april
Jubileumsaulan , Gula stråket 2B
Deuteration of 18FF-FDOPA extends the biological half-life of the tracer in the brain thus enhancing the specific signal in PET imaging and improving the quantitation of brain dopamine synthesis.
Deuterium substitution can profoundly alter substrate reaction rates, with consequences for the disposition of radiopharmaceuticals for molecular imaging by positron emission tomography (PET). In a classic instance, deuteration of the monoamine oxidase (MAO) ligand [11C]deprenyl imparted superior binding properties in the living brain due to the slower reaction with the target enzyme, thus giving better kinetic separation of perfusion and binding rates. Enzymatic decarboxylation of the classic dopamine synthesis tracer [18F]fluoroDOPA (FDOPA) in brain tissue yields [18F]fluorodopamine, which is trapped in synaptic vesicles.
However, the specific PET signal progressively declines due to the formation and washout of diffusible metabolites formed via MAO. Indeed, kinetic modelling of FDOPA PET indicates a biological half-life of about 90 min for [18F]fluorodopamine in striatum; preclinical evidence indicates that alpha-deuteration of levodopa prolongs the half-life of dopamine formed in the brain. By extension, we predict that FDOPA-d1 should impart better retention of the decarboxylated metabolite formed in living tissue, thus constituting a superior PET tracer for brain PET imaging and also neurooncolgy. Enhancement of the specific signal in FDOPA PET studies would thus improve the quantitation of brain dopamine synthesis in neuropsychiatry research, and in the clinical detection of neuroendocrine tumors, possibly eventually coming to replace ordinary FDOPA PET and rationalizing the use of levodopa-d1 in the treatment of Parkinson’s disease . Given this background, we summarize the state of development of a route to the radiochemical synthesis of FDOPA-d1, and plans for its testing in vivo.
