Departments of Radiology, Thomas Jefferson University, Philadelphia, PA, USA.
School of Chemistry and Chemical Engineering, Henan Normal University, Xinxiang, China.
Mol Imaging Biol. 2019 Feb;21(1):130-139. doi: 10.1007/s11307-018-1207-x.
In recent years, considerable progress has been made in the use of gallium-68 labeled receptor-specific peptides for imaging oncologic diseases. The objective was to examine the stability and pharmacokinetics of [Ga]NODAGA and DOTA-peptide conjugate targeting VPAC [combined for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP)] receptors on tumor cells.
A VPAC receptor-specific peptide was chosen as a model peptide and conjugated to NODAGA and DOTA via solid-phase synthesis. The conjugates were characterized by HPLC and MALDI-TOF. Following Ga-68 chelation, the radiochemical purity of Ga-68 labeled peptide conjugate was determined by radio-HPLC. The stability was tested against transmetallation using 100 nM Fe/Zn/Ca ionic solution and against transchelation using 200 μM DTPA solution. The ex vivo and in vivo stability of the Ga-68 labeled peptide conjugate was tested in mouse plasma and urine. Receptor specificity was determined ex vivo by cell binding assays using human breast cancer BT474 cells. Positron emission tomography (PET)/X-ray computed tomography (CT) imaging, tissue distribution, and blocking studies were performed in mice bearing BT474 xenografts.
The chemical and radiochemical purity was greater than 95 % and both conjugates were stable against transchelation and transmetallation. Ex vivo stability at 60 min showed that the NODAGA-peptide-bound Ga-68 reduced to 42.1 ± 3.7 % (in plasma) and 37.4 ± 2.9 % (in urine), whereas the DOTA-peptide-bound Ga-68 was reduced to 1.2 ± 0.3 % (in plasma) and 4.2 ± 0.4 % (in urine) at 60 min. Similarly, the in vivo stability for [Ga]NODAGA-peptide was decreased to 2.1 ± 0.2 % (in plasma) and 2.2 ± 0.4 % (in urine). For [Ga]DOTA-peptide, it was decreased to 1.4 ± 0.3 % (in plasma) and 1.2 ± 0.4 % (in urine) at 60 min. The specific BT474 cell binding was 53.9 ± 0.8 % for [Ga]NODAGA-peptide, 25.8 ± 1.4 % for [Ga]-DOTA-peptide, and 18.8 ± 2.5 % for [Ga]GaCl at 60 min. Inveon microPET/CT imaging at 1 h post-injection showed significantly (p < 0.05) higher tumor to muscle (T/M) ratio for [Ga]NODAGA-peptide (3.4 ± 0.3) as compared to [Ga]DOTA-peptide (1.8 ± 0.6). For [Ga]GaCl and blocked mice, their ratios were 1.5 ± 0.6 and 1.5 ± 0.3 respectively. The tissue distributions data were similar to the PET imaging data.
NODAGA is superior to DOTA in terms of radiolabeling kinetics. The method of radiolabeling was reproducible and yielded higher specific activity. Although both agents have relatively low in vivo stability, PET/CT imaging studies delineated BC tumors with [Ga]NODAGA-peptide, but not with [Ga]DOTA-peptide.
近年来，镓-68 标记的受体特异性肽在肿瘤疾病成像方面取得了相当大的进展。本研究旨在研究靶向血管活性肠肽 (VIP) 和垂体腺苷酸环化酶激活肽 (PACAP) 受体的 VPAC [联合] 受体的 [Ga]NODAGA 和 DOTA-肽缀合物在肿瘤细胞上的稳定性和药代动力学。
选择 VPAC 受体特异性肽作为模型肽，并通过固相合成将其与 NODAGA 和 DOTA 缀合。通过 HPLC 和 MALDI-TOF 对缀合物进行了表征。镓-68 螯合物形成后，通过放射性 HPLC 测定 Ga-68 标记肽缀合物的放射化学纯度。使用 100 nM Fe/Zn/Ca 离子溶液进行转金属化测试，使用 200 μM DTPA 溶液进行转螯合测试来测试稳定性。通过在小鼠血浆和尿液中进行稳定性测试，评估 Ga-68 标记肽缀合物的体外和体内稳定性。使用人乳腺癌 BT474 细胞进行细胞结合实验来确定受体特异性。在携带 BT474 异种移植物的小鼠中进行正电子发射断层扫描 (PET)/X 射线计算机断层扫描 (CT) 成像、组织分布和阻断研究。
化学和放射化学纯度均大于 95%，两种缀合物均能抵抗转螯合和转金属化。60 分钟时的体外稳定性研究表明，NODAGA-肽结合的 Ga-68 减少到 42.1±3.7%（血浆）和 37.4±2.9%（尿液），而 DOTA-肽结合的 Ga-68 减少到 1.2±0.3%（血浆）和 4.2±0.4%（尿液）在 60 分钟时。类似地，[Ga]NODAGA-肽的体内稳定性降低至 2.1±0.2%（血浆）和 2.2±0.4%（尿液）。对于 [Ga]DOTA-肽，它在 60 分钟时降低至 1.4±0.3%（血浆）和 1.2±0.4%（尿液）。[Ga]GaCl 在 60 分钟时的特异性 BT474 细胞结合率分别为 53.9±0.8%、25.8±1.4%和 18.8±2.5%。注射后 1 小时，Inveon 小动物 PET/CT 成像显示 [Ga]NODAGA-肽的肿瘤与肌肉（T/M）比值明显更高（3.4±0.3），而 [Ga]DOTA-肽的比值为 1.8±0.6。对于 [Ga]GaCl 和阻断的小鼠，它们的比值分别为 1.5±0.6 和 1.5±0.3。组织分布数据与 PET 成像数据相似。
NODAGA 在放射性标记动力学方面优于 DOTA。放射性标记的方法具有可重复性，并产生了更高的比活度。尽管两种试剂的体内稳定性都相对较低，但 PET/CT 成像研究用 [Ga]NODAGA-肽可描绘 BC 肿瘤，而用 [Ga]DOTA-肽则不可。
