title: A novel radiofluorinated agouti-related protein for tumor angiogenesis imaging.
abstract: A novel protein scaffold based on the cystine knot domain of the agouti-related protein (AgRP) has been used to engineer mutants that can bind to the α(v)β(3) integrin receptor with high affinity and specificity. In the current study, an (18)F-labeled AgRP mutant (7C) was prepared and evaluated as a positron emission tomography (PET) probe for imaging tumor angiogenesis. AgRP-7C was synthesized by solid phase peptide synthesis and site-specifically conjugated with 4-nitrophenyl 2-(18/19)F-fluoropropionate ((18/19)F-NFP) to produce the fluorinated peptide, (18/19)F-FP-AgRP-7C. Competition binding assays were used to measure the relative affinities of AgRP-7C and (19)F-FP-AgRP-7C to human glioblastoma U87MG cells that overexpress α(v)β(3) integrin. In addition, biodistribution, metabolic stability, and small animal PET imaging studies were conducted with (18)F-FP-AgRP-7C using U87MG tumor-bearing mice. Both AgRP-7C and (19)F-FP-AgRP-7C specifically competed with (125)I-echistatin for binding to U87MG cells with half maximal inhibitory concentration (IC(50)) values of 9.40 and 8.37 nM, respectively. Non-invasive small animal PET imaging revealed that (18)F-FP-AgRP-7C exhibited rapid and good tumor uptake (3.24 percentage injected dose per gram [% ID/g] at 0.5 h post injection [p.i.]). The probe was rapidly cleared from the blood and from most organs, resulting in excellent tumor-to-normal tissue contrasts. Tumor uptake and rapid clearance were further confirmed with biodistribution studies. Furthermore, co-injection of (18)F-FP-AgRP-7C with a large molar excess of blocking peptide c(RGDyK) significantly inhibited tumor uptake in U87MG xenograft models, demonstrating the integrin-targeting specificity of the probe. Metabolite assays showed that the probe had high stability, making it suitable for in vivo applications. (18)F-FP-AgRP-7C exhibits promising in vivo properties such as rapid tumor targeting, good tumor uptake, and excellent tumor-to-normal tissue ratios, and warrants further investigation as a novel PET probe for imaging tumor angiogenesis.
authors.affiliation: Department of Nuclear Medicine, Second Affiliated Hospital of Zhejiang University School of Medicine, Institute of Nuclear Medicine and Molecular Imaging of Zhejiang University, Key Laboratory of Medical Molecular Imaging of Zhejiang Province, Hangzhou 310009, China.
authors.forename: Han
authors.initials: H
authors.lastname: Jiang
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Moore
authors.forename: Shuanglong
authors.initials: S
authors.lastname: Liu
authors.forename: Hongguang
authors.initials: H
authors.lastname: Liu
authors.forename: Zheng
authors.initials: Z
authors.lastname: Miao
authors.forename: Frank V
authors.initials: FV
authors.lastname: Cochran
authors.forename: Yang
authors.initials: Y
authors.lastname: Liu
authors.forename: Mei
authors.initials: M
authors.lastname: Tian
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Cochran
authors.forename: Hong
authors.initials: H
authors.lastname: Zhang
authors.forename: Zhen
authors.initials: Z
authors.lastname: Cheng
mesh_terms: D054369:Agouti-Related Protein / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D045744:Cell Line, Tumor; D003952:Diagnostic Imaging; D005260:Female; D005462:Fluorine Radioisotopes / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000473:pathology; D009389:Neovascularization, Pathologic / Q000175:diagnosis / Q000000981:diagnostic imaging; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals / Q000737:chemistry / Q000378:metabolism
chemical_list: D054369:Agouti-Related Protein; D005462:Fluorine Radioisotopes; D019275:Radiopharmaceuticals