(18F)FCWAY and the Blood-Brain Barrier

• Tariquidar will increase uptake of 18F-FCWAY in brain
  

• Tariquidar will delay brain peak of 18F-FCWAY
  

Objective:

We use the radioligand [(11)C]dLop (N-desmethyl-loperamide) in positron emission tomography (PET) studies to measure function of P-gp, an efflux transporter at the blood-brain barrier. Because [(11)C]dLop is an avid substrate for P-gp, we see almost no radioactivity in brain at baseline in healthy volunteers. However, we do see increased radioactivity in brain in some patients with dementia, or when we co-administer a medication which blocks the function of P-gp. While [(11)C]dLop is useful for detecting increased radioactivity in brain, a disadvantage of [(11)C]dLop is that it is not useful for detecting decreased radioactivity in brain. The reason for this is that we have a floor effect, where we are unable to detect less radioactivity than zero. Preclinical studies indicate that increases in P-gp activity (which would manifest as decreased radioactivity in brain) correlate with drug-resistant epilepsy and HIV. To better understand diseases associated with not only increased but also decreased P-gp activity, we wish to identify a radioligand which is a moderate substrate of P-gp. We suspect that [(18)F]FCWAY is a moderate substrate for P-gp, because some radioligand gets into brain at baseline, but more gets into brain after administering a drug (disulfiram) which inhibits P-gp. The objective of this study is to determine whether the serotonin 1A antagonist [(18)F]FCWAY is a substrate of P-gp.

Study Population:

We will study up to 30 healthy adults, ages 18-50. Participants must be free of medications, with the exception of birth control pills, as medications may confound our data.

Design:

Healthy adults will undergo a single PET scan of the brain with [(18)F]FCWAY, either at baseline, or during infusion of intravenous tariquidar at 2 mg.kg. Tariquidar is an inhibitor of P-gp.

Outcome Measures:

If [(18)F]FCWAY is a substrate of P-gp, pre-treatment with tariquidar will increase its brain uptake of [(18)F]FCWAY and delay the time of peak uptake.