Effect of Roxadustat on the Pharmacokinetics of Simvastatin, Rosuvastatin, and Atorvastatin in Healthy Subjects: Results From 3 Phase 1, Open-Label, 1-Sequence, Crossover Studies.

Roxadustat inhibits breast cancer resistance protein and organic anion transporting polypeptide 1B1, which can affect coadministered statin concentrations. Three open-label, 1-sequence crossover phase 1 studies in healthy subjects were conducted to assess effects from steady-state 200-mg roxadustat on pharmacokinetics and tolerability of 40-mg simvastatin (CL-0537 and CL-0541), 40-mg atorvastatin (CL-0538), or 10-mg rosuvastatin (CL-0537). Statins were dosed concomitantly with roxadustat in 28 (CL-0537) and 24 (CL-0538) healthy subjects, resulting in increases of maximum plasma concentration (Cmax ) and area under the plasma concentration-time curve from the time of dosing extrapolated to infinity (AUCinf ) 1.87- and 1.75-fold for simvastatin, 2.76- and 1.85-fold for simvastatin acid, 4.47- and 2.93-fold for rosuvastatin, and 1.34- and 1.96-fold for atorvastatin, respectively. Additionally, simvastatin dosed 2 hours before, and 4 and 10 hours after roxadustat in 28 (CL-0541) healthy subjects, resulted in increases of Cmax and AUCinf 2.32- to 3.10-fold and 1.56- to 1.74-fold for simvastatin and 2.34- to 5.98-fold and 1.89- to 3.42-fold for simvastatin acid, respectively. These increases were not attenuated by time-separated statin dosing. No clinically relevant differences were observed for terminal elimination half-life. Concomitant 200-mg roxadustat and a statin was generally well tolerated during the study period. Roxadustat effects on statin Cmax and AUCinf were statin and administration time dependent. When coadministered with roxadustat, statin-associated adverse reactions and the need for statin dose reduction should be evaluated.

Effect of the Phosphate Binders Sevelamer Carbonate and Calcium Acetate on the Pharmacokinetics of Roxadustat After Concomitant or Time-separated Administration in Healthy Individuals.

PURPOSE: Roxadustat, a hypoxia-inducible factor prolyl hydroxylase inhibitor, treats anemia in chronic kidney disease. Hyperphosphatemia, a common complication in chronic kidney disease, is treated with phosphate binders (PBs). This study in healthy individuals investigated the effect of 2 PBs, sevelamer carbonate and calcium acetate, on the pharmacokinetic properties of a single oral dose of roxadustat administered concomitantly or with a time lag. METHODS: This 2-part, Phase I study was conducted with an open-label, randomized, 3-way (part 1) or 5-way (part 2) crossover design, with 5-day treatment periods. On day 1 of each period, participants received 200 mg roxadustat administered alone or (1) concomitantly with sevelamer carbonate (2400 mg) or calcium acetate (1900 mg) (part 1) or (2) 1 hour before or 1, 2, or 3 hours after sevelamer carbonate (part 2A) or calcium acetate (part 2B); 5 additional PB doses were administered during 2 days. In both parts, PBs were administered with meals. Primary pharmacokinetic variables were AUC0-∞ and Cmax. FINDINGS: Twenty-four individuals were randomized in part 1; 60 individuals were randomized in part 2 (part 2A, n = 30; part 2B, n = 30). All participants completed the study in part 1; 28 and 27 individuals completed the study in part 2A and part 2B, respectively. Compared with roxadustat alone, concomitant sevelamer carbonate and calcium acetate administration reduced roxadustat's AUC0-∞ by 67% (90% CI, 63.5%-69.3%) and 46% (90% CI, 41.7%-50.9%), respectively, and reduced roxadustat's Cmax by 66% (90% CI, 61.6%-69.4%) and 52% (90% CI, 46.2%-57.2%), respectively. This effect was attenuated when roxadustat and PB administration occurred with a time lag. Roxadustat's AUC0-∞ was reduced by 41% and 22% to 25%, respectively, when roxadustat was administered 1 hour before or 1 to 3 hours after sevelamer carbonate and by 31% and 14% to 18%, respectively, when administered 1 hour before or 1 to 3 hours after calcium acetate. Roxadustat's Cmax was reduced by 26% and 12%, respectively, when roxadustat was administered 1 hour before and 1 hour after sevelamer carbonate; it was reduced by 19% when administered 1 hour before calcium acetate and was not affected when administered 1 hour after. Roxadustat was well tolerated. IMPLICATIONS: Concomitant administration of roxadustat with sevelamer carbonate or calcium acetate reduced exposure to roxadustat in healthy individuals. This effect was attenuated when roxadustat was administered ≥1 hour before or after either PB. Results from this study helped inform dosing and administration guidelines aimed at reducing interactions between roxadustat and these PBs.

Effect of Multiple Doses of Omeprazole on the Pharmacokinetics, Safety, and Tolerability of Roxadustat in Healthy Subjects.

BACKGROUND AND OBJECTIVES: Roxadustat is an orally active hypoxia-inducible factor prolyl hydroxylase inhibitor for the treatment of anemia in chronic kidney disease. This study investigated the effect of multiple daily oral doses of omeprazole on the pharmacokinetics, safety, and tolerability of a single oral dose of roxadustat. METHODS: This phase 1, open-label, two-period, one-sequence, crossover study enrolled healthy subjects. During Period 1, subjects received a single oral dose of 100 mg roxadustat. After a ≥ 7-day washout, subjects started Period 2 and received daily oral doses of 40 mg omeprazole on Days 1-9, and a single oral dose of 100 mg roxadustat on Day 7. Roxadustat pharmacokinetics were assessed on Days 1-4 in Period 1 and on Days 7-10 in Period 2. Primary endpoints were area under the concentration-time profile from the time of dosing extrapolated to infinity (AUCinf) and maximum concentration (Cmax). Safety was assessed by vital signs, laboratory tests, electrocardiograms, and nature, frequency, and severity of treatment-emergent adverse events (TEAEs). RESULTS: Eighteen subjects were enrolled. The geometric least squares mean ratio for both AUCinf and Cmax of roxadustat (with omeprazole/alone) was 104.5%; 90% confidence intervals were within the no-effect boundaries of 80.0 and 125.0%, indicating no significant effect of omeprazole on the pharmacokinetics of roxadustat. No serious TEAEs were reported. CONCLUSION: Multiple daily oral doses of 40 mg omeprazole had no significant effect on the pharmacokinetics of a single oral dose of 100 mg roxadustat. Roxadustat was considered safe and well tolerated when administered alone or in combination with multiple daily oral doses of 40 mg omeprazole in healthy subjects.

Effect of Moderate Hepatic Impairment on the Pharmacokinetics and Pharmacodynamics of Roxadustat, an Oral Hypoxia-Inducible Factor Prolyl Hydroxylase Inhibitor.

BACKGROUND AND OBJECTIVE: Roxadustat is a hypoxia-inducible factor prolyl hydroxylase inhibitor in phase III development for the treatment of anaemia associated with chronic kidney disease. This study evaluated the effects of moderate hepatic impairment on roxadustat pharmacokinetics, pharmacodynamics and tolerability. METHODS: This was an open-label study in which eight subjects with moderate hepatic impairment (liver cirrhosis Child-Pugh score 7-9) and eight subjects with normal hepatic function (matched for body mass index, age and sex) received a single oral 100 mg roxadustat dose under fasted conditions. Blood samples were collected until 144 h post-dose in subjects with moderate hepatic impairment and until 96 h post-dose in subjects with normal hepatic function. RESULTS: In subjects with moderate hepatic impairment, area under the concentration-time curve (AUC) from the time of drug administration to infinity (AUC∞) and observed maximum concentration (C max) were 23 % higher [geometric least-squares mean ratio (GMR) 123 %; 90 % CI 86.1-175] and 16 % lower (GMR 83.6 %; 90 % CI 67.5-104), respectively, than in subjects with normal hepatic function. Mean terminal half-life (t ½) appeared to be longer (17.7 vs. 12.8 h) in subjects with moderate hepatic impairment, however intersubject variability on apparent total systemic clearance after single oral dosing (CL/F), apparent volume of distribution at equilibrium after oral administration (V z/F) and t ½ was approximately twofold higher. Erythropoietin (EPO) baseline-corrected AUC from administration to the last measurable EPO concentration (AUCE,last) and maximum effect (E max) were 31 % (GMR 68.95 %; 90 % CI 29.29-162.29) and 48 % (GMR 52.29 %; 90 % CI 28.95-94.46) lower, respectively, than in subjects with normal hepatic function. The single oral roxadustat dose was generally well tolerated. CONCLUSIONS: This study demonstrated the effect of moderate hepatic impairment on the pharmacokinetics and pharmacodynamics of roxadustat relative to subjects with normal hepatic function. These differences are not expected to be of clinical significance.

The Hypoxia-inducible Factor Prolyl-Hydroxylase Inhibitor Roxadustat (FG-4592) and Warfarin in Healthy Volunteers: A Pharmacokinetic and Pharmacodynamic Drug-Drug Interaction Study.

PURPOSE: Roxadustat is a small-molecule hypoxia-inducible factor prolyl-hydroxylase inhibitor in late-stage clinical development for the treatment of anemia in patients with chronic kidney disease (CKD). Warfarin is an oral anticoagulant with a narrow therapeutic window that is often prescribed to treat coexisting cardiovascular diseases in patients with CKD. This clinical trial was designed to evaluate the effect of roxadustat on warfarin pharmacokinetic and pharmacodynamic parameters. METHODS: This open-label, single-sequence crossover study was conducted in healthy volunteers (male or female) aged 18 to 55 years with a body mass index of 18.5 to 30.0 kg/m(2). The study consisted of 2 periods separated by a minimum washout period of 14 days. After an overnight fast, volunteers received a single oral dose of 25 mg (5 × 5 mg tablets) warfarin on Day 1 of Period 1 and Day 7 of Period 2. Volunteers received oral doses of 200 mg (2 × 100 mg tablets) roxadustat on Days 1, 3, 5, 7 (concomitant with warfarin), 9, 11, 13, and 15 of Period 2. Plasma S- and R-warfarin (unbound and total concentrations) and prothrombin time were determined at multiple time points up to 216 hours postdose. Pharmacokinetic and pharmacodynamic parameters were estimated via noncompartmental methods. Tolerability was evaluated by monitoring adverse events, laboratory assays, vital signs, and 12-lead ECGs. FINDINGS: The geometric mean ratios and 90% CIs for Cmax and AUC∞ of total and unbound S- and R-warfarin (with and without roxadustat) were within the standard bioequivalence interval of 80.00% to 125.00%. Roxadustat increased the geometric mean (GM) prothrombin (PT) and international normalized ratio (INR) AUC from time zero to last measurable sample (AUCPT,last and AUCINR,last) by 24.4%. Coadministration of roxadustat and warfarin in healthy volunteers was associated with a favorable tolerability profile, with most treatment-associated adverse events mild in severity. IMPLICATIONS: Based on the lack of clinically significant pharmacokinetic interactions and the limited influence on warfarin pharmacodynamic parameters, no dose adjustment of warfarin should be required when coadministered with roxadustat. ClinicalTrials.gov identifier: NCT02252731.

The effect of mirabegron, a potent and selective ß3-adrenoceptor agonist, on the pharmacokinetics of CYP2D6 substrates desipramine and metoprolol.

Mirabegron is a potent and selective ß3-adrenoceptor agonist developed for the treatment of overactive bladder. In vitro studies demonstrated that mirabegron partly acts as a (quasi-) irreversible, metabolism-dependent inhibitor of CYP2D6. The effect of steady-state mirabegron on single doses of the sensitive CYP2D6 substrates metoprolol (100 mg) and desipramine (50 mg) was assessed in two open-label, one-sequence crossover studies in healthy subjects (CYP2D6 extensive metabolizers). Mirabegron 160 mg/day increased metoprolol maximum plasma concentration (C max) 1.90-fold (90 % confidence interval [CI] 1.54; 2.33) and total exposure (AUC0-∞) 3.29-fold (90 % CI 2.70; 4.00) in 12 males (study 1). Mean metoprolol half-life increased from 2.96 to 4.11 h. α-Hydroxymetoprolol C max and AUC to last measurable concentration decreased 2.6-fold and 2.2-fold, respectively. In study 2, mirabegron 100 mg/day increased desipramine C max 1.79-fold (90 % CI 1.69; 1.90) and AUC0-∞ 3.41-fold (90 % CI 3.07; 3.80) in 14 males and 14 females. Mean desipramine half-life increased from 19.5 to 35.8 h. C max of 2-hydroxydesipramine decreased ~twofold, while AUC increased ~1.3-fold. Desipramine was administered again 2 weeks after the last mirabegron dose. Desipramine C max and AUC0-∞ were still ~1.13-fold increased; the 90 % CIs fell within the 0.80-1.25 interval. All treatments were well tolerated. In conclusion, mirabegron is a moderate CYP2D6 inhibitor (ratio and 90 % CI <5.0).

D optimal designs for three Poisson dose-response models.

The objective of this paper was to find and investigate the performance of the D optimal designs for three Poisson dose-response models. Phase II dose ranging studies are pivotal in the drug development program, being used to select dose(s) for phase III. Count data is encountered in a number of clinical areas. The Poisson distribution provides an intuitive platform for modelling such data, especially when combined with random effects which allow subjects to differ in their response rates. This work investigated three Poisson dose-response models of increasing complexity. A simple E(max) model was used to describe the drug effect, and D optimal designs under a range of different parameter values (scenarios) were found. The relative performances between scenarios were assessed using: the precision of all parameters, the precision of the drug effect parameters, and the percent coefficient of variation (%CV) of the ED(50) parameter. The results showed that the D optimal designs were similar across models and scenarios, with the D optimal designs consisting of placebo, the maximum dose, and a dose just below the ED(50). However the relative performance of the optimal designs was very different. For example, with 1,000 subjects, the %CV of the ED(50) parameter ranged from 1.4 to 91 %. Performance typically improved with higher baseline counts, smaller random effects, and larger E(max). This work introduces a framework for determining and evaluating the performance of D optimal designs for phase II dose ranging studies with count data as the primary endpoint.

Effect of renal or hepatic impairment on the pharmacokinetics of mirabegron.

BACKGROUND AND OBJECTIVES: Mirabegron, a selective ß3-adrenoceptor agonist for the treatment of overactive bladder (OAB), is eliminated by renal and metabolic routes. The potential influence of renal or hepatic impairment on the pharmacokinetics of mirabegron was evaluated. METHODS: Two separate open-label, single-dose, parallel-group studies were conducted. Male and female subjects (n = 8 per group) were categorized according to their baseline renal function (mild, moderate, severe or no impairment as determined by estimated glomerular filtration rate [eGFR] using the abbreviated modification of diet in renal disease formula) or hepatic function (mild, moderate or no impairment as determined by the Child-Pugh classification). All subjects received a single oral 100 mg dose of mirabegron. Non-compartmental pharmacokinetic parameters were determined from plasma and urine concentration-time data of mirabegron and metabolites. RESULTS: Compared with healthy subjects who were similar overall in terms of age, sex and body mass index (BMI), the geometric mean area under the plasma concentration-time curve from time zero extrapolated to infinity (AUC(∞)) for mirabegron was 31, 66 and 118 % higher in subjects with mild, moderate and severe renal impairment, respectively. Peak plasma concentrations (C(max)) increased 6, 23 and 92 %, respectively, in subjects with mild, moderate and severe renal impairment. Renal clearance but not apparent total body clearance of mirabegron correlated well with renal function. Compared with healthy subjects matched for age, sex and BMI, mirabegron AUC(∞) values were 19 and 65 % higher in subjects with mild and moderate hepatic impairment, respectively. Mirabegron C(max) was 9 and 175 % higher, respectively, compared with matched healthy subjects. No clear relationship was evident between pharmacokinetic parameters and Child-Pugh scores. Protein binding was approximately 71 % in healthy subjects and was not altered to a clinically significant extent in subjects with renal or hepatic impairment. No consistent changes in mirabegron elimination half-life were observed in subjects with renal or hepatic impairment. There was high pharmacokinetic variability and significant overlap in exposures between subjects with renal or hepatic impairment and healthy subjects. CONCLUSION: Mirabegron AUC(∞) and C(max) increased 118 and 92 %, respectively, in subjects with severe renal impairment, and 65 and 175 %, respectively, in subjects with moderate hepatic impairment. Pharmacokinetic changes observed in subjects with mild or moderate renal impairment or mild hepatic impairment are of small magnitude and likely to be without clinical importance.

Pharmacokinetic properties of mirabegron, a ß3-adrenoceptor agonist: results from two phase I, randomized, multiple-dose studies in healthy young and elderly men and women.

BACKGROUND: Mirabegron (YM178) is a ß(3)-adrenoceptor agonist for the treatment of overactive bladder (OAB). As part of the clinical development program for mirabegron, 2 human volunteer studies were performed to derive detailed data on the multiple-dose pharmacokinetic (PK) properties of mirabegron. OBJECTIVE: Two randomized Phase I studies were conducted to evaluate the PK properties of mirabegron, including metabolic profile and effects of age and sex, following multiple oral doses in healthy subjects. METHODS: In study 1, mirabegron oral controlled absorption system (OCAS) tablets were administered once daily to healthy young subjects (18-55 years) at doses of 50, 100, 200, and 300 mg and in elderly subjects (65-80 years) at 50 and 200 mg in a double-blind placebo-controlled, parallel-group design. In study 2, mirabegron OCAS was administered once daily to healthy young (18-45 years) and older (≥55 years) subjects at doses of 25, 50, and 100 mg in an open-label crossover design. Blood samples were collected up to 72 hours (study 1) and 168 hours (study 2) after the last dose. Urine samples were collected up to 24 hours after the last dose. Plasma and urine concentrations of mirabegron and its metabolites (study 2 only) were analyzed by LC-MS/MS. PK parameters were determined using noncompartmental methods. Tolerability assessments included physical examinations, supine blood pressure and pulse rate, orthostatic stress testing (study 1), resting 12-lead ECGs, clinical laboratory tests (biochemistry, hematology, and urinalysis), and adverse-events (AE) monitoring using investigators' questionnaires and subjects' spontaneous reports. RESULTS: Thirty-two young male (mean age, 30.3 years; mean weight, 77.1 kg), 32 young female (27.6 years; 64.6 kg), 16 elderly male (69.8 years; 79.3 kg), and 16 elderly female (68.1 years; 67.4 kg) subjects were enrolled in study 1. Eighteen young male (mean age, 28.6 years; mean weight, 68.9 kg), 18 young female (28.7 years; 58.8 kg), 21 older male (63.4 years; 72.6 kg), and 18 older female (65.1 years; 62.3 kg) subjects were enrolled in study 2. Most of the subjects were white (91% in study 1 and 88% in study 2). Mirabegron plasma concentrations peaked at ∼3 to 5 hours and declined multiexponentially with a t of ∼32 hours in study 1 and 60 hours in study 2. Steady state was achieved within 7 days of once daily administration, with an accumulation ratio of ∼2. Mirabegron and its metabolites demonstrated a greater-than-dose-proportional increase in C(max) and AUC(0-τ) after multiple-dose administration. Two major circulating metabolites were observed, representing 17% and 10% of total drug-related AUC(0-τ). Excretion of unchanged mirabegron in urine over the 24-hour dosing interval (Ae(0-τ)%) increased from approximately 7% at 25 mg to 18% at 300 mg once daily in young subjects. Renal clearance (CL(R)) of mirabegron was independent of dose and averaged ∼13 L/h. Mirabegron C(max) and AUC(0-τ) were similar in older and young subjects. Women exhibited ∼40% higher mirabegron C(max) and AUC(0-τ) than men; weight-corrected values were ∼20% higher in women. Mirabegron was generally well tolerated up to 300 mg once daily. No clear trends for increased incidence of AEs occurred with higher doses of mirabegron. The AE with the highest incidence was headache. CONCLUSION: Oral mirabegron exhibited a greater-than-dose-proportional increase in exposure. Sex but not age significantly affected mirabegron exposure. ClinicalTrials.gov identifier: NCT01478503 (Study 1) and NCT01285596 (Study 2).

Single dose pharmacokinetics and absolute bioavailability of mirabegron, a ß3-adrenoceptor agonist for treatment of overactive bladder.

BACKGROUND AND OBJECTIVES: Mirabegron is a potent and selective ß3-adrenoceptor agonist in development for treatment of overactive bladder. METHODS: Mirabegron pharmacokinetics after single intravenous (i.v.) and oral doses, absolute bioavailability (F), dose proportionality, sex differences and tolerability were assessed in 2 single-dose, open-label, randomized, parallel-group, cross-over studies in healthy men (exploratory Study 1, n = 12) and men and women (Study 2, n = 91). RESULTS: After oral dosing (25 - 150 mg), peak plasma concentrations were attained after ~ 4 h. Mean half-life was around 40 h for both routes of administration. Volume of distribution at steady state was 1,670 l and total clearance was around 57 l/h for i.v. dosing. Mirabegron pharmacokinetics were linear after i.v. dosing (7.5 - 50 mg), but exposure increased more than proportionally after oral dosing due to increased F (29% for 25 mg to 45% at 150 mg). About 20% of the (absorbed) dose was excreted unchanged into urine. Area under the curve (AUC) was 27% and 64% higher in females than males after i.v. and oral dosing respectively; differences were mostly attributed to body weight, and for oral dosing, also to F. CONCLUSIONS: Mirabegron pharmacokinetics were linear after i.v. dosing (7.5 - 50 mg), but increased more than proportionally after oral dosing (25 - 150 mg) as a result of increased F. Sex differences in exposure could be explained by body weight and for oral dosing, also by F. Mirabegron was in general well tolerated up to the highest doses studied, 50 mg i.v. and 150 mg oral.

Absorption, metabolism and excretion of [(14)C]mirabegron (YM178), a potent and selective ß(3)-adrenoceptor agonist, after oral administration to healthy male volunteers.

The mass balance and metabolite profiles of 2-(2-amino-1,3-thiazol-4-yl)-N-[4-(2-{[(2R)-2-hydroxy-2-phenylethyl]amino}ethyl)[U-(14)C]phenyl]acetamide ([(14)C]mirabegron, YM178), a ß(3)-adrenoceptor agonist for the treatment of overactive bladder, were characterized in four young, healthy, fasted male subjects after a single oral dose of [(14)C]mirabegron (160 mg, 1.85 MBq) in a solution. [(14)C]Mirabegron was rapidly absorbed with a plasma t(max) for mirabegron and total radioactivity of 1.0 and 2.3 h postdose, respectively. Unchanged mirabegron was the most abundant component of radioactivity, accounting for approximately 22% of circulating radioactivity in plasma. Mean recovery in urine and feces amounted to 55 and 34%, respectively. No radioactivity was detected in expired air. The main component of radioactivity in urine was unchanged mirabegron, which accounted for 45% of the excreted radioactivity. A total of 10 metabolites were found in urine. On the basis of the metabolites found in urine, major primary metabolic reactions of mirabegron were estimated to be amide hydrolysis (M5, M16, and M17), accounting for 48% of the identified metabolites in urine, followed by glucuronidation (M11, M12, M13, and M14) and N-dealkylation or oxidation of the secondary amine (M8, M9, and M15), accounting for 34 and 18% of the identified metabolites, respectively. In feces, the radioactivity was recovered almost entirely as the unchanged form. Eight of the metabolites characterized in urine were also observed in plasma. These findings indicate that mirabegron, administered as a solution, is rapidly absorbed after oral administration, circulates in plasma as the unchanged form and metabolites, and is recovered in urine and feces mainly as the unchanged form.

An example of optimal phase II design for exposure response modelling.

This paper presents an example of how optimal design methodology was used to help design a phase II clinical study. The planned analysis would relate the clinical endpoint to exposure (measured via the area under the curve (AUC)), rather than dose. Optimal design methodology was used to compare a number of candidate phase II designs, and an algorithm for finding optimal designs was employed. The sigmoidal E(max) with baseline (E0) model was used to relate the clinical endpoint to individual subject AUCs, and the primary metrics were D optimality and the standard error (SE) of the AUC required to yield a clinically relevant change in the clinical endpoint. The performance of the candidate designs were compared across four different 'true' exposure response relationships (determined from the analysis of an earlier proof of concept (PoC) study). The results suggested the total sample size should be increased from the planned 540 individuals, and that the optimal design with 700 individuals would be equivalent to 812 individuals with the reference design (a 16% gain). The performance with this design was considered acceptable, although all designs performed poorly if the true exposure response relationship was very flat. This work allowed a prospective assessment of the likely performance and precision from the exposure response modelling prior to the start of the phase II study, and hence allowed the design to be revised to ensure the subsequent analysis would be of most value.

Pharmacokinetic/pharmacodynamic modelling of the anti-hyperalgesic and anti-nociceptive effect of adenosine A1 receptor partial agonists in neuropathic pain.

The objective of this investigation was to characterise the pharmacokinetic-pharmacodynamic correlation of adenosine A1 receptor partial agonists in the chronic constriction injury model of neuropathic pain. Following intravenous administration of 8-methylamino-N6-cyclopentyl-adenosine (MCPA; 10 mg/kg) and 2'deoxyribose-N6-cyclopentyl-adenosine (2'dCPA; 20 mg/kg), the time course of the effect on the mechanical paw pressure threshold was determined in conjunction with plasma concentrations. Population pharmacokinetic/pharmacodynamic analysis was applied to derive individual concentration-effect relationships. A composite model consisting of an E(max) model for the anti-hyperalgesic effect in combination with a linear model for the anti-nociceptive effect accurately described the concentration-effect relationship. For both compounds, a full anti-hyperalgesic effect was observed. The values of the EC50 for the anti-hyperalgesic effect were (mean+/-S.D.): 3170+/-1460 and 2660+/-1200 ng/ml for MCPA and 2'dCPA versus 178+/-51 ng/ml for the reference full agonist 5'deoxyribose-N6-cyclopentyl-adenosine (5'dCPA). The values of the slope for the anti-nociceptive effect were 1.9+/-0.30 and 1.2+/-0.20 g.microl/ng, respectively, versus 55+/-8 g microl/ng for 5'dCPA. Adenosine A1 receptor partial agonists behave as full agonists with regard to the anti-hyperalgesic effect in neuropathic pain, but the anti-nociceptive effect is diminished.

Brain penetration of synthetic adenosine A1 receptor agonists in situ: role of the rENT1 nucleoside transporter and binding to blood constituents.

The blood-brain barrier (BBB) transport of synthetic A(1) receptor agonists was studied in an in situ brain perfusion model in the presence and absence of the selective nucleoside transport inhibitor S-(4-nitrobenzyl)-6-thioinosine (NBTI). For 8-methylamino-N(6)cyclopentyladenosine (MCPA), N(6)-cyclopentyladenosine (CPA), 2'deoxy-N(6)-cyclopentyladenosine (2'dCPA) and 5'deoxy-N(6)-cyclopentyl adenosine (5'dCPA) the brain uptake clearance was low with values of 0.0045+/-0.0012, 0.018+/-0.0020, 0.022+/-0.0028 and 0.12+/-0.054 ml min(-1)g(-1), respectively. In the presence of an average NBTI plasma concentration of 2.6+/-0.3 microg ml(-1) (NBTI dose: 3 mg kg(-1) i.v.) the values of the brain uptake clearance were 0.0062+/-0.0012, 0.013+/-0.0017, 0.014+/-0.0030 and 0.13+/-0.066 ml min(-1)g(-1), respectively and not significantly different from the values in the absence of NBTI. In a separate experiment the brain uptake of MCPA from phosphate buffered saline (PBS) and whole blood were compared. The brain uptake clearance from whole blood (0.0012+/-0.001 ml min(-1)g(-1)) was significantly lower than from PBS (0.0045+/-0.0012 ml min(-1)g(-1)). The results of these studies show that the rENT1 nucleoside transporter does not contribute significantly to the transport of synthetic A(1) receptor agonists across the BBB and that binding to blood constituents restricts the brain uptake.

Population pharmacokinetic-pharmacodynamic modelling of the anti-hyperalgesic effect of 5'deoxy-N6-cylopentyladenosine in the mononeuropathic rat.

The objective of this investigation was to characterise the pharmacokinetic-pharmacodynamic correlation of 5'-deoxy-N6-cyclopentyl-adenosine (5'dCPA) in the chronic constriction injury model of neuropathic pain. Following intravenous administration of 5'dCPA (0.30 or 0.75 mg kg(-1)), the time course of the drug concentration in plasma was determined in conjunction with the effect on (1) the mechanical paw pressure and (2) the Von Frey Hair monofilament withdrawal threshold. Population pharmacokinetic-pharmacodynamic analysis was applied to derive individual concentration-effect relationships. For mechanical paw pressure a composite model consisting of an Emax model for the anti-hyperalgesic effect in combination with a linear model for the anti-nociceptive effect accurately described the data. The EC50 for the anti-hyperalgesic effect was 178+/-51 ng ml(-1) and the slope of the anti-nociceptive effect 0.055+/-0.008 g ml ng(-1). For the Von Frey Hair monofilament withdrawal threshold responders and non-responders were observed. Typically, in responders, full pain relief was observed at concentrations exceeding 100 ng ml(-1). The high plasma concentrations required for the anti-hyperalgesic effect relative to the receptor affinity are consistent with restricted transport of 5'dCPA to the site of action in the spinal cord and/or the brain.

Blood-brain barrier transport of synthetic adenosine A1 receptor agonists in vitro: structure transport relationships.

Transport of 11 structurally related adenosine A(1) receptor agonists was determined in an in vitro BBB model of brain-capillary-endothelial-cells and astrocytes. Inhibitor S-(4-nitrobenzyl)-6-thioinosine (NBTI) was used to quantify the contribution of the es nucleoside transporter to the overall transport. The N(6)-substituted adenosine analogues N(6)-cyclobutyladenosine (CBA), N(6)-cyclopentyladenosine (CPA) and N(6)-cyclohexyladenosine (CHA) showed concentration-dependent clearance and their transport could be inhibited by NBTI. The V(max) was 1.5+/-0.2 pmol min(-1) and the Km values were 2.2+/-0.2, 1.8+/-0.3 and 15+/-4 microM for CBA, CPA and CHA, respectively. Further chemical modification such as substitution in the C8-position or modification at the ribose-moiety resulted in loss of affinity for the es nucleoside transporter. Transport by passive diffusion was slow with clearances ranging from 0.21+/-0.01 microl min(-1) for 8-(methylamino)-CPA (MCPA) to 1.8+/-0.18 microl min(-1) for 5'-deoxy-CPA (5'dCPA). Regression analysis showed no relationship between transport clearance by passive diffusion and the GTP-shift, a non-linear relationship between the transport clearance by passive diffusion and the dynamic polar surface area (Cl=0.469e(-0.071DPSA); R2=0.88) and a linear relationship between transport clearance and prediction of BBB transport on basis of the Abraham equation (logCl=1.53logBB-1.56; R2=0.83). It is concluded that the transport of synthetic A(1) adenosine derivatives across the blood-brain barrier is generally quite slow. In addition, transport by the es nucleoside transporter may contribute to the transport of certain structurally distinct analogues.

Functional role of adenosine receptor subtypes in the regulation of blood-brain barrier permeability: possible implications for the design of synthetic adenosine derivatives.

The objective of this investigation was to determine the functional role of adenosine receptor subtypes in the regulation of blood-brain barrier (BBB) permeability. The presence of the equilibrative es and ei nucleoside transporters at the BBB was also determined. Studies were conducted in an experimental in vitro BBB model comprising bovine brain capillary endothelial cells (BCECs) and rat astrocytes (RAs). The presence of the receptors and transporters was investigated by a combination of RT-PCR and radioligand binding assays. Changes in paracellular permeability were investigated on basis of changes in trans-endothelial-electrical-resistance (TEER) and transport of paracellular markers. In BCECs the presence of A(2A) and A(3) receptors and the es nucleoside transporter was demonstrated. The A(1) receptor was absent, while the presence of the A(2B) receptor and the ei nucleoside transporter remained uncertain. In RAs the presence of all four receptor subtypes and the es and ei nucleoside transporters was demonstrated. Upon application of selective agonists no significant changes in TEER or the transport of the paracellular markers were observed. The functional role of adenosine receptor subtypes in regulating the paracellular permeability of the BBB is probably small. It is unlikely therefore that the BBB transport of synthetic adenosine analogues is modified by permeability changes. The es nucleoside transporter might play a role in the BBB transport of synthetic adenosine analogues.