title: Preparation and characterization of 99mTc(CO)3-BPy-RGD complex as alphav beta3 integrin receptor-targeted imaging agent.
abstract: The aim of this study is to develop a novel arginine-glycine-aspartic acid (RGD) peptide-containing ligand for (99m)Tc labeling as alpha(v)beta(3) integrin receptor-targeted imaging agent. BPy-RGD conjugate was successfully synthesized by coupling of 5-carboxylate-2,2'-bipyridine and c(RGDyK) peptide through EDC/SNHS in aqueous solution and was characterized by MADLI-TOF-MS (m/z=802.72, C(38)H(48)N(11)O(9)). (99m)Tc(CO)(3)-BPy-RGD was prepared by exchange reaction between [(99m)Tc(H(2)O)(3)(CO)(3)](+) and BPy-RGD. Final product was purified by HPLC and tested for octanol/water partition coefficient. Cell-binding assays of BPy-RGD and unmodified c(RGDyK) were tested in MDA-MB-435 cells ((125)I-echistatin as radioligand). Preliminary biodistribution of the (99m)Tc(I)-labeled radiotracer in orthotopic MDA-MB-435 breast tumor xenograft model was also evaluated. The BPy-RGD conjugate had good integrin-binding affinity (50% inhibitory concentration (IC(50))=92.51+/-22.69 nM), slightly lower than unmodified c(RGDyK) (IC(50)=59.07+/-11.03 nM). The hydrophilic radiotracer also had receptor-mediated activity accumulation in MDA-MB-435 tumor (1.45+/-0.25 percentage of injected dose per gram (%ID/g) at 1.5h postinjection (p.i.)), which is known to be integrin positive. After blocking with c(RGDyK), the tumor uptake was reduced from 0.71+/-0.01%ID/g to 0.33+/-0.18%ID/g at 4h p.i. (99m)Tc(I) tricarbonyl complex of cyclic RGD peptide is a promising strategy for integrin targeting. Further modification of the bipyridine-conjugated RGD peptide by using more potent RGD peptides and fine tuning of the tether group between the RGD moiety and (99m)Tc(CO)(3)(+) core to improve the tumor targeting efficacy and in vivo kinetic profiles is currently in progress.
authors.affiliation: Department of Radiology, Molecular Imaging Program at Stanford and Bio-X, Stanford University School of Medicine, Stanford, CA 94305, USA. zhangxzh@gmail.com
authors.forename: Xianzhong
authors.initials: X
authors.lastname: Zhang
authors.forename: Xiaoyuan
authors.initials: X
authors.lastname: Chen
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism*; D005260:Female; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D007553:Isotope Labeling / Q000379:methods; D008657:Metabolic Clearance Rate; D051379:Mice; D008819:Mice, Nude; D009842:Oligopeptides / Q000737:chemistry* / Q000493:pharmacokinetics*; D009928:Organ Specificity; D015609:Organotechnetium Compounds / Q000737:chemistry* / Q000493:pharmacokinetics*; D019275:Radiopharmaceuticals / Q000138:chemical synthesis / Q000493:pharmacokinetics; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*
chemical_list: C516853:99mTc(CO)3-BPy-RGD complex; D039302:Integrin alphaVbeta3; D009842:Oligopeptides; D015609:Organotechnetium Compounds; D019275:Radiopharmaceuticals