Preclinical pharmacological evaluation of the fatty acid amide hydrolase inhibitor BIA 10-2474

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.

A perspective review on fatty acid amide hydrolase (FAAH) inhibitors as potential therapeutic agents

Fatty acid amide hydrolase (FAAH) is an important enzyme creditworthy of hydrolyzing endocannabinoids and related-amidated signalling lipids, discovery of which has pioneered novel arena of pharmacological canvasses to unwrap its curative potency in various diseased circumstances. It presents contemporary basis for understanding molecules regulating and mediating inflammatory reactions, pain, anxiety, depression, and neurodegeneration. FAAH inhibitors form vital approach for discovery of therapeutic agents that are concerned with local elevation of endocannabinoids under certain stimuli, debarring adverse/unwanted secondary effects from global activation of cannabinoid receptors by exogenous cannabimimetics. During past decades, several molecules with excellent potency developed through tailor-made approaches entered into clinical trials, but none could reach market. Hence, hunt for novel, non-toxic and selective FAAH inhibitors are on horizon. This review summarizes present perception on FAAH in conjunction with its structure, mechanism of catalysis and biological functions. It also foregrounds recent development of molecules belonging to diverse chemical classes as potential FAAH inhibitors bobbing up from in-depth chemical, mechanistic and computational studies published since 2015-November 2019, focusing on their potency. This review will assist readers to obtain rationale on FAAH as potential target for addressing various disease conditions, acquiring significant knowledge on recently established inhibitor scaffolds and their development potentials. New technologies including MD-MM simulations and 3D-QSAR studies allow mechanistic characterization of enzyme. Assessment of in-vitro and in-vivo efficacy of existing FAAH inhibitors will facilitate researchers to design novel ligands utilizing modern drug design methods. The discussions will also impose precaution in decision making process, quashing possibility of late stage failure.

One-pot synthesis of 1,3,4-oxadiazol-2(3H)-ones with CO2 as a C1 synthon promoted by hypoiodite

A convenient and efficient route has been developed to synthesize 1,3,4-oxadiazol-2(3H)-ones from CO₂, hydrazines and aryl or aliphatic aldehydes. Promoted by hypoiodite (IO^-) generated in situ from KI and oxidant TBHP, the one-pot synthesis could proceed smoothly to afford the desired products in moderate to high yields. Mechanism studies revealed that nitrile imine was an important intermediate in this transformation. Notably, a commercial herbicide Oxadiazon could be successfully synthesized by this route.

KI-catalyzed reactions of aryl hydrazines with α-oxocarboxylic acids in the presence of CO2: access to 1,3,4-oxadiazol-2(3H)-ones

A novel KI-catalyzed synthesis of 1,3,4-oxadiazol-2(3H)-ones from aryl hydrazines, α-oxocarboxylic acids and CO₂ was reported.

Discovery of a Potent, Long-Acting, and CNS-Active Inhibitor (BIA 10-2474) of Fatty Acid Amide Hydrolase

Fatty acid amide hydrolase (FAAH) can be targeted for the treatment of pain associated with various medical conditions. Herein we report the design and synthesis of a novel series of heterocyclic-N-carboxamide FAAH inhibitors that have a good alignment of potency, metabolic stability and selectivity for FAAH over monoacylglycerol lipase (MAGL) and carboxylesterases (CEs). Lead optimization efforts carried out with benzotriazolyl- and imidazolyl-N-carboxamide series led to the discovery of clinical candidate 8 l (3-(1-(cyclohexyl(methyl)carbamoyl)-1H-imidazol-4-yl)pyridine 1-oxide; BIA 10-2474) as a potent and long-acting inhibitor of FAAH. However, during a Phase I clinical trial with compound 8 l, unexpected and unpredictable serious neurological adverse events occurred, affecting five healthy volunteers, including the death of one subject.

A metal-free and mild approach to 1,3,4-oxadiazol-2(3H)-ones via oxidative C–C bond cleavage using molecular oxygen

A metal-free aerobic oxidative C–C bond cleavage reaction for the synthesis of 1,3,4-oxadiazol-2(3H)-ones is described.

Identification of selective covalent inhibitors of platelet activating factor acetylhydrolase 1B2 from the screening of an oxadiazolone-capped peptoid-azapeptoid hybrid library

A potent and selective inhibitor of platelet-activating factor acetylhydrolase 1B2 (PAFAH1B2) is described. The compound was derived by improvement of a modest affinity primary hit isolated from the screening of a bead-displayed peptoid-azapeptoid hybrid library tethered to an oxadiazolone 'warhead'. The oxadiazolone moiety of the inhibitors was found to react covalently with the active site serine residue of PAFAH1B2. This screening strategy may be useful for the identification of many selective, covalent inhibitors of serine hydrolases.

Synthesis and structure–activity relationships of ionizable 1,3,4-oxadiazol-2(3H)-ones as peripherally selective FAAH inhibitors with improved aqueous solubility

Novel 5-(2,4-difluorophenoxy)-3-aryl-1,3,4-oxadiazol-2(3H)-ones were prepared and in vivo SAR are discussed. Ionisable substituents on the N-phenyl ring provided compounds with significantly improved aqueous solubility. In addition, these analogues retained equivalent or improved potency against FAAH enzyme compared to the parent phenols 2–3. FAAH inhibition by the 2-(piperazin-1-yl)ethyl and 3-(piperazin-1-yl)propyl derivatives 24 and 30 was confined to the periphery in mice (30 mg/kg), whereas hepatic FAAH activity was inhibited by over 90%.

Revisiting 1,3,4-Oxadiazol-2-ones: Utilization in the Development of ABHD6 Inhibitors

This article describes our systematic approach to exploring the utility of the 1,3,4-oxadiazol-2-one scaffold in the development of ABHD6 inhibitors. Compound 3-(3-aminobenzyl)-5-methoxy-1,3,4-oxadiazol-2(3H)-one (JZP-169, 52) was identified as a potent inhibitor of hABHD6, with an IC₅₀ value of 216 nM. This compound at 10 μM concentration did not inhibit any other endocannabinoid hydrolases, such as FAAH, MAGL and ABHD12, or bind to the cannabinoid receptors (CB₁ and CB₂). Moreover, in competitive activity-based protein profiling (ABPP), compound 52 (JZP-169) at 10 μM selectively targeted ABHD6 of the serine hydrolases of mouse brain membrane proteome. Reversibility studies indicated that compound 52 inhibited hABHD6 in an irreversible manner. Finally, homology modelling and molecular docking studies were used to gain insights into the binding of compound 52 to the active site of hABHD6.

Palladium-catalyzed oxidative carbonylation of hydrazides: synthesis of 1,3,4-oxadiazol-2(3H)-ones

A novel palladium-catalyzed oxidative carbonylation reaction was developed via the carbon monoxide insertions between the amine group and the carbonyl group to realize the intramolecular cyclization, which provides efficient access to 1,3,4-oxadiazol-2(3H)-ones with a wide range of substrates under mild conditions, resulting in good to excellent yields.

Chiral 1,3,4-oxadiazol-2-ones as highly selective FAAH inhibitors

In the present study, identification of chiral 1,3,4-oxadiazol-2-ones as potent and selective FAAH inhibitors has been described. The separated enantiomers showed clear differences in the potency and selectivity toward both FAAH and MAGL. Additionally, the importance of the chirality on the inhibitory activity and selectivity was proven by the simplification approach by removing a methyl group at the 3-position of the 1,3,4-oxadiazol-2-one ring. The most potent compound of the series, the S-enantiomer of 3-(1-(4-isobutylphenyl)ethyl)-5-methoxy-1,3,4-oxadiazol-2(3H)-one (JZP-327A, 51), inhibited human recombinant FAAH (hrFAAH) in the low nanomolar range (IC50 = 11 nM), whereas its corresponding R-enantiomer 52 showed only moderate inhibition toward hrFAAH (IC50 = 0.24 μM). In contrast to hrFAAH, R-enantiomer 52 was more potent in inhibiting the activity of hrMAGL compared to S-enantiomer 51 (IC50 = 4.0 μM and 16% inhibition at 10 μM, respectively). The FAAH selectivity of the compound 51 over the supposed main off-targets, MAGL and COX, was found to be >900-fold. In addition, activity-based protein profiling (ABPP) indicated high selectivity over other serine hydrolases. Finally, the selected S-enantiomers 51, 53, and 55 were shown to be tight binding, slowly reversible inhibitors of the hrFAAH.

1,3,4-Oxadiazol-2-ones as fatty-acid amide hydrolase and monoacylglycerol lipase inhibitors: Synthesis, in vitro evaluation and insight into potency and selectivity determinants by molecular modelling

Inhibition of the key hydrolytic enzymes of the endocannabinoid system, fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL), has been proposed as potential mode of action for various therapeutic applications. Continuing our previous work, we take the first steps of structure-activity relationship exploration and show that 1,3,4-oxadiazol-2-ones can serve as scaffold for both selective FAAH and MAGL inhibitors, and also function as a dual FAAH/MAGL inhibitor at sub-micromolar IC50 values. Moreover, 10-fold selectivity against MAGL over FAAH was achieved with compound 3d (FAAH and MAGL IC50; 2.0 and 0.22 μM). Lastly, enzyme and ligand features contributing to the potency and selectivity differences are analysed by molecular docking.

Analysis of the discriminative inhibition of mammalian digestive lipases by 3-phenyl substituted 1,3,4-oxadiazol-2(3H)-ones

We report here the reactivity and selectivity of three 5-Methoxy-N-3-Phenyl substituted-1,3,4-Oxadiazol-2(3H)-ones (MPOX, as well as meta and para-PhenoxyPhenyl derivatives, i.e.MmPPOX and MpPPOX) with respect to the inhibition of mammalian digestive lipases: dog gastric lipase (DGL), human (HPL) and porcine (PPL) pancreatic lipases, human (HPLRP2) and guinea pig (GPLRP2) pancreatic lipase-related proteins 2, human pancreatic carboxyl ester hydrolase (hCEH), and porcine pancreatic extracts (PPE). All three oxadiazolones displayed similar inhibitory activities on DGL, PLRP2s and hCEH than the FDA-approved anti-obesity drug Orlistat towards the same enzymes. These compounds appeared however to be discriminative of HPL (poorly inhibited) and PPL (fully inhibited). The inhibitory activities obtained experimentally in vitro were further rationalized using in silico molecular docking. In the case of DGL, we demonstrated that the phenoxy group plays a key role in specific molecular interactions within the lipase's active site. The absence of this group in the case of MPOX, as well as its connectivity to the neighbouring aromatic ring in the case of MmPPOX and MpPPOX, strongly impacts the inhibitory efficiency of these oxadiazolones and leads to a significant gain in selectivity towards the lipases tested. The powerful inhibition of PPL, DGL, PLRP2s, hCEH and to a lesser extend HPL, suggests that oxadiazolone derivatives could also provide useful leads for the development of novel and more discriminative inhibitors of digestive lipases. These inhibitors could be used for a better understanding of individual lipase function as well as for drug development aiming at the regulation of the whole gastrointestinal lipolysis process.