Department of Radiology, Thomas Jefferson University, Philadelphia, PA, USA.
Department of Cancer Biology, Thomas Jefferson University, Philadelphia, PA, USA.
Mol Imaging Biol. 2020 Apr;22(2):293-302. doi: 10.1007/s11307-019-01388-5.
Scintigraphic imaging of malignant glioblastoma (MG) continues to be challenging. We hypothesized that VPAC1 cell surface receptors can be targeted for positron emission tomography (PET) imaging of orthotopically implanted MG in a mouse model, using a VPAC1-specific peptide [Cu]TP3805.
The expression of VPAC1 in mouse GL261 and human U87 glioma cell lines was determined by western blot. The ability of [Cu]TP3805 to bind to GL261 and U87 cells was studied by cell-binding. Receptor-blocking studies were performed to validate receptor specificity. GL261 tumors were implanted orthotopically in syngeneic T-bet knockout C57BL/6 mouse brain (N = 15) and allowed to grow for 2-3 weeks. Mice were injected i.v., first with ~ 150 μCi of 2-deoxy-2-[F]fluoro-D-glucose ([F]FDG) then 24 h later with ~ 200 μCi of [Cu]TP3805. In another set of tumor-bearing mice, (N = 5), ionic [Cu]Cl was injected as a control. Mice were imaged at a 2-h post-injection using an Inveon micro-PET/CT, sacrificed and % ID/g of [Cu]TP3805 and [Cu]Cl were calculated in a tumor, normal brain, and other tissues. For histologic tissue examination, 3-μm thick sections of the tumors and normal brain were prepared, digital autoradiography (DAR) was performed, and then the sections were H&E stained for histologic examination.
Western blots showed a strong signal for VPAC1 on both cell lines. [Cu]TP3805 cell-binding was 87 ± 1.5 %. Receptor-blocking reduced cell-binding to 24.3 ± 1.5 % (P < 0.01). PET imaging revealed remarkable accumulation of [Cu]TP3805 in GL261 MG with a negligible background in the normal brain, as compared to [F]FDG. Micro-PET/CT image analyses and tissue distribution showed that the brain tumor uptake for [Cu]TP3805 was 8.2 ± 1.7 % ID/g and for [Cu]Cl 2.1 ± 0.5 % ID/g as compared to 1.0 ± 0.3 % ID/g and 1.4 ± 0.3 % ID/g for normal mouse brains, respectively. The high tumor/normal brain ratio for [Cu]TP3805 (8.1 ± 1.1) allowed tumors to be visualized unequivocally. Histology and [Cu]TP3805 DAR differentiated malignant tumors from healthy brain and confirmed PET findings.
Targeting VPAC1 receptors using [Cu]TP3805 for PET imaging of MG is a promising novel approach and calls for further investigation.
恶性神经胶质瘤（MG）的闪烁成像仍然具有挑战性。我们假设，使用 VPAC1 特异性肽 [Cu]TP3805，VPAC1 细胞表面受体可以针对原位植入的 MG 进行正电子发射断层扫描（PET）成像。
通过 Western blot 确定了小鼠 GL261 和人 U87 神经胶质瘤细胞系中 VPAC1 的表达。通过细胞结合研究了 [Cu]TP3805 与 GL261 和 U87 细胞结合的能力。进行了受体阻断研究以验证受体特异性。将 GL261 肿瘤原位植入同基因 T-bet 敲除 C57BL/6 小鼠脑（N=15）中，并允许其生长 2-3 周。将小鼠静脉内注射150μCi 的 2-脱氧-2-[F]氟-D-葡萄糖（[F]FDG），24 小时后再注射200μCi 的 [Cu]TP3805。在另一组荷瘤小鼠（N=5）中，注射离子[Cu]Cl 作为对照。在注射后 2 小时，使用 Inveon 微型 PET/CT 对小鼠进行成像，然后处死并计算肿瘤、正常脑和其他组织中 [Cu]TP3805 和 [Cu]Cl 的每克放射性计数（% ID/g）。用于组织学检查，制备 3μm 厚的肿瘤和正常脑组织切片，进行数字放射自显影（DAR），然后对切片进行 H&E 染色进行组织学检查。
Western blot 显示两种细胞系上均有强烈的 VPAC1 信号。[Cu]TP3805 的细胞结合率为 87±1.5%。受体阻断将细胞结合率降低至 24.3±1.5%（P<0.01）。PET 成像显示，与 [F]FDG 相比，GL261 MG 中 [Cu]TP3805 的积聚非常显著，而正常脑中的背景可忽略不计。Micro-PET/CT 图像分析和组织分布显示，[Cu]TP3805 在脑肿瘤中的摄取率为 8.2±1.7% ID/g，而 [Cu]Cl 为 2.1±0.5% ID/g，而正常小鼠脑的摄取率分别为 1.0±0.3% ID/g 和 1.4±0.3% ID/g。[Cu]TP3805 的高肿瘤/正常脑比（8.1±1.1）允许明确显示肿瘤。组织学和 [Cu]TP3805 DAR 将恶性肿瘤与健康脑组织区分开来，并证实了 PET 结果。
使用 [Cu]TP3805 针对 MG 进行 PET 成像以靶向 VPAC1 受体是一种很有前途的新方法，需要进一步研究。
