Good Stephan, Walter Martin A, Waser Beatrice, Wang Xuejuan, Müller-Brand Jan, Béhé Martin P, Reubi Jean-Claude, Maecke Helmut R
Division of Radiological Chemistry, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland.
Eur J Nucl Med Mol Imaging. 2008 Oct;35(10):1868-77. doi: 10.1007/s00259-008-0803-4. Epub 2008 May 29.
Diethylenetriamine-pentaacetic acid (DTPA)-coupled minigastrins are unsuitable for therapeutic application with the available beta-emitting radiometals due to low complex stability. Low tumour-to-kidney ratio of the known radiopharmaceuticals is further limiting their potency. We used macrocyclic chelators for coupling to increase complex stability, modified the peptide sequence to enhance radiolytic stability and studied tumour-to-kidney ratio and metabolic stability using (111)In-labelled derivatives.
Gastrin derivatives with decreasing numbers of glutamic acids were synthesised using (111)In as surrogate for therapeutic radiometals for in vitro and in vivo studies. Gastrin receptor affinities of the (nat)In-metallated compounds were determined by receptor autoradiography using (125)I-CCK as radioligand. Internalisation was evaluated in AR4-2J cells. Enzymatic stability was determined by incubating the (111)In-labelled peptides in human serum. Biodistribution was performed in AR4-2J-bearing Lewis rats.
IC(50) values of the (nat)In-metallated gastrin derivatives vary between 1.2 and 4.8 nmol/L for all methionine-containing derivatives. Replacement of methionine by norleucine, isoleucine, methionine-sulfoxide and methionine-sulfone resulted in significant decrease of receptor affinity (IC(50) between 9.9 and 1,195 nmol/L). All cholecystokinin receptor affinities were >100 nmol/L. All (111)In-labelled radiopeptides showed receptor-specific internalisation. Serum mean-life times varied between 2.0 and 72.6 h, positively correlating with the number of Glu residues. All (111)In-labelled macrocyclic chelator conjugates showed higher tumour-to-kidney ratios after 24 h (0.37-0.99) compared to (111)In-DTPA-minigastrin 0 (0.05). Tumour wash out between 4 and 24 h was low. Imaging studies confirmed receptor-specific blocking of the tumour uptake.
Reducing the number of glutamates increased tumour-to-kidney ratio but resulted in lower metabolic stability. The properties of the macrocyclic chelator-bearing derivatives make them potentially suitable for clinical purposes.
由于络合物稳定性低，二乙烯三胺五乙酸（DTPA）偶联的小胃泌素不适用于与现有的发射β射线的放射性金属进行治疗应用。已知放射性药物的肿瘤与肾脏比值低进一步限制了它们的效力。我们使用大环螯合剂进行偶联以提高络合物稳定性，修饰肽序列以增强辐射稳定性，并使用铟-111标记的衍生物研究肿瘤与肾脏比值和代谢稳定性。
使用铟-111替代治疗性放射性金属合成谷氨酸数量逐渐减少的胃泌素衍生物，用于体外和体内研究。通过以碘-125标记的胆囊收缩素（CCK）作为放射性配体的受体放射自显影法测定天然铟金属化化合物的胃泌素受体亲和力。在AR4-2J细胞中评估内化情况。通过在人血清中孵育铟-111标记的肽来测定酶稳定性。在携带AR4-2J的Lewis大鼠中进行生物分布研究。
对于所有含甲硫氨酸的衍生物，天然铟金属化胃泌素衍生物的半数抑制浓度（IC50）值在1.2至4.8 nmol/L之间变化。用正亮氨酸、异亮氨酸、甲硫氨酸亚砜和甲砜替代甲硫氨酸导致受体亲和力显著降低（IC50在9.9至1195 nmol/L之间）。所有胆囊收缩素受体亲和力均>100 nmol/L。所有铟-111标记的放射性肽均显示出受体特异性内化。血清平均半衰期在2.0至72.6小时之间变化，与谷氨酸残基数量呈正相关。与铟-111-DTPA-小胃泌素0（0.05）相比，所有铟-111标记的大环螯合剂缀合物在24小时后显示出更高的肿瘤与肾脏比值（0.37 - 0.99）。4至24小时之间肿瘤清除率较低。成像研究证实了肿瘤摄取的受体特异性阻断。
减少谷氨酸数量可提高肿瘤与肾脏比值，但会导致代谢稳定性降低。携带大环螯合剂的衍生物的特性使其有可能适用于临床目的。
