Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China.
Hubei Province Key Laboratory of Molecular Imaging, Wuhan, China.
J Immunother Cancer. 2024 Jul 23;12(7):e009010. doi: 10.1136/jitc-2024-009010.
Lymphocyte activation gene 3 (LAG-3) is expressed on activated immune cells and has emerged as a promising target for immune checkpoints blockade. However, conflicting findings have been reported regarding the association between LAG-3 expression in tumors and patient prognosis, indicating the need for further investigation into the significance of LAG-3 expression levels in tumor therapies. In this study, Ga-NOTA-XH05, a novel peptide-based positron emission tomography (PET) tracer targeting LAG-3, was constructed to non-invasively detect LAG-3 expression in melanoma after CpG oligonucleotide (CpG) treatment and explore the relationship between LAG-3 expression and therapeutic effect.
The tracer Ga-NOTA-XH05 was identified by high-performance liquid chromatography after being prepared and purified. Cell uptake and blocking essays were performed to verify the specificity of the tracer in vitro. The expression of LAG-3 in B16-F10 subcutaneous tumors was monitored by flow cytometry, and its correlation with the tracer uptake was analyzed to evaluate the tracer specificity. PET imaging and biodistribution studies were conducted after CpG treatment of unilateral or bilateral B16-F10 subcutaneous tumor models to assess the ability of Ga-NOTA-XH05 in monitoring immunotherapy efficacy and the abscopal effect of CpG.
Following purification, Ga-NOTA-XH05 exhibited high radiochemical purity and specificity. Flow cytometry analysis revealed a positive correlation between LAG-3 expression in tumors and the uptake of Ga-NOTA-XH05. In B16-F10 bearing mice treated with CpG, PET imaging using Ga-NOTA-XH05 demonstrated a higher tumor to blood ratio (TBR) compared with the control group. Furthermore, TBR values obtained from CpG-treated mice allowed for differentiation between responders and non-responders. In a bilateral subcutaneous tumor model where only right-sided tumors were treated with intratumoral injection of CpG, TBR values of left-sided tumors were significantly higher than those in the control group, indicating that Ga-NOTA-XH05 could effectively monitor the systemic effect of local CpG injection.
Our findings highlight the detection capability of Ga-NOTA-XH05 in assessing LAG-3 expression levels within tumors and evaluating response to immunotherapy, thereby suggesting promising clinical translational prospects.
淋巴细胞激活基因 3（LAG-3）在活化的免疫细胞上表达，已成为免疫检查点阻断的有前途的靶点。然而，关于肿瘤中 LAG-3 表达与患者预后之间的关系，已有相互矛盾的研究结果报道，这表明需要进一步研究肿瘤治疗中 LAG-3 表达水平的意义。在这项研究中，构建了一种新型的基于肽的正电子发射断层扫描（PET）示踪剂 Ga-NOTA-XH05，用于在 CpG 寡核苷酸（CpG）治疗后非侵入性地检测黑色素瘤中的 LAG-3 表达，并探讨 LAG-3 表达与治疗效果之间的关系。
制备和纯化后，通过高效液相色谱法鉴定示踪剂 Ga-NOTA-XH05。进行细胞摄取和阻断实验，以验证示踪剂的体外特异性。通过流式细胞术监测 B16-F10 皮下肿瘤中 LAG-3 的表达，并分析其与示踪剂摄取的相关性，以评估示踪剂的特异性。在单侧或双侧 B16-F10 皮下肿瘤模型中进行 CpG 治疗后，进行 PET 成像和生物分布研究，以评估 Ga-NOTA-XH05 监测免疫治疗效果和 CpG 远隔效应的能力。
Ga-NOTA-XH05 经纯化后表现出高放射化学纯度和特异性。流式细胞术分析显示，肿瘤中 LAG-3 的表达与 Ga-NOTA-XH05 的摄取呈正相关。在接受 CpG 治疗的 B16-F10 荷瘤小鼠中，使用 Ga-NOTA-XH05 的 PET 成像显示肿瘤与血液的比值（TBR）高于对照组。此外，从接受 CpG 治疗的小鼠中获得的 TBR 值可区分应答者和无应答者。在双侧皮下肿瘤模型中，仅对右侧肿瘤进行瘤内注射 CpG 治疗，左侧肿瘤的 TBR 值明显高于对照组，表明 Ga-NOTA-XH05 可有效监测局部 CpG 注射的全身效应。
我们的研究结果强调了 Ga-NOTA-XH05 在评估肿瘤内 LAG-3 表达水平和评估免疫治疗反应方面的检测能力，这表明其具有有前途的临床转化前景。
