Synthesis of a 11 C-Isotopologue of the B-Raf-Selective Inhibitor Encorafenib Using In-Loop [ 11 C]CO 2 Fixation.

The serine/threonine kinase B-Raf is an essential regulator of cellular growth, differentiation, and survival. B-Raf protein expression is elevated throughout melanoma progression, making it an attractive target for noninvasive imaging using positron-emission tomography. Encorafenib is a potent and highly selective inhibitor of B-Raf used in the clinical management of melanoma. In this study, the radiosynthesis of a C-11-isotopologue of encorafenib was developed using an in-loop [C-11]CO2 fixation reaction. Optimization of reaction conditions reduced the formation of a radiolabeled side product and improved the isolated yields of r jencorafenib (14.5 +/- 2.4% radiochemical yield). The process was fully automated using a commercial radiosynthesizer for the production of 6845 +/- 888 MBq of [C-11]encorafenib in high molar activity (177 +/- 5 GBq mu mol(-1)), in high radiochemical purity (99%), and in a formulation suitable for animal injection. An in vitro cellular binding experiment demonstrated saturable binding of the radiotracer to A375 melanoma cells.