title: Improved metabolic stability for 18F PET probes rapidly constructed via tetrazine trans-cyclooctene ligation.
abstract: The fast kinetics and bioorthogonal nature of the tetrazine trans-cyclooctene (TCO) ligation makes it a unique tool for PET probe construction. In this study, we report the development of an (18)F-labeling system based on a CF3-substituted diphenyl-s-tetrazine derivative with the aim of maintaining high reactivity while increasing in vivo stability. c(RGDyK) was tagged by a CF3-substituted diphenyl-s-tetrazine derivative via EDC-mediated coupling. The resulting tetrazine-RGD conjugate was combined with a (19)F-labeled TCO derivative to give HPLC standards. The analogous (18)F-labeled TCO derivative was combined with the diphenyl-s-tetrazine-RGD at μM concentration. The resulting tracer was subjected to in vivo metabolic stability assessment, and microPET studies in murine U87MG xenograft models. The diphenyl-s-tetrazine-RGD combines with an (18)F-labeled TCO in high yields (>97% decay-corrected on the basis of TCO) using only 4 equiv of tetrazine-RGD relative to the (18)F-labeled TCO (concentration calculated based on product's specific activity). The radiochemical purity of the (18)F-RGD peptides was >95% and the specific activity was 111 GBq/μmol. Noninvasive microPET experiments demonstrated that (18)F-RGD had integrin-specific tumor uptake in subcutaneous U87MG glioma. In vivo metabolic stability of (18)F-RGD in blood, urine, and major organs showed two major peaks: one corresponded to the Diels-Alder conjugate and the other was identified as the aromatized analog. A CF3-substituted diphenyl-s-tetrazine displays excellent speed and efficiency in (18)F-PET probe construction, providing nearly quantitative (18)F labeling within minutes at low micromolar concentrations. The resulting conjugates display improved in vivo metabolic stability relative to our previously described system.
authors: †Brown Laboratories, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19803, United States.
authors: Ramajeyam
authors: R
authors: Selvaraj
authors: ‡Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
authors: Benjamin
authors: B
authors: Giglio
authors: §Molecular Imaging Center, Department of Radiology, University of Southern California, Los Angeles, California 90033, United States.
authors: Shuanglong
authors: S
authors: Liu
authors: ‡Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
authors: Hui
authors: H
authors: Wang
authors: ‡Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
authors: Mengzhe
authors: M
authors: Wang
authors: ‡Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
authors: Hong
authors: H
authors: Yuan
authors: †Brown Laboratories, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19803, United States.
authors: Srinivasa R
authors: SR
authors: Chintala
authors: §Molecular Imaging Center, Department of Radiology, University of Southern California, Los Angeles, California 90033, United States.
authors: Li-Peng
authors: LP
authors: Yap
authors: §Molecular Imaging Center, Department of Radiology, University of Southern California, Los Angeles, California 90033, United States.
authors: Peter S
authors: PS
authors: Conti
authors: †Brown Laboratories, Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19803, United States.
authors: Joseph M
authors: JM
authors: Fox
authors: ‡Department of Radiology and Biomedical Research Imaging Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States.
authors: Zibo
authors: Z
authors: Li
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D034242:Cyclooctanes / Q000737:chemistry / Q000378:metabolism*; D005260:Female; D005462:Fluorine Radioisotopes / Q000737:chemistry / Q000378:metabolism*; D006573:Heterocyclic Compounds, 1-Ring / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D049268:Positron-Emission Tomography / Q000379:methods; D023041:Xenograft Model Antitumor Assays / Q000379:methods
chemical_list: D034242:Cyclooctanes; D005462:Fluorine Radioisotopes; D006573:Heterocyclic Compounds, 1-Ring; C000598289:tetrazine dye 10