ABSTRACT
Objective (1) To evaluate the effect of insertion of two 15-amino-4,7,10,13-tetraoxapentadecanoic (2 PEG4 ) linkers into cyclic Arg-Gly-Asp (RGD) Dimer E [c(RGDfK)]2 on receptor binding in vitro, (2) to assess its biodistribution in vivo and (3) to investigate the value of 99Tcm labeled 2PEG4-Dimer for integrin αvβ3-positive tumors imaging.Methods The expression of U87 human glioma cells and integrin αv β3 was determined by immunofluorescence staining.The half-inhibition concentrations (IC50) for 125 I-cyclo (Arg-Gly-Asp-D-Tyr-Lys) (c(RGDyK) ) of c ( RGDyK ), hydrazinonictinamide ( HYNIC )-Dimer and HYNIC-2PEG4-Dimer binding to integrin αvβ3 were measured.99Tcm-HYNIC-Dimer and 99Tcm-HYNIC-2PEG4-Dimer were synthesized using non-SnCl2 formulation.Biodistribution and imaging studies were performed in nude mice bearing human glioma xenografts.The unpaired t test was used for statistical analysis.Results The labeling yield of the two radiotracers was more than 95%, and the radiochemical purity was more than 99% through Sep-Pek C18 cartridge.HYNIC-2PEG4-Dimer had significantly higher binding affinity of integrin αvβ3 than c(RGDyK) and HYNIC-Dimer (IC50 = 0.8 nmol/L, 27 nmol/L and 2.4 nmol/L, respectively).Biodistribution study showed that 99Tcm-HYNIC-2PEG4-Dimer was mainly excreted via the kidney.The tumor uptake of 99Tcm-HYNIC-2PEG4-Dimer was higher than that of 99Tcm-HYNIC-Dimer at 2h post injection ((5.71 ±0.96) and (2.10 ±0.50) % ID/g, t =4.80, P＜0.05).The xenografted tumors were visible at 0.5 h post injection and the image contrast increased with time due to the tracer clearance of the background tissue.Conclusion 99 Tcm-HYNIC-2PEG4-Dimer is a promising radiotracer for integrin αvβ3-positive tumor imaging.
ABSTRACT
Objective Multimeric cyclic RGD (Arg-Gly-Asp) peptides are capable of improving the integrin αvβ3-binding affinity due to the polyvalence effect.In this study,the authors prepare 99Tcm-la-bearing cyclic RGD tetramer E{E[c(RGDfK)]2}2,and evaluate its biodistribution and imaging in nude mice beating U87 MG human glioma xenografts with integrinαvβ3-positive.Methods 99Tcm-hydrazino-nictinamide (HYNIC)-E{E[c(RGDfK)]2}2 was prepared by two-step method,while HYNIC wag chosen as bifunctional chelator,and tricine and trisodium triphenylphosphine-3,3,3-trisuifonate (TPPTS) as coligands.The af-finity of c (RGDyK) monomer,HYNIC-E[c(RGDfK)]2 dimer and HYNIC-E{E[c(RGDfK)]2}2 tetramer to integrin αvβ3 was compared by in vitro competitive assay against binding of 125I-c(RGDyK)to integrin αvβ3.positive U87 MG human glioma cells.The biodistribution [the percentage of injection dose per gram of tissue(%ID/g)] and imaging were performed in nude mice bearing UB7MG human glioma xenografts.Re-suits The labeling yield of 99Tcm-HYNIC-E{E[c(RGDfK)2}2 was over 95%,and the radiochemical purity was more than 99%after purification with Sop-Pak C18 cartridge.The 50%inhibiting concentration (IC30) val-ues of c(RGDyk),HYNIC-E[c(RGDfK)]2 and HYNIC-E{E[c(RGDfK)]2}2 were 85.9,9.5 and 4.5 nmol/L, respectively.The result indicated that RGD tetramer possessed a significantly higher affinity to in-tegrinαvβ3.The biodistribution data showed that 99Tcm-HYNIC-E{E[c(RGDfK)]2}2 was excreted mainly through kidneys.The tumor uptake of 99Tcm-HYNIC-E{E[c(RGDfK)]2}2 was two times higher than 99Tcm- HYNIC-E[c(RGDfK)]2,at 1h postinjection,with the uptake of(10.32±0.07)%ID/g and(5.15±0.52)%ID/g,respectively,which was consistent with the in vitro competitive binding data.The tumor up-tale of 99Tcm-HYNIC.E{E[c(RGDfK)]2}2 was still as higher as(9.35±1.35)%ID/g at 4 h postinjec-tion, which demonstrated that the retention time of radiotracer in tumor was long enough.The imaging showed that tumor was clearly visualized at 1h postinjection,and the image at 4 h postinjection Was better.Conclusion The higher tumor uptake and longer retention time in tumor make 99Tem-HYNIC-E{E[c(RG-DfK)J 2}2 a promising radiotracer for integrinαvβ3-positive tumors imaging,furthermore,suggest that radi-onuelides(such as 90Y).1abeled RGD tetramer is more suitable for the therapy of integrin αvβ3-positive tumors.