Evaluation of [¹⁸F]VUF 5000 as a potential PET ligand for brain imaging of the histamine H₃ receptor

[¹⁸F]VUF 5000 was evaluated as a potential PET ligand for the histamine H₃ receptor. In the rat a high uptake of [¹⁸F]VUF 5000 was observed in liver, lung and kidney and a low uptake in the brain. In order to explain these findings we determined the LogD(oct,7.2) of [¹⁸F]VUF 5000, studied the biodistribution in the presence of carrier VUF 5000, modified [¹⁸F]VUF 5000 chemically and studied the binding of [¹⁸F]VUF 5000 to human serum albumin. From the results of these experiments it was concluded that [¹⁸F]VUF 5000 is not suitable as a PET ligand for brain imaging of the histamine H₃ receptor, since [¹⁸F]VUF 5000 hardly penetrates into the brain.