A Second Generation of Carbamate‐Based Fatty Acid Amide Hydrolase Inhibitors with Improved Activity in vivo

Abstract

The fatty acid ethanolamides are a class of signaling lipids that include agonists at cannabinoid and type-α peroxisome proliferator-activated receptors. In the brain, these compounds are primarily hydrolyzed by the intracellular serine enzyme fatty acid amide hydrolase (FAAH). Oaryl carbamate FAAH inhibitors such as URB597 are being evaluated clinically for the treatment of pain and anxiety, but interactions with carboxylesterases in liver might limit their usefulness. Here we explore two strategies aimed at overcoming this limitation. Lipophilic N-terminal substitutions, which enhance FAAH recognition, yield potent inhibitors but render such compounds both susceptible to attack by broad-spectrum hydrolases and inactive in vivo. By contrast, polar electron-donating O-aryl substituents, which decrease carbamate reactivity, yield compounds, such as URB694, that are highly potent FAAH inhibitors in vivo and less reactive with off-target carboxylesterases. The results suggest that an approach balancing inhibitor reactivity with target recognition produces FAAH inhibitors that display significantly improved drug-likeness.

Effects of Fatty Acid Amide Hydrolase (FAAH) Inhibitors in Non-Human Primate Models of Nicotine Reward and Relapse

“…These findings are in agreement with those previously reported for mice (Clapper et al, 2009). Furthermore, concentrations of anandamide, PEA, and OEA, all of which are FAAH substrates (Cravatt et al, 1996), were significantly elevated in the midbrain of monkeys receiving URB597 or URB694, whereas levels of 2-AG, which is degraded by monoacylglycerol lipase (MGL), remained unaffected (Figure 1c-f; effect of treatment; anandamide: F 2, 11 = 61.99, po0.0001, PEA: F 2, 11 = 47.04, po0.0001, OEA: F 2, 11 = 72.56, po0.0001, 2-AG: F 2, 10 = 0.20, p = 0.82).…”

“…Prior work has shown that URB694 inhibits FAAH activity in the rat brain (Clapper et al, 2009), but the pharmacokinetic properties of this compound have not been reported. Because understanding these properties is relevant to interpretation of the effects of drugs on reward-related behaviors, which are strongly dependent on the kinetics of penetration into the brain, we administered URB694 (3 and 10 mg/kg, IP) to rats and measured circulating levels of the compound by LC/MS at various times (0-480 min) after injection.…”

“…Furthermore, as most previous research has involved a single chemical entity, URB597, it would also be valuable to investigate newer FAAH inhibitors with improved properties. An interesting compound in this regard is URB694 that displays greater plasma stability, higher water solubility, lower propensity to inhibit liver esterases, and higher potency as a FAAH inhibitor than its parent compound URB597 (Clapper et al, 2009;Vacondio et al, 2011).…”

Understanding the role of carbamate reactivity in fatty acid amide hydrolase inhibition by QM/MM mechanistic modelling

“…This indicates that the electronic distribution of the carbamate has a negligible effect on Ser241 carbamoylation, in spite of its profound importance for chemical and plasmatic stability of these compounds. 12 This can be understood as this TS structure is characterized by deprotonation of Ser241 (H 1 is found between O 1 and O 2 ), with the nucleophile O 1 still approaching the carbonyl carbon of the inhibitor ( Table 1).…”

“…12 Structure-activity relationship (SAR) studies showed that conjugated, electron-donor groups on the biphenyl scaffold of URB524 (which increase electron density around the carbamate carbon) are associated with enhanced carbamate stability both in alkaline buffer and in rat plasma. 13 Conversely, these groups do not affect FAAH inhibitor potency in vitro.…”