Development of the First Aliphatic 18F-Labeled Tetrazine Suitable for Pretargeted PET Imaging – Expanding the Bioorthogonal Tool Box

Abstract

<p>Pretargeting imaging of nanomedicines have attracted considerable interest in nuclear medicine since it has the potential to increase imaging contrast while simultaneously reducing radiation burden to healthy tissue. Currently, the tetrazine ligation is the fastest bioorthogonal reaction available for this strategy and consequently, the state-of-art choice for <i>in vivo</i>chemistry. We have recently identified key properties for tetrazines to be applied in pretargeting. We have also developed a method to <sup>18</sup>F-label highly reactive tetrazines using an aliphatic nucleophilic substitution strategy.<a> In this study, we combined this knowledge and developed an <sup>18</sup>F-labeled tetrazine for pretargeted imaging. In order to develop this ligand, a small structure-property study was carried out. The most promising compound - with respect to reactivity, hydrophilicity and <i>ex vivo</i> blocking effect - was selected for labeling and subsequent PET <i>in vivo</i> imaging. Radiolabeling was achieved in satisfying radiochemical yields, molar activities as well as in high radiochemical purities. The tracer </a><a>displayed favorable pharmacokinetics and remarkable target-to-background ratios in pretargeted experiments - already one hour post injection.</a> We believe that the developed pretargeting imaging agent is a promising candidate for translation into clinical studies.</p>

[11C]Carboxylated Tetrazines for Facile Labeling of Trans‐Cyclooctene‐Functionalized PeptoBrushes

“…Recently, we reported several new methodologies to radiolabel Tzs with fluorine‐18. [ 37–40 ] In particular, aryl stannane Tz derivatives were employed as precursors allowing for the first‐time direct aromatic 18 F‐fluorination of this scaffold. [ 38 ] At the same time, the preparation of 11 C‐labeled carboxylic acids from aryl stannane precursors and [ 11 C]CO 2 via a copper‐mediated carboxylation was reported by other authors.…”

Synergistic Experimental and Computational Investigation of the Bioorthogonal Reactivity of Substituted Aryltetrazines

“…Considering the recent development of radiolabeled 18 Fphenyltetrazines with improved bioorthogonal performance, our findings will aid the design of next-generation tetrazines for in vivo pretargeting. 12,23,31 ■ EXPERIMENTAL SECTION Chemistry. All reagents and solvents were dried prior to use according to standard methods.…”

“…Reactivities of the tetrazines in the reaction with TCO were determined by pseudo-first-order measurements in CH 3 CN at 25 °C and in DPBS at 37 °C by stopped-flow spectrophotometry. 31 Solutions of TCO in anhydrous CH 3 CN and axTCO-PEG 4 in DPBS were employed for the analysis. 31,32 The data obtained are reported in Table 1.…”

“…31 Solutions of TCO in anhydrous CH 3 CN and axTCO-PEG 4 in DPBS were employed for the analysis. 31,32 The data obtained are reported in Table 1.…”