Avoiding barriers to PET radioligand development: cellular assays of brain efflux transporters.

PET provides a uniquely sensitive and powerful means for studying a clinically relevant protein target within the brain, provided that an adequately specific and sensitive radiotracer is available. Interesting targets, which include neurotransmitter receptors, neurotransmitter transporters, enzymes, and plaques, far exceed the availability of effective radiotracers. Most PET radiotracers are designed to bind avidly and reversibly with their target. This type of radiotracer is usually termed a radioligand. Candidate radioligands for imaging must ideally satisfy an array of demanding criteria. These include ability to penetrate the blood–