The pharmacokinetics of [C-11]methoxy-norchloroprogabidic acid, a potential PET tracer for GABA receptors in the brain

We have described the kinetic properties of [C-11]methoxy-norchloroprogabid ic acid, a potential radioligand for the gamma-aminobutyric acid (GABA) rec eptor. Early metabolism in mice was ne,negligible. Protein binding in human plasma was 89 +/- 7%. Distribution volumes were 89.6 +/- 29.41 whereas the elimination half-life was 41.6 +/- 14.3 min. Animal and human positron emi ssion tomography (PET) data demonstrate limited uptake of the activity in b rain tissue. Displacement studies in mice suggest a nonsignificant fraction of specific receptor binding. [C-11] Methoxy-norchloroprogabidic acid is t herefore unsuitable for brain PET.