Abstract
1096
Objectives There is a high demand for new methods that efficiently introduce 18F to biological macromolecules for PET imaging applications. Here we describe 18F-sTCO, a new radiotracer based on the most reactive trans-cyclooctene dienophile described to date. This highly reactive radiotracer is used for the rapid construction of 18F-PET probes through tetrazine ligation.
Methods Starting from the tosylated precursor, an 18F labeled sTCO derivative was synthesized. The reaction rate constant of sTCO and an a diphenyl-s-tetrazine was measured by stopped flow kinetic analysis. A cyclic RGD-tetrazine conjugate was prepared from 18F-sTCO and the resulting imaging probe was subjected to in vitro stability and micro PET studies in human U87MG tumor bearing mice.
Results sTCO can be labeled with an isolation yield of 9.3+/- 2.4% with high specific activity. Extremely fast reactivity (up to 2.86 x 105 M-1s-1 in water at rt) was observed in the reaction of sTCO and tetrazine derivatives. The 18F-sTCO-Tetrazine-RGD probe demonstrated prominent and persistent tumor uptake in vivo with good tumor to background contrast.
Conclusions A conformationally strained trans-cyclooctene, 18F-sTCO, was developed and shown to have extremely fast reaction rate in tetrazine ligation. The constructed PET probe demonstrated specific tumor uptake and good tumor to background contrast.
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