Nanfang PET Center, Nanfang Hospital, Southern Medical University, 1838 Guangzhou Avenue North, Guangzhou, 510515, Guangdong Province, China.
PET/CT Center, The First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong Province, China.
Mol Imaging Biol. 2020 Feb;22(1):134-143. doi: 10.1007/s11307-019-01356-z.
Hepatocellular carcinoma (HCC) remains one of the most challenging diseases worldwide. Glypican-3 (GPC-3) is a cell surface proteoglycan that is overexpressed on the membrane of HCC cells. The purpose of this study was to develop a target-specific radiofluorinated peptide for positron emission tomography (PET) imaging of GPC3 expression in hepatocellular carcinoma.
New GPC3-binding peptides (GP2076 and GP2633) were radiolabeled with F-18 using Al[F]F labeling approach, and the resulting PET probes were subsequently subject to biological evaluations. A highly hydrophilic linker was incorporated into GP2633 with an aim of reducing the probe uptake in liver and increasing tumor-to-liver (T/L) contrast. Both GP2076 and GP2633 were radiolabeled using Al[F]F chelation approach. The binding affinity, octanol/water partition coefficient, cellular uptake and efflux, and stability of both F-18 labeled peptides were tested. Tumor targeting efficacy and biodistribution of Al[F]F-GP2076 and Al[F]F-GP2633 were determined by PET imaging in HCC-bearing mice. Immunohistochemistry analyses were performed to compare the findings from PET scans.
Al[F]F-GP2076 and Al[F]F-GP2633 were rapidly radiosynthesized within 20 min in excellent radiochemical purity (> 97 %). Al[F]F-GP2633 was determined to be more hydrophilic than Al[F]F-GP2076 in terms of octanol/water partition coefficient. Both Al[F]F-GP2076 and Al[F]F-GP2633 demonstrated good in vitro and in vivo stability and binding specificity to GPC3-positive HepG2 cells. For PET imaging, Al[F]F-GP2633 exhibited enhanced uptake in HepG2 tumor (%ID/g 3.37 ± 0.35 vs. 2.13 ± 0.55, P = 0.031) and reduced accumulation in liver (%ID/g 1.70 ± 0.26 vs. 3.70 ± 0.98, P = 0.027) at 60 min post-injection (pi) as compared to Al[F]F-GP2076, resulting in significantly improved tumor-to-liver (T/L) contrast (ratio 2.00 ± 0.18 vs. 0.59 ± 0.14, P = 0.0004). Higher uptake of Al[F]F-GP2633 in GPC3-positive HepG2 tumor was observed as compared to GPC3-negative McA-RH7777 tumor (%ID/g 3.37 ± 0.35 vs. 1.64 ± 0.03, P = 0.001) at 60 min pi, confirming GPC3-specific accumulation of Al[F]F-GP2633 in HepG2 tumor.
The results demonstrated that Al[F]F-GP2633 is a promising probe for PET imaging of GPC3 expression in HCC. Convenient preparation, excellent GPC3 specificity in HCC, and favorable excretion profile of Al[F]F-GP2633 warrant further investigation for clinical translation. PET imaging with a GPC3-specific probe would provide clinicians with vital diagnostic information that could have a significant impact on the management of HCC patients.
肝细胞癌（HCC）仍然是全球最具挑战性的疾病之一。Glypican-3（GPC-3）是一种细胞表面蛋白聚糖，在 HCC 细胞的膜上过度表达。本研究旨在开发一种针对 HCC 中 GPC3 表达的特异性放射性肽，用于正电子发射断层扫描（PET）成像。
使用 Al[F]F 标记方法对新的 GPC3 结合肽（GP2076 和 GP2633）进行放射性标记，并对所得 PET 探针进行生物学评估。将高度亲水性接头引入 GP2633 中，旨在降低探针在肝脏中的摄取量并增加肿瘤与肝脏（T/L）的对比。GP2076 和 GP2633 均采用 Al[F]F 螯合方法进行放射性标记。测试了 F-18 标记肽的结合亲和力、辛醇/水分配系数、细胞摄取和外排以及稳定性。通过 HCC 荷瘤小鼠的 PET 成像确定 Al[F]F-GP2076 和 Al[F]F-GP2633 的肿瘤靶向功效和生物分布。通过 PET 扫描进行免疫组织化学分析，以比较发现。
Al[F]F-GP2076 和 Al[F]F-GP2633 在 20 分钟内以优异的放射化学纯度（>97%）快速合成。Al[F]F-GP2633 的辛醇/水分配系数比 Al[F]F-GP2076 更亲水。Al[F]F-GP2076 和 Al[F]F-GP2633 均表现出良好的体外和体内稳定性以及与 GPC3 阳性 HepG2 细胞的结合特异性。对于 PET 成像，与 Al[F]F-GP2076 相比，Al[F]F-GP2633 在 HepG2 肿瘤中的摄取增加（%ID/g 3.37±0.35 对 2.13±0.55，P=0.031），在肝脏中的积累减少（%ID/g 1.70±0.26 对 3.70±0.98，P=0.027），在 60 分钟注射后（pi），导致肿瘤与肝脏（T/L）的对比明显改善（比值 2.00±0.18 对 0.59±0.14，P=0.0004）。与 GPC3 阴性 McA-RH7777 肿瘤相比，在 GPC3 阳性 HepG2 肿瘤中观察到 Al[F]F-GP2633 的摄取更高（%ID/g 3.37±0.35 对 1.64±0.03，P=0.001），证实 Al[F]F-GP2633 在 HepG2 肿瘤中的 GPC3 特异性积累。
结果表明，Al[F]F-GP2633 是一种有前途的用于 HCC 中 GPC3 表达的 PET 成像探针。方便的制备、HCC 中 GPC3 的优异特异性以及 Al[F]F-GP2633 的良好排泄特征，为其临床转化提供了进一步的研究依据。使用 GPC3 特异性探针进行 PET 成像将为临床医生提供重要的诊断信息，这可能对 HCC 患者的管理产生重大影响。
