Simultaneous determination of tandospirone and its active metabolite, 1-[2-pyrimidyl]-piperazine in rat plasma by LC-MS/MS and its application to a pharmacokinetic study.

A rapid, sensitive and selective liquid chromatography-tandem mass spectrometry method for the detection of tandospirone (TDS) and its active metabolite 1-[2-pyrimidyl]-piperazine (1-PP) in Sprague-Dawley rat plasma is described. It was employed in a pharmacokinetic study. These analytes and the internal standards were extracted from plasma using protein precipitation with acetonitrile, then separated on a CAPCELL PAK ADME C18 column using a mobile phase of acetonitrile and 5 mm ammonium formate acidified with formic acid (0.1%, v/v) at a total flow rate of 0.4 mL/min. The detection was performed with a tandem mass spectrometer equipped with an electrospray ionization source. The method was validated to quantify the concentration ranges of 1.000-500.0 ng/mL for TDS and 10.00-500.0 ng/mL for 1-PP. Total time for each chromatograph was 3.0 min. The intra-day precision was between 1.42 and 6.69% and the accuracy ranged from 95.74 to 110.18% for all analytes. Inter-day precision and accuracy ranged from 2.47 to 6.02% and from 98.37 to 105.62%, respectively. The lower limits of quantification were 1.000 ng/mL for TDS and 10.00 ng/mL for 1-PP. This method provided a fast, sensitive and selective analytical tool for quantification of tandospirone and its metabolite 1-PP in plasma necessary for the pharmacokinetic investigation.

Quantification of peptides using N-terminal isotope coding and C-terminal derivatization for sensitive analysis by micro liquid chromatography-tandem mass spectrometry.

Stable isotope-coding coupled with mass spectrometry is a popular method for quantitative proteomics and peptide quantification. However, the efficiency of the derivatization reaction at a particular functional group, especially in complex structures, can affect accuracy. Here, we present a dual functional-group derivatization of bioactive peptides followed by micro liquid chromatography-tandem mass spectrometry (LC-MS/MS). By separating the sensitivity-enhancement and isotope-coding derivatization reactions, suitable chemistries can be chosen. The peptide amino groups were reductively alkylated with acetaldehyde or acetaldehyde-d4 to afford N-alkylated products with different masses. This process is simple, quick and high-yield, and accurate comparative analysis can be achieved for the mass-differentiated peptides. Then, the carboxyl groups were derivatized with 1-(2-pyrimidinyl)piperazine to increase MS/MS sensitivity. Angiotensins I-IV, bradykinin and neurotensin were analyzed after online solid phase extraction by micro LC-MS/MS. In all instances, a greater than 17-fold increase in sensitivity was achieved, compared with the analyses of the underivatized peptides. Furthermore, the values obtained from the present method were in agreement with the result from isotope dilution quantification using isotopically labeled angiotensin I [Asp-Arg-(Val-d8 )-Tyr-Ile-His-Pro-(Phe-d8 )-His-Leu]. Copyright © 2016 John Wiley & Sons, Ltd.

The influences of aconitine, an active/toxic alkaloid from aconitum, on the oral pharmacokinetics of CYP3A probe drug buspirone in rats.

Aconitine (AC), an active/toxic alkaloid from Aconitum species, is commonly present in Traditional Chinese Medicine (TCM) prescriptions because of the great effectiveness of Aconitum for the treatment of rheumatoid arthritis, cardiovascular diseases, and tumors in clinic. Buspirone (BP) is a sensitive CYP3A probe drug that is administered through oral/intravenous routes as recommended by the U.S. Food and Drug Administration. This study aims to investigate the influences of AC (0.125 mg/kg, oral) on first-pass (intestinal and hepatic) CYP3A activity by using oral BP as the probe in rats. The pharmacokinetics of oral buspirone hydrochloride at different doses (12.5, 25, and 50 mg/kg) were conducted. The pharmacokinetics of oral BP in rats pretreated with single dose or multiple doses (7-day) of AC were investigated. The plasma concentrations of BP and its major metabolites [1-(2-pyrimidinyl)piperazine (1-PP) and 6'-hydroxybuspirone (6'-OH-BP)] were determined. The formation ratios of 1-PP and 6'-OH-BP from BP (AUC0-∞ of 1-PP/AUC0-∞ of BP and AUC0-∞ of 6'-OH-BP/AUC0-∞ of BP values) showed no alternation when the dose of BP changed. Single dose of AC decreased the AUC0-∞ of BP by 53% but increased the formation ratio of 6'-OH-BP by 74% (P<0.05). Multiple AC exposure increased the AUC0-∞ of BP by 110%, and the formation ratios of 1-PP and 6'-OH-BP from BP were increased by 229% and decreased by 95%, respectively (P<0.05). Conclusively, single/multiple AC exposure did not alter the first-pass CYP3A activity when using oral BP as probe in rats. Nevertheless, multiple AC exposure had markedly changed the production of BP metabolites.

[Effects of buspirone complex with glycyrrhizic acid on behavior of mice with anxious-depressive state].

We report here studies of the effects of subchronic administration of 5-HT1A receptor agonist buspirone and its novel complex with glycyrrhizic acid (GA) to C57BL/6J mice at the different stages of the anxious-depressive state formation, induced by conditions of social stress. The experiment of agents' administration during the conditions of stress (beginning with initial stage) showed that only complex had a protective effect revealed in prevention of the anxiety with the high level of mice communicativeness maintenance. At the stage when the anxious-depressive state is completely formed, buspirone and its complex with GA decreased mice motor activity however complex--less significantly. Here we discuss a possible mechanism of action of investigated agents on the background of changes in the sensitivity of 5-HT1A receptors, induced by the formation of the anxious-depressive state of mice with experience of social stress. Despite of different effects of agents depending on the stage of the anxious-depressive state development, novel buspirone complex with GA has some advantage over buspirone.

The exposure of highly toxic aconitine does not significantly impact the activity and expression of cytochrome P450 3A in rats determined by a novel ultra performance liquid chromatography-tandem mass spectrometric method of a specific probe buspirone.

Aconitum species are widely used to treat rheumatism, cardiovascular diseases, and tumors in China and other Asian countries. The herbs are always used with drugs such as paclitaxel. Aconitine (AC) is one of the main bioactive/high-toxic alkaloids of Aconitum roots. AC is metabolized by cytochrome P450 (CYP) 3A. However, whether AC inhibits/induces CYP3A, which causes drug-drug interaction (DDI) is unclear. Our study aims to explore the potent effects of AC, as a marker component of Aconitum, on CYP3A using the probe buspirone in rats. The effects of oral AC on pharmacokinetics of buspirone were evaluated. CYP3A activity and protein levels in rat liver microsomes pretreated with oral AC were also measured using in vitro buspirone metabolism and Western blot. Buspirone and its major metabolites 1-(2-pyrimidinyl)piperazine and 6'-hydroxybuspirone were determined using a newly validated UPLC-MS/MS method. Single dose and 7-day AC administration at 0.125mg/kg had no effect on CYP3A activity since no change in the formation of 1-(2-pyrimidinyl)piperazine and 6'-hydroxybuspirone. CYP3A activity and protein levels in liver microsomes were also not affected by 7-day AC pretreatment at 0.125mg/kg. Therefore, AC neither inhibits nor induces CYP3A in rats, indicating AC does not cause CYP3A-related DDI in the liver.

Development of oral extended release formulations of 6-hydroxybuspirone.

Reducing the maximum plasma concentration whilst maintaining the exposure was shown to ameliorate adverse events following the oral administration of 6-hydroxybuspirone. This observation, along with a desire to provide for once daily dosing of this compound, provided the basis for the development of an extended release formulation. Hydrophilic matrix tablets based on hydroxypropyl methylcellulose and containing citric acid to provide for an acid microenvironment were prepared and evaluated by in vitro drug release studies and in vivo pharmacokinetic and scintigraphic studies using samarium oxide (¹5³Sm) labelled dosage forms. The dosage forms were found to release the contained drug by a predominantly diffusion mechanism and the release rate was relatively independent of environmental pH. Following administration of the extended release formulations to volunteers, comparative pharmacokinetic data indicated that the extended release formulations provided for a reduction in the maximum plasma concentration of 64-70% relative to that provided by the same dose given as an oral solution, whilst maintaining exposure relative to the oral solution. By examination of absorption curves derived by Wagner-Nelson analysis of pharmacokinetic data it was noted that drug release in vivo correlated well with drug release observed in vitro and no marked change in rate of absorption was noted when dosage forms were located in and releasing drug in the colon. The robust control of drug release seen in vitro translated to a good in vivo performance.

Intravenous buspirone for the prevention of postoperative nausea and vomiting.

RATIONALE: Buspirone, a partial 5HT(1A) agonist and D2 and D3 antagonist, has shown promising antiemetic efficacy when given parenterally in animal models, but its efficacy for the prevention of postoperative nausea and vomiting (PONV) is unknown. OBJECTIVE: To study the efficacy and dose-responsiveness of intravenous buspirone for the prevention of PONV. METHODS: A randomised, double-blind, placebo-controlled study was performed in adults at moderate to high PONV risk undergoing surgery with a general anaesthetic. Patients were randomised to receive an intravenous dose of buspirone (0.3, 1.0, 2.0, 3.0 mg) or placebo at the end of surgery. The primary endpoint was the cumulative 24-h PONV incidence (i.e. any nausea and/or vomiting). Vomiting included retching. Nausea was defined as a score of ≥ 4 on an 11-point verbal rating scale running from zero (no nausea) to ten (the worst nausea imaginable). RESULTS: A total of 257 patients received the study drug and fulfilled the criteria for inclusion in the primary efficacy and safety analyses. With placebo, the mean 24-h PONV incidence was 49.0 % (90 % confidence interval [CI] 37.5-60.5 %). With buspirone, that incidence ranged from a mean of 40.8 % (29.3-52.4 %) in the 1 mg arm to 58.0 % (46.5-69.5 %) in the 0.3 mg arm (P > 0.05 for all comparisons). There was no difference between placebo and buspirone at any dose for any other efficacy endpoint, nor in the number or severity of adverse events or any other safety measures. CONCLUSION: We were unable to show that intravenous single-dose buspirone, at the tested dose-range, was effective at preventing PONV in surgical adult patients. The present study emphasises the difficulty in extrapolating from animal models of emesis to clinical efficacy in PONV.

Carboxy group derivatization for enhanced electron-transfer dissociation mass spectrometric analysis of phosphopeptides.

A novel strategy based on carboxy group derivatization is presented for specific characterization of phosphopeptides. By tagging the carboxy group with 1-(2-pyrimidyl) piperazine (PP), the ion charge states of phosphopeptides can be largely enhanced, showing great advantages for sequencing phosphorylated peptides with electron-transfer dissociation MS. Besides, after PP-derivatization, most non-specific bindings can be avoided by eliminating the interaction between the carboxy group and TiO(2), greatly improving the specificity of TiO(2)-based phosphopeptide enrichment strategy. Moreover, being tagged with a hydrophobic group, the retention time of phosphopeptides in RPLC can be prolonged, overcoming the difficulty of separating phosphopeptides in RPLC-based approach. Together with several other advantages, such as ease of handling, rapid reaction time, broad applicability and good reproducibility, this PP-derivatization method is promising for high-throughput phosphoproteome research.

The molecular interactions of buspirone analogues with the serotonin transporter.

A major problem with the selective serotonin reuptake inhibitors (SSRIs) is the delayed onset of action. A reason for that may be that the initial SSRI-induced increase in serotonin levels activates somatodendritic 5-HT(1A) autoreceptors, causing a decrease in serotonin release in major forebrain areas. It has been suggested that compounds combining inhibition of the serotonin transport protein with antagonistic effects on the 5-HT(1A) receptor will shorten the onset time. The anxiolytic drug buspirone is known as 5-HT(1A) partial agonist. In the present work, we are studying the inhibition of the serotonin transporter protein by a series of buspirone analogues by molecular modelling and by experimental affinity measurements. Models of the transporter protein were constructed using the crystal structure of the Escherichia coli major facilitator family transporter-LacY and the X-ray structure of the neurotransmitter symporter family (NSS) transporter-LeuT(Aa) as templates. The buspirone analogues were docked into both SERT models and the interactions with amino acids within the protein were analyzed. Two putative binding sites were identified on the LeuT(Aa) based model, one suggested to be a high-affinity site, and the other suggested to be a low-affinity binding site. Molecular dynamic simulations of the LacY based model in complex with ligands did not induce a helical architecture of the LacY based model into an arrangement more similar to that of the LeuT(Aa) based model.

Pharmacokinetics of 6-hydroxybuspirone and its enantiomers administered individually or following buspirone administration in humans.

The objective of this study was to assess the pharmacokinetics of 6-hydroxybuspirone (6OHB) when given orally via three forms: racemate (BMS-528215), S-enantiomer (BMS-442606) and R-enantiomer (BMS-442608), versus following the administration of buspirone. A double-blind, randomized, four-period, four-treatment, crossover study balanced for residual effects in healthy subjects was conducted (n=20). Subjects received single 10 mg doses of each compound in a randomized fashion with pharmacokinetics determined over a 24 h period. There was a 4-day washout between each dosing period. All three forms of 6OHB (racemate, S-enantiomer and R-enantiomer) were well tolerated. There was nterconversion between enantiomers. The dominant enantiomer was the S-enantiomer no matter which form of 6OHB was administered. All three forms of 6OHB produced approximately 2- to 3-fold greater exposure to total 6OHB than did buspirone. All three forms produced equal exposure to 1-(2-pyrimidinyl)-piperazine (1-PP) which was approximately 30% less than the 1-PP exposure derived from buspirone administration. All three forms of 6OHB produced approximately 3-fold higher 6OHB:1-PP ratios and approximately 2.5-fold higher total 6OHB exposures than did buspirone administration. All compounds were well tolerated. There seemed to be no advantage of one of the enantiomers of 6OHB over the racemate. Therefore, the racemate was chosen for further clinical development.

6-Hydroxybuspirone is a major active metabolite of buspirone: assessment of pharmacokinetics and 5-hydroxytryptamine1A receptor occupancy in rats.

The pharmacokinetics and in vivo potency of 6-hydroxybuspirone (6-OH-buspirone), a major metabolite of buspirone, were investigated. The plasma clearance (47.3 +/- 3.5 ml/min/kg), volume of distribution (2.6 +/- 0.3 l/kg), and half-life (1.2 +/- 0.2 h) of 6-OH-buspirone in rats were similar to those for buspirone. Bioavailability was higher for 6-OH-buspirone (19%) compared with that for buspirone (1.4%). After intravenous infusions to steady-state levels in plasma, 6-OH-buspirone and buspirone increased 5-hydroxytryptamine (HT)(1A) receptor occupancy in a concentration-dependent manner with EC(50) values of 1.0 +/- 0.3 and 0.38 +/- 0.06 microM in the dorsal raphe and 4.0 +/- 0.6 and 1.5 +/- 0.3 microM in the hippocampus, respectively. Both compounds appeared to be approximately 4-fold more potent in occupying presynaptic 5-HT(1A) receptors in the dorsal raphe than the postsynaptic receptors in the hippocampus. Oral dosing of buspirone in rats resulted in exposures (area under the concentration-time profile) of 6-OH-buspirone and 1-(2-pyrimidinyl)-piperazine (1-PP), another major metabolite of buspirone, that were approximately 12 (6-OH-buspirone)- and 49 (1-PP)-fold higher than the exposure of the parent compound. As a whole, these preclinical data suggest that 6-OH-buspirone probably contributes to the clinical efficacy of buspirone as an anxiolytic agent.

Pharmacokinetics of a newly identified active metabolite of buspirone after administration of buspirone over its therapeutic dose range.

The objective of this study was to assess the pharmacokinetics of a newly identified active metabolite of buspirone, 6-hydroxybuspirone (6OHB), over the therapeutic dose range of buspirone. A 26-day, open-label, nonrandomized, single-sequence, dose-escalation study in normal healthy volunteers was conducted (N = 13). Subjects received escalating doses of buspirone with each dose administered for 5 days starting at a dose of 5 mg twice daily and increasing up to 30 mg twice daily. Plasma concentrations of 6OHB were approximately 40-fold greater than those of buspirone. 6OHB was rapidly formed following buspirone administration, and exposure increased proportionally with buspirone dose. Further research regarding the safety and efficacy of 6OHB itself is warranted.

Pharmacokinetics of buspirone in autistic children.

Buspirone is used to treat generalized anxiety disorder in children and may be useful in developmental disorders in which brain serotonin synthesis is altered. Autistic children (13 boys, 7 girls) were given a single oral dose of 2.5 mg (2-3 years) or 5.0 mg (4-6 years). Blood was collected for 8 hours, and plasma was assayed for buspirone and its metabolite 1-pyrimidinylpiperazine (1-PP). The peak concentration of buspirone averaged 1141 +/- 748 pg/mL with a time to maximum concentration of 0.8 hours. Half-life was 1.6 +/- 0.3 hours. Peak concentrations of 1-PP were 4.5-fold higher than for buspirone. Girls had higher peak concentrations (1876 vs 746 pg/mL) for buspirone and a lower peak 1-PP/buspirone concentration ratio. These results suggest that buspirone is rapidly absorbed and eliminated in young children with extensive metabolism to 1-PP. Plasma concentrations with 2.5- to 5.0-mg doses were similar to those observed in older children receiving 7.5- to 15-mg doses.

Oral buspirone causes a shift in the dose-response curve between the elevated-plus maze and Vogel conflict tests in Long-Evans rats: relation of brain levels of buspirone and 1-PP to anxiolytic action.

Most studies concerning the effects of oral buspirone in the rat elevated plus-maze (EPM) test, spontaneous motor activity (SMA) test, and Vogel conflict (VC) test have used Sprague-Dawley or Wistar rats. Although it has been documented that the behavior of Long-Evans rats is more sensitive to detection of anxiolytics when compared to the aforementioned strains, the effects of oral buspirone have not been fully characterized in the Long-Evans strain in the EPM and VC tests. Thus, we studied the effects of orally administered buspirone (0.03-10.0 mg/kg) in the EPM, SMA, and VC (0.3-60.0 mg/kg) tests in Long-Evans rats. In a separate experiment, brain and plasma concentrations of buspirone and 1-(2-pyrimidinyl)-piperazine (1-PP) were determined after oral administration of buspirone (0.3 and 10 mg/kg) to relate the behavioral effects of buspirone with brain and plasma concentrations of buspirone and 1-PP. Our results showed that buspirone exhibited an inverted-U-shaped dose-response curve in both the EPM and the VC tests. In the EPM, buspirone produced anxiolytic activity in a low, narrow dose-range (0.03, 0.1, 0.3 mg/kg, p.o.) with maximum efficacy at 0.3 mg/kg, whereas in the VC test, significant anxiolytic activity was observed in a high, narrow dose-range (10, 30 mg/kg, p.o.) with maximum efficacy occurring at 10 mg/kg. In the SMA test, buspirone (10 mg/kg, p.o.) significantly decreased horizontal activity and vertical movements suggestive of sedation. Also, one hour following oral doses of buspirone (0.3 and 10 mg/kg), both buspirone and 1-PP concentrations were higher in brain when compared with those in plasma. Additionally, the concentrations of 1-PP were always higher in brain and in plasma compared with the concentrations of buspirone. Of particular interest is our finding of the shift in the dose-response curve between the EPM and VC tests. This shift in the dose-response curve is discussed in relation to brain levels of buspirone and 1-PP levels and their anxiolytic action.

Hybrid triple quadrupole-linear ion trap mass spectrometry in fragmentation mechanism studies: application to structure elucidation of buspirone and one of its metabolites.

The use of a hybrid triple quadrupole-linear ion trap (QqQ(LIT)) mass spectrometer system for a comprehensive study of fragmentation mechanisms is described. The anxiolytic drug, buspirone, was chosen as a model compound for this study. With the advent of a QqQ(LIT) instrument, both the traditional quadrupole and the new linear ion trap scans (LIT) could be performed in a single LC run. In the past, a sample had to be run on two different instruments, namely, a triple quadrupole instrument (QqQ) and a 3D ion trap (3D IT) to obtain similar information. With the new QqQ(LIT) technology, collision-induced dissociation (CID) occur in a quadrupole collision cell, q2, and fragment ions are trapped and analyzed in Q3 operated in LIT mode. In this work, high-sensitivity product ion spectra of buspirone were obtained from the one-stage 'Enhanced Product Ion' scan (EPI) with rich product ions and no low mass cut-off. Furthermore, detailed fragmentation pathways were elucidated by further dissociation of each of the fragment ions in the EPI spectrum using MS(3) mode in the same run. The MS(3) scan was performed by incorporating CID in q2, and trapping, cooling, isolation, and resonance-excitation in Q3 when operating in LIT mode. This approach allowed unambiguous assignment of all fragment ions quickly with fewer experiments and easier interpretation than the previous approach. The overall sensitivity for obtaining complete fragment ion data was significantly improved for QqQ(LIT) as compared with that of QqQ and 3D IT mass spectrometers. This is beneficial for structure determination of unknown trace components. The method allowed structure determination of metabolites of buspirone in rat microsomes at 1 microM concentration, which was a 10-fold lower concentration than was needed for QqQ or 3D IT instruments. The QqQ(LIT) instrument provided a simple, rapid, sensitive and powerful approach for structure elucidation of trace components.

Inhibitory effects of the 5-HT(1A) receptor agonist buspirone on stress-induced hyperglycemia in mice: involvement of insulin and a buspirone metabolite, 1-(2-pyrimidinyl)piperazine (1-PP).

Effects of serotonergic anxiolytic buspirone on immobilization-induced hyperglycemia were studied in mice. Stress elicited hyperglycemia in mice. Pretreatment with buspirone significantly reduced immobilization-induced hyperglycemia. Buspirone increased serum insulin levels in both non- and stressed mice. The major metabolite of buspirone, 1-(2-pyrimidinyl)piperazine (1-PP) also increased and this further inhibited immobilization-induced hyperglycemia, since 1-PP increased serum insulin levels in both non-stressed and stressed mice, similar to the increases induced by buspirone. These results suggest that buspirone can reduce stress-induced hyperglycemia by facilitating insulin release. Moreover, 1-PP, a metabolite of buspirone may participate in the effects of buspirone. Since 1-PP is an antagonist of alpha(2) receptors, alpha(2) receptors may be related to effects of 1-PP.

1-(2-pyrimidinyl)-piperazine, a buspirone metabolite, modulates bladder function in the anesthetized rat.

AIMS: To examine the effects of 1-(2-pyrimidinyl)-piperazine (1-PP), a buspirone metabolite, on bladder function in vivo. METHODS: Micturition reflexes in the rat were evaluated in two models of bladder function; a constant infusion model employing 0.5% acetic acid and an isovolumic model. RESULTS: In the constant infusion model, 1-PP (0.14-1.32 mg/kg) dose-dependently and significantly decreased the number of bladder contractions measured during a 30 min recording period, with little effect on the pressure developed during each contraction. 1-PP is an alpha2-adrenergic receptor antagonist. The alpha2 antagonists BRL44408 (alpha2A vs. alpha2B selective; 0.3 and 1 mg/kg), imiloxan (alpha(2B) vs. alpha2A selective; 1 mg/kg), and yohimbine (non-subtype selective; 1 mg/kg; but not 0.3 mg/kg) also significantly reduced the number of contractions. Vehicle was without effect. In the isovolumic model, 1-PP (0.03-1.0 mg/kg) produced a dose-dependent and significant reduction in the number of bladder contractions recorded during a 15 min assessment period, with the maximum effect observed at 0.3 mg/kg. 1-PP had little effect on blood pressure; the only effect was observed at the highest dose (1 mg/kg) where it produced a transient 17% decrease in pressure. Cromakalim and tolterodine served as comparitors in all studies. CONCLUSIONS: 1-PP decreased the number of bladder contractions evoked by the micturition reflex at doses that had little effect on either the pressure developed during each bladd er contraction or on blood pressure. The effects of 1-PP are likely mediated primarily by alpha2 receptor antagonism.

Prediction of the affinity of the newly synthesised azapirone derivatives for 5-HT1A receptors based on artificial neural network analysis of chromatographic retention data and calculation chemistry parameters.

The performance of artificial neural network (ANN) in predicting the affinity of a series of 65 new azapirone derivatives for rat brain serotonin 5-HT1A receptors based on high-performance liquid chromatography (HPLC) retention data and on non-empirical structural parameters of the compounds' was studied. Affinity of the agents for rat brain 5-HT1A receptors were assessed in vitro and expressed as inhibitor constant values, Ki. The retention parameters determined in 14 HPLC systems along with compounds' structural descriptors from calculation chemistry were considered in ANN analysis. Supervised method of ANN learning with back-propagation strategy was used in ANN calculations. Two models of ANN of similar architecture were designed: the first one for the data based on chromatographic retention data and the second based on structural parameters of the agents. Each ANN model was trained with the data of training set. It was next used to classify the agents from the testing set into two groups: active (Ki < 50 nM) and inactive compounds (Ki > 50 nM). A high prediction performance of both ANN models considered as regards the affinity of new azapirone derivatives for the serotonin 5-HT1A receptors was demonstrated. However, the percent of correctly classified compounds was higher in the case of the ANN processing of the non-empirical structural descriptors of azapirone derivatives. Since the ANN analysis of the retention data and of the structural parameters originating from calculation chemistry allows to segregate drug candidates according to their pharmacological properties that, in consequence, may be of help to limit the number of biological assays in the search for new drugs.

Intrinsic activity and comparative molecular dynamics of buspirone analogues at the 5-HT(1A) receptors.

In CNS, the 5-hydroxytryptamine(1A) (5-HT(1A)) receptors exist in two different populations with different behavioural and physiological effects: (1) somatodendritic autoreceptors located pre-synaptically of 5-HT containing neurons and (2) receptors located post-synaptic to 5-HT containing neurons. Clinical studies have shown that 5-HT(1A) partial agonists have anxiolytic properties, while antagonists of pre-synaptical autoreceptors shorten the onset time of selective serotonin reuptake inhibitors (SSRIs). In the present study, the pre- and post-synaptic activity of structural analogues of buspirone was evaluated in animal models. A three dimensional model of the 5-HT(1A) receptor was used to study their interaction modes and helical displacements upon receptor binding. The predicted receptor-ligand interactions indicated similarities in the receptor binding modes for all buspirone analogues, and no clear relationship between receptor contact residues and activity at pre- and post-synaptic receptors. Comparative molecular dynamics (MD) simulations for 650ps indicated that pre-synaptic antagonistic behaviour is connected to large displacements of transmembrane helix (TMH) 7 upon binding, while pre-synaptic agonistic behaviour is connected to large displacements of TMH2 and small displacements of TMH7. Post-synaptic partial agonist behaviour is connected to large displacements of TMH4 and TMH5 upon binding, while post-synaptic antagonists only slightly displace these helices.

New imide 5-HT1A receptor ligands - modification of terminal fragment geometry.

Two sets of new o-methoxyphenylpiperazine (MPP; series a) and 1,2,3,4-tetrahydroisoquinoline (THIQ; series b) derivatives, containing various imide moieties derived from NAN190, were synthesized and evaluated in vitro for their ability to bind to the serotonin 5-HT(1A) and 5-HT(2A) receptors. All new derivatives from series a demonstrated high 5-HT(1A) affinities, whereas THIQ analogues were much less active. With respect to 5-HT(2A) receptors, three MPP derivatives presented moderate activity but the rest of the investigated compounds were practically inactive. The influence of changes in terminus geometry on 5-HT(1A) receptor affinity was analyzed in regard to model compounds NAN190and MM199.