Search

BACKGROUND AND PURPOSE In 2016, one person died and four others had mild-to-severe neurological symptoms during a phase I trial of the fatty acid amide hydrolase (FAAH) inhibitor BIA 10-2474. EXPERIMENTAL APPROACH Pharmacodynamic and pharmacokinetic studies were performed with BIA 10-2474, PF-04457845 and JNJ-42165279 using mice, rats and human FAAH expressed in COS cells. Selectivity was evaluated by activity-based protein profiling (APBB) in rats. BIA 10-2474 effect in stroke-prone spontaneously hypertensive rats (SHRSP) was investigated. KEY RESULTS BIA 10-2474 was 10-fold less potent than PF-04457845 in inhibiting human FAAH in situ but inhibited mouse brain and liver FAAH with ED50 values of 13.5 and 6.2 μg·kg-1 , respectively. Plasma and brain BIA 10-2474 levels were consistent with in situ potency and neither BIA 10-2474 nor its metabolites accumulated following repeat administration. FAAH and α/β-hydrolase domain containing 6 were the primary targets of BIA 10-2474 and, at higher exposure levels, ABHD11, PNPLA6, PLA2G15, PLA2G6 and androgen-induced protein 1. At 100 mg·kg-1 for 28 days, the level of several lipid species containing arachidonic acid increased. Daily treatment of SHRSP with BIA 10-2474 did not affect mortality rate or increased the incidence of haemorrhage or oedema in surviving animals. CONCLUSIONS AND IMPLICATIONS BIA 10-2474 potently inhibits FAAH in vivo, similarly to PF-04457845 and interacts with a number of lipid processing enzymes, some previously identified in human cells as off-targets particularly at high levels of exposure. These interactions occurred at doses used in toxicology studies, but the implication of these off-targets in the clinical trial accident remains unclear.

Fatty acid amide hydrolase (FAAH) is a key enzyme responsible for the degradation of the endocannabinoid anandamide. FAAH inactivation is emerging as a strategy to treat several CNS and peripheral diseases, including inflammation and pain. The search for effective FAAH inhibitors has thus become a key focus in present drug discovery.Patents and patent applications published from 2009 to 2014 in which novel chemical classes are claimed to inhibit FAAH.FAAH is a promising target for treating many disease conditions including pain, inflammation and mood disorders. In the last few years, remarkable efforts have been made to develop new FAAH inhibitors (either reversible and irreversible) characterized by excellent potency and selectivity, to complete the arsenal of tools for modulating FAAH activity. The failure of PF-04457845 in a Phase II study on osteoarthritis pain has not flattened the interest in FAAH inhibitors. New clinical trials on 'classical' FAAH inhibitors are now ongoing, and new strategies based on compounds with peculiar in vivo distribution (e.g., peripheral) or with multiple pharmacological activities (e.g., FAAH and COX) are under investigation and could boost the therapeutic potential of this class in the next future.

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT • Inhibition of fatty acid amide hydrolase-1 (FAAH1) and the subsequent elevation of fatty acid amides has been proposed as a strategy to induce the analgesic properties of cannabinoids without the accompanying negative side effects such as impairment in cognition, motor control and predisposition to psychoses. PF-04457845 is a potent and selective irreversible FAAH1 inhibitor which has been shown to elevate fatty acid amide concentrations in animal models and induce responses in behavioural models suggestive of analgesia. WHAT THIS STUDY ADDS • This study is the first to investigate a FAAH1 inhibitor in humans. PF-04457845 is well tolerated following single and multiple dosing to healthy volunteers and has pharmacokinetic and pharmacodynamic properties that make nearly complete inhibition of FAAH1 possible with once daily dosing. AIMS To evaluate the pharmacology and tolerability of PF-04457845, an orally available fatty acid amide hydrolase-1 (FAAH1) inhibitor, in healthy subjects. METHODS Double-blind, randomized, placebo-controlled single and multiple rising dose studies and an open-label, randomized, food effect study were conducted. Plasma and urine PF-04457845 concentrations, plasma fatty acid amide concentrations and FAAH1 activity in human leucocytes were measured. Tolerability, including effects on cognitive function, were assessed. RESULTS PF-04457845 was rapidly absorbed (median tmax 0.5–1.2 h). Exposure increased supraproportionally to dose from 0.1 to 10 mg and proportionally between 10 and 40 mg single doses. The pharmacokinetics appeared dose proportional following 14 days once daily dosing between 0.5 and 8 mg. Steady-state was achieved by day 7. Less than 0.1% of the dose was excreted in urine. Food had no effect on PF-04457845 pharmacokinetics. FAAH1 activity was almost completely inhibited (>97%) following doses of at least 0.3 mg (single dose) and 0.5 mg once daily (multiple dose) PF-04457845. Mean fatty acid amide concentrations increased (3.5- to 10-fold) to a plateau and then were maintained following PF-04457845. FAAH1 activity and fatty acid amide concentrations returned to baseline within 2 weeks following cessation of dosing at doses up to 4 mg. There was no evidence of effects of PF-04457845 on cognitive function. PF-04457845, at doses up to 40 mg single dose and 8 mg once daily for 14 days, was well tolerated. CONCLUSIONS PF-04457845 was well tolerated at doses exceeding those required for maximal inhibition of FAAH1 activity and elevation of fatty acid amides.

Positron emission tomography with [11C]CURB was recently developed to quantify fatty acid amide hydrolase (FAAH), the enzyme responsible for hydrolyzing the endocannabinoid anandamide. This study investigated the test–retest reliability of [11C]CURB as well as its in vivo specificity and the validity of the kinetic model by using the highly specific FAAH inhibitor, PF-04457845. Five healthy volunteers completed test–retest [11C]CURB scans 1 to 2 months apart and six subjects completed baseline and blocking scans on the same day after PF-04457845 (p.o.) administration (1, 4, or 20 mg; n = 2 each). The composite parameter γ k3 (an index of FAAH activity, γ = K1/ k2) was estimated using an irreversible two-tissue compartment model with plasma input function. There were no clinically observable responses to oral PF-04457845 or [11C]CURB injection. Oral administration of PF-04457845 reduced [11C]CURB binding to a homogeneous level at all three doses, with γ k3 values decreased by ≥91%. Excellent reproducibility and good reliability (test–retest variability = 9%; intraclass correlation coefficient = 0.79) were observed across all regions of interest investigated. Our findings suggest that γ k3/[11C]CURB is a reliable, highly sensitive, and selective tool to measure FAAH activity in human brain in vivo. Moreover, PF-04457845 is a highly potent FAAH inhibitor (>95% inhibition at 1 mg) in living human brain.

Introduction Fatty acid amide hydrolase (FAAH) has a significant role in regulating endocannabinoid signaling in the central nervous system. As such, FAAH inhibitors are being actively sought for pain, addiction, and other indications. This has led to the recent pursuit of positron emission tomography (PET) radiotracers targeting FAAH. We report herein the preparation and preclinical evaluation of [ 11 C- carbonyl ]PF-04457845, an isotopologue of the potent irreversible FAAH inhibitor. Methods PF-04457845 was radiolabeled at the carbonyl position via automated [ 11 C]CO 2 -fixation. Ex vivo brain biodistribution of [ 11 C- carbonyl ]PF-04457845 was carried out in conscious rats. Specificity was determined by pre-administration of PF-04457845 or URB597 prior to [ 11 C- carbonyl ]PF-04457845. In a separate experiment, rats injected with the title radiotracer had whole brains excised, homogenized and extracted to examine irreversible binding to brain parenchyma. Results The title compound was prepared in 5 ± 1% (n = 4) isolated radiochemical yield based on starting [ 11 C]CO 2 (decay uncorrected) within 25 min from end-of-bombardment in > 98% radiochemical purity and a specific activity of 73.5 ± 8.2 GBq/μmol at end-of-synthesis. Uptake of [ 11 C- carbonyl ]PF-04457845 into the rat brain was high (range of 1.2–4.4 SUV), heterogeneous, and in accordance with reported FAAH distribution. Saturable binding was demonstrated by a dose-dependent reduction in brain radioactivity uptake following pre-treatment with PF-04457845. Pre-treatment with the prototypical FAAH inhibitor, URB597, reduced the brain radiotracer uptake in all regions by 71–81%, demonstrating specificity for FAAH. The binding of [ 11 C- carbonyl ]PF-04457845 to FAAH at 40 min post injection was irreversible as 98% of the radioactivity in the brain could not be extracted. Conclusions [ 11 C- carbonyl ]PF-04457845 was rapidly synthesized via an automated radiosynthesis. Ex vivo biodistribution studies in conscious rodents demonstrate that [11C PF-04457845 is a promising candidate radiotracer for imaging FAAH in the brain with PET. These results coupled with the known pharmacology and toxicology of PF-04457845 should facilitate clinical translation of this radiotracer.

The effect of PF-04457845, a potent and selective fatty acid amide hydrolase-1 (FAAH1) inhibitor, on pain due to osteoarthritis of the knee was investigated in a randomised placebo and active-controlled clinical trial. The trial involved 2 periods (separated by a 2-week washout) consisting of a 1-week wash-in phase followed by 2weeks double-blind treatment. Patients received single-blind placebo throughout the wash-in and washout periods. Patients were randomised to receive either 4mg q.d. PF-04457845 followed by placebo (or vice versa), or 500mg b.i.d. naproxen followed by placebo (or vice versa). The primary end point was the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain score. The trial had predefined decision rules based on likelihood that PF-04457845 was better or worse than the standard of care (considered to be a 1.8 reduction in WOMAC pain score compared to placebo). A total of 74 patients were randomised to 1 of 4 treatment sequences. The mean differences (80% confidence intervals) from placebo in WOMAC pain score were 0.04 (-0.63 to 0.71) for PF-04457845 and -1.13 (-1.79 to -0.47) for naproxen, indicating that whilst naproxen seemed efficacious, PF-04457845 was not differentiated from placebo. The study was stopped at the interim analysis for futility. PF-04457845 decreased FAAH activity by >96% and substantially increased 4 endogenous substrates (fatty acid amides). PF-04457845 was well tolerated in osteoarthritis patients, and there was no evidence of cannabinoid-type adverse events. The lack of analgesic effect of FAAH1 inhibition in humans is in contrast to data from animal models. This apparent disconnect between species needs further study.

Fatty acid amide hydrolase (FAAH) is an integral membrane serine hydrolase that degrades the fatty acid amide family of signaling lipids, including the endocannabinoid anandamide. Genetic or pharmacological inactivation of FAAH leads to analgesic and anti-inflammatory phenotypes in rodents without showing the undesirable side effects observed with direct cannabinoid receptor agonists, indicating that FAAH may represent an attractive therapeutic target for the treatment of inflammatory pain and other nervous system disorders. Herein, we report the discovery and characterization of a highly efficacious and selective FAAH inhibitor PF-04457845 (23). Compound 23 inhibits FAAH by a covalent, irreversible mechanism involving carbamylation of the active-site serine nucleophile of FAAH with high in vitro potency (k(inact)/K(i) and IC(50) values of 40300 M(-1) s(-1) and 7.2 nM, respectively, for human FAAH). Compound 23 has exquisite selectivity for FAAH relative to other members of the serine hydrolase superfamily as demonstrated by competitive activity-based protein profiling. Oral administration of 23 at 0.1 mg/kg results in efficacy comparable to that of naproxen at 10 mg/kg in a rat model of inflammatory pain. Compound 23 is being evaluated in human clinical trials.

The endogenous cannabinoid (endocannabinoid) anandamide is principally degraded by the integral membrane enzyme fatty acid amide hydrolase (FAAH). Pharmacological blockade of FAAH has emerged as a potentially attractive strategy for augmenting endocannabinoid signaling and retaining the beneficial effects of cannabinoid receptor activation, while avoiding the undesirable side effects, such as weight gain and impairments in cognition and motor control, observed with direct cannabinoid receptor 1 agonists. Here, we report the detailed mechanistic and pharmacological characterization of N-pyridazin-3-yl-4-(3-{[5-(trifluoromethyl)pyridin-2-yl]oxy}benzylidene)piperidine-1-carboxamide (PF-04457845), a highly efficacious and selective FAAH inhibitor. Mechanistic studies confirm that PF-04457845 is a time-dependent, covalent FAAH inhibitor that carbamylates FAAH's catalytic serine nucleophile. PF-04457845 inhibits human FAAH with high potency (k(inact)/K(i) = 40,300 M(-1)s(-1); IC(50) = 7.2 nM) and is exquisitely selective in vivo as determined by activity-based protein profiling. Oral administration of PF-04457845 produced potent antinociceptive effects in both inflammatory [complete Freund's adjuvant (CFA)] and noninflammatory (monosodium iodoacetate) pain models in rats, with a minimum effective dose of 0.1 mg/kg (CFA model). PF-04457845 displayed a long duration of action as a single oral administration at 1 mg/kg showed in vivo efficacy for 24 h with a concomitant near-complete inhibition of FAAH activity and maximal sustained elevation of anandamide in brain. Significantly, PF-04457845-treated mice at 10 mg/kg elicited no effect in motility, catalepsy, and body temperature. Based on its exceptional selectivity and in vivo efficacy, combined with long duration of action and optimal pharmacokinetic properties, PF-04457845 is a clinical candidate for the treatment of pain and other nervous system disorders.