title: Impact of multiple negative charges on blood clearance and biodistribution characteristics of 99mTc-labeled dimeric cyclic RGD peptides.
abstract: 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 diisopropylethylamine. Their IC50 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 ∼5× 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 (2.20-3.11%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 αvβ3 binding affinity (41 ± 6 nM versus 31 ± 5 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 αvβ3-specific. SPECT/CT studies were performed using (99m)Tc-P6G-RGD2 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-P6G-RGD2, and its tumor uptake depends on the integrin αvβ3 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.
authors.affiliation: School of Health Sciences, Purdue University , 550 Stadium Mall Drive, West Lafayette, Indiana 47907, United States.
authors.forename: Yong
authors.initials: Y
authors.lastname: Yang
authors.forename: Shundong
authors.initials: S
authors.lastname: Ji
authors.forename: Shuang
authors.initials: S
authors.lastname: Liu
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D019281:Dimerization; D005260:Female; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism; D007700:Kinetics; D051379:Mice; D009842:Oligopeptides / Q000097:blood / Q000737:chemistry* / Q000493:pharmacokinetics*; D015609:Organotechnetium Compounds; D011854:Radiochemistry; D013329:Structure-Activity Relationship; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon; D014057:Tomography, X-Ray Computed
chemical_list: D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D015609:Organotechnetium Compounds; C047981:arginyl-glycyl-aspartic acid