Development of a Solid Supersaturable Micelle of Revaprazan for Improved Dissolution and Oral Bioavailability Using Box-Behnken Design

PURPOSE

To enhance the oral bioavailability of revaprazan (RVP), a novel solid, supersaturable micelle (SSuM) was developed.

METHODS

Surfactants and solid carriers were screened based on a solubility and a flowability test, respectively. Supersaturating agents, including Poloxamer 407 (P407), were screened. The SSuM was optimized using a Box-Behnken design with three independent variables, including Gelucire 44/14:Brij L4 (G44/BL4; X1) and the amounts of Florite PS-10 (FLO; X2) and Vivapur 105 (VP105; X3), and three response variables, ie, dissolution efficiency at 30 min (Y1), dissolution enhancing capacity (Y2), and Carr's index (Y3). The solid state property was evaluated, and a dissolution test was conducted. RVP, Revanex®, solid micelle (P407-free from the composition of SSuM), and SSuM were orally administrated to rats (RVP 20 mg equivalent/kg) for in vivo pharmacokinetic study.

RESULTS

G44 and BL4 showed great solubility, with a critical micelle concentration range of 119.2-333.0 μg/mL. P407 had an excellent supersaturating effect. FLO and VP105 were selected as solid carriers, with a critical solidifying ratio (g/mL) of 0.30 and 0.91, respectively. With optimized values of X1 (-0.41), X2 (0.31), and X3 (-0.78), RVP (200 mg)-containing SSuM consisting of G44 (253.8 mg), BL4 (106.2 mg), FLO (99.3 mg), VP105 (199.8 mg), and P407 (40 mg) was developed, resulting in Y1 (40.3%), Y2 (0.008), and Y3 (12.3%). RVP existed in an amorphous state in the optimized SSuM, and the SSuM formed a nanosized dispersion in the aqueous phase, with approximately 71.7% dissolution at 2 h. The optimized SSuM improved the relative bioavailability of RVP in rats by approximately 478%, 276%, and 161% compared to raw RVP, Revanex®, and solid micelle, respectively.

CONCLUSION

The optimized SSuM has great potential for the development of solidified formulations of poorly water-soluble drugs with improved oral absorption.

Applications of Higenamine in pharmacology and medicine

ETHNOPHARMACOLOGICAL RELEVANCE

Aconitum has been used as local and traditional medicines in many asian regions for the treatment of various diseases such as collapse, syncope, painful joints, oedema, bronchial asthma et al. Higenamine, a plant-based alkaloid, was initially isolated from Aconitum and identified as the active cardiotonic component of Aconitum. It has been tested as a candidate of pharmacologic stress agent in the detection of coronary artery diseases (CADs) and now researchers have just accomplished the phase III clinical studies successfully in China. Besides, a large number of studies have revealed the various pharmacological properties and potentially multi-spectral medical applications of higenamine. However, to date, no comprehensive review on higenamine has been published.

AIM OF THE REVIEW

This present paper aims to compile a comprehensive update regarding the biochemistry, pharmacokinetic features, pharmacological activities, clinical and potential clinical uses and toxicities on higenamine with the ultimate objective of providing a guide for future research on this drug.

MATERIALS AND METHODS

The selection of relevant data was made through a search using the keyword "higenamine" in "Web of science", "Pubmed", and "China Knowledge Resource Integrated (CNKI)". Information was also acquired from local classic herbal literature, government reports and conference papers.

RESULTS

In addition to Aconitum, higenamine also exists in many other plants including Tinospora crispa, Nandina domestica T_HUNBERG, Gnetum Parvifolium C.Y. Cheng, sarum Heterotropoides_,Nelumbo nucifera_,N.nucifera. The pharmacokinetic studies conducted in animals and humans showed that higenamine conformed to a two-compartment pharmacokinetic model. Studies over the last four decades on higenamine have revealed its various pharmacological properties such as positive inotropic and chronotropic effect, activating slow channel effect, vascular and tracheal relaxation effect, anti-thrombotic, anti-apoptotic and anti-oxidative effect, anti-inflammatory and immunomodulatory effect. This phytochemical constituent has shown its potential therapeutic effects for diseases like heart failure, disseminated intravascular coagulation (DIC), shock, arthritis, asthma, ischemia/reperfusion (I/R) injuries and erectile dysfunction.

CONCLUSIONS

Extensive basic and clinical studies on higenamine showed valuable therapeutic effects on different disorders. However, the underlying mechanisms of higenamine have not been established. Therefore, the safety, tolerability and efficacy of higenamine are as yet, not fully understood. Additionally, some of the studies were small sample-sized and unreliable. To sum up, there is a need for deeper investigation in the mechanisms of higenamine action, as well as well-designed preclinical and clinical trials studies to test the safety and clinical value of the drug.

Pilot PET Study to Assess the Functional Interplay Between ABCB1 and ABCG2 at the Human Blood-Brain Barrier

ABCB1 and ABCG2 work together at the blood-brain barrier (BBB) to limit brain distribution of dual ABCB1/ABCG2 substrates. In this pilot study we used positron emission tomography (PET) to assess brain distribution of two model ABCB1/ABCG2 substrates ([(11) C]elacridar and [(11) C]tariquidar) in healthy subjects without (c.421CC) or with (c.421CA) the ABCG2 single-nucleotide polymorphism (SNP) c.421C>A. Subjects underwent PET scans under conditions when ABCB1 and ABCG2 were functional and during ABCB1 inhibition with high-dose tariquidar. In contrast to the ABCB1-selective substrate (R)-[(11) C]verapamil, [(11) C]elacridar and [(11) C]tariquidar showed only moderate increases in brain distribution during ABCB1 inhibition. This provides evidence for a functional interplay between ABCB1 and ABCG2 at the human BBB and suggests that both ABCB1 and ABCG2 need to be inhibited to achieve substantial increases in brain distribution of dual ABCB1/ABCG2 substrates. During ABCB1 inhibition c.421CA subjects had significantly higher increases in [(11) C]tariquidar brain distribution than c.421CC subjects, pointing to impaired cerebral ABCG2 function.

Tumor Targeting and Pharmacokinetics of a Near-Infrared Fluorescent-Labeled δ-Opioid Receptor Antagonist Agent, Dmt-Tic-Cy5

Fluorescence molecular imaging can be employed for the development of novel cancer targeting agents. Herein, we investigated the pharmacokinetics (PK) and cellular uptake of Dmt-Tic-Cy5, a delta-opioid receptor (δOR) antagonist-fluorescent dye conjugate, as a tumor-targeting molecular imaging agent. δOR expression is observed normally in the CNS, and pathologically in some tumors, including lung liver and breast cancers. In vitro, in vivo, and ex vivo experiments were conducted to image and quantify the fluorescence signal associated with Dmt-Tic-Cy5 over time using in vitro and intravital fluorescence microscopy and small animal fluorescence imaging of tumor-bearing mice. We observed specific retention of Dmt-Tic-Cy5 in tumors with maximum uptake in δOR-expressing positive tumors at 3 h and observable persistence for >96 h; clearance from δOR nonexpressing negative tumors by 6 h; and systemic clearance from normal organs by 24 h. Live-cell and intravital fluorescence microscopy demonstrated that Dmt-Tic-Cy5 had sustained cell-surface binding lasting at least 24 h with gradual internalization over the initial 6 h following administration. Dmt-Tic-Cy5 is a δOR-targeted agent that exhibits long-lasting and specific signal in δOR-expressing tumors, is rapidly cleared from systemic circulation, and is not retained in non-δOR-expressing tissues. Hence, Dmt-Tic-Cy5 has potential as a fluorescent tumor imaging agent.

Design, synthesis, and pharmacological evaluation of JDTic analogs to examine the significance of the 3- and 4-methyl substituents

The design and discovery of JDTic as a potent and selective kappa opioid receptor antagonist used the N-substituted trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine pharmacophore as the lead structure. In order to determine if the 3-methyl or 4-methyl groups were necessary in JDTic and JDTic analogs for antagonistic activity, compounds 4a-c, and 4d-f which have either the 3-methyl or both the 3- and 4-methyl groups removed, respectively, from JDTic and analogs were synthesized and evaluated for their in vitro opioid receptor antagonist activities using a [(35)S]GTPγS binding assay. Other ADME properties were also assessed for selected compounds. These studies demonstrated that neither the 3-methyl or 3,4-dimethyl groups present in JDTic and analogs are required to produce potent and selective κ opioid receptor antagonists.

Phase I study of the safety and pharmacokinetics of trabectedin with docetaxel in patients with advanced malignancies

PURPOSE

Combination therapy with trabectedin and docetaxel was evaluated in patients with advanced malignancies.

METHODS

In this open-label phase 1 study, docetaxel (60 or 75 mg/m(2); 1-h intravenous infusion) was given on day 1 of a 21-day cycle in combination with escalating doses of trabectedin (0.4-1.3 mg/m(2) by 3-h intravenous infusion, 1 h after docetaxel) and prophylactic granulocyte colony-stimulating factor (G-CSF). Maximum tolerated dose (MTD) as primary objective and safety, plasma pharmacokinetics, and antitumor activity as secondary objectives were assessed.

RESULTS

Patients (N = 49) received a median of four cycles of treatment. MTD was 1.3 mg/m(2) trabectedin and 60 mg/m(2) docetaxel for patients with limited and 1.1 mg/m(2) trabectedin and 60 mg/m(2) docetaxel for patients with unlimited prior chemotherapy. Dose-limiting toxicities (during cycle 1) included elevated alanine aminotransferase (ALT) and fatigue in patients with limited prior chemotherapy and elevated ALT and febrile neutropenia in those with unlimited prior chemotherapy. The most common drug-related adverse events were nausea (65 %), fatigue (63 %), and neutropenia (53 %). One patient achieved a complete response. Thirty patients had stable disease, and 11 had stable disease for ≥6 months. Pharmacokinetic results for trabectedin plus docetaxel were similar to those previously reported for the single agents.

CONCLUSION

In patients with previously treated, advanced malignancies, the combination of therapeutic doses of trabectedin and docetaxel showed clinical activity and was tolerable with prophylactic G-CSF, with no evidence of clinically important drug interactions.

Therapeutic benefit in patients switching tolterodine to other novel antimuscarinic agents

OBJECTIVES

To explore in the daily clinical practice setting that antimuscarinic, Fesoterodine or Solifenacin, provides a greater clinical benefit after changing their prior Overactive Bladder (OAB) therapy with tolterodine extended-release (ER) to other novel antimuscarinic agents.

MATERIAL AND METHODS

A post-hoc analysis of data from an observational multicenter, cross-sectional, retrospective study. Adult patients of both sexes, with OAB and OAB-V8 score≥8, who switched to fesoterodine or solifenacin within the 3-4 months before study visit from their prior tolterodine-ER-based therapy due to poor response were included. 92 patients were selected for each treatment group, matched (1:1) according to conditioned probability using the propensity score. Benefit of treatment change perceived by the physician and patient was evaluated by means of the Clinical Global Impression of Improvement subscale (CGI-I) and Treatment Benefit Scale (TBS), respectively. Degree of worry, bother and interference with daily living activities due to urinary symptoms, level of satisfaction, and preference for current treatment were also assessed.

RESULTS

Fesoterodine provided a significantly greater improvement than solifenacina in terms of therapeutic benefit perceived by the physician according to ICG-I. 96.7% of the patients on fesoterodine treatment vs. 81.6% of the solifenacin group showed a score of improvement in TBS (P<.05). Fesoterodine was also better rated than solifenacin with regard to satisfaction and preference for the new treatment (93.4 vs. 78.2% P<.05).

CONCLUSIONS

In daily clinical practice the switch from tolterodine LP to fesoterodine seems to provide greater benefits both from the physician's and the patient's point of view compared with those provided by solifenacin.

Saturable active efflux by p-glycoprotein and breast cancer resistance protein at the blood-brain barrier leads to nonlinear distribution of elacridar to the central nervous system

The study objective was to investigate factors that affect the central nervous system (CNS) distribution of elacridar. Elacridar inhibits transport mediated by P-glycoprotein (P-gp) and breast cancer resistance protein (Bcrp) and has been used to study the influence of transporters on brain distribution of chemotherapeutics. Adequate distribution of elacridar across the blood-brain barrier (BBB) and into the brain parenchyma is necessary to target tumor cells in the brain that overexpress transporters and reside behind an intact BBB. We examined the role of P-gp and Bcrp on brain penetration of elacridar using Friend leukemia virus strain B wild-type, Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice. Initially, the mice were administered 2.5 mg/kg of elacridar intravenously, and the plasma and brain concentrations were determined. The brain-to-plasma partition coefficient of elacridar in the wild-type mice was 0.82, as compared with 3.5 in Mdr1a/b(-/-) mice, 6.6 in Bcrp1(-/-) mice, and 15 in Mdr1a/b(-/-)Bcrp1(-/-) mice, indicating that both P-gp and Bcrp limit the brain distribution of elacridar. The four genotypes were then administered increasing doses of elacridar, and the CNS distribution of elacridar was determined. The observed and model predicted maximum brain-to-plasma ratios (Emax) at the highest dose were not significantly different in all genotypes. However, the ED50 was lower for Mdr1a/b(-/-) mice compared with Bcrp1(-/-) mice. These findings correlate with the relative expression of P-gp and Bcrp at the BBB in these mice and demonstrate the quantitative enhancement in elacridar CNS distribution as a function of its dose. Overall, this study provides useful concepts for future applications of elacridar as an adjuvant therapy to improve targeting of chemotherapeutic agents to tumor cells in the brain parenchyma.

A phase I study on pharmacokinetics and pharmacodynamics of higenamine in healthy Chinese subjects

AIM

To investigate the pharmacokinetics, pharmacodynamics, and safety of higenamine, an active ingredient of Aconite root, in healthy Chinese volunteers.

METHODS

Ten subjects received continuous, intravenous infusion of higenamine at gradually escalating doses from 0.5 to 4.0 μg·kg(-1)·min(-1), each dose was given for 3 min. Blood and urine samples were collected at designated time points to measure the concentrations of higenamine. Pharmacodynamics was assessed by measuring the subject's heart rate. A nonlinear mixed-effect modeling approach, using the software Phoenix NLME, was used to model the plasma concentration-time profiles and heart rate.

RESULTS

Peak concentrations (C(max)) of higenamine ranged from 15.1 to 44.0 ng/mL. The half-life of higenamine was 0.133 h (range, 0.107-0.166 h), while the area under concentration-time curve (AUC), extrapolated to infinity, was 5.39 ng·h·mL(-1) (range, 3.2-6.8 ng·h·mL(-1)). The volume of distribution (V) was 48 L (range, 30.8-80.6 L). The total clearance (CL) was 249 L/h (range, 199-336 L/h). Within 8 h, 9.3% (range, 4.6%-12.4%) of higenamine was recovered in the urine. The pharmacokinetics of higenamine was successfully described using a two-compartment model with nonlinear clearance. In the pharmacodynamic model, heart rates were related to the plasma drug concentrations using a simple direct effect model with baseline. The E(0), E(max), and EC(50) were 68 bpm, 73 bpm and 8.1 μg/L, respectively.

CONCLUSION

Higenamine has desirable pharmacokinetic and pharmacodynamic characteristics. The results provide important information for future clinical studies on higenamine.

Bioavailability and tolerability of combination treatment with revaprazan 200 mg + itopride 150 mg: a randomized crossover study in healthy male Korean volunteers

BACKGROUND

To date, no definitive treatment of functional dyspepsia (FD) has been proven to be effective and reasonably well-tolerated. Proton pump inhibitors (PPIs) combined with prokinetic agents are considered an effective option. Revaprazan is a selective potassium-competitive acid blocker that reversibly inhibits gastric H(+)/K(+)-ATPase and shows effective acid suppression comparable to PPIs. Itopride is a prokinetic agent that has anticholinesterase activity as well as dopamine D(2) receptor antagonistic activity. For this reason, revaprazan and itopride have been prescribed for FD; however, no available studies have reported the pharmacokinetic interactions of these 2 drugs.

OBJECTIVE

The objective of this study was to compare the bioavailability and tolerability of revaprazan and itopride combination therapy to those of equally dosed monotherapies to acquire basic drug-drug interaction information about revaprazan.

METHODS

This multiple-dose, randomized crossover study was conducted in healthy male Korean subjects. Subjects received, in randomized sequence, a 7-day oral dose of revaprazan 200 mg once daily, itopride 50 mg TID, or both. Each treatment period was separated by a 7-day washout period. Blood samples were collected for up to 24 hours following the last dose at steady state, and drug concentrations were determined using validated LC/MS-MS. Pharmacokinetic properties were obtained using noncompartmental analysis. Drug tolerability was assessed throughout the study, using measurements of vital signs, clinical chemistry testing, and interviews.

RESULTS

A total of 30 subjects were enrolled in the study. Among them, 28 subjects completed revaprazan treatment, and 27 completed the study (3 subjects were withdrawn). The geometric mean ratios (GMRs) (90% CI) of C(max,ss), and AUC(τ,ss) with revaprazan were 0.92 (0.84-1.00) and 0.96 (0.89-1.03), respectively. The GMRs of C(max,ss) and AUC(τ,ss) with itopride were 1.07 (0.96-1.20) and 1.12 (1.06-1.18), respectively. A total of 15 adverse events (AEs) were reported in 8 subjects. All AEs were considered to be mild, and there were no clinically significant differences between treatment groups.

CONCLUSION

The findings from this study suggest bioequivalence between revaprazan given as monotherapy and in combination with itopride in these healthy Korean male volunteers, with no clinical significant drug-drug interaction. All treatments in this study was generally well tolerated. ClinicalTrials.gov identifier: NCT0133289.

[Advantages of quinapril therapy in patients with arterial hypertension and functional class III chronic heart failure with preserved left ventricular ejection fraction]

AIM

To determine advantages of therapy of functional class (FC) I-II chronic heart failure (CHF) with preserved left ventricular (LV) ejection fraction in patients with hypertensive disease (HD) with metoprolol succinate or quinapril and to assess their effect on regulatory-adaptive status.

METHODS

Two hundred patients with I-II FC CHF and LVEF >50% at the background of stage I-II hypertensive disease participated in this study. They were randomized into 2 groups. Group I comprised 104 patients (mean age 52.8+1.9 years) who were prescribed metoprolol succinate 87.7+/-7.6 mg/day. Patients of group 2 (n=96, mean age 55.0+/-1.4 years) were prescribed quinapril 21.0+55 mg/day. Examination at baseline and after 6 months of therapy included 6 min walk test, treadmillometry with assessment of maximal oxygen consumptiion (VO2max), echocardiography, 24 hour blood pressure monitoring, measurement of N-terminal precursor of brain natriuretic peptide (NT-proBNP); test of cardio-respiratory synchronism was used for objective qualitative determination of the state of the ,renin-angiotensin system.

RESULTS

Both drugs improved parameters of LV diastolic function, but only quinapril effectively changed LV structural geometric parameters and systolic function. Only treatment with quinapril was associated with improvement of RAS, elevation of tolerance to physical effort, and increased VO2max. Quinapril more substantially lowered level of NT-proBNP.

CONCLUSION

Quinapril has an advantage over metoprolol succinate in therapy of patients with FC I-II CHF and preserved LF EF at the background of stage I-II HD.

Evaluation of limiting brain penetration related to P-glycoprotein and breast cancer resistance protein using [(11)C]GF120918 by PET in mice

PURPOSE

GF120918 has a high inhibitory effect on P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP). We developed [(11)C]GF120918 as a positron emission tomography (PET) probe to assess if dual modulation of P-gp and BCRP is useful to evaluate brain penetration.

PROCEDURES

PET studies using [(11)C]GF120918 were conducted on P-gp and/or Bcrp knockout mice as well as wild-type mice.

RESULTS

In PET studies, the AUC(brain) ([0-60 min]) and K (1) value in P-gp/Bcrp knockout mice were nine- and 26-fold higher than that in wild-type mice, respectively. These results suggest that brain penetration of [(11)C]GF120918 is related to modulation of P-gp and BCRP and is limited by two transporters working together.

CONCLUSIONS

PET using [(11)C]GF120918 may be useful for evaluating the function of P-gp and BCRP. PET using P-gp/Bcrp knockout mice may be an effective method to understand the overall contributions the functions of P-gp and BCRP.

Solifenacin pharmacology

Antimuscarinics are the drugs of choice for the treatment of overactive bladder syndrome, and their benefit/risk ratio depends largely on selectivity for the different subtypes of muscarinic receptors. Solifenacin is the antimuscarinic that presents greatest selectivity for M3 bladder receptors, which may translate into a lower incidence of undesirable effects related to other receptor subtypes. Metabolic pathways of the antimuscarinics may impact efficacy and appearance of interactions. Solifenacin is metabolized only by the CYP3A4, giving three inactive metabolites and one with a similar activity to the original compound. However, other drugs in the group are also a substrate for the CYP 2D6 which presents polymorphisms, whereby their pharmacokinetics may be modified in slow metabolizers. The risk of interactions of solifenacin is low, and it is lower than that of the antimuscarinics which are also metabolized by the CYP 2D6. The unaltered fraction of solifenacin which is eliminated in urine, together with the active metabolite, can contribute to the therapeutic effect by acting on the urothelium receptors. It is not necessary to adjust doses of solifenacin in elderly patients or those with moderate liver or kidney impairment.

Fast and sensitive liquid chromatography/electrospray mass spectrometry method to study ocular penetration of EDL-155, a novel antitumor agent for retinoblastoma in rats

Our group has used the tetrahydroisoquinoline derivative EDL-155 to treat glioblastoma in animal models and it is currently being evaluated in the treatment of ocular cancers. The purpose of this study was to develop a rapid and sensitive liquid chromatography and tandem mass spectrometry (LC-MS/MS) method to study the plasma and vitreous humor disposition of EDL-155 in rats. Animals received a single periocular injection of EDL-155 (20 mg/kg). Animals were sacrificed at specified times (5, 60, 120, 240 and 360 min) and plasma and vitreous humor samples were obtained. EDL-155 was isolated by protein precipitation and the extracts were analyzed by reversed-phase high-pressure liquid chromatography (HPLC) with MS/MS detection. A structurally similar analog was used as internal standard (IS). The chromatographic run time was 3.5 min per injection. The mass spectrometer was operated in positive-ion, multiple reaction monitoring (MRM) mode. The mass transitions monitored were m/z332.2 --> 167.2 (EDL-155) and m/z391.2 --> 200.2 (IS). The lower limit of quantification (LLOQ) was 0.1 ng/ml in both vitreous humor and plasma. The method was validated for selectivity, linearity, accuracy and precision in rat vitreous humor and partially validated for accuracy and precision in rat plasma. The ion suppression, recovery and stability of the analyte in the biological matrix were also tested. The assay was rapid, sensitive and robust enough to support EDL-155 ocular penetration studies in a rodent model of intraocular cancer. Application of this method revealed that EDL-155 was rapidly passed into the vitreous humor following periocular administration. Further, vitreous humor exposure exceeded systemic exposure by approximately sevenfold. High local concentrations coupled with minimal systemic exposure supports further testing of EDL-155 as localized therapy for intraocular cancers.

Phase I trial of weekly trabectedin (ET-743) and gemcitabine in patients with advanced solid tumors

PURPOSE

To determine the maximum tolerated dose (MTD) of trabectedin plus gemcitabine administered on a weekly schedule in patients with advanced solid tumors.

METHODS

Patients with ECOG performance status 0-1 and adequate organ function were enrolled. On days 1, 8, and 15 of a 28-day cycle, patients received gemcitabine (starting dose, 800 mg/m(2)) followed by trabectedin (starting dose, 0.3 mg/m(2)). Strict liver function test treatment criteria were employed to avoid hepatic toxicity seen in previous trabectedin studies. Plasma samples were collected during cycles 1 and 2 for pharmacokinetic analyses.

RESULTS

Fifteen patients received >or=1 dose, with a median of two treatment cycles (range 1-10). The most common drug-related toxicity was hepatic. Dose reductions were required for trabectedin in four (27%) patients and gemcitabine in six (40%) patients. Cycle delays/dose holds were required in 11 (73%) patients and doses above trabectedin 0.4 mg/m(2) and gemcitabine 1,000 mg/m(2), which is the recommended phase II dose, were not feasible. Seven patients maintained stable disease after two cycles. Gemcitabine and trabectedin pharmacokinetics were not altered substantially with concomitant administration.

CONCLUSIONS

Given the lack of pharmacokinetic interaction and potential efficacy of trabectedin and gemcitabine combination therapy, further study is warranted with alternate schedules.

Dopamine D1 Receptor Imaging in the Rodent and Primate Brain Using the Isoquinoline (+)-[11C]A-69024 and Positron Emission Tomography

In vivo pharmacokinetic and brain binding characteristics of (+)-[(11)C]A-69024, a high-affinity-D1-selective dopamine receptor antagonist, were assessed with micro-PET and beta-microprobes in the rat and PET in the baboon. The biodistribution of (+)-[(11)C]A-69024 in rats and baboons showed a rapid brain uptake (reaching a maximal value at 5 and 15 min postinjection in rats and baboons, respectively), followed by a slow wash out. The region/cerebellum concentration ratio was characterized by a fourfold higher uptake in striatum and a twofold higher uptake in cortical regions, consistent with in vivo specific binding of the radiotracer in these cerebral regions. Furthermore, this specific (+)-[(11)C]A-69024 binding significantly correlated with the reported in vitro distribution of dopamine D1-receptors. Finally, the specific uptake of the tracer in the striatum and cortical regions was completely prevented by either a pretreatment with large doses of nonradioactive (+/-)A-69024 or of the D1-selective antagonist SCH23390, resulting in a similar uptake in the reference region (cerebellum) and in other brain regions. Thus, (+)-[(11)C]A-69024 appears to be a specific and enantioselective radioligand to visualize and quantify brain dopamine D1 receptors in vivo using positron emission tomography.

Pharmacokinetics and bioequivalence study of the two 20-mg quinapril hydrochloride tablet formulations in healthy Thai male volunteers

OBJECTIVE

To determine the pharmacokinetics and bioequivalence of two 20-mg quinapril hydrochloride tablet preparations; Quinaril (The Biolab Ltd, Bangkok, Thailand) as the test and Accupril as the reference.

MATERIAL AND METHOD

The present study was a single dose, randomized two-period crossover design conducted in 24 healthy volunteers under fasting conditions with a 7-day washout period. Serial plasma concentrations of quinapril and its active metabolite quinaprilat up to 24 h after dosing were determined by HPLC with UV detection. The pharmacokinetic parameters were analyzed by noncompartmental analysis and the ANOVA was carried out using logarithmically transformed data of the AUC and C as well as untransformed T(max).

RESULTS

There were no significant differences between the two preparations regarding the T(max) of quinapril and quinaprilat and their median T(max) were 0.5 h and 1.4 - 1.5 h, respectively. The half-life of quinapril (1.2 h) was faster than quinaprilat (1.8-1.9 h) although the volume of distribution (Vd/F) of quinapril (1.1 L/kg) was larger than quinaprilat (0.3 L/kg), however, its clearance rate (CL/F) was faster when compared to quinaprilat (20-26 ml/min/kg vs. 1.7 ml/min/kg). The mean (90% CI) for the ratios Reference/Test of quinapril were 0.99 (0.89-1.10), 0.99 (0.90-1.09) and 1.01 (0.90-1.14), respectively for AUC(0-24), AUC(0-infinity) and C(max). Similarly, the corresponding values for quinaprilat were 0.95 (0.90-1.01), 0.95 (0.90-1.01) and 1.03 (1.00-1.07), respectively. These values were within the bioequivalence range of 0.80 - 1.25, thus, demonstrated the bioequivalence of the two preparations.

CONCLUSION

The results of the present study indicated that the two quinapril HCL preparations are bioequivalent and it can be assumed that they are therapeutically equivalent and exchangeable in clinical practice.

Modulation of trabectedin (ET-743) hepatobiliary disposition by multidrug resistance-associated proteins (Mrps) may prevent hepatotoxicity

Trabectedin is a promising anticancer agent, but dose-limiting hepatotoxicity was observed during phase I/II clinical trials. Dexamethasone (DEX) has been shown to significantly reduce trabectedin-mediated hepatotoxicity. The current study was designed to assess the capability of sandwich-cultured primary rat hepatocytes (SCRH) to predict the hepato-protective effect of DEX against trabectedin-mediated cytotoxicity. The role of multidrug resistance-associated protein 2 (Mrp2; Abcc2) in trabectedin hepatic disposition also was examined. In SCRH from wild-type Wistar rats, cytotoxicity was observed after 24-h continuous exposure to trabectedin. SCRH pretreated with additional DEX (1 microM) exhibited a 2- to 3-fold decrease in toxicity at 100 nM and 1000 nM trabectedin. Unexpectedly, toxicity in SCRH from Mrp2-deficient (TR(-)) compared to wild-type Wistar rats was markedly reduced. Depletion of glutathione from SCRH using buthionine sulfoximine (BSO) mitigated trabectedin toxicity associated with 100 nM and 1000 nM trabectedin. Western blot analysis demonstrated increased levels of CYP3A1/2 and Mrp2 in SCRH pretreated with DEX; interestingly, Mrp4 expression was increased in SCRH after BSO exposure. Trabectedin biliary recovery in isolated perfused livers from TR(-) rats was decreased by approximately 75% compared to wild-type livers. In conclusion, SCRH represent a useful in vitro model to predict the hepatotoxicity of trabectedin observed in vivo. The protection by DEX against trabectedin-mediated cytotoxicity may be attributed, in part, to enhanced Mrp2 biliary excretion and increased metabolism by CYP3A1/2. Decreased trabectedin toxicity in SCRH from TR(-) rats, and in SCRH pretreated with BSO, may be due to increased basolateral excretion of trabectedin by Mrp3 and/or Mrp4.

Pharmacological characterization of JNJ-28583867, a histamine H3 receptor antagonist and serotonin reuptake inhibitor

Wake-promoting agents such as modafinil are used in the clinic as adjuncts to antidepressant therapy in order to alleviate lethargy. The wake-promoting action of histamine H(3) receptor antagonists has been evidenced in numerous animal studies. They may therefore be a viable strategy for use as an antidepressant therapy in conjunction with selective serotonin reuptake inhibitors. JNJ-28583867 (2-Methyl-4-(4-methylsulfanyl-phenyl)-7-(3-morpholin-4-yl-propoxy)-1,2,3,4-tetrahydro-isoquinoline) is a selective and potent histamine H(3) receptor antagonist (K(i)=10.6 nM) and inhibitor of the serotonin transporter (SERT) (K(i)=3.7 nM), with 30-fold selectivity for SERT over the dopamine and norepinephrine transporters. After subcutaneous administration, JNJ-28583867 occupied both the histamine H(3) receptor and the SERT in rat brain at low doses (<1 mg/kg). JNJ-28583867 blocked imetit-induced drinking (3-10 mg/kg i.p.), confirming in vivo functional activity at the histamine H(3) receptor and also significantly increased cortical extracellular levels of serotonin at doses of 0.3 mg/kg (s.c.) and higher. Smaller increases in cortical extracellular levels of norepinephrine and dopamine were also observed. JNJ-28583867 (3-30 mg/kg p.o.) showed antidepressant-like activity in the mouse tail suspension test. JNJ-28583867 (1-3 mg/kg s.c.) caused a dose-dependent increase in the time spent awake mirrored by a decrease in NREM. Concomitantly, JNJ-28583867 produced a potent suppression of REM sleep from the dose of 1 mg/kg onwards. JNJ-28583867 has good oral bioavailability in the rat (32%), a half-life of 6.9 h and a C(max) of 260 ng/ml after 10 mg/kg p.o. In summary, JNJ-28583867 is a combined histamine H(3) receptor antagonist-SERT inhibitor with in vivo efficacy in biochemical and behavioral models of depression and wakefulness.

[Metabolites of 1-(1-(6-methoxyl-2-naphthyl)ethyl)-2-(4-nitrobenzyl)-6,7-dimethoxyl-1,2,3,4-tetrahydroisoquinoline hydrobromide in rat by LC-MS/MS method]

To investigate the principal metabolites of 1-(1-(6-methoxyl-2-naphthyl) ethyl)-2-(4-nitrobenzyl)-6,7-dimethoxyl-1,2,3,4-tetrahydroisoquinoline hydrobromide (code designation: P91024) in rats after ig administration by LC-MS/MS, the phase I metabolites were discovered by comparing the fullscan and SIM chromatograms of the test samples with the corresponding blanks. The structures of phase I metabolites were identified by ESI-MS spectra and the product spectra of the corresponding adduct ions. The phase II metabolites were identified in the test samples after the phase I metabolites were completely removed with solvent extraction and then treated with glucuronidase for enzymolysis of phase II glucuronide conjugates and the hydrolysates. Two phase I metabolites of P91024 were identified in rat feces, one phase I and five phase II in bile, one phase I and three phase II in urine, and four phase I and one phase II in plasma. Their structures were elucidated, separately. P91024 was extensively metabolized in rat. The metabolites can be easily screened and identified by LC-MS/MS method.

Plasma and cerebrospinal fluid pharmacokinetics of the novel tetrahydroisoquinoline EDL-155 in rats

PURPOSE

Tetrahydroisoquinolines (THIs) have demonstrated anti-cancer activity in rodent models of glioma, a form of brain cancer refractory to therapeutic intervention. In this study, peripheral and cerebrospinal fluid (CSF) pharmacokinetics in rats were determined to assess the drug developability of the novel THI EDL-155 for the treatment of glioma.

METHODS

Serial blood and CSF samples were collected from rats following intravenous bolus administration of EDL-155 (10-20 mg/kg). Samples were analyzed by LC/MS/MS. Pharmacokinetic analyses using compartmental and noncompartmental methods were performed using the computer program WinNonlin. Plasma protein binding was measured using the charcoal adsorption method. The in vivo efficacy of EDL-155 (i.p. 20 mg/kg twice daily for 7 days) was assessed in rats with stereotactically implanted C6 glioma cells into the caudate.

RESULTS

EDL-155 plasma concentration data were described by a one-compartment model. EDL-155 demonstrated rapid clearance (342.5+/-49.9 ml/min/kg), high volume of distribution (13.0+/-1.2 l/kg) and a terminal half-life of 23.7+/-1.5 min. Dose-normalized CSF area under the curve (AUC(CSF)) as a percentage of peripheral exposure (AUC(Plasma)) was 1.4%. EDL-155 was highly bound to plasma proteins (>93%). Intracranial tumor volume at 7 days post-implantation was approximately 30% smaller in animals treated with EDL-155 when compared to vehicle control animals (13.2+/-5.3 mm(3) vs. 18.7+/-6.3 mm(3); P=0.04).

CONCLUSION

High clearance and extensive protein binding limit the brain availability of EDL-155 following systemic administration. EDL-155 treatment resulted in reduced tumor size despite limited blood brain barrier penetrability, which suggests that analogs with increased metabolic stability and brain penetrability may provide a therapeutic option for primary central nervous system tumors such as glioma. On-going studies are focused on the design, synthesis, and testing of novel analogs based upon these findings.

P-glycoprotein-mediated active efflux of the anti-HIV1 nucleoside abacavir limits cellular accumulation and brain distribution

P-glycoprotein (P-gp)-mediated efflux at the blood-brain barrier has been implicated in limiting the brain distribution of many anti-HIV1 drugs, primarily protease inhibitors, resulting in suboptimal concentrations in this important sanctuary site. The objective of this study was to characterize the interaction of abacavir with P-gp and determine whether P-gp is an important mechanism in limiting abacavir delivery to the central nervous system (CNS). In vitro and in vivo techniques were employed to characterize this interaction. Abacavir stimulated P-gp ATPase activity at high concentrations. The cellular accumulation of abacavir was significantly decreased by approximately 70% in Madin-Darby canine kidney II (MDCKII)-MDR1 monolayers compared with wild-type cells and was completely restored by the P-gp inhibitors ((R)-4-((1aR,6R,10bS)-1,2-difluoro-1,1a,6,10b-tetrahydrodibenzo(a,e)cyclopropa(c)cycloheptan-6-yl)-alpha-((5-quinoloyloxy)methyl)-1-piperazineethanol, trihydrochloride) (LY335979) and N-[4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)ethyl]phenyl]-5-methoxy-9-oxo-10H-acridine-4-carboxamide (GF120918). Directional flux experiments indicated that abacavir had greater permeability in the basolateral-to-apical direction (1.58E-05 cm/s) than in the apical-to-basolateral direction (3.44E-06 cm/s) in MDR1-transfected monolayers. The directionality in net flux was abolished by both LY335979 and GF120918. In vivo brain distribution studies showed that the AUC(plasma) in mdr1a(-/-) CF-1 mutant mice was approximately 2-fold greater than the AUC(plasma) in the wild type, whereas the AUC(brain) in the mutant was 20-fold higher than that in the wild type. Therefore, the CNS drug targeting index, defined as the ratio of AUC brain-to-plasma for mutant over wild type, was greater than 10. These data are the first in vitro and in vivo evidence that a nucleoside reverse transcriptase inhibitor is a P-gp substrate. The remarkable increase in abacavir brain distribution in P-gp-deficient mutant mice over wild-type mice suggests that P-gp may play a significant role in restricting the abacavir distribution to the CNS.

Mechanism-based Pharmacokinetic/Pharmacodynamic Meta-analysis of Trabectedin (ET-743, Yondelis) Induced Neutropenia

Myelosuppression was found to be one of the main toxicities of trabectedin (ET-743, Yondelis) during phase I/II studies. Our objective was to develop a pharmacokinetic-pharmacodynamic (PK/PD) model that describes the time course of the absolute neutrophil counts (ANCs) in cancer patients receiving trabectedin. Data from 699 patients who received intravenous trabectedin as monotherapy (dose range: 0.006-1.8 mg/m2) as a 1-, 3-, or 24-h infusion every 21 days; 1- or 3-h infusion on days 1, 8, and 15 every 28 days; or a 1-h infusion daily for 5 consecutive days every 21 days were used to develop (N=405; ANCs=7,291) and validate (N=294; ANCs=5,029) the model. The PK/PD model comprised a trabectedin-sensitive progenitor cell compartment, linked to the peripheral blood compartment, through three transition compartments representing the maturation chain in the bone marrow. To capture the rebound effect due to endogenous growth factors, the model included a feedback mechanism. The model estimated three system-related parameters: ANC at baseline (Circ0), mean transit time in bone marrow (MTT), and a feedback parameter (gamma). A first-order process quantified by the rate constant k(e0) described the trabectedin concentrations at the effect compartment (C(e)), which were assumed to reduce the proliferation rate and/or to increase the killing rate of the progenitor cells according to the function alphaC(e)beta. The model was qualified and simulations were undertaken to evaluate the neutropenia schedule dependency and the effects of selected covariates. NONMEM software was used to perform the modeling and simulation analyses. For a typical man of 70 kg, the mean values (between-subject variability; %) of the Circ0, MTT, gamma, k(e0), alpha, and beta were estimated to be 4.46 x 10(9)/l (37.9%), 4.0 days (37.5%), 0.218 (41.8%), 2.09 h(-1) (77.9%), 2.00 l/microg (85.1%), and 1.26, respectively. Although in women, k(e0) was reduced by 29% and a 25% increase in body weight resulted in a 12.6% reduction in the beta parameter, the clinical relevance of these effects is limited. The model evaluation procedure indicated accurate prediction of the observed incidence of neutropenia grades 3 and 4 across the dosing regimens evaluated. Simulations indicated that trabectedin dose and interdose interval, but not infusion duration, are the main determinants of the neutropenia severity. The model-predicted time course of the ANC and its variability confirmed that neutropenia is reversible, of short duration, and non-cumulative. The extent and time course of neutropenia following six different dosing regimens of trabectedin were well predicted by the semiphysiological PK/PD model.

Pharmacokinetics, safety, and tolerability of solifenacin in patients with renal insufficiency

To evaluate the pharmacokinetics, safety, and tolerability of solifenacin in patients with mild, moderate, or severe renal disease, eighteen patients with renal disease and six healthy volunteers received a single oral dose of solifenacin (10 mg). Pharmacokinetic parameters were assessed from blood samples drawn over a 360-h period. Safety and tolerability were also evaluated. Total mean +/- S.D. exposure (ng . h/mL) to solifenacin in healthy individuals (1190 +/- 403) was increased in patients with renal disease (mild: 1784 +/- 792, moderate: 1559 +/- 555, severe: 2530 +/- 700), and elimination half-life (mean +/- S.D. [h]) was prolonged (healthy: 68.2 +/- 27.2, mild: 89.1 +/- 34.5, moderate: 90.6 +/- 27.3, severe: 111 +/- 38.3). A significant correlation was found between creatinine clearance and pharmacokinetic parameters for exposure and apparent oral clearance. No deaths or serious adverse events occurred during the study. Solifenacin 10 mg was well tolerated in patients with renal disease. Solifenacin displays a higher exposure and a prolonged half-life in patients with renal impairment, especially severe. Therefore, while no special cautions are necessary for patients with mild/moderate renal impairment, patients with severe renal impairment should receive no more than 5 mg solifenacin once daily.

Clearance of Imidapril, an Angiotensin-Converting Enzyme Inhibitor, During Hemodialysis in Hypertensive Renal Failure Patients: Comparison With Quinapril and Enalapril

The dialyzability of imidaprilat, an active metabolite of the angiotensin-converting enzyme (ACE) inhibitor imidapril, was determined and compared with those of enalaprilat and quinaprilat in hypertensive patients on chronic hemodialysis. Imidapril (5 mg/d, n = 6), enalapril (2.5 mg/d, n = 6), or quinapril (2.5 mg/d, n = 6) was given for at least 8 weeks prior to the trial. During dialysis, enalaprilat, but not imidaprilat or quinaprilat, concentrations in both sides decreased significantly. Compared to enalaprilat, the dialyzabilities of imidaprilat and quinaprilat were significantly lower (dialyzer clearance [mL/min/m(2)]: enalaprilat, 41.8 +/- 7.4; imidaprilat, 19.0 +/- 7.8; quinaprilat, 8.9 +/- 1.3). The dialyzabilities of the 3 drugs were negatively correlated with their respective protein-binding rates. During hemodialysis, blood pressure did not change significantly in any group. These results suggest that imidapril provides good blood pressure control without a large fluctuation of drug concentration in hypertensive patients undergoing chronic hemodialysis.

Novel tetrahydroisoquinolines are histamine H3 antagonists and serotonin reuptake inhibitors

A series of novel 4-aryl-1,2,3,4-tetrahydroisoquinoline-based histamine H(3) ligands that also have serotonin reuptake transporter inhibitor activity is described. The synthesis, in vitro biological data, and select pharmacokinetic data for these novel compounds are discussed.

Promotion of sleep by targeting the orexin system in rats, dogs and humans

Orexins are hypothalamic peptides that play an important role in maintaining wakefulness in mammals. Permanent deficit in orexinergic function is a pathophysiological hallmark of rodent, canine and human narcolepsy. Here we report that in rats, dogs and humans, somnolence is induced by pharmacological blockade of both orexin OX(1) and OX(2) receptors. When administered orally during the active period of the circadian cycle, a dual antagonist increased, in rats, electrophysiological indices of both non-REM and, particularly, REM sleep, in contrast to GABA(A) receptor modulators; in dogs, it caused somnolence and increased surrogate markers of REM sleep; and in humans, it caused subjective and objective electrophysiological signs of sleep. No signs of cataplexy were observed, in contrast to the rodent, dog or human narcolepsy syndromes. These results open new perspectives for investigating the role of endogenous orexins in sleep-wake regulation.

Validation of 8-[123I]iodo-L-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid as an imaging agent for prostate cancer in experimental models of human prostate cancer

INTRODUCTION

Very few tracers are currently available for the detection and staging of prostate cancer with positron emission tomography and single-photon emission computed tomography. This study evaluates the potential of 8-[123I]iodo-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid [ITIC(OH)] as an imaging agent for prostate cancer in experimental models of human prostate cancer.

METHODS

ITIC(OH) was prepared by the IODO-GEN method, with 82+/-7% radiochemical yield and >99% radiochemical purity after high-performance liquid chromatography. Thereafter, ITIC(OH) was examined in CD-1 nu/nu mice engrafted with human PC-3 and DU-145 prostate cancer in the flank or orthotopically in the prostate. Bioevaluation involved examination of the in vivo stability and uptake characteristics of ITIC(OH) into tumors and different organs by dynamic in vivo analysis and gamma counting of organs of interest after dissection.

RESULTS

ITIC(OH) showed good in vivo stability for biological investigations and was primary cleared through urine. In vivo, ITIC(OH) accumulated highly and specifically in tumors, reaching 13.6+/-2.1% to 16.2+/-2.5% injected dose per gram (ID/g) in heterotopic tumors compared with 14.8+/-2.6% and 17.6+/-3.4% ID/g in orthotopic tumor engrafts at 60 and 240 min postinjection, respectively. In contrast, radioactivity uptake in the blood, spleen, liver and gastrointestinal tract was moderate and decreased with time, resulting in marked tumor-to-background and excellent visualization of tumors.

CONCLUSION

These results suggest that ITIC(OH) is a promising candidate as radiotracer for detecting prostate cancer and warrants further studies in patients to ascertain its potential as an imaging agent for clinical use.

Population Pharmacokinetic Meta-Analysis of Trabectedin (ET-743,??Yondelis??) in Cancer Patients

OBJECTIVE

To characterise the population pharmacokinetics of trabectedin (ET-743, Yondelis(R)) in cancer patients.

METHODS

A total of 603 patients (945 cycles) receiving intravenous trabectedin as monotherapy at doses ranging from 0.024 to 1.8 mg/m(2) and given as a 1-, 3- or 24-hour infusion every 21 days; a 1- or 3-hour infusion on days 1, 8 and 15 of a 28-day cycle; or a 1-hour infusion daily for 5 consecutive days every 21 days were included in the analysis. An open four-compartment pharmacokinetic model with linear elimination, linear and nonlinear distribution to the deep and shallow peripheral compartments, respectively, and a catenary compartment off the shallow compartment was developed to best describe the index dataset using NONMEM V software. The effect of selected patient covariates on trabectedin pharmacokinetics was investigated. Model evaluation was performed using goodness-of-fit plots and relative error measurements for the test dataset. Simulations were undertaken to evaluate covariate effects on trabectedin pharmacokinetics.

RESULTS

The mean (SD) trabectedin elimination half-life was approximately 180 (61.4) hours. Plasma accumulation was limited when trabectedin was given every 3 weeks. Systemic clearance (31.5 L/h, coefficient of variation 51%) was 19.2% higher in patients receiving concomitant dexamethasone. The typical values of the volume of distribution at steady state for male and female patients were 6070L and 5240L, respectively. Within the range studied, age, body size variables, AST, ALT, alkaline phosphatase, lactate dehydrogenase, total bilirubin, creatinine clearance, albumin, total protein, Eastern Cooperative Oncology Group performance status and presence of liver metastases were not statistically related to trabectedin pharmacokinetic parameters. The pharmacokinetic parameters of trabectedin were consistent across the infusion durations and dose regimens evaluated.

CONCLUSIONS

The integration of trabectedin pharmacokinetic data demonstrated linear elimination, dose-proportionality up to 1.8 mg/m(2) and time-independent pharmacokinetics. The pharmacokinetic impact of dexamethasone and sex covariates is probably limited given the moderate to large interindividual pharmacokinetic variability of trabectedin. The antiemetic and hepatoprotective effects are still a valid rationale to recommend dexamethasone as a supportive treatment for trabectedin.

Solifenacin provides effective antimuscarinic therapy for the complete management of overactive bladder

Solifenacin is an antimuscarinic agent, administered once daily, which has been newly approved for the treatment of overactive bladder (OAB). Solifenacin administered at 5- and 10-mg once-daily doses shows efficacy for all the symptoms of OAB in both 'wet' and 'dry' patients, including improvements in patient quality of life and satisfaction. These improvements are observed as early as week 2 of treatment and are maintained over 12-week and 1-year time periods, without being compromised by the age or gender of the patient. Solifenacin demonstrates a favourable tolerability profile, with mild dry mouth as the most common adverse event associated with its use, both at the 5- and 10-mg doses; this allows for flexibility in the dosing regimen, in which physicians can administer solifenacin 5 mg, with the option to safely increase the dose to 10 mg if necessary based on the severity of patient's symptoms. The favourable efficacy and safety profile of solifenacin, coupled with its dose flexibility, are consistent with solifenacin being a convenient treatment option for patients with OAB.

Tetrahydroisoquinoline PPARγ agonists: Design of novel, highly selective non-TZD antihyperglycemic agents

Novel tetrahydroisoquinolines have been developed as potent PPAR ligands. Evaluation of these compounds in PPARgamma responsive models of type 2 diabetes is described.

Pharmacokinetic interaction of solifenacin with an oral contraceptive containing ethinyl estradiol and levonorgestrel in healthy women: a double-blind, placebo-controlled study

BACKGROUND

Solifenacin succinate (YM905; Vesicare, Astellas Pharma Inc., Tokyo, Japan) is a new once-daily, orally administered muscarinic receptor antagonist under investigation for the treatment of overactive bladder.

OBJECTIVE

The aim of this study was to evaluate the effect of solifenacin on the pharmacokinetic (PK) parameters of an oral contraceptive (OC) containing ethinyl estradiol (EE) and levonorgestrel (LNG).

METHODS

In a double-blind, placebo-controlled, 2-period, crossover study, 24 healthy, young, white women received a combined OC (EE 30 microg + LNG 150 microg) daily for two 21-day cycles, separated by a 7-day washout. On day 12 of each cycle, subjects began a 10-day regimen of solifenacin 10 mg QD, which is 2 times the suggested starting dose, or placebo. Subjects crossed over to the other treatment arm for the second cycle. Primary PK end points were C(max) and AUC from time 0 to 24 hours (AUC(0-24 h)) for EE and LNG. Women ranged in age from 20 to 37 years and had a mean body weight of 64 kg, mean height of 167.4 cm, and mean body mass index of 23 kg/m2. Seven women had never smoked, while 5 were former smokers and 12 were regular smokers. Safety assessments included the nature, frequency, and severity of spontaneously reported or observed adverse events, vital signs, electrocardiogram, laboratory values, and physical examination.

RESULTS

Statistical analysis of AUC(0-24 h)/product of baseline concentration and total blood sampling time, and C(max)/baseline concentration ratios of solifenacin versus placebo for EE and LNG found the 90% CI to be within the predefined range of 0.8 to 1.25 (EE: 0.854-1.164 and 0.822-1.167; LNG: 0.920-1.125 and 0.910-1.139). The number of samples with non-quantifiable luteinizing hormone (LH) and folliclestimulating hormone (FSH) levels were comparable after administration of the OC with either solifenacin or placebo. The adverse event most frequently reported was dry mouth (solifenacin, n = 25 [9 mild, 13 moderate, and 3 severe] vs placebo, n = 1 [moderate]). There were no clinically relevant effects on vital signs, electrocardiogram, or laboratory parameters.

CONCLUSIONS

A PK interaction between solifenacin and the OC containing EE and LNG was not found in this study. Solifenacin was not found to have altered suppression of LH or FSH. The drug was well tolerated in these healthy, young, white, adult female volunteers.

Development of a P-glycoprotein knockout model in rodents to define species differences in its functional effect at the blood-brain barrier

The objective of this study was to establish the optimal blood concentrations of the potent P-glycoprotein (P-gp) inhibitor GF120918 (Elacridar) required to achieve maximal knockout of this efflux transporter in the blood-brain barrier (BBB) of mice, rats, and guinea pigs. Genetic mdr1a/b(-/-) knockout mice and "chemical" P-gp knockout mice, rats, and guinea pigs, generated by 24 h continuous infusion of GF120918, were used to investigate the effects of P-gp modulation on the brain penetration of SB-487946. Genetic mdr1a/b(-/-) knockout mice demonstrated a >70-fold increase in brain:blood ratio of SB-487946 compared to mdr1a/b(+/+) wild-type mice. There was a similar increase in SB-487946 brain:blood ratio in GF120918-treated mice (ca. >67-fold) and rats (ca. 95-fold) but a significantly smaller increase (ca. 10-fold) in guinea pigs treated with GF120918. An appreciable difference was found in the BBB functional effect of P-gp efflux in rodents. GF120918 blood EC90 in mice and rats were similar however, the EC90 in guinea pigs was ca. 10-fold higher, suggesting a species difference in the activity of P-gp at the BBB in some rodents. This study establishes the optimal blood concentrations of GF120918 in relation to SB-487946, to achieve chemically induced P-gp knockout in rodents.

Simultaneous delivery of doxorubicin and GG918 (Elacridar) by new polymer-lipid hybrid nanoparticles (PLN) for enhanced treatment of multidrug-resistant breast cancer

Multidrug-resistant (MDR) cancer may be treated using combinations of encapsulated cytotoxic drugs and chemosensitizers. To optimize for the effectiveness of this combinational approach, novel polymer-lipid hybrid nanoparticle (PLN) formulations capable of delivering a cytotoxic drug, doxorubicin (Dox), a chemosensitizer, GG918, or their combination were prepared. Both acute and long-term anticancer activities of various combinations of Dox and GG918 in solution or PLN form were evaluated in a human MDR breast cancer cell line (MDA435/LCC6/MDR1) using trypan blue exclusion and clonogenic assays. Cellular Dox uptake and drug distribution within the cells were determined by fluoremetry and fluorescence microscopy. The results showed that the encapsulation efficiencies of Dox and GG918 in PLN were up to 89% and were not compromised by co-encapsulation of the two agents. Of various combinational treatment approaches, the Dox and GG918 co-encapsulated PLN formulation ((DG)n) demonstrated the greatest Dox uptake and anticancer activity to the MDR cells, while co-administration of two single-agent loaded PLN was least effective. Fluorescence microscopy indicated cellular internalization of (DG)n. These findings suggest that in addition to the total drug concentrations, the simultaneous delivery of Dox and GG918 to the same cellular location is critical in determining the therapeutic effectiveness of this anticancer drug-chemosensitizer combination.

Metabolism of trabectedin (ET-743, Yondelis™) in patients with advanced cancer

PURPOSE

Trabectedin (ET-743, Yondelis) is a novel anti-cancer drug currently undergoing phase II-III evaluation, that has shown remarkable activity in pre-treated patients with soft tissue sarcoma. Despite extensive pharmacokinetic studies, the human disposition and metabolism of trabectedin remain largely unknown. We aimed to determine the metabolic profile of trabectedin and to identify its metabolites in humans.

METHODS

We analysed urine and faeces (the major excretory route) from eight cancer patients after a 3 or 24 h intravenous administration of [14C]trabectedin. Using liquid chromatography with tandem quadrupole mass spectrometric detection (LC-MS/MS) and radiochromatography with off-line radioactivity detection by liquid scintillation counting (LC-LSC), we characterised the metabolic profile in 0-24 h urine and 0-120 h faeces.

RESULTS

By radiochromatography, a large number of trabectedin metabolites were detected. Incubation with beta-glucuronidase indicated the presence of a glucuronide metabolite in urine. Trabectedin, ET-745, ET-759A, ETM-259, ETM-217 (all available as reference compounds) and a proposed new metabolite coined ET-731 were detected using LC-MS/MS. The inter-individual differences in radiochromatographic profiles were small and did not correlate with polymorphisms in drug-metabolising enzymes (CYP2C9, 2C19, 2D6, 2E1, 3A4, GST-M1, P1, T1 and UGT1A1 2B15) as determined by genotyping.

CONCLUSIONS

Trabectedin is metabolically converted to a large number of compounds that are excreted in both urine and faeces. In urine and faeces we have confirmed the presence of trabectedin, ET-745, ET-759A, ETM-259, ETM-217 and ETM-204. In addition we have identified a putative new metabolite designated ET-731. Future studies should be aimed at further identification of possible metabolites and assessment of their activity.

Tetrahydroisoquinolines as MCH-R1 antagonists

A series of potent and selective inhibitors of h-MCH-R1 has been developed based on the piperidine glycineamide compounds I and II. These structurally more rigid tetrahydroisoquinolines (III and IV) showed better pharmacokinetics. The highly potent compounds 12d and 12g displayed excellent rat pk.

Pharmacokinetic Effect of Ketoconazole on Solifenacin in Healthy Volunteers

Solifenacin succinate (YM905) is a new, once-daily, orally administered muscarinic receptor antagonist designed to treat overactive bladder. The metabolism of solifenacin involves hepatic cytochrome P450 (CYP) 3A4; therefore, the pharmacokinetics of solifenacin may be affected by drugs that inhibit CYP3A4. This study aimed to examine the effects of co-administration of ketoconazole, a potent CYP3A4 inhibitor, on the pharmacokinetics of solifenacin in healthy volunteers. In a single-site, open-label, monosequence, crossover study, 17 healthy men and women aged 18 to 65 years received a single 10 mg oral dose of solifenacin, which is is the highest available dose. After a 14-day wash-out period, they began 20 days of oral ketoconazole at a dose of 200 mg once daily. A single 10 mg dose of solifenacin was administered again on day 7 of ketoconazole treatment. Pharmacokinetics was assessed using the standard measurements of maximum plasma concentration (Cmax), time to Cmax, area under the curve (AUC), and elimination half-life (t1/2). Co-administration of ketoconazole resulted in a 1.43 times increase in the C(max) of solifenacin and an approximately 2 times increase in AUC. The mean t1/2 of solifenacin was extended from 49.3 to 77.5 hr whereas time to Cmax did not change. No substantial increase in the overall rate of adverse events, and no significant effects on vital signs, electrocardiography, clinical laboratory values, or physical examinations were noted. Administration of 200 mg ketoconazole once daily in healthy male volunteers resulted in a 2 times increase in exposure of a single 10 mg dose of solifenacin. Since ketoconazole is one of the strongest inhibitors of CYP3A4, it is expected that co-administration of other CYP3A4 inhibitors will not result in a stronger increase in solifenacin exposure.

Differential in vivo sensitivity to inhibition of P-glycoprotein located in lymphocytes, testes, and the blood-brain barrier

A major functional component of the blood-brain barrier is P-glycoprotein. In principle, inhibition of this efflux transporter would permit greater distribution of its substrates into the brain and increased central effects. Tariquidar and elacridar, potent and selective P-glycoprotein inhibitors, were investigated in this regard using the opioid loperamide as an in vivo probe in mice. Pretreatment with both inhibitors converted intravenous loperamide from a drug without central effects to one producing antinociception. Radiolabeled loperamide tissue distribution studies indicated that inhibition was associated with increased uptake into brain and testes in the absence of changes in plasma levels, along with enhanced efflux of rhodamine 123 from CD3e+ T-lymphocytes. However, with tariquidar, the loperamide dose-response curves for testes/plasma and brain/plasma concentration ratios were shifted 6- (p = 0.07) and 25-fold (p < 0.01) to the right, respectively (ED50 = 1.48 and 5.65 mg/kg), compared with the rhodamine 123 efflux curve (ED50 0.25 mg/kg). Less pronounced shifts were noted with elacridar where the brain/plasma ratio was shifted only 2-fold relative to the rhodamine 123 efflux data (ED50 = 2.36 versus 1.34 mg/kg, respectively; p 0.01). These results indicate that the P-glycoprotein localized in the blood-brain barrier and, to a lesser extent, the testes-blood barrier is more resistant to inhibition than at other tissue sites such as the lymphocyte; moreover, the extent of this effect depends on the inhibitor. Such resistance can be overcome by a sufficiently high dose of an inhibitor; however, whether this is safely attainable in the clinical situation remains to be determined.

1-Benzyl-1,2,3,4-tetrahydroisoquinoline passes through the blood–brain barrier of rat brain: An in vivo microdialysis study

Previous work has established that 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1-BnTIQ) causes a parkinsonian syndrome in rats. The present study reports the blood-brain barrier (BBB) permeability of 1-BnTIQ in freely moving rats with the aid of in vivo microdialysis-based measurements. The microdialysis probe was implanted in the frontal cortex of rat brain. Brain dialysate samples were analyzed using an HPLC-MS/MS assay. 1-BnTIQ, when administered i.p., dose-dependently appeared in brain extracellular fluid (ECF), reaching a maximum concentration after about 40 min. Two other tetrahydroisoquinoline derivatives, 1,2,3,4-tetrahydroisoquinoline (TIQ) and 6,7-dihydroxy-1-methyl-1,2,3,4-tetrahydroisoquinoline [salsolinol (SAL)], served as positive and negative controls, respectively. The results confirmed an earlier report that SAL does not reach the brain after i.p. administration. In contrast, TIQ readily passed through the BBB. The brain dialysate concentration of 1-BnTIQ was about 24% that of TIQ when administered i.p. at the same dose. Both of them decreased quickly with a half-life of about 50 min.

Preparation and tumor affinity testing of the radioiodinated tetrahydroisoquinoline derivative [123I]TIC(OH) for targeting prostate cancer

This work describes the synthesis and tumor affinity testing of 8-[123I]iodo-l-1,2,3,4-tetrahydro-7-hydroxyisoquinoline-3-carboxylic acid [ITIC(OH)], a cyclic non-naturally occurring amino acid as an imaging probe for prostate cancer. Parameters for labelling were optimized with regard to the amount of precursor, the temperature and time. Thereafter, ITIC(OH) was evaluated in terms of its uptake in primary human PC-3 and DU-145 prostate cancer cells, followed by analysis of the underlying mechanisms of the radioactivity accumulation in tumor cells. No-carrier-added ITIC(OH) was obtained in 80+/-15% radiochemical yield and >98% radiochemical purity by a one-step radioiodination, using IODO-GEN as oxidant. The total synthesis time was less than 30 min, and compatible with a clinical routine production. ITIC(OH) accumulated intensively in primary human prostate cancer cells. The radioactivity incorporation in tumor following a 10-min incubation at 37 degrees C/pH 7.4 varied from 35% to 58% of the total loaded activity per 10(6) tumor cells (355-540 cpm/1000 cells). Inhibition experiments revealed that ITIC(OH) was taken up into tumor by an active transport different from the common amino acid carrier systems, including the sodium-dependent system A and B+,0, and the sodium-independent L- and ASC-type transporter. In contrast, the cellular incorporation was dependent on the membrane potential and correlated with the activity of the mitochondria. In conclusion, the specific and high-level accumulation of ITIC(OH) in human prostate carcinoma cells, indicates that the new radiopharmaceutical is a good candidate for further in vivo investigations to ascertain its potential as an imaging probe for prostate cancer by SPET.

Open-Label Study of the Safety and Pharmacokinetics of Solifenacin in Subjects With Hepatic Impairment

Determining the pharmacokinetics and safety of solifenacin succinate, a once-daily, oral antimuscarinic agent indicated for treatment of overactive bladder, in subjects with hepatic impairment. In this open-label study, 16 subjects (eight with moderate hepatic impairment [defined as a Child-Pugh score of 7 - 9], eight healthy) received a single oral 10 mg solifenacin dose. Blood and urine were collected for pharmacokinetic assessments. Pharmacokinetic parameters (primary: area under the plasma concentration-time curve from time 0 to infinity [AUC(0-infinity)] and maximum plasma concentration [C(max)]) and safety were evaluated for solifenacin and its metabolites. There were no clinically relevant differences in safety. Moderate hepatic impairment increased AUC(0-infinity) by 60%, and the mean elimination half-life of solifenacin and several of its metabolites was longer versus healthy subjects. Mean C(max) values were comparable between the groups. A single oral dose of solifenacin was well tolerated in hepatically impaired and healthy subjects; however, moderate hepatic impairment influenced solifenacin pharmacokinetics. In patients with mild hepatic impairment, solifenacin may be used without special caution; however, in patients with moderate hepatic impairment, doses greater than 5 mg are not recommended and the 5 mg dose should be used with caution.

Trabectedin

Trabectedin [Ecteinascidin 743, Yondelis, ET 743, NSC 684766] is a tetrahydroisoquinoline alkaloid derived from the Caribbean marine tunicate, Ecteinascidia turbinata. The drug is being developed by PharmaMar (Zeltia) in partnership with Johnson & Johnson Pharmaceutical Research & Development LLC. It was synthetically isolated and developed by the University of Illinois and licensed to PharmaMar; the company has completed the hemisynthesis of agent. Trabectedin interacts with the minor groove of DNA and alkylates guanine at the N2 position, which bends towards the major groove. In this manner, it is thought that the drug affects various transcription factors involved in cell proliferation, particularly via the transcription-coupled nucleotide excision repair system. Trabectedin blocks the cell cycle at the G(2) phase, while cells at the G(1 )phase are most sensitive to the drug. It also inhibits overexpression of the multidrug resistance-1 gene (MDR-1) coding for the P-glycoprotein that is a major factor responsible for cells developing resistance to cancer drugs. The agent is also thought to interfere with the nucleotide excision repair pathways of cancer cells, suggesting that it could be effective in the treatment of many cancer types including melanoma and sarcoma, as well as lung, breast, ovarian, endometrial and prostate cancers; clinical evaluations are underway in these indications. PharmaMar and Ortho Biotech Products (Johnson & Johnson) entered into an agreement in August 2001 for the joint development and commercialisation of trabectedin. PharmaMar retains commercialisation rights in Europe, including Eastern Europe. Ortho Biotech will market the product in the US, Japan and the rest of the world; Tibotec Therapeutics (a division of Ortho Biotech) will commercialise it in the US. PharmaMar will receive an initial payment from Ortho Biotech plus future milestone and royalty payments linked to development targets and sales; the upfront payment would be approximately 20 million US dollars with royalties contributing 10-20% of total sales of the drug. Although details of the licensing transaction for trabectedin were undisclosed, analysts estimate the figure to be around 100 million US dollars. Previously, PharmaMar signed an agreement granting Bristol-Myers Squibb the option to evaluate and develop as many as 12 of PharmaMar's marine-derived anticancer compounds on an exclusive worldwide basis. However, it appears that Bristol-Myers Squibb had chosen not to exercise the option. Trabectedin is undergoing clinical trials in soft tissue sarcoma (Sarcoma in the Phase table), ovarian, breast, endometrial, prostate and non-small-cell lung cancers. PharmaMar indicated in January 2004 that it intends to launch trabectedin in one of these indications in 2006. PharmaMar raised funds from a round of financing in June 2005 that will be used to fund further clinical trials of its anticancer products, including trabectedin. The US FDA granted trabectedin orphan drug status for ovarian cancer in April 2005. Trabectedin also received orphan drug status from the European Commission for the treatment of ovarian cancer in October 2003. This followed a positive opinion by the Committee for Orphan Medicinal Products (COMP) of the EMEA. Trabectedin has undergone a phase II study for the second- or third-line treatment of ovarian cancer in Europe (England and Belgium), the US and Canada. The trial was initiated in October 2002 and evaluated a weekly schedule of trabectedin (0.58 mg/m(2)) via IV infusion for 3 weeks followed by a week of rest. Final results from this study have been presented. A separate phase II trial evaluating the antitumour activity of trabectedin as a second-line therapy in advanced ovarian cancer was conducted by researchers at the Southern Europe New Drugs Organization (SENDO) in Milan, Italy. PharmaMar and Johnson & Johnson are conducting a pivotal (STS-201) trial to compare a weekly and daily dosing regimen of trabectedin among patients with advanced or metastatic soft tissue sarcoma who are unresponsive to standard chemotherapy of doxorubicin and ifosfamide. The randomised, multicentre, open-label trial has completed enrolment of 270 patients during the second quarter of 2005. Positive data from the STS-201 trial have been announced. An independent data monitoring committee has found that interim data supports a positive trend in time to disease progression favouring patients receiving the daily dosing regimen. Consequently, all patients have been offered the option of switching to the daily regimen. Final results from the STS-201 trial will form the basis of MAA re-submission with European regulatory authorities. PharmaMar has held a pre-submission meeting with the EMEA and has presented a formal letter of intent to file for approval of trabectedin for soft tissue sarcoma. Previously, PharmaMar first filed for EU registration of trabectedin for treatment of advanced soft tissue sarcoma in November 2001, which was accepted for review by the EMEA and Swiss Health Authorities. However, the CPMP confirmed its recommendation not to grant trabectedin marketing authorisation in November 2003 following PharmaMar's appeal against the CPMP's negative opinion first announced in July 2003; the opinion was adopted by a majority vote rather than by consensus. Trabectedin was granted orphan drug status in Europe for recurrent soft tissue sarcoma in 2001. It was also granted orphan drug status by the FDA for the same indication in October 2004. Phase I studies are being conducted to evaluate trabectedin in combination with doxorubicin and liposomal doxorubicin for the treatment of soft tissue sarcoma. PharmaMar is also conducting a phase I study of sequential paclitaxel followed by trabectedin in patients with soft tissue sarcoma. At additional dose levels, patients with other tumour types will be enrolled to assess the antitumour activity of the combination. The US NCI has approved and is partially funding a phase I clinical programme to determine the feasibility of using trabectedin to treat children with soft tissue sarcoma and bone sarcoma who are resistant to conventional therapies. PharmaMar has reported that trabectedin can be safely administered to children at doses up to 1100mg given as a 3-hour infusion, and that this dose will be used in further paediatric studies. Trabectedin has completed phase II studies for small round cell sarcoma and rhabdomyosarcoma, which are aggressive tumours occurring predominantly in children. A phase II study evaluating two dosing schedules of trabectedin has been conducted in patients with leiomyosarcomas or liposarcomas refractory to standard doxorubicin + ifosfamide chemotherapy. The study was conducted in Australia, Canada, Russia and the US.

Solifenacin in the management of the overactive bladder syndrome

Overactive bladder (OAB) is the term used to describe the symptom complex of urinary frequency and urgency, with or without urge incontinence. Whilst antimuscarinic drug therapy has proven to be effective in the management of patients with symptoms of the OAB syndrome, compliance with medication is often affected by the bothersome antimuscarinic adverse effects of dry mouth, constipation, somulence and blurred vision. The development of bladder selective M3 specific antagonists offers the possibility of increasing efficacy whilst minimising adverse effects. At present, there are no M3 specific antagonists currently available, although solifenacin and darifenacin are under development and are due to be registered in 2004-2005. The purpose of this article is to review the pharmacology and clinical trial data available for solifenacin in addition to examining its emerging role in the treatment of the OAB syndrome.

The Steady-State Michaelis–Menten Analysis of P-Glycoprotein Mediated Transport Through a Confluent Cell Monolayer Cannot Predict the Correct Michaelis Constant Km

PURPOSE

Typically, the kinetics of membrane transport is analyzed using the steady-state Michaelis-Menten (or Eadie-Hofstee or Hanes) equations. This approach has been successful when the substrate is picked up from the aqueous phase, like a water-soluble enzyme, for which the Michaelis-Menten steady-state analysis was developed. For membrane transporters whose substrate resides in the lipid bilayer of the plasma membrane, like P-glycoprotein (P-gp), there has been no validation of the accuracy of the steady-state analysis because the elementary rate constants for transport were not known.

METHODS

Recently, we fitted the mass action elementary kinetic rate constants of P-gp transport of three different drugs through a confluent monolayer of MDCKII-hMDR1 cells. With these elementary rate constants in hand, we use computer simulations to assess the accuracy of the steady-state Michaelis-Menten parameters. This limits the simulation to parameter ranges known to be physiologically relevant.

RESULTS

Using over 2,300 different vectors of initial elementary parameters spanning the space bounded by the three drugs, which defines 2,300 "virtual substrates", the concentrations of substrate transported were calculated and fitted to Eadie-Hofstee plots. Acceptable plots were obtained for 1,338 cases.

CONCLUSION

The fitted steady-state Vmax values from the analysis correlated to within a factor of 2-3 with the values predicted from the elementary parameters. However, the fitted Km value could be generated by a wide range of underlying "molecular" Km values. This is because of the convolution of the drug passive permeability kinetics into the fitted Km. This implies that Km values measured in simpler systems, e.g., microsomes or proteoliposomes, even if accurate, would not predict the Km values for the confluent monolayer system or, by logical extension, in vivo. Reliable in vitro-in vivo extrapolation seems to require using the elementary rate constants rather than the Michaelis-Menten steady-state parameters.

1-Methyl-1,2,3,4-tetrahydroisoquinoline enhances the anticonvulsant action of carbamazepine and valproate in the mouse maximal electroshock seizure model

1-Methyl-1,2,3,4-tetrahydroisoquinoline (1-MeTHIQ - an endogenous parkinsonism-preventing substance) administered intraperitoneally at a dose of 20 mg/kg considerably elevated the threshold for electroconvulsions in mice from 6.4 to 8.4 mA (P < 0.05). In contrast, the agent administered at 5 and 10 mg/kg had no significant impact on the electroconvulsive threshold in mice. Moreover, 1-MeTHIQ (at a subthreshold dose of 10 mg/kg) potentiated the anticonvulsant action of valproate (VPA) against maximal electroshock (MES)-induced seizures in mice, reducing its median effective dose (ED50) from 232 to 170 mg/kg (P < 0.001). Similarly, 1-MeTHIQ (at 10 mg/kg) enhanced the antielectroshock activity of carbamazepine (CBZ) in mice, decreasing its ED50 from 10.8 to 7.8 mg/kg (P < 0.05). In contrast, 1-MeTHIQ (at 10 mg/kg) did not affect the anticonvulsant action of phenytoin and phenobarbital against MES-induced seizures in mice. The evaluation of acute neurotoxic effects of the studied antiepileptic drugs (AEDs) in combination with 1-MeTHIQ, as regards motor coordination impairment in the chimney test, revealed no significant changes in median toxic doses (TD50) of conventional AEDs after systemic administration of 1-MeTHIQ (up to 10 mg/kg). Pharmacokinetic characterization of interactions between 1-MeTHIQ (10 mg/kg) and VPA (170 mg/kg) or CBZ (7.8 mg/kg) revealed no significant changes in total brain concentrations of CBZ and VPA, indicating that the observed enhancement of antiseizure effects of CBZ and VPA by 1-MeTHIQ was pharmacodynamic in nature. Based on our preclinical study, it may be concluded that 1-MeTHIQ exerts the anticonvulsant effects increasing the threshold for electroconvulsions and potentiating the antiseizure action of CBZ and VPA against maximal electroshock. The antiseizure properties of 1-MeTHIQ (an endogenous parkinsonism-preventing substance) and its exact physiological role in the brain need extensive examination in further neuropharmacological studies.

SPE-HPLC determination of new tetrahydroisoquinoline derivatives in rat plasma

Recently a novel class of non-competitive AMPA receptor (AMPAR) antagonists, such as, N-acetyl-1-(p-chlorophenyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline (PS3Ac) have been developed using molecular modeling studies. In this study we present a validated method for detecting PS3Ac in biological matrices by high performance liquid chromatography with ultraviolet detection. In this study PS3Ac was administered to Wistar rats. After intraperitoneal administration, the plasma concentrations of PS3Ac and its potential metabolic products, i.e., PS3OH, PS3 and PS3OHAc were determined. Serum samples (0.5 ml) were purified by solid-phase extraction of analytes using Oasis cartridges. The chromatographic separation was performed on a LiChrosorb RP-1 at 30 degrees C. The eluent was made of potassium dihydrogen phosphate/acetonitrile in ratio of 50:50 (v/v); the flow rate was 1 ml/min. The detection was performed at 220 nm. The method exhibited a large linear range from 0.05 to 5 microg/ml for all studied compounds. The intra-assay accuracy ranged from 92% determined at 0.1 microg/ml of PS3OH, to 108% determined at 0.05 microg/ml of PS3OHAc. The average coefficient of variation of inter-assay was 6.27%. The average recovery from plasma was 78.5%. The limits of quantification for all the tetrahydroisoquinoline derivatives was 20 ng. The method proved to be highly sensitive and specific for the determination of the studied compounds in rat plasma and has been successfully applied to the evaluation of the pharmacokinetic profile of the inoculated compound.