Radiosynthesis of no-carrier-added 75,77Br-brombenperidol

Radiosynthesis of (N-[11C]methyl)benperidol for PET investigation of D2 receptor binding

A procedure for the reliable production of the novel PET D2 receptor ligand (N-[11C]methyl)benperidol ([11C]NMB) is described. The method is based on N-methylation of benperidol using [11C]methyl iodide from the PETtrace MeI MicroLab, with product purification via normal-phase HPLC. Batch yields of 2.5±0.9 GBq (68±25 mCi) of [11C]NMB are routinely (n=16) obtained, with a radiochemical purity >98% and an average specific activity of over 40.7 TBq (1100 Ci)/mmol. The overall radiosynthesis, purification, and pre-release quality control testing is accomplished within 50 minutes. The procedure described herein produces a radiopharmaceutical product that is suitable for D2 receptor studies using PET or microPET imaging.

PET radioligands for dopamine receptors and re-uptake sites: chemistry and biochemistry

This report, based on the past experience of European centres, offers practical guidance on the chemistry and biochemistry of PET radioligands used for the in vivo imaging of dopamine receptors and re-uptake sites. It mainly summarizes methods for the preparation of D1 and D2 receptor ligands labelled with positron-emitting radioisotopes. Some of these ligands (11C-labelled SCH23390, raclopride and nomifensine, 18F-labelled butyrophenones, [76Br]bromolisuride), which have been found useful in PET clinical investigations, have been emphasized. This report is intended as an introduction and guideline for new PET-groups who want to start research in the dopaminergic neurotransmission imaging field.

Bromination, no-carrier-added radiobromination and simultaneously-occurring chlorination by chloramine T

Factors regulating initial rates of bromination, no-carrier-added radiobromination and simultaneously-occurring chlorination by chloramine T were studied using a neuroleptic drug spiperone as the substrate. Besides the factors such as initial concentrations of chloramine T, substrate and bromide ions, upon which the rates were dependent in first, second or zero-order, the water-acetic acid composition or the hydrogen ion concentration of the solutions, where the reactions took place, was found to play a key role. By controlling these factors, optimal radiobromination conditions, where radiobromination proceeds effectively whilst simultaneously-occurring chlorination is kept from proceeding at a high rate, thus resulting in radiobrominated radiopharmaceuticals of high specific activity (10 Ci/mumol) and high radiochemical and chemical purity, could be fulfilled.

Psychosis and positron tomography

The new technology of positron emission tomography (PET) offers hope in developing objective biological indices and correlates of various psychotic states, including schizophrenia. PET is of the order of a million to a billion times more sensitive than MRI (magnetic resonance imaging) and is now successfully measuring the densities of various brain neurotransmitter receptors in health and disease. PET data in schizophrenia patients confirm that delusions and hallucinations are controlled by neuroleptics when the D2 dopamine receptors are specifically blocked. D1 receptors are not involved. The elevation of D2 receptors as a possible basis for psychotic symptoms needs additional investigation because of technical difficulties which need to be resolved. The rapid development of PET indicates its promise for differential diagnosis as well as its value in treating the psychoses.

Evaluation of 75Br-labelled butyrophenone neuroleptics for imaging cerebral dopaminergic receptor areas using positron emission tomography

A comparative evaluation of three radiobrominated butyrophenone neuroleptics--bromospiperone (BSP), brombenperidol (BBP), and bromperidol (BP)--was made to assess the applicability of these compounds as radiopharmaceuticals labelled with the positron emitter 75Br (T1/2 = 1.6 h) for mapping cerebral dopaminergic receptor areas non-invasively with positron emission tomography (PET). BSP, BBP, and BP were prepared in high specific activities with high radiochemical yields, using electrophilic reactions with no-carrier-added 77Br- or 75Br-. Screening tests in rats using 77Br-labelled compounds indicated D2-specific localization for 77Br-BSP and 77Br-BBP, whereas PET experiments in baboons showed that only 75Br-BSP preferentially localized in cerebral tissues rich in dopaminergic receptors. The data suggest an inverse relationship between cerebral uptake and receptor-specific localization, which was attributed to a complicated interplay between the D2 receptor binding affinity, lipophilicity, % ionization and molecular weight of the radioligand, and the binding capacity of the cerebral tissues. 75Br-BSP gave a striatum-to-cerebellum ratio of 3 in baboon brain 5 h post-injection, which allowed visualization of dopaminergic-receptor-containing areas of the living brain using PET.