Determination of the monoamine oxidase B inhibitor Ro 19-6327 in plasma by high-performance liquid chromatography using precolumn derivatization with fluorescamine and fluorescence detection

In vivo properties of N-(2-aminoethyl)-5-halogeno-2-pyridinecarboxamide 18F- and 123I-labelled reversible inhibitors of monoamine oxidase B

The reversible and highly selective monoamine oxidase B (MAO-B) inhibitor Ro 19-6327, a picolinic acid derivative, was selected for the development of new radiopharmaceuticals, whereby in place of Cl either 123I or 18F was introduced. The respective labelling procedures have been described earlier. In this study, some metabolic properties were investigated. Blood and urine samples were analysed, and halogenated picolinylglycine, a more hydrophilic compound, was identified as the main metabolite. This shows that the amine is oxidised to the respective carboxylate, but the intermediate imine or aldehyde that was proposed earlier could not be detected. First experiments with single photon emission tomography and positron emission tomography (PET) showed that the iodo compound can be used to investigate MAO-B in vivo while the fluoro compound is accumulated in the brain to such a low degree that no PET studies can be performed. We conclude that the main reason for the poor uptake of the fluoro compound is its lower lipophilicity as compared to the iodo compound and, to a lesser degree, its metabolism, which is similar for both compounds.

Determination of Ro 19-6327 (Lazabemide) in human plasma and urine by gas chromatography-negative chemical ionization mass spectrometry

A sensitive and specific analytical method was developed for determination of Ro 19-6327 (Lazabemide) in human plasma and urine samples to provide pharmacokinetic data from clinical trials. The new method employs a simple liquid-liquid extraction to isolate the drug from biological samples. The extract is reacted to form the trifluoroacetyl derivative of Ro 19-6327 and then analyzed by gas chromatography-negative chemical ionization mass spectrometry (GC-NCIMS). The lower limit of quantitation of the assay is 0.05 ng/ml for plasma and 5.0 ng/ml for urine, based on 1-ml aliquots. No interferences from anticoagulants, collection devices, or endogenous constituents of plasma and urine were observed. Recovery (64.3%), inter-assay precision (< 8% R.S.D.), and accuracy (> 85%) of the method were considered acceptable. The assay proved reliable enough to be automated for unattended sample analysis of approximately 50 samples daily. In an additional series of tests, Ro 19-6327 was shown to be stable under conditions that might be encountered during the analysis of samples from clinical trials.

[123I/125I]-Ro 43-0463, a site specific tracer for MAO-B mapping with autoradiography as well as with SPET

The compound Ro 43-0463 [N-(2-aminoethyl)-5-iodo-2-pyridinecarboxamide)] is the iodo-analogue of Lazabemid (Ro 19-6327). The latter is well known to bind site specifically with KD = 15.7 nmol/l to the enzyme monoamine oxidase type B (MAO-B) which it inhibits (IC50 = 2 *10(-8) mol/l) time dependently and reversibly. Ro 43-0463 having an IC50 of 3*10(-8) mol/l was labelled with 123I as well as with 125I to get a tool for measuring the MAO-B distribution autoradiographically and in the human brain with SPET (Single Photon Emission Tomography). The halogen exchange reaction of the bromo-precursor (Ro 18-4950) in the presence of CuSO4 and ascorbic acid was applied. The reaction conditions were optimized, varying the parameters time (30 to 105 min), precursor concentration (1 to 3.5 mg) and temperature (130 to 200 degrees C). The purification of [123I/125I]-Ro 43-0463 was performed on HPLC (Lichrosorb RP-18, 5 mu m, 250 x 8 mm) with 0.36 M H3PO4/EtOH 97/3 and 0.01 M (NH4)2HPO4 (1.5 ml/min) as eluent. The labelling yield was found to range between 60 and 70%. The activity concentration ranged between 18.5 and 37 MBq/ml. Autoradiography with rat brain slices was performed using 5 nM [125I]-Ro 43-0463 in TRIS-buffer (pH 7.4) for 90 min at 20 degrees C. It showed a radioactivity pattern corresponding to the known distribution of MAO-B in the rat brain and proved, after displacement with L-Deprenyl (1 mu M), the high specificity of binding Ro 43-0463.

Quantification of 3'-amino-3'-deoxythymidine, a toxic catabolite of 3'-azido-3'-deoxythymidine (zidovudine) in human plasma by high-performance liquid chromatography using precolumn derivatization with fluorescamine and fluorescence detection

A specific and sensitive high-performance liquid chromatographic (HPLC) assay with precolumn derivatization and fluorescence detection was developed for the determination of 3'-amino-3'-deoxythymidine (AMT), a recently characterized toxic catabolite of 3'-azido-3'-deoxythymidine (zidovudine, AZT). After extraction with tert.-butyl methyl ether-1-butanol (6:4, v/v) and back-extraction into basified aqueous phase, the solution was neutralized with phosphate buffer and the compound derivatized with fluorescamine. Fluorescamine-labeled AMT was chromatographed on a reversed-phase C18 column using a mixture of phosphate buffer-methanol-acetonitrile (47:48:5, v/v/v) as mobile phase and fluorescence detection (excitation wavelength 265 nm, emission wavelength 475 nm). The limit of quantification was 3 ng/ml using a 200-microliters plasma sample. The recovery of the extraction procedure averaged at 94.4% in the range of 3-200 ng/ml. The HPLC analysis time required per sample was 16 min. Replicate analyses of quality control samples (5-80 ng/ml) gave satisfactory intra- and inter-assay precision (coefficient of variation varied from 1.9 to 6.7%) and accuracy.