Study the effect of a pseudo-carrier on pharmacokinetics of 9-fluoropropyl-(+)-dihydrotetrabenazine in rat plasma by ultra-performance liquid chromatography-tandem mass spectrometry

Rapid screening of nine unradiolabeled candidate compounds as PET brain imaging agents using cassette-wave microdosing and LC-MS/MS

The R&D of PET imaging agents is a complex system engineering, simplifying screening steps and increasing screening efficiency have become popular issues. The purpose of this study is to develop a new screening procedure using cassette-wave microdosing and LC-MS/MS to enhance the screening throughput of unradiolabeled candidate compounds as PET imaging agents. Nine compounds were divided into 3 sets and made into 3 cassettes. Fifteen rats were randomly divided into 3 groups, and every animal received three intravenous bolus injections at three different time points; the doses were at microdose levels. This dosing approach takes advantage of temporal and spatial differences and is likened to an input wave; therefore, this approach was named cassette-wave microdosing. The samples of different brain regions such as the hypothalamus, striatum, hippocampus, cortex, cerebellum and the remainder of the brain were detected by LC-MS/MS analysis. The research potential of the compounds as PET imaging agents is evaluated in terms of brain biodistribution data. The screening method is rapid, highly efficient, reliable and reduces animal usage. Additionally, it can shorten the evaluation process of radiopharmaceuticals and enhance the screening throughput of PET radiopharmaceuticals without the use of radioactive agents.

Developing a cassette microdosing approach to enhance the throughput of PET imaging agent screening

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.

Brain uptake of a non-radioactive pseudo-carrier and its effect on the biodistribution of [(18)F]AV-133 in mouse brain

INTRODUCTION

9-[(18)F]Fluoropropyl-(+)-dihydrotetrabenazine ([(18)F]AV-133) is a new PET imaging agent targeting vesicular monoamine transporter type II (VMAT2). To shorten the preparation of [(18)F]AV-133 and to make it more widely available, a simple and rapid purification method using solid-phase extraction (SPE) instead of high-pressure liquid chromatography (HPLC) was developed. The SPE method produced doses containing the non-radioactive pseudo-carrier 9-hydroxypropyl-(+)-dihydrotetrabenazine (AV-149). The objectives of this study were to evaluate the brain uptake of AV-149 by UPLC-MS/MS and its effect on the biodistribution of [(18)F]AV-133 in the brains of mice.

METHODS

The mice were injected with a bolus including [(18)F]AV-133 and different doses of AV-149. Brain tissue and blood samples were harvested. The effect of different amounts of AV-149 on [(18)F]AV-133 was evaluated by quantifying the brain distribution of radiolabelled tracer [(18)F]AV-133. The concentrations of AV-149 in the brain and plasma were analyzed using a UPLC-MS/MS method.

RESULTS

The concentrations of AV-149 in the brain and plasma exhibited a good linear relationship with the doses. The receptor occupancy curve was fit, and the calculated ED50 value was 8.165mg/kg. The brain biodistribution and regional selectivity of [(18)F]AV-133 had no obvious differences at AV-149 doses lower than 0.1mg/kg. With increasing doses of AV-149, the brain biodistribution of [(18)F]AV-133 changed significantly.

CONCLUSION

The results are important to further support that the improved radiolabelling procedure of [(18)F]AV-133 using an SPE method may be suitable for routine clinical application.

Mapping the target localization and biodistribution of non-radiolabeled VMAT2 ligands in rat brain

Imaging targeting vesicular monoamine transporter (VMAT2) alterations is a sensitive tool for early diagnosis of Parkinson's disease. Our group has reported several novel 2-amino-DTBZ derivatives as potential VMAT2 imaging agents. The objective of this paper is to develop a non-radiolabeled methodology to screen the candidate compounds for accelerating the drug discovery process. 9-[(18)F]fluoropropyl-(+)-dihydrotetrabenazine ([(18)F]AV-133) is a PET imaging agent targeting VMAT2 binding sites in the brain. Nonradioactive AV-133 was injected (iv) into rats, at the end of the allotted time, the animals were killed and six regions of brain and plasma from each animal were processed for quantitative measurement of AV-133 by LC-MS/MS. These data were converted to the percentage injected dose per gram tissue weight (%ID/g tissue) and the brain target tissue to background ratios to allow direct comparison with data obtained by gamma counting of the injected radioactive [(18)F]AV-133. The %ID/g and the brain target tissue to background ratios calculated using the LC-MS/MS method were highly correlated to the values obtained by standard radioactivity measurements of [(18)F]AV-133. The pattern of AV-133 in rat brain was consistent with the known distribution of VMAT2. The concordance indicated that high-sensitivity LC-MS/MS is an indispensable tool in evaluating the quantity of administered chemical in tissue as part of the development of new molecular imaging probes. Furthermore, several novel 2-amino-DTBZ derivatives were detected using this methodology, and their biodistribution data in rat brain were obtained. The information about target engagements of candidates was provided.

Preliminary evaluation of the interactions of Panax ginseng and Salvia miltiorrhiza Bunge with 5-fluorouracil on pharmacokinetics in rats and pharmacodynamics in human cells

An increasing number of cancer patients are using herbs in combination with conventional chemotherapeutic treatment. It is therefore important to study the potential consequences of the interactions between herbs and anticancer drugs. The effects of extracts from Panax ginseng (PGS) and Salvia miltiorrhiza Bunge (SMB) on the pharmacokinetics of 5-fluorouracil (5-FU) were performed in vivo and detected by high performance liquid chromatography (HPLC), while, an ATP assay was used to study the pharmacodynamic interactions in vitro. The results of the pharmacokinetic experiments showed a significant increase in the elimination half-life (t1/2(k e )) of 5-FU in the PGS-pretreated group and in the area under the curve (AUC) in the SMB-pretreated group compared with the control group. However, after SMB pretreatment, weight loss was observed in rats. The results of pharmacodynamic experiments showed that neither PGS nor SMB, when used alone, directly inhibited cancer cell growth at 0.1-100 μg/ml. Moreover, PGS had a synergistic cytotoxic effect with 5-FU on human gastric cancer cells but not on normal gastric cells. The results imply that when combined with 5-FU, PGS may be a better candidate for further study. This study might provide insights for the selection of herbal-chemotherapy agent interactions.

Dose-response relationships of FMISO between trace dose and various macro-doses in rat by ultra-performance liquid chromatography with mass spectrometry and radioactivity analysis

Screening the pharmacokinetics of candidates using liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) may be efficacious and safe for the research and development of new PET imaging agents. However, the PET imaging agent is administered as trace dose and the sensitivity of LC-MS/MS is often insufficient. If the dose was increased to be quantifiable, it should be necessary to prove whether the pharmacokinetics between trace and macro-doses is consistent or not. In this paper, fluoromisonidazole (FMISO), a tumor PET imaging agent, was chosen to evaluate the dose-response pharmacokinetics by administering various single intravenous doses (0.1, 0.4, 1.6 and 6.4 mg/kg) in male Sprague-Dawley rats. The plasma concentration of FMISO was determined by an ultra-performance liquid chromatography-tandem mass spectrometric (UPLC-MS/MS) method, and the blood radioactivity of [(18)F]FMISO was detected by a gamma counter. By calculating and comparing the pharmacokinetic parameters, the total area under the plasma concentration-time curve from time zero to infinity (AUC(0-∞)) and peak plasma concentration (C(max)) values increased with the selected FMISO doses, and showing linear dose-dependent. On the other hand, some parameters related to time, such as the elimination half-lives (t(1/2)) and elimination rate constant (K(e)) were dose-independent, and there is no significant deference between trace dose and various macro-doses. The data should be useful to evaluate the novel 2-nitroimidazole derivatives as potential PET tumor imaging agents.

Imaging of VMAT2 binding sites in the brain by (18)F-AV-133: the effect of a pseudo-carrier

OBJECTIVES

Recently, 9-[(18)F]fluoropropyl-(+)-dihydrotetrabenazine ((18)F-AV-133) was reported as a new vesicular monoamine transporter (VMAT2) imaging agent for diagnosis of Parkinson's disease (PD). To shorten the preparation of (18)F-AV-133 and to make it more widely available, we evaluated a simple, rapid purification with a solid-phase extraction method (SPE) using an Oasis HLB cartridge instead of high pressure liquid chromatography (HPLC). The SPE method produced doses containing a pseudo-carrier, 9-hydroxypropyl-(+)-dihydrotetrabenazine (AV-149).

METHODS

To test the possible side effects of this pseudo-carrier, comparative dynamic PET scans of the brains of normal monkeys (2 each) and uni-laterally 6-OH-dopamine-lesioned PD monkeys (2 each) were performed using (18)F-AV-133 doses prepared by either SPE (containing pseudo-carrier) or HPLC (containing no pseudo-carrier). Autoradiographs of post mortem monkey brain sections were evaluated to confirm the relative (18)F-AV-133 uptake in the PD monkey brains and the effects of the pseudo-carrier on VMAT2 binding.

RESULTS

The radiochemical purity of the (18)F-AV-133, whether prepared by SPE or by HPLC, was excellent (>99%). PET scans of normal and PD monkey brains showed an expected reduction of VMAT2 in the lesioned areas of the striatum. It was not affected by the presence of the pseudo-carrier, AV-149 (maximally 250 μg/dose). The reduced uptake in the striatum of the lesioned monkey brains was confirmed by autoradiography. Ex vivo inhibition studies of (18)F-AV-133 binding in rat brains, conducted with increasing amounts of AV-149, suggested that at the highest concentration (3.5mg/kg) the VMAT2 binding in the striatum was only moderately blocked (20% reduction).

CONCLUSIONS

The pseudo-carrier, AV-149, did not affect the (18)F-AV-133/PET imaging of VMAT2 binding sites in normal or uni-laterally lesioned monkey brains. The new streamlined SPE purification method will enable (18)F-AV-133 to be widely available for routine clinical application in determining changes in monoamine neurons for patient with movement disorders or other psychiatric illnesses.

Determination of the penetration of 9-fluoropropyl-(+)-dihydrotetrabenazine across the blood-brain barrier in rats by microdialysis combined with liquid chromatography-tandem mass spectrometry

To evaluate the penetration of the blood-brain barrier by 9-fluoropropyl-(+)-dihydrotetrabenazine (AV-133), microdialysis probes were implanted simultaneously into rat blood and brain, and a liquid chromatography-tandem mass spectrometric method was developed and validated to monitor the AV-133 concentration in the microdialysates. The chromatographic separation was performed on an XTerra C(18) column (150 mm × 2.1 mm i.d., 5 μm particles) with gradient elution. The mass spectrometer was operated in positive mode using electrospray ionization. The analytes were measured using the multiple-reaction-monitoring mode. The calibration curves were linear over the range of 5.00-1000 ng/mL AV-133, with a coefficient of determination >0.995. The accuracies ranged from 99.5% to 105.0% and the precisions were <10% for AV-133. This method was used to determine the concentrations of AV-133 and its pharmacokinetics in the brains and blood of rats. The blood and brain concentration-time profiles for AV-133 were obtained, and the blood-brain barrier penetration was evaluated.