The
metabotropic glutamate receptor 5 (mGluR5)
ligands fenobam and
AZD9272 have been reported to induce
psychosis-like adverse events and to bind at unknown, non-GluR5-related, sites. Based on similarities of the regional binding patterns for [11C]
AZD9272 and the
monoamine oxidase-B (
MAO-B) radioligand [11C]
L-deprenyl-D2 in PET studies of the human brain we tested the hypothesis that the unique binding of
fenobam and
AZD9272 may represent specific binding to the
MAO-B. PET data previously acquired for subjects examined using [11C]
AZD9272 or [11C]
L-deprenyl-D2 were re-evaluated to assess the correlations between radioligand binding parameters in human brain. In addition, the pharmacology of
AZD9272 binding sites was characterized using competition binding studies carried out in vivo in non-human primates (NHPs) and in vitro using autoradiography in selected human brain regions. The regional binding of [11C]
AZD9272 in human brain was closely correlated with that of [11C]
L-deprenyl-D2. In PET studies of NHP brain administration of the
MAO-B ligand L-deprenyl inhibited binding of radiolabeled
AZD9272 and administration of
fenobam inhibited binding of [11C]
L-deprenyl-D2. Binding of radiolabeled
AZD9272 in vitro was potently inhibited by
fenobam or
MAO-B compounds, and [11C]
L-deprenyl-D2 binding was inhibited by
fenobam or
AZD9272. The findings are consistent with the hypothesis that both
fenobam and
AZD9272 bind to the
MAO-B, which may be of relevance for understanding the mechanism of the
psychosis-like adverse events reported for these compounds. Such understanding may serve as a lead to generate new models for the pathophysiology of
psychosis.