Impact of Multiple Negative Charges on Blood Clearance and Biodistribution Characteristics of Tc-Labeled Dimeric Cyclic RGD Peptides

摘要

This study sought to evaluate the impact of multiple negative charges on blood clearance kinetics and biodistribution properties of ~(99m)Tc-labeled RGD peptide dimers. Bioconjugates HYNIC-P6G-RGD2 and HYNIC-P6D-RGD2 were prepared by reacting P6G- RGD2 and P6D-RGD2, respectively, with excess HYNIC-OSu in the presence of diisopropylefhylamine. Their IC_(50) values were determined to be 31 ± 5 and 41 ± 6 nM, respectively, against ~(125)I-echistatin bound to U87MG glioma cells in a whole-cell displacement assay. Complexes [~(99m)Tc(HYNIC-P6G-RGD2)(tricine)(TPPTS)] (~(99m)Tc-P6G-RGD2) and [~(99m)Tc(HYNIC-P6D-RGD2)(tricine)(TPPTS)] (~(99m)Tc-P6D-RGD2) were prepared ,in high radiochemical purity (RCP > 95%) and specific activity (37—110 GBq/μmol). They were evaluated in athymic nude mice bearing U87MG glioma xenografts for their biodistribution. The most significant difference between ~(99m)Tc-P6D-RGD2 and ~(99m)Tc-P6G-RGD2 was their blood radioactivity levels and tumor uptake. The initial blood radioactivity level for ~(99m)Tc-P6D- RGD2 (4.71 ±1.00%ID/g) was ~SX higher than that of ~(99m)Tc-P6G-RGD2 (0.88 ± 0.05%ID/ g), but this difference disappeared at 60 min p.i. ~(99m)Tc-P6D-RGD2 had much lower tumor uptake .(2.26-3.11%ID/g) than ~(99m)Tc-P6G-RGD2 (7.82-9.27%ID/g) over a 2 h period. Since HYNIC-P6D-RGD2 and HYNIC- P6G-RGD2. shared a similar,integrin α_vβ3 binding affinity (41 ± 6 nM versus 31 ± S nM), the difference in their blood activity and tumor uptake is most'likely related to the nine negative charges and high protein binding of ~(99m)Tc-P6D-RGD2. Despite its low uptake in U87MG tumors, the tumor uptake of ~(99m)Tc-P6D-RGD2 was integrin a/3-specific. SPECT/CT studies were performed using ~(99m)Tc-P6G-RGDj in athymic nude mice bearing U87MG glioma and MDA-MB-231 breast cancer xenografts. The SPECT/CT data demonstrated the tumor-targeting capability of ~(99m)Tc-PeG-RGD2, and its tumor uptake depends on the integrin α_vβ3 expression levels on tumor cells and neovasculature. It was concluded that the multiple negative charges have a significant impact on the blood clearance kinetics and tumor uptake of ~(99m)Tc-labeled dimeric cyclic RGD peptides.