LY-2183240

LY-2183240 (5-biphenyl-4-ylmethyl-tetrazole-1-carboxylic acid dimethylamide; CAS 874902-19-9) is a heterocyclic carbamoyl tetrazole originally developed at Eli Lilly and Company as a potent and selective inhibitor of the cellular reuptake of the endocannabinoid anandamide (arachidonoylethanolamide). The compound inhibits anandamide uptake in RBL-2H3 cells with a reported IC50 of approximately 0.27 nanomolar, placing it among the most potent endocannabinoid transport blockers characterized to date [1]. Following intraperitoneal administration in rats, LY-2183240 elevates brain anandamide concentrations approximately fivefold and produces antinociceptive effects in the formalin model of inflammatory pain without overt impairment of motor function [1, 2].

Subsequent investigation by Alexander and Cravatt (2006), employing activity-based protein profiling with fluorophosphonate probes, revealed that LY-2183240 is also a potent, covalent, irreversible inhibitor of fatty acid amide hydrolase (FAAH), the principal degradative enzyme for anandamide, with an IC50 of approximately 12.4 nanomolar [3]. The compound inactivates FAAH through carbamylation of the catalytic serine nucleophile (Ser241), a mechanism shared with the O-aryl carbamate class of FAAH inhibitors but enacted through the heterocyclic urea pharmacophore of the tetrazole ring. Activity-based proteomic screening further identified several additional brain serine hydrolases as targets of LY-2183240, including monoacylglycerol lipase (MAGL; IC50 approximately 5.3 nanomolar), the uncharacterized hydrolase KIAA1363 (IC50 approximately 8.2 nanomolar), and the lysophospholipase-like protein bh6 (IC50 approximately 0.09 nanomolar) [3]. This broad serine hydrolase reactivity, attributed to the electrophilic character of the carbamoyl tetrazole warhead, prompted the conclusion that the blockade of anandamide uptake observed with LY-2183240 may be due primarily to the inactivation of FAAH rather than to selective inhibition of a dedicated transporter protein, and that the heterocyclic urea represents a chemotype with potentially excessive protein reactivity for therapeutic drug design [3].

Despite this recharacterization, LY-2183240 remains a widely used pharmacological tool in endocannabinoid research. In behavioral pharmacology, the compound reduces fear-potentiated startle in mice selectively bred for high alcohol preference, enhances alcohol-induced conditioned place preference, produces dose-dependent increases in maximal electroshock seizure thresholds through CB1 receptor-dependent mechanisms, and elevates endocannabinoid tone across multiple tissue compartments [4, 5, 6]. The compound has also appeared on the European recreational drug market as a designer drug, raising regulatory and public health considerations distinct from its research applications [7]. LY-2183240 was never advanced to human clinical trials by its originator and has no registered therapeutic indication. Its principal value in the current research landscape is as a reference compound for the study of endocannabinoid transport mechanisms, as a comparator for more selective FAAH inhibitors (URB597, PF-04457845, JNJ-42165279), and as a chemical biology probe for activity-based profiling of the serine hydrolase superfamily. This monograph reviews the chemistry, synthesis, and structure-activity relationships of LY-2183240; the dual-target pharmacology and the proteomic evidence for broad serine hydrolase engagement; the available pharmacokinetic and in vivo pharmacology data; the preclinical evidence base across pain, anxiety, seizure, and alcohol-related behavioral models; sourcing and handling considerations; stack interactions; adverse-event and safety signal; and a comparative assessment of five endocannabinoid system modulators against LY-2183240 on five competency standards.