-1具有更好的成像能力，每克注射剂量的肿瘤摄取更高，为1.35±0.33％，注射后60分钟时肿瘤与肌肉的比率为17.18±3.20。此外，[68Ga]Ga-CC09-1可以检测PBL小鼠的脾、肺和唾液腺中的LAG-3淋巴细胞浸润。在黑色素瘤和非小细胞肺癌患者中，与 [18F]FDG PET 相比，[68Ga]Ga-CC09-1 PET 中观察到具有适度肿瘤摄取的原发灶。更重要的是，[68Ga]Ga-CC09-1描绘了大肿瘤内LAG-3表达的异质性。这些发现巩固了[68Ga]Ga-CC09-1是一种有前途的PET示踪剂，用于量化肿瘤微环境中的LAG-3表达，表明其作为抗 LAG-3 治疗中患者分层和治疗反应监测的伴随诊断的潜力。© 作者（或其雇主）2024。根据 CC BY-NC 允许重复使用。禁止商业再利用。请参阅权利和权限。英国医学杂志出版。

Lymphocyte activation gene 3 (LAG-3) has been considered as the next generation of immune checkpoint and a promising prognostic biomarker of immunotherapy. As with programmed cell death protein-1/programmed death-ligand 1 and cytotoxic T-lymphocyte antigen-4 inhibitors, positron emission tomography (PET) imaging strategies could benefit the development of clinical decision-making of LAG-3-related therapy. In this study, we developed and validated 68Ga-labeled cyclic peptides tracers for PET imaging of LAG-3 expression in bench-to-bedside studies.A series of LAG-3-targeted cyclic peptides were modified and radiolabeled with 68GaCl3 and evaluated their affinity and specificity, biodistribution, pharmacokinetics, and radiation dosimetry in vitro and in vivo. Furthermore, hu-PBL-SCID (PBL) mice models were constructed to validate the capacity of [68Ga]Ga-CC09-1 for mapping of LAG-3+ lymphocytes infiltrates using longitudinal PET imaging. Lastly, [68Ga]Ga-CC09-1 was translated into the first-in-human studies to assess its safety, biodistribution and potential for imaging of LAG-3 expression.A series of cyclic peptides targeting LAG-3 were employed as lead compounds to design and develop 68Ga-labeled PET tracers. In vitro binding assays showed higher affinity and specificity of [68Ga]Ga-CC09-1 in Chinese hamster ovary-human LAG-3 cells and peripheral blood mononuclear cells. In vivo PET imaging demonstrated better imaging capacity of [68Ga]Ga-CC09-1 with a higher tumor uptake of 1.35±0.33 per cent injected dose per gram and tumor-to-muscle ratio of 17.18±3.20 at 60 min post-injection. Furthermore, [68Ga]Ga-CC09-1 could detect the LAG-3+ lymphocyte infiltrates in spleen, lung and salivary gland of PBL mice. In patients with melanoma and non-small cell lung cancer, primary lesions with modest tumor uptake were observed in [68Ga]Ga-CC09-1 PET, as compared with that of [18F]FDG PET. More importantly, [68Ga]Ga-CC09-1 delineated the heterogeneity of LAG-3 expression within large tumors.These findings consolidated that [68Ga]Ga-CC09-1 is a promising PET tracer for quantifying the LAG-3 expression in tumor microenvironment, indicating its potential as a companion diagnostic for patients stratification and therapeutic response monitoring in anti-LAG-3 therapy.© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.