%0 Journal Article %A Selvaraj, Ramajeyam %A Giglio, Benjamin %A Liu, Shuanglong %A Wang, Hui %A Wang, Mengzhe %A Yuan, Hong %A Chintala, Srinivasa R. %A Yap, Li-Peng %A Conti, Peter S. %A Fox, Joseph M. %A Li, Zibo %D 2015 %T Improved Metabolic Stability for 18F PET Probes Rapidly Constructed via Tetrazine trans-Cyclooctene Ligation %U https://acs.figshare.com/articles/journal_contribution/Improved_Metabolic_Stability_for_sup_18_sup_F_PET_Probes_Rapidly_Constructed_via_Tetrazine_i_trans_i_Cyclooctene_Ligation/2185129 %R 10.1021/acs.bioconjchem.5b00089.s001 %2 https://acs.figshare.com/ndownloader/files/3819295 %K bioorthogonal nature %K μ M concentration %K micromolar concentrations %K PET probe construction %K 18 F %K TCO %K subcutaneous U 87MG glioma %K aromatized analog %K 18 F PET Probes Rapidly Constructed %K Metabolic Stability %K vivo stability %K HPLC standards %K murine U 87MG xenograft models %K stability assessment %K CF %K microPET studies %K conjugates display %K radiochemical purity %K 4 equiv %X 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 18F-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 19F-labeled TCO derivative to give HPLC standards. The analogous 18F-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 18F-labeled TCO in high yields (>97% decay-corrected on the basis of TCO) using only 4 equiv of tetrazine-RGD relative to the 18F-labeled TCO (concentration calculated based on product’s specific activity). The radiochemical purity of the 18F-RGD peptides was >95% and the specific activity was 111 GBq/μmol. Noninvasive microPET experiments demonstrated that 18F-RGD had integrin-specific tumor uptake in subcutaneous U87MG glioma. In vivo metabolic stability of 18F-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 18F-PET probe construction, providing nearly quantitative 18F labeling within minutes at low micromolar concentrations. The resulting conjugates display improved in vivo metabolic stability relative to our previously described system. %I ACS Publications