Radiopharmaceuticals for assessing ABC transporters at the blood-brain barrier.

ABC transporters protect the brain by transporting neurotoxic compounds from the brain back into the blood. P-glycoprotein (P-gp) is the most investigated ABC (efflux) transporter, as it is implicated in neurodegenerative diseases such as Alzheimer's disease. Altered function of P-gp can be studied in vivo, using Positron Emission Tomography (PET). To date, several radiopharmaceuticals have been developed to image P-gp function in vivo. So far, attempts to image expression levels of P-gp using radiolabeled P-gp inhibitors have not been successful. Improved knowledge of compound behavior toward P-gp from in vitro studies should increase predictability of in vivo outcome.