RT Journal Article
SR Electronic
T1 Preliminary in vivo evaluation of a 11C-labeled tetrazine for bioorthogonal reaction within CNS
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 1051
OP 1051
VO 57
IS supplement 2
A1 Steen, Johanna
A1 Lehel, Szabolcs
A1 Jorgensen, Jesper
A1 Norregaard, Kamilla
A1 Hansen, Hanne
A1 Madsen, Jacob
A1 Kjaer, Andreas
A1 Knudsen, Gitte
A1 Kristensen, Jesper
A1 Herth, Matthias
YR 2016
UL http://jnm.snmjournals.org/content/57/supplement_2/1051.abstract
AB 1051Objectives Due to its fast reaction kinetics and orthogonality towards biological functionalities, the inverse-electron-demand Diels-Alder cycloaddition between an electron deficient 1,2,4,5-tetrazine and a trans-cyclooctene has proven to be a useful application for in vivo chemistry in the field of molecular imaging. We have previously reported a 11C-labeled tetrazine, which rapidly reacts with trans-cyclooctene. Here, we describe its preliminary evaluation in respect to in vitro and in vivo stability, its capability to cross the blood-brain-barrier and its conjugation to a trans-cyclooctene functionalized polyglumatic acid (PGA), which was used as a model to test reaction kinetics and feasibility of the inverse-electron-demand Diels-Alder cycloaddition of this particular reaction.Methods A 4-(hydroxy)benzamide substituted bispyridyl-tetrazine was radiolabeled with 11C using [11C]CH3I. The [11C]tetrazine was conjugated to a polyglutamic acid functionalized with trans-cyclooctene (11.4%). Analysis was performed by radio-HPLC using size exclusion chromatography and by radio-TLC. In vitro metabolism studies were conducted in human plasma and analyzed by radio-HPLC. The in vivo stability assessment and PET imaging were performed in Danish landrace pigs.Results The [11C]tetrazine was formed in a radiochemical yield of 33% and >98% radiochemical purity. The subsequent inverse-electron-demand Diels-Alder cycloaddition with trans-cyclooctene tagged PGA was performed in water at 40 °C and completed within 1 min. The in vitro metabolic stability studies of the free [11C]tetrazine in human plasma showed 82% intact tracer after 30 min, whereas the in vivo experiments showed 26% intact tracer after 10 min. Furthermore, a summed PET image of the pig brain 6-20 min after injection of the free [11C]tetrazine demonstrated brain uptake.Conclusions The 11C-labeled tetrazine is to our knowledge the first tetrazine described to cross the blood brain barrier. In addition, it reacts rapidly and efficiently with a trans-cyclooctene tagged polymer. We aim to use these results as a starting point for future pretargeted neuroimaging using click chemistry.