Dijkgraaf Ingrid, Liu Shuang, Kruijtzer John A W, Soede Annemieke C, Oyen Wim J G, Liskamp Rob M J, Corstens Frans H M, Boerman Otto C
Department of Nuclear Medicine, Radboud University Nijmegen Medical Center, PO Box 9101, HB Nijmegen 6500, The Netherlands.
Nucl Med Biol. 2007 Jan;34(1):29-35. doi: 10.1016/j.nucmedbio.2006.10.006.
Due to the selective expression of the alpha(v)beta3 integrin in tumors, radiolabeled arginine-glycine-aspartic acid (RGD) peptides are attractive candidates for tumor targeting. Minor modifications of these peptides could have a major impact on in vivo characteristics. In this study, we systematically investigated the effects of linker modification between two cyclic RGD sequences and DOTA (1,4,7,10-tetraazadodecane-N,N',N",N'''-tetraacetic acid) on the in vitro and in vivo characteristics of the tracer.
A dimeric RGD peptide was synthesized and conjugated either directly with DOTA or via different linkers: PEG4 (polyethylene glycol), glutamic acid or lysine. The RGD peptides were radiolabeled with 111In, and their in vitro and in vivo alpha(v)beta3-binding characteristics were determined.
LogP values varied between -2.82+/-0.06 and -3.95+/-0.33. The IC50 values for DOTA-E-[c(RGDfK)]2, DOTA-PEG4-E-[c(RGDfK)]2, DOTA-E-E-[c(RGDfK)]2 and DOTA-K-E-[c(RGDfK)]2 were comparable. Two hours after injection, the tumor uptakes of the 111In-labeled compounds were not significantly different. The kidney accumulation of [111In]-DOTA-K-E-[c(RGDfK)]2 [4.05+/-0.20% of the injected dose per gram (ID/g)] was significantly higher as compared with that of [111In]-DOTA-E-[c(RGDfK)]2 (2.63+/-0.19% ID/g; P<.05) as well as that of [111In]-DOTA-E-E-[c(RGDfK)]2 (2.16+/-0.21% ID/g; P<.01). The liver uptake of [111In]-DOTA-E-E-[c(RGDfK)]2 (2.12+/-0.09% ID/g) was significantly higher as compared with that of [111In]-DOTA-E-[c(RGDfK)]2 (1.64+/-0.1% ID/g; P<.05) as well as that of [111In]-DOTA-K-E-[c(RGDfK)]2 (1.52+/-0.04% ID/g; P<.01).
Linker variation did not affect affinity for alpha(v)beta3 and tumor uptake. Insertion of lysine caused enhanced kidney retention; that of glutamic acid also resulted in enhanced retention in the kidneys. PEG4 appeared to be the most suitable linker as compared with glutamic acid and lysine because it has the highest tumor-to-blood ratio and the lowest uptake in the kidney and liver.
由于α(v)β3整合素在肿瘤中选择性表达，放射性标记的精氨酸-甘氨酸-天冬氨酸（RGD）肽是肿瘤靶向的有吸引力的候选物。这些肽的微小修饰可能对体内特性产生重大影响。在本研究中，我们系统地研究了两个环状RGD序列与DOTA（1,4,7,10-四氮杂环十二烷-N,N',N",N'''-四乙酸）之间的连接子修饰对示踪剂体外和体内特性的影响。
合成了一种二聚体RGD肽，并将其直接与DOTA或通过不同的连接子：PEG4（聚乙二醇）、谷氨酸或赖氨酸进行偶联。用111In对RGD肽进行放射性标记，并测定其体外和体内α(v)β3结合特性。
LogP值在-2.82±0.06和-3.95±0.33之间变化。DOTA-E-[c(RGDfK)]2、DOTA-PEG4-E-[c(RGDfK)]2、DOTA-E-E-[c(RGDfK)]2和DOTA-K-E-[c(RGDfK)]2的IC50值相当。注射后两小时，111In标记化合物的肿瘤摄取无显著差异。[111In]-DOTA-K-E-[c(RGDfK)]2的肾脏摄取量[每克注射剂量的4.05±0.20%（ID/g）]显著高于[111In]-DOTA-E-[c(RGDfK)]2（2.63±0.19% ID/g；P<0.05）以及[111In]-DOTA-E-E-[c(RGDfK)]2（2.16±0.21% ID/g；P<0.01）。[111In]-DOTA-E-E-[c(RGDfK)]2的肝脏摄取量（2.12±0.09% ID/g）显著高于[111In]-DOTA-E-[c(RGDfK)]2（1.64±0.1% ID/g；P<0.05）以及[111In]-DOTA-K-E-[c(RGDfK)]2（1.52±0.04% ID/g；P<0.01）。
连接子的变化不影响对α(v)β3的亲和力和肿瘤摄取。赖氨酸的插入导致肾脏滞留增强；谷氨酸的插入也导致肾脏滞留增强。与谷氨酸和赖氨酸相比，PEG4似乎是最合适的连接子，因为它具有最高的肿瘤与血液比值以及最低的肾脏和肝脏摄取。
