A novel radiofluorinated agouti-related protein for tumor angiogenesis imaging

• Published in: Amino acids Vol. 44; no. 2; pp. 673 - 681
• Main Authors: Jiang, Han, Moore, Sarah J., Liu, Shuanglong, Liu, Hongguang, Miao, Zheng, Cochran, Frank V., Liu, Yang, Tian, Mei, Cochran, Jennifer R., Zhang, Hong, Cheng, Zhen
• Format: Journal Article
• Language: English
• Published: Vienna Springer Vienna 01.02.2013; Springer Nature B.V
• Subjects: Affinity; Agouti-related protein; Agouti-Related Protein - chemistry; Agouti-Related Protein - metabolism; Analytical Chemistry; Angiogenesis; Animals; Binding; Biochemical Engineering; Biochemistry; Biodistribution; Biomedical and Life Sciences; Cell Line, Tumor; Diagnostic Imaging; Female; Fluorine isotopes; Fluorine Radioisotopes - chemistry; Fluorine Radioisotopes - metabolism; Glioblastoma; Humans; Imaging; Life Sciences; Medical imaging; Metabolites; Mice; Mice, Nude; Mutants; Neoplasms - diagnosis; Neoplasms - diagnostic imaging; Neoplasms - pathology; Neovascularization, Pathologic - diagnosis; Neovascularization, Pathologic - diagnostic imaging; Neurobiology; Original Article; Peptide synthesis; Peptides; Positron emission; Positron emission tomography; Proteins; Proteomics; Radionuclide Imaging; Radiopharmaceuticals - chemistry; Radiopharmaceuticals - metabolism; Solid phases; Stability; Tomography; Tumors; Uptakes; Xenotransplantation; α; β; Knottin; integrin; F; PET
• ISSN: 0939-4451; 1438-2199; 1438-2199
• DOI: 10.1007/s00726-012-1391-y

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.