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 (kinact/Ki and IC50 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.

Optimisation of oral bioavailability is a continuing challenge for the pharmaceutical and biotechnology industries. The number of potential drug candidates requiring in vivo evaluation has significantly increased with the advent of combinatorial chemistry. In addition, drug discovery programmes are increasingly forced into more lipophilic and lower solubility chemical space. To aid in the use of in vitro and in silico tools as well as reduce the number of in vivo studies required, a team-based discussion tool is proposed that provides a 'road map' to guide the selection of profiling assays that should be considered when optimising oral bioavailability. This road map divides the factors that contribute to poor oral bioavailability into two interrelated categories: absorption and metabolism. This road map provides an interface for cross discipline discussions and a systematic approach to the experimentation that drives the drug discovery process towards a common goal - acceptable oral bioavailability using minimal resources in an acceptable time frame.

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