PET radioligands with low molar activity (MA) may underestimate the quantity of the target of interest because of competitive binding of the target with unlabeled ligand. The aim of this study was to evaluate the change in the whole-body distribution of ¹⁸F-PSMA-1007 targeting prostate-specific membrane antigen (PSMA) when solutions with different peptide concentrations are used. Methods: Mouse xenograft models of LNCaP (PSMA-positive prostate cancer) (n = 18) were prepared and divided into 3 groups according to the peptide concentration injected: a high-MA group (1,013 ± 146 GBq/μmol; n = 6), a medium-MA group (100.7 ± 23.1 GBq/μmol; n = 6), and a low-MA group (10.80 ± 2.84 GBq/μmol; n = 6). Static PET scans were performed 1 h after injection (scan duration, 10 min). SUV_mean in tumor and normal organs was compared by the multiple-comparison test. Immunohistochemical staining and Western blot analysis were performed to confirm expression of PSMA in tumor, salivary gland, and kidney. Results: The low-MA group (SUV_mean, 1.12 ± 0.30) showed significantly lower uptake of ¹⁸F-PSMA-1007 in tumor than did the high-MA group (1.97 ± 0.77) and the medium-MA group (1.81 ± 0.57). On the other hand, in salivary gland, both the low-MA group (SUV_mean, 0.24 ± 0.04) and the medium-MA group (0.57 ± 0.08) showed significantly lower uptake than the high MA group (1.27 ± 0.28). The tumor-to-salivary gland SUV_mean ratio was 1.73 ± 0.55 in the high-MA group, 3.16 ± 0.86 in the medium-MA group, and 4.78 ± 1.29 in the low-MA group. The immunohistochemical staining and Western blot analysis revealed significant overexpression of PSMA in tumor and low expression in salivary gland and kidney. Conclusion: A decrease in the MA level of the injected ¹⁸F-PSMA-1007 solution resulted in decreased uptake in tumor and, to a greater degree, in normal salivary gland. Thus, there is a possibility of minimizing the adverse effects in salivary gland by setting an appropriate MA level in PSMA-targeting therapy.

具有低摩尔活性（MA）的PET放射性配体可能会低估目标靶标的量，因为该靶标与未标记的配体竞争性结合。这项研究的目的是评估当使用具有不同肽浓度的溶液时，靶向前列腺特异性膜抗原（PSMA）的¹⁸ F-PSMA-1007的全身分布变化。方法：制备小鼠LNCaP（PSMA阳性前列腺癌）异种移植模型（n = 18），并根据注射的肽浓度分为三组：高MA组（1,013±146 GBq /μmol；n = 6） ，中MA组（100.7±23.1 GBq /μmol; n = 6）和低MA组（10.80±2.84 GBq /μmol; n= 6）。注射后1 h进行静态PET扫描（扫描持续时间10分钟）。通过多重比较测试比较了肿瘤和正常器官中的SUV_平均值。进行了免疫组织化学染色和蛋白质印迹分析，以确认PSMA在肿瘤，唾液腺和肾脏中的表达。结果：低MA组（SUV_平均值，1.12±0.30）显示出肿瘤中对¹⁸ F-PSMA-1007的摄取显着低于高MA组（1.97±0.77）和中MA组（1.81±0.57） ）。另一方面，在唾液腺中，低MA组（SUV_平均值，0.24±0.04）和中MA组（0.57±0.08）均显示出摄取水平明显低于高MA组（1.27±0.28）。肿瘤到唾液腺的SUV高MA组的_平均比率为1.73±0.55，中MA组的_平均比率为3.16±0.86，低MA组的_平均比率为4.78±1.29。免疫组织化学染色和Western印迹分析显示，PSMA在肿瘤中显着过表达，在唾液腺和肾脏中低表达。结论：注射的¹⁸ F-PSMA-1007溶液的MA水平降低导致肿瘤吸收减少，并且在更大程度上导致正常唾液腺吸收。因此，有可能通过在PSMA靶向治疗中设定适当的MA水平来最大程度地减少唾液腺的不良反应。