Development and preparation of a novel carbon-11 containing radiotracer for non-invasive PET-Imaging of EphB4

Ziel/Aim:

Members of the Eph receptor tyrosine kinase family play an essential role in the pathogenesis of cancer and, therefore, are promising candidates for molecular imaging purposes, e.g. by PET. In this regard, radiochemical access to 11C-radiotracers derived from potent inhibitors (IC₅₀ = 1.3 nM, calcd. logP = 3.42) targeting EphB4 kinase domain and bearing the indazolylpyrazole structural motif was developed.

Methodik/Methods:

The evaluation of a protecting group strategy based on the ethoxyethyl moiety (EOE) was necessary for the regioselective labeling with [¹¹C]CH₃I due to three secondary amino groups of the precursor. The labeling was accomplished in a remotely controlled synthesis module in three steps. The first step involved the preparation of [¹¹C]CH₃I from [¹¹C]CH₄, the second step comprehended the radiolabeling of the protected precursor and the final step included the cleavage of the protecting group.

Ergebnisse/Results:

The synthesis of the reference as well as the precursor was done starting from EOE protected indazole. Subsequent reaction with 2,4-diochloropyrimidine give the first substructure. For the preparation of the precursor, the first substructure was treated with 3,5-di(morpholino)aniline under Buchwald-Hartwig conditions. For the preparation of the reference, the first substructure was first methylated and then treated with 3,5-di(morpholino)aniline. The radiolabeling was done starting with ~ 1-1.5 GBq [¹¹C]CH₃I under basic conditions. After 2 min reaction time 1 M HCl was added and the mixture was maintained for 2 min. Approx. 200 MBq of the desired radiotracer could be obtained within 20 min after EOB (30-35% d.c. yield based on [¹¹C]CH₄).

Schlussfolgerungen/Conclusions:

The two-step radiolabeling of a novel indazolylpyrazole derivative with [¹¹C]CH₃I was successfully demonstrated. First stability tests showed beneficial behaviour ex vivo. Further biological studies for an application as radiotracer for functional tumor imaging are ongoing.

Literatur/References:

Mamat C, Mosch B et al. (2012) ChemMedChem 7:1991-2003.