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Cassette dosing is also known as N-in-One dosing: several compounds are simultaneously administrated to a single animal and then the samples are rapidly detected by LC-MS/MS. This approach is a successful strategy to enhance the efficiency of drug discovery and reduce animal usage. However, no report on the utility of the cassette approach in radiotracer discovery has appeared in the literature. This study designed a cassette microdose with LC-MS/MS method to enhance the throughput for screening radiopharmaceutical biodistribution in the rat brain directly. Three unradiolabeled compounds (FPBM FPBM2 and AV-133) were chosen as model drugs administrated intravenously to the rats as a cassette as opposed to discrete study. The rat brain biodistribution data, target localization, the differential uptake ratio (%ID/g) and the brain tissue-specific binding ratio were obtained by the LC-MS/MS analysis. These data matched very well with the values obtained by the standard radioactivity measurements. Moreover, no significant differences between discrete dosing and cassette dosing were observed. By circumventing the need for radiolabeled molecules, this method may be high-throughput and safe for the research and development of new PET imaging agents. The combination of cassette microdosing and LC-MS/MS would be a medium throughput screening tool at an early stage in the discovery/development process of PET imaging agents., (Copyright © 2018 Elsevier B.V. All rights reserved.)

During solution formulation study of tetrabenazine (TBZ), a dopamine depleting agent, used in chorea associated with Huntington's disease and symptomatic treatment of hyperkinetic movement disorder it was observed a strong discoloration upon storage. We investigated this physico-chemical behavior by implementing forced degradation studies. It was observed yellowing only under Suntest(®) light exposure of TBZ solution. LC-MS (liquid chromatography coupled to mass spectrometer detection) analysis of light exposed TBZ samples allowed us to propose 1,11b-dedihydrotetrabenazine (DTBZ) and 1,3,4,11b-detetrahydrotetrabenazine (TTBZ) as the main TBZ impurities. Synthesis and complete structural determination of DTBZ and TTBZ·HCl by NMR and X-ray crystallography were carried out. They were identical in LC-MS with polar impurities found in light exposed TBZ samples. However, even if these TBZ degradation products are correlated with discoloration of TBZ solution there is no evidence they are directly responsible of it., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The two enantiomers of alpha-dihydrotetrabenazine were separated using chiral high performance liquid chromatography. The (+)-isomer showed high affinity in vitro (Ki = 0.97 +/- 0.48 nM) for the vesicular monoamine transporter (VMAT2) in rat brain striatum, whereas the (-)-isomer was inactive (Ki = 2.2 +/- 0.3 microM). Each isomer was then synthesized in carbon-11 labeled form, and regional brain biodistributions in mice determined after intravenous injection. Only (+)-alpha-dihydrotetrabenazine showed selective and specific accumulations in regions of dense monoaminergic innervation (e.g., striatum, hypothalamus), which could be blocked by coinjection of unlabeled tetrabenazine. Binding of alpha-dihydrotetrabenazine to the vesicular monoamine transporter is thus stereospecific.