Strategies for designing novel positron emission tomography (PET) radiotracers to cross the blood–brain barrier

Positron emission tomography (PET) is a powerful tool for imaging biological processes in the central nervous system (CNS). Designing PET radiotracers capable of crossing the blood–brain barrier (BBB) remains a major challenge. In addition to being brain-penetrant, a quantifiable CNS PET radiotracer must have high target affinity and selectivity, appropriate pharmacokinetics, minimal non-specific binding, negligible radiometabolites in the brain, and generally must be amenable to labeling with carbon-11 (¹¹C) or fluorine-18 (¹⁸F). This review aims to give an overview of some of the critical physicochemical and biochemical contributors specific for CNS PET radiotracer design and how they can differ from pharmaceutical drug development, including in vitro assays, in silico predictions, and in vivo studies, with examples for how such methods can be implemented to optimize brain uptake of radiotracers based on experiences from our neuroimaging program.