TRPA1 Antagonist LY3526318 Inhibits the Cinnamaldehyde-Evoked Dermal Blood Flow Increase: Translational Proof of Pharmacology.

Transient receptor potential Ankyrin 1 (TRPA1) is an ion channel expressed by sensory neurons, where it mediates pain signaling. Consequently, it has emerged as a promising target for novel analgesics, yet, to date, no TRPA1 antagonists have been approved for clinical use. In the present translational study, we utilized dermal blood flow changes evoked by TRPA1 agonist cinnamaldehyde as a target engagement biomarker to investigate the in vivo pharmacology of LY3526318, a novel TRPA1 antagonist. In rats, LY3526318 (1, 3, and 10 mg/kg, p.o.) dose-dependently reduced the cutaneous vasodilation typically observed following topical application of 10% v/v cinnamaldehyde. The inhibition was significant at the site of cinnamaldehyde application and also when including an adjacent area of skin. Similarly, in a cohort of 16 healthy human volunteers, LY3526318 administration (10, 30, and 100 mg, p.o.) dose-dependently reduced the elevated blood flow surrounding the site of 10% v/v cinnamaldehyde application, with a trend toward inhibition at the site of application. Comparisons between both species reveal that the effects of LY3526318 on the cinnamaldehyde-induced dermal blood flow are greater in rats relative to humans, even when adjusting for cross-species differences in potency of the compound at TRPA1. Exposure-response relationships suggest that a greater magnitude response may be observed in humans if higher antagonist concentrations could be achieved. Taken together, these results demonstrate that cinnamaldehyde-evoked changes in dermal blood flow can be utilized as a target engagement biomarker for TRPA1 activity and that LY3526318 antagonizes the ion channel both in rats and humans.

First-in-human development of a pharmacodynamic biomarker for PAC1 receptor antagonists using intradermal injections of maxadilan.

Maxadilan, a potent vasodilator peptide, selectively activates the PAC1 receptor, a promising target for migraine therapy. Therefore, maxadilan has been suggested as a tool to study the pharmacodynamics (PDs) of PAC1 receptor antagonists. The objectives of this first-in-human study were to: (1) determine the safety, tolerability, dose response, and time course of the dermal blood flow (DBF) changes after intradermal (i.d.) injections of maxadilan in the human forearm, and (2) assess the inter-arm and inter-period reproducibility of this response. This was a single-center, open-label study in healthy subjects, comprising three parts: (1) dose-response (n = 25), (2) response duration (n = 10), and (3) reproducibility (n = 15). DBF measurements were performed using laser Doppler imaging (LDI) up to 60 min postinjection, or up to 5 days for the response duration assessments. To assess reproducibility, the intraclass correlation coefficient (ICC) and sample sizes were calculated. The i.d. maxadilan (0.001, 0.01, 0.1, 0.9, 3, and 10 ng) produced a well-tolerated, dose-dependent increase in DBF, with a half-maximal effective concentration fitted at 0.0098 ng. The DBF response to 0.9 ng maxadilan was quantifiable with LDI up to 72 h postinjection. The inter-period reproducibility of the DBF response was better upon 0.9 ng (ICC > 0.6) compared to 0.01 ng (ICC < 0.4) maxadilan. However, irrespective of the study design or maxadilan dose, a sample size of 11 subjects is sufficient to detect a 30% difference in DBF response with 80% power. In conclusion, intradermal maxadilan provides a safe, well-tolerated, and reproducible PD biomarker for PAC1 receptor antagonists in vivo in humans.

Relative Bioavailability of Enalapril Administered as Orodispersible Minitablets in Healthy Adults.

The angiotensin-converting enzyme inhibitor enalapril is commonly used to treat chronic heart failure in children. Because some children are unable to swallow capsules or tablets, a new, age-appropriate, orodispersible minitablet (ODMT) containing 1 mg of enalapril was developed within the EU-funded LENA (Labeling of Enalapril from Neonates up to Adolescents) consortium. In order to support the clinical evaluation of this new formulation in children, a relative bioavailability study was performed in healthy adults, comparing the bioavailability of enalapril in the ODMT with that of a reference product (RP) Renitec, a registered standard enalapril tablet formulation. In this open-label, randomized 3-way crossover study, 24 healthy subjects received a 10-mg enalapril dose administered as (1) 2 × 5-mg tablets of the RP swallowed with water, (2) 10 × 1-mg ODMT swallowed with water, and (3) 10 × 1 mg ODMT dispersed on the tongue. When the relative bioavailability of the ODMT formulation swallowed with water was compared with that of the RP, the estimated 90%CIs for the ratio of area under the concentration-time curve (AUC0-∞ ) and or peak concentration (Cmax ) of enalapril were 92.34% to 106.49% and 91.28% to 115.72%, respectively, which are within the accepted bioequivalence limits of 80% to 125%. Following dispersion of the ODMT in the mouth, a slightly higher Cmax for enalapril was observed as compared with the RP with an upper 90%CI of 127.57%, slightly exceeding the bioequivalence limit. Taken together, it was demonstrated that the method of administration of the ODMT, swallowed or dispersed, did not significantly affect the bioavailability of enalapril.

Phase 1, randomized, parallel-group, double-blind, placebo-controlled trial to evaluate the effects of erenumab (AMG 334) and concomitant sumatriptan on blood pressure in healthy volunteers.

OBJECTIVES: The aim of this study was to assess the effects of concomitant administration of erenumab and sumatriptan on resting blood pressure, pharmacokinetics, safety, and tolerability in healthy subjects. METHODS: In this phase 1, parallel-group, one-way crossover, double-blind, placebo-controlled study, healthy adult subjects were randomized (1:2) to receive either intravenous placebo and subcutaneous sumatriptan 12 mg (i.e. two 6-mg injections separated by 1 hour) or intravenous erenumab 140 mg and subcutaneous sumatriptan 12 mg. Blood pressure was measured pre-dose and at prespecified times post-dose. The primary endpoint was individual time-weighted averages of mean arterial pressure, measured from 0 hours to 2.5 hours after the first dose of sumatriptan. Pharmacokinetic parameters for sumatriptan were evaluated by calculating geometric mean ratios (erenumab and sumatriptan/placebo and sumatriptan). Adverse events and anti-erenumab antibodies were also evaluated. RESULTS: A total of 34 subjects were randomized and included in the analysis. Least squares mean (standard error) time-weighted averages of mean arterial pressure were 87.4 (1.0) mmHg for the placebo and sumatriptan group and 87.4 (1.2) mmHg for the erenumab and sumatriptan group. Mean difference in mean arterial pressure between groups was -0.04 mmHg (90% confidence interval: -2.2, 2.1). Geometric mean ratio estimates for maximum plasma concentration of sumatriptan was 0.95 (90% confidence interval: 0.82, 1.09), area under the plasma concentration-time curve (AUC) from time 0 to 6 hours was 0.98 (90% confidence interval: 0.93, 1.03), and AUC from time 0 to infinity was 1.00 (90% confidence interval: 0.96, 1.05). No clinically relevant safety findings for co-administration of sumatriptan and erenumab were identified. CONCLUSION: Co-administration of erenumab and sumatriptan had no additional effect on resting blood pressure or on pharmacokinetics of sumatriptan. Trial registration: ClinicalTrials.gov, NCT02741310.

Fatty Acid Amide Hydrolase Inhibition by JNJ-42165279: A Multiple-Ascending Dose and a Positron Emission Tomography Study in Healthy Volunteers.

Inhibition of fatty acid amide hydrolase (FAAH) potentiates endocannabinoid activity and is hypothesized to have therapeutic potential for mood and anxiety disorders and pain. The clinical profile of JNJ-42165279, an oral selective FAAH inhibitor, was assessed by investigating the pharmacokinetics, pharmacodynamics, safety, and binding to FAAH in the brain of healthy human volunteers. Concentrations of JNJ-42165279 (plasma, cerebrospinal fluid (CSF), urine) and fatty acid amides (FAA; plasma, CSF), and FAAH activity in leukocytes was determined in a phase I multiple ascending dose study. A positron emission tomography study with the FAAH tracer [11 C]MK3168 was conducted to determine brain FAAH occupancy after single and multiple doses of JNJ-42165279. JNJ-42165279 administration resulted in an increase in plasma and CSF FAA. Significant blocking of brain FAAH binding of [11 C]MK3168 was observed after pretreatment with JNJ-42165279. JNJ-42165279 produces potent central and peripheral FAAH inhibition. Saturation of brain FAAH occupancy occurred with doses ≥10 mg of JNJ-42165279. No safety concerns were identified.

Phase I, Randomized, Double-blind, Placebo-controlled, Single-dose, and Multiple-dose Studies of Erenumab in Healthy Subjects and Patients With Migraine.

Monoclonal antibodies (mAbs) targeting calcitonin gene-related peptide (CGRP) signaling are being explored as prophylactic treatments for migraine. Erenumab (AMG 334) is the first potent, selective, and competitive human mAb antagonist of the CGRP receptor. We report the data from two phase I studies assessing the safety, pharmacokinetics (PK), and pharmacodynamics of single and multiple administrations of erenumab in healthy subjects and patients with migraine. The results indicate that the PK profile of erenumab is nonlinear from 1 mg to 70 mg and the linear portion of the clearance from 70 mg to 210 mg is consistent with other human immunoglobulin G2 antibodies. Single doses of erenumab resulted in >75% inhibition of capsaicin-induced dermal blood flow, with no apparent dose-dependency for erenumab ≥21 mg. Erenumab was generally well tolerated, with an acceptable safety profile, supporting further clinical development of erenumab for migraine prevention.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers.

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis. Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement. Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF). Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1-600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.

Pharmacokinetic-Pharmacodynamic Relationship of Erenumab (AMG 334) and Capsaicin-Induced Dermal Blood Flow in Healthy and Migraine Subjects.

PURPOSE: Capsaicin-induced dermal blood flow (CIDBF) is a validated biomarker used to evaluate the target engagement of potential calcitonin gene-related peptide-blocking therapeutics for migraine. To characterize the pharmacokinetics (PK) and quantify the inhibitory effects of erenumab (AMG 334) on CIDBF, CIDBF data were pooled from a single- and a multiple-dose study in healthy and migraine subjects. METHODS: Repeated capsaicin challenges and DBF measurements were performed and serum erenumab concentrations determined. A population analysis was conducted using a nonlinear mixed-effects modeling approach. Effects of body weight, gender, and age on model parameters were evaluated. RESULTS: Two-compartment target-mediated drug disposition (TMDD) model assuming binding of erenumab in the central compartment best described the nonlinear PK of erenumab. Subcutaneous absorption half-life was 1.6 days and bioavailability was 74%. Erenumab produced a maximum inhibition of 89% (95% confidence interval: 87-91%). Erenumab concentrations required for 50% and 99% of maximum inhibition were 255 ng/mL and 1134 ng/mL, respectively. Increased body weight was associated with increased erenumab clearance but had no effect on the inhibitory effect on CIDBF. CONCLUSIONS: Our results show that erenumab pharmacokinetics was best characterized by a TMDD model and resulted in potent inhibition of CIDBF.

What We Observe In Vivo Is Not Always What We See In Vitro: Development and Validation of 11C-JNJ-42491293, A Novel Radioligand for mGluR2.

Positive allosteric modulators (PAM) of metabotropic glutamate receptor 2 (mGluR2) are a potential therapy for anxiety, schizophrenia, and addiction. Aside from pathophysiologic imaging studies, an mGluR2 PET tracer would enable confirmation of sufficient central target engagement and assist dose selection for proof-of-concept studies of PAM compounds. 11C-JNJ-42491293, a novel high-affinity radioligand (human 50% inhibitory concentration = 9.6 nM) for the PAM site of mGluR2, was evaluated as a selective mGluR2 PAM PET tracer. METHODS: In vitro and ex vivo autoradiography binding experiments in Wistar and in mGluR2 knockout and wildtype rats as well as in vivo biodistribution and brain PET imaging studies in wildtype and mGluR2 knockout rats in a primate and in humans were performed. RESULTS: In vitro binding studies and in vivo imaging studies in Wistar rats showed moderate brain uptake, with a distribution pattern fully consistent with the reported intracerebral distribution of mGluR2. Given these promising findings, biodistribution, dosimetry, and brain kinetic modeling of 11C-JNJ-42491293 were determined in humans. Because of an unexpected high myocardial retention, additional 11C-JNJ-42491293 imaging studies were performed in recently available mGluR2 knockout and wildtype rats and in a monkey using a structurally distinct mGluR2 PAM ligand with affinity for the same site, demonstrating off-target binding in vivo that could not have been anticipated from previous in vitro experiments. To date, the target of this non-mGluR2 tracer binding remains unknown. CONCLUSION: On the basis of in vivo selectivity issues suggested by human distribution and demonstrated in knockout rat models, 11C-JNJ-42491293 was considered unsuitable as a specific PET ligand for in vivo imaging of mGluR2. These results emphasize the importance of elaborated in vitro/in vivo comparative studies and, when available, validation with knockout animal models or structurally distinct ligands with affinity for the same site, in radiotracer development.

Translational Pharmacodynamics of Calcitonin Gene-Related Peptide Monoclonal Antibody LY2951742 in a Capsaicin-Induced Dermal Blood Flow Model.

LY2951742, a monoclonal antibody targeting calcitonin gene-related peptide (CGRP), is being developed for migraine prevention and osteoarthritis pain. To support the clinical development of LY2951742, capsaicin-induced dermal blood flow (DBF) was used as a target engagement biomarker to assess CGRP activity in nonhuman primates and healthy volunteers. Inhibition of capsaicin-induced DBF in nonhuman primates, measured with laser Doppler imaging, was dose dependent and sustained for at least 29 days after a single intravenous injection of the CGRP antibody. This information was used to generate a pharmacokinetic/pharmacodynamic model, which correctly predicted inhibition of capsaicin-induced DBF in humans starting at a single subcutaneous 5-mg dose. As expected, the degree of inhibition in capsaicin-induced DBF increased with higher LY2951742 plasma concentrations. Utilization of this pharmacodynamic biomarker with pharmacokinetic data collected in phase I studies provided the dose-response relationship that assisted in dose selection for the phase II clinical development of LY2951742.

Characterization of the novel GlyT1 PET tracer [18F]MK-6577 in humans.

Decreased glutamatergic neurotransmission is hypothesized to be involved in the pathophysiology of schizophrenia. Inhibition of glycine transporter Type-1 (GlyT1) reuptake is expected to increase the glutamatergic neurotransmission and may serve as treatment for cognitive and negative symptoms of schizophrenia. In this article, we present human data from a novel GlyT1 PET tracer, [(18) F]MK-6577. In the process of developing a GlyT1 inhibitor therapeutic, a PET tracer can assist in determining the dose with a high probability of sufficiently testing the mechanism of action. This article reports the human PET studies with [(18) F]MK-6577 for measuring GlyT1 receptor availability at baseline in normal human subjects and occupancy with a GlyT1 inhibitor, MK-2637. Studies were also performed to measure radiation burden and the baseline test-retest (T-RT) variability of the tracer. The effective dose from sequential whole-body dosimetry scans in three male subjects was estimated to be 24.5 ± 2.9 µSV/MBq (mean ± SD). The time-activity curves from T-RT scans modeled satisfactorily using a two tissue compartmental model. The tracer uptake was highest in the pons (VT = 6.7 ± 0.9, BPND = 4.1 ± 0.43) and lowest in the cortex (VT = 2.1 ± 0.5, BPND = 0.60 ± 0.23). VT T-RT variability measured in three subjects was <12% on average. The occupancy scans performed in a cohort of 15 subjects indicated absence of a reference region. The in vivo potency (Occ50 ) of MK-2637 was determined using two methods: A: Lassen plot with a population input function (Occ50 = 106 nM, SE = 20 nM) and B: pseudo reference tissue model using cortex as the pseudo reference region (Occ50 = 141 nM, SE = 21 nM).

(11)C-MK-8278 PET as a tool for pharmacodynamic brain occupancy of histamine 3 receptor inverse agonists.

UNLABELLED: The histamine 3 (H3) receptor is a presynaptic autoreceptor in the central nervous system that regulates the synthesis and release of histamine and modulates the release of other major neurotransmitters. H3 receptor inverse agonists (IAs) may be efficacious in the treatment of various central nervous system disorders, including excessive daytime sleepiness, attention deficit hyperactivity disorder, Alzheimer disease, ethanol addiction, and obesity. METHODS: Using PET and a novel high-affinity and selective radioligand (11)C-MK-8278, we studied the tracer biodistribution, quantification, and brain H3 receptor occupancy (RO) of MK-0249 and MK-3134, 2 potential IA drugs targeting cerebral H3 receptors, in 6 healthy male subjects (age, 19-40 y). The relationship among H3 IA dose, time on target, and peripheral pharmacokinetics was further investigated in 15 healthy male volunteers (age, 18-40 y) with up to 3 PET scans and 3 subjects per dose level. RESULTS: The mean effective dose for (11)C-MK-8278 was 5.4 ± 1.1 µSv/MBq. Human brain kinetics showed rapid high uptake and fast washout. Binding potential values can be assessed using the pons as a reference region, with a test-retest repeatability of 7%. Drug RO data showed low interindividual variability per dose (mean RO SD, 2.1%), and a targeted 90% RO can be reached for both IAs at clinically feasible doses. CONCLUSION: (11)C-MK-8278 is a useful novel PET radioligand for determination of human cerebral H3 receptor binding and allows highly reproducible in vivo brain occupancy of H3-targeting drugs, hereby enabling the evaluation of novel compounds in early development to select doses and schedules.

In vivo quantification of calcitonin gene-related peptide receptor occupancy by telcagepant in rhesus monkey and human brain using the positron emission tomography tracer [11C]MK-4232.

Calcitonin gene-related peptide (CGRP) is a potent neuropeptide whose agonist interaction with the CGRP receptor (CGRP-R) in the periphery promotes vasodilation, neurogenic inflammation and trigeminovascular sensory activation. This process is implicated in the cause of migraine headaches, and CGRP-R antagonists in clinical development have proven effective in treating migraine-related pain in humans. CGRP-R is expressed on blood vessel smooth muscle and sensory trigeminal neurons and fibers in the periphery as well as in the central nervous system. However, it is not clear what role the inhibition of central CGRP-R plays in migraine pain relief. To this end, the CGRP-R positron emission tomography (PET) tracer [(11)C]MK-4232 (2-[(8R)-8-(3,5-difluorophenyl)-6,8-[6-(11)C]dimethyl-10-oxo-6,9-diazaspiro[4.5]decan-9-yl]-N-[(2R)-2'-oxospiro[1,3-dihydroindene-2,3'-1H-pyrrolo[2,3-b]pyridine]-5-yl]acetamide) was discovered and developed for use in clinical PET studies. In rhesus monkeys and humans, [(11)C]MK-4232 displayed rapid brain uptake and a regional brain distribution consistent with the known distribution of CGRP-R. Monkey PET studies with [(11)C]MK-4232 after intravenous dosing with CGRP-R antagonists validated the ability of [(11)C]MK-4232 to detect changes in CGRP-R occupancy in proportion to drug plasma concentration. Application of [(11)C]MK-4232 in human PET studies revealed that telcagepant achieved only low receptor occupancy at an efficacious dose (140 mg PO). Therefore, it is unlikely that antagonism of central CGRP-R is required for migraine efficacy. However, it is not known whether high central CGRP-R antagonism may provide additional therapeutic benefit.

The effects of laropiprant, a selective prostaglandin D2 receptor 1 antagonist, on the antiplatelet activity of clopidogrel or aspirin.

Laropiprant (LRPT) is being developed in combination with Merck's extended-release niacin (ERN) formulation for the treatment of dyslipidemia. LRPT, an antagonist of the prostaglandin PGD2 receptor DP1, reduces flushing symptoms associated with ERN. LRPT also has affinity for the thromboxane A2 receptor TP (approximately 190-fold less potent at TP compared with DP1). Aspirin and clopidogrel are two frequently used anti-clotting agents with different mechanisms of action. Since LRPT may potentially be co-administered with either one of these agents, these studies were conducted to assess the effects of steady-state LRPT on the antiplatelet activity of steady-state clopidogrel or aspirin. Bleeding time at 24 h post-dose (trough) was pre-specified as the primary pharmacodynamic endpoint in both studies. Two separate, double-blind, randomized, placebo-controlled, crossover studies evaluated the effects of multiple-dose LRPT on the pharmacodynamics of multiple-dose clopidogrel or aspirin. Healthy subjects were randomized to once-daily oral doses of LRPT 40 mg or placebo to LRTP co-administered with clopidogrel 75 mg or aspirin 81 mg for 7 days with at least a 21-day washout between treatments. In both studies, bleeding time and platelet aggregation were assessed 4 and 24 hours post-dose on Day 7. Comparability was declared if the 90% confidence interval for the estimated geometric mean ratio ([LRPT+clopidogrel]/clopidogrel alone or [LRPT+aspirin]/aspirin alone) for bleeding time at 24 hours post-dose on Day 7 was contained within (0.66, 1.50). Concomitant daily administration of LRPT 40 mg with clopidogrel 75 mg or aspirin 81 mg resulted in an approximate 4-5% increase in bleeding time at 24 hours after the last dose vs. bleeding time after treatment with clopidogrel or aspirin alone, demonstrating that the treatments had comparable effects on bleeding time. Percent inhibition of platelet aggregation was not significantly different between LRPT co-administered with clopidogrel or aspirin vs. clopidogrel or aspirin alone at 24 hours post-dose at steady state. At 4 hours after the last dose, co-administration of LRPT 40 mg resulted in 3% and 41% increase in bleeding time vs. bleeding time after treatment with aspirin or clopidogrel alone, respectively. Co-administration of LPRT with clopidogrel or aspirin was generally well tolerated in healthy subjects. Co-administration of multiple doses of LRPT 40 mg and clopidogrel 75 mg or aspirin 81 mg had no clinically important effects on bleeding time or platelet aggregation.

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.

No arguments for increased endothelial nitric oxide synthase activity in migraine based on peripheral biomarkers.

OBJECTIVES: To assess whether migraine patients display a chronic nitric oxide synthase (NOS) hyperactivity by comparing the nitric oxide (NO) production before and following a loading dose of L-arginine between migraine patients (interictally) and matched healthy control subjects. In addition, we evaluated whether a loading dose of L-arginine triggers an acute migraine headache in migraineurs. SUBJECTS AND METHODS: Twenty healthy subjects and 20 migraine patients participated in a 2-period, randomised, double-blind, placebo-controlled study. Each subject received a 30-min infusion, by peripheral vein, of 30 g L-arginine hydrochloride or placebo (i.e. an equal volume of 0.9% saline solution). Meanwhile, biomarkers associated with the L-arginine-NO pathway (i.e. exhaled NO/nasal NO), plasma citrulline and urinary excretion of nitrite/nitrate and cGMP were assessed before and for 6 h following the start of the infusion. RESULTS: At baseline, exhaled NO and nasal NO were higher in migraineurs compared to healthy subjects (mean±95% confidence interval): 15.9 (8.8, 23.0) parts per billion (ppb) versus 10.8 (7.0, 14.5) ppb for exhaled NO (P=0.04) and 76.3 (61.2, 91.4) versus 61.6 (51.2, 72.0) ppb for nasal NO (P=0.03), respectively. The AUC0-6 in ppb for exhaled NO and nasal NO following L-arginine or saline infusion did not differ between both groups. The increase in L-citrulline, following L-arginine infusion, was smaller in migraine patients (15 (13, 18) µmol/l) compared to healthy volunteers (19 (16, 23) µmol/l; P=0.046). In healthy subjects, both nitrate and cGMP excretion were higher following L-arginine compared to placebo infusion: 132.63 (100.24, 165.02) versus 92.07 (66.33, 117.82) µmol/mmol creatinine for nitrate (P=0.014) and 50.53 (42.19, 58.87) versus 39.64 (33.94, 45.34) nmol/mmol creatinine for cGMP (P=0.0003), respectively. In migraineurs, excretion of these biomarkers was comparable following L-arginine or saline infusion. CONCLUSIONS: The results of the present study do not support the idea of a generalised increase in NO synthase activity in migraine patients outside of a migraine attack. The smaller increase in plasma L-citrulline, urinary nitrate and cGMP excretion following L-arginine infusion in migraine patients might indicate dysfunction of endothelial NO synthase.

Inhibition of capsaicin-induced increase in dermal blood flow by the oral CGRP receptor antagonist, telcagepant (MK-0974).

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT: * Calcitonin gene-related peptide (CGRP) was first described as a potent vasodilator. * CGRP is also increasingly recognized as a key player in the pathophysiology of migraine, and CGRP receptor antagonists potentially offer a new approach for treating migraine. * A novel pharmacodynamic assay to measure CGRP receptor antagonist activity non-invasively in humans has been developed, which involves measuring the increase in dermal blood flow induced by topical application of capsaicin on the forearm. WHAT THIS STUDY ADDS: * This study shows that the novel oral CGRP receptor antagonist, telcagepant, inhibits the increases in dermal blood flow induced by the topical application of capsaicin on the human forearm. * This experimental medicine model may have utility to assist in dose selection for the development of CGRP receptor antagonists. AIMS: To evaluate inhibition of capsaicin-induced increase in dermal blood flow (DBF) following telcagepant (MK-0974), a potent and selective orally bioavailable calcitonin gene-related peptide (CGRP) receptor antagonist being developed for the acute treatment of migraine. METHODS: A three-period crossover study in 12 healthy adult men. Each subject received a single oral dose of telcagepant 300 mg, telcagepant 800 mg or placebo at 0 h, followed 0.5 and 3.5 h later by two topical doses of 300 and 1000 microg capsaicin per 20 microl water-ethanol mixture. Capsaicin was applied at two sites on the volar surface of the subjects' left and right forearms. DBF was assessed by laser Doppler perfusion imaging immediately before ('baseline'), and 0.5 h after each capsaicin application at 1 and 4 h. Plasma samples to determine telcagepant concentrations were collected immediately after laser Doppler perfusion imaging. A pharmacodynamic model was developed to explore the relationship between plasma concentration and inhibition of capsaicin-induced increase in DBF. RESULTS: Geometric mean plasma concentrations after dosing with 300 mg and 800 mg telcagepant were 720 and 1146 nm, respectively, at 1 h, vs. 582 and 2548 nm, respectively, at 4 h. The pharmacodynamic model suggested that the EC(90) for telcagepant inhibition of capsaicin-induced increases in DBF was 909 nm. CONCLUSIONS: Telcagepant inhibits the increases in DBF induced by the topical application of capsaicin on the human forearm. This experimental medicine model may have utility to assist in dose selection for the development of CGRP receptor antagonists.

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 t(max) of 1.0 to 2.0 hours and a t(1/2) of approximately 74 to 104 hours. Moderate accumulation was observed in C(max) (1.18- to 1.40-fold) and AUC(0-24 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 AUC(0-24 h) and C(max) 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.

[18F]MK-9470, a positron emission tomography (PET) tracer for in vivo human PET brain imaging of the cannabinoid-1 receptor.

[(18)F]MK-9470 is a selective, high-affinity, inverse agonist (human IC(50), 0.7 nM) for the cannabinoid CB1 receptor (CB1R) that has been developed for use in human brain imaging. Autoradiographic studies in rhesus monkey brain showed that [(18)F]MK-9470 binding is aligned with the reported distribution of CB1 receptors with high specific binding in the cerebral cortex, cerebellum, caudate/putamen, globus pallidus, substantia nigra, and hippocampus. Positron emission tomography (PET) imaging studies in rhesus monkeys showed high brain uptake and a distribution pattern generally consistent with that seen in the autoradiographic studies. Uptake was blocked by pretreatment with a potent CB1 inverse agonist, MK-0364. The ratio of total to nonspecific binding in putamen was 4-5:1, indicative of a strong specific signal that was confirmed to be reversible via displacement studies with MK-0364. Baseline PET imaging studies in human research subject demonstrated behavior of [(18)F]MK-9470 very similar to that seen in monkeys, with very good test-retest variability (7%). Proof of concept studies in healthy young male human subjects showed that MK-0364, given orally, produced a dose-related reduction in [(18)F]MK-9470 binding reflecting CB1R receptor occupancy by the drug. Thus, [(18)F]MK-9470 has the potential to be a valuable, noninvasive research tool for the in vivo study of CB1R biology and pharmacology in a variety of neuropsychiatric disorders in humans. In addition, it allows demonstration of target engagement and noninvasive dose-occupancy studies to aid in dose selection for clinical trials of CB1R inverse agonists.

Clinical study of solid dispersions of itraconazole prepared by hot-stage extrusion.

The aim of this study was to investigate the performance of three new solid dispersion formulations of itraconazole in human volunteers in comparison with Sporanox, the marketed form. Solid dispersions made up of itraconazole (40%, w/w) and HPMC 2910, Eudragit E100 or a mixture of Eudragit E100-PVPVA64 were manufactured by hot-stage extrusion and filled in gelatin capsules. The formulations were tested in eight human volunteers in a double blind, single dose, and cross-over study. Concentrations of the drug and its metabolite hydroxyitraconazole in the plasma were determined using HPLC. The in vivo performance was evaluated by comparing the mean area under the plasma concentration-time curves (AUC), the mean maximum plasma concentration (C(max)), and the mean time to reach C(max) (T(max)). The mean bioavailability of itraconazole was comparable after administration of the HPMC solid dispersion, compared to Sporanox, while it was lower after administration of the Eudragit E100 or Eudragit E100-PVPVA64 dispersions. Due to high variability, a significant decrease in AUC and C(max) was only observed for the Eudragit E100-PVPVA formulation. Although the solid dispersions showed different in vitro dissolution behaviour, T(max) values were comparable. The same observations with respect to AUC, C(max) and T(max) could be made for hydroxyitraconazole. The present results indicate that hot-stage extrusion can be considered as a valuable alternative for manufacturing solid dispersions of itraconazole.