Marleen Depré

Comparative Inhibitory Activity of Rofecoxib, Meloxicam, Diclofenac, Ibuprofen, and Naproxen on COX‐2 versus COX‐1 in Healthy Volunteers

Steady‐state inhibitory activity of rofecoxib (Vioxx™) on COX‐2 versus COX‐1 was compared with that of commonly used nonsteroidal anti‐inflammatory drugs (NSAIDs) in 76 healthy volunteers randomized to placebo, rofecoxib 12.5 mg qd, rofecoxib 25 mg qd, diclofenac 50 mg tid, ibuprofen 800 mg tid, sodium naproxen 550 mg bid, or meloxicam 15 mg qd. All of these doses include the high end of the approved clinical dose range. Ex vivo whole‐blood assays were used to determine the effect on COX‐2 and COX‐1 activity, respectively. Urinary prostanoids were also measured. Mean inhibition of COX‐2 (measured as the weighted average inhibition [WAI] of lipopolysaccharide [LPS]‐induced PGE2 generation over 8 hours on day 6 vs. baseline) was −2.4%, 66.7%, 69.2%, 77.5%, 93.9%, 71.4%, and 71.5% for placebo, rofecoxib 12.5 mg, rofecoxib 25 mg, meloxicam, diclofenac, ibuprofen, and naproxen, respectively. Corresponding values for mean inhibition of COX‐1 (measured as TXB2 generation in clotting whole blood) were −5.15%, 7.98%, 6.65%, 53.3%, 49.5%, 88.7%, and 94.9%. Rofecoxib had no significant effect on urinary excretion of 11‐dehydro TXB2, a COX‐ 1‐derived product. These data support the contention that rofecoxib is the only drug of the regimens tested that uniquely inhibits COX‐2 without affecting COX‐1.

The acyclic CB1R inverse agonist taranabant mediates weight loss by increasing energy expenditure and decreasing caloric intake

Cannabinoid 1 receptor (CB1R) inverse agonists are emerging as a potential obesity therapy. However, the physiological mechanisms by which these agents modulate human energy balance are incompletely elucidated. Here, we describe a comprehensive clinical research study of taranabant, a structurally novel acyclic CB1R inverse agonist. Positron emission tomography imaging using the selective CB1R tracer [(18)F]MK-9470 confirmed central nervous system receptor occupancy levels ( approximately 10%-40%) associated with energy balance/weight-loss effects in animals. In a 12-week weight-loss study, taranabant induced statistically significant weight loss compared to placebo in obese subjects over the entire range of evaluated doses (0.5, 2, 4, and 6 mg once per day) (p < 0.001). Taranabant treatment was associated with dose-related increased incidence of clinical adverse events, including mild to moderate gastrointestinal and psychiatric effects. Mechanism-of-action studies suggest that engagement of the CB1R by taranabant leads to weight loss by reducing food intake and increasing energy expenditure and fat oxidation.

The effect of mk-0591, a novel 5-lipoxygenase activating protein inhibitor, on leukotriene biosynthesis and allergen-induced airway responses in asthmatic subjects in-vivo

BACKGROUND The 5-lipoxygenase metabolites of arachidonic acid are likely to be involved in the pathophysiology of atopic asthma. We investigated the effect of pretreatment with MK-0591, a novel 5-lipoxygenase activating protein inhibitor, on allergen-induced early asthmatic reactions (EARs) and late asthmatic reactions (LARs), and subsequent airway hyperresponsiveness to histamine. METHODS Eight atopic men with mild to moderate asthma aged 19 to 31 years, (forced expiratory volume in 1 second [FEV1] > or = 67% of predicted value, histamine provocative concentration causing a 20% fall in FEV1 [PC20] < 4 mg/ml) and documented EAR and LAR to house dust mite extract participated in a two-period, double-blind, placebo-controlled, crossover study. During each study period histamine PC20 was measured 2 days before and 1 day after a standardized allergen inhalation challenge test. MK-0591 was administered in 3 oral doses of 250 mg each at 24, 12, and 1.5 hours before inhalation of allergen. Biochemical activity of MK-0591 was determined by calcium ionophore A-23187-stimulated leukotriene (LT)B4 biosynthesis in whole blood ex vivo and by urinary LTE4 excretion. Airway response to allergen was measured by FEV1 (percent fall from baseline). The EAR (0 to 3 hours) and the LAR (3 to 8 hours) were expressed as corresponding areas under the time-response curves. RESULTS MK-0591 and placebo did not differ in their effects on prechallenge FEV1 (p = 0.10). As compared with the value before pretreatment, MK-0591 blocked LTB4 biosynthesis and LTE4 excretion by a mean of 98% (range, 96% to 99%; p < 0.002) and 87% (range, 84% to 96%; p < 0.046), respectively, from 0 to 24 hours after allergen challenge. Both the EAR and the LAR were significantly reduced after administration of MK-0591 as compared with placebo, with a mean inhibition of 79% (p = 0.011) and 39% (p = 0.040), respectively. Allergen-induced airway hyperresponsiveness was not significantly different between the two pretreatment periods (p = 0.37). CONCLUSIONS In this study oral MK-0591 prevented leukotriene biosynthesis after allergen challenge in patients with mild to moderate asthma. The results of our study indicate that 5-lipoxygenase products play an important role during the EAR, whereas their contribution to the pathophysiology of the LAR seems to be of less importance.

Tolerance and pharmacokinetics of propacetamol, a paracetamol formulation for intravenous use

Summary— In 12 healthy volunteers, paracetamol pharmacokinetics were compared following administration of 1 g propacetamol HCl given intravenously over a 15‐min period and 500 mg paracetamol given orally. Mean ± SD total AUC (μg/ml·h) following the iv formulation was significantly (P < 0.01) greater than following oral paracetamol (25.53 ± 4.27 vs 21.04 ± 4.49) corresponding to a mean oral bioavailability of paracetamol of 82.2 ± 9.4%. Between 1 and 2 h after administration, paracetamol plasma concentrations became very similar following both formulations. In another study, 2 g propacetamol HCl was given both as a 15‐min infusion and as a 2‐min bolus injection to six healthy volunteers. Contrary to mild to moderate local discomfort experienced during the 2‐min bolus injection, the 15‐min infusion was well tolerated without any complaints reported.

Pharmacokinetics, COX-2 specificity, and tolerability of supratherapeutic doses of rofecoxib in humans.

AbstractObjective: Prostaglandin synthesis is catalyzed by a constitutive cyclo-oxygenase isoform (COX-1) and an inducible isoform (COX-2). It is hypothesized that the analgesic and anti-inflammatory effects of nonsteroidal anti-inflammatory drugs (nonspecific COX-1/COX-2 inhibitors) such as ibuprofen principally derive from COX-2 inhibition. The purpose of this study was to evaluate steady-state pharmacokinetics, biochemical selectivity and tolerability of rofecoxib (VioxxTM), characterized in vitro as a COX-2 inhibitor. Methods: Four panels of healthy men (n=8 per panel) were administered rofecoxib (n=6) (25, 100, 250, 375 mg) or placebo (n=2) once daily on day 1 and days 3–14. Blood samples for assays of rofecoxib plasma concentration and COX isoform activity were obtained pre-dose and at specified time points post-dose. Results: Rofecoxib pharmacokinetics were found to be complex and nonlinear. Elimination half-life ranged from 9.9 h to 17.5 h after multiple dosing with an accumulation ratio close to 2 for all doses. COX-2 inhibitory activity as assessed by average inhibition of whole blood lipopolysaccharide-stimulated prostaglandin E2 over the 8-h post-dose period on day 14 was 0.3, 67, 96, 92 and 96% for the placebo and the 25-, 100-, 250- and 375-mg treatment groups, respectively. No treatment group showed significant inhibition of COX-1 as assessed by thromboxane B2 generation in clotting whole blood. Side effects were mild and transient. Conclusion: The results indicate that rofecoxib is a potent and specific inhibitor of COX-2 in humans even at doses more than tenfold higher than those associated with efficacy in patients with osteoarthritis.

Multiple-Dose Pharmacokinetics, Pharmacodynamics, and Safety of Taranabant, a Novel Selective Cannabinoid-1 Receptor Inverse Agonist, in Healthy Male Volunteers

Taranabant is a cannabinoid‐1 receptor inverse agonist for the treatment of obesity. This study evaluated the safety, pharmacokinetics, and pharmacodynamics of taranabant (5, 7.5, 10, or 25 mg once daily for 14 days) in 60 healthy male subjects. Taranabant was rapidly absorbed, with a median tmax of 1.0 to 2.0 hours and a t1/2 of approximately 74 to 104 hours. Moderate accumulation was observed in Cmax (1.18‐ to 1.40‐fold) and AUC0–24 h (1.5‐ to 1.8‐fold) over 14 days for the 5‐, 7.5‐, and 10‐mg doses, with an accumulation half‐life ranging from 15 to 21 hours. Steady state was reached after 13 days. After multiple‐dose administration, plasma AUC0–24 h and Cmax of taranabant increased dose proportionally (5–10 mg) and increased somewhat less than dose proportionally for 25 mg. Taranabant was generally well tolerated up to doses of 10 mg and exhibited multiple‐dose pharmacokinetics consistent with once‐daily dosing.

Pharmacokinetics, Pharmacodynamics, and Safety of a Prostaglandin D2 Receptor Antagonist

Laropiprant is a selective antagonist of the prostaglandin D2 (PGD2) receptor subtype 1 (DP1). Three double‐blind, randomized, placebo‐controlled studies evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple oral doses of laropiprant in healthy male volunteers. Single doses up to 900 mg and multiple doses up to 450 mg were generally well tolerated. Laropiprant exhibited dose‐proportional pharmacokinetics. Oral absorption is rapid (Tmax=0.8–2.0 h) and the terminal half‐life is approximately 12–18 h. The pharmacokinetics of laropiprant was not affected by food. Single doses of 6 mg and higher were effective in suppressing PGD2‐induced cyclic AMP accumulation in platelets, demonstrating laropiprant target engagement with DP1. Laropiprant has detectable off‐target antagonist effects at the thromboxane A2 receptor but no clinically significant effect on collagen‐induced platelet aggregation or bleeding times with multiple doses up to 200 mg.

Effect of Montelukast on the Pharmacokinetics and Pharmacodynamics of Warfarin in Healthy Volunteers

Montelukast, a cysteinyl leukotriene receptor antagonist, is being developed for the treatment of asthma and related diseases. This study was designed to evaluate whether montelukast at clinically used dosage levels would interfere with the anticoagulant effect of warfarin. In a two‐period, double‐blind, randomized crossover study, 12 healthy male subjects received a single oral dose of 30 mg warfarin on the 7th day of a 12‐day treatment with montelukast, 10 mg daily by mouth, or a placebo. Montelukast had no significant effect on the area under the plasma concentration‐time curves and peak plasma concentrations of either R‐ or S‐warfarin. However, slight but statistically significant decreases in time to peak concentration of both warfarin enantiomers and in elimination half‐life of the less potent R‐warfarin were observed in the presence of montelukast. These changes were not considered as clinically relevant. Montelukast had no significant effect on the anticoagulant effect of warfarin, as assessed by the international normalized ratio (INR) for prothrombin time (AUC0–144 and INR maximum). The results of this study suggest that a clinically important interaction between these drugs is unlikely to occur in patients requiring concomitant administration of both drugs.

Efficient radiosynthesis of 3'-deoxy-3'-18F-fluorothymidine using electrowetting-on-dielectric digital microfluidic chip.

Access to diverse PET tracers for preclinical and clinical research remains a major obstacle to research in cancer and other disease research. The prohibitive cost and limited availability of tracers could be alleviated by microfluidic radiosynthesis technologies combined with a high-yield microscale radiosynthetic method. In this report, we demonstrate the multistep synthesis of 3′-deoxy-3′-18F-fluorothymidine (18F-FLT) with high yield on an electrowetting-on-dielectric (EWOD) microfluidic radiosynthesizer, previously developed in our group. We have identified and established several parameters that are most critical in the microscale radiosynthesis, such as the reaction time, reagent concentration, and molar ratios, to successfully synthesize 18F-FLT in this compact platform. Methods: 18F-FLT was synthesized from the 3-N-Boc-1-[5-O-(4,4′-dimethoxytrityl)-3-O-nosyl-2-deoxy-β-d-lyxofuranosyl] thymine precursor on the EWOD chip starting from the first solvent exchange and 18F-fluoride ion activation step to the final deprotection step. The fluorination reaction was performed in a mixture of thexyl alcohol and dimethyl sulfoxide. The crude product after deprotection was collected from the chip and purified on a custom-made solid-phase extraction cartridge and subjected to quality control testing. The purified 18F-FLT was suitable for small-animal PET studies in multiple nude mice xenografted with the A431 carcinoma cell line. Results: 18F-FLT was successfully synthesized on the EWOD microdevice coupled with an off-chip solid-phase extraction purification with a decayed-corrected radiochemical yield of 63% ± 5% (n = 5) and passed all of the quality control tests required by the U.S. Pharmacopeia for radiotracers to be injected into humans. We have successfully demonstrated the synthesis of several batches of 18F-FLT on EWOD, starting with approximately 333 MBq of radioactivity and obtained up to 52 MBq (non–decay-corrected) of 18F-FLT on cartridge purification. The specific activity of 2 representative preparations of 18F-FLT synthesized on the EWOD chip were measured to be 1,800 and 2,400 GBq/μmol. Conclusion: The EWOD microchip and optimized synthesis method in combination represent an effective platform for synthesizing 18F-FLT with high yield and of good quality for imaging. This compact platform, with configurable synthesis steps, could potentially form the basis of a stand-alone system that decouples PET probe production from the cyclotron and specialized radiochemistry facilities and increases diversity and flexibility in probe production.

The potent calcitonin gene-related peptide receptor antagonist, telcagepant, does not affect nitroglycerin-induced vasodilation in healthy men

AIMS To assess the effect of the calcitonin gene-related peptide (CGRP) receptor antagonist, telcagepant, on the haemodynamic response to sublingual nitroglycerin (NTG). METHODS Twenty-two healthy male volunteers participated in a randomized, placebo-controlled, double-blind, two-period, crossover study. Subjects received 500 mg telcagepant or placebo followed, 1.5 h later, by 0.4 mg NTG. To assess the haemodynamic response the following vascular parameters were measured: blood pressure, aortic augmentation index (AIx) and brachial artery diameter (BAD). Data are presented as mean (95% confidence interval, CI). RESULTS The aortic AIx following NTG decreased by -18.50 (-21.02, -15.98) % after telcagepant vs. -17.28 (-19.80, -14.76) % after placebo. The BAD fold increase following NTG was 1.14 (1.12, 1.17) after telcagepant vs. 1.13 (1.10, 1.15) after placebo. For both AIx and BAD, the hypothesis that telcagepant does not significantly affect the changes induced by NTG is supported (P < 0.0001). In addition, no vasoconstrictor effect of telcagepant could be demonstrated. CONCLUSIONS Telcagepant did not affect NTG-induced haemodynamic changes. These data suggest that NTG-induced vasodilation is not CGRP dependent.