A highly reproducible method for the measurement of [6‐O‐methyl‐11C]diprenorphine and its radio‐metabolites based on solid‐phase extraction and radio‐high‐pressure liquid chromatography

Described here is a method for the measurement of the radio-metabolites of the positron emission tomography radiotracer [6-O-methyl-11C]diprenorphine ([11C]diprenorphine) using in-line solid-phase extraction (SPE) combined with radio-high-pressure liquid chromatography analysis. We believe that this method offers a reliable and reproducible approach to [11C]diprenorphine metabolite analysis. In addition, different SPE stationary phases are assessed for their efficiency for loading, retention and elution of the parent molecule and its metabolites. Having assessed C4, phenyl and C18 stationary phase, we concluded that a C18 SPE was optimal for our method. Finally, in silico predictions of diprenorphine metabolism were compared with in vivo metabolism of [11C]diprenorphine induced by hepatic microsomal digestion and analysed by matrix-assisted laser desorption/ionisation mass spectrometry. It was found that there was a high degree of agreement between the two methods and in particular the formation of the diprenorphine-3-glucuronide metabolite.