Phytocannabinoids, such as the principal bioactive component of marijuana, ⌬ 9 -tetrahydrocannabinol, have been used for thousands of years for medical and recreational purposes. ⌬ 9 -Tetrahydrocannabinol and endogenous cannabinoids (e.g., anandamide) initiate their agonist properties by stimulating the cannabinoid family of G protein-coupled receptors (CB 1 and CB2). The biosynthesis and physiology of anandamide is well understood, but its mechanism of uptake (resulting in signal termination by fatty acid amide hydrolase) has been elusive. Mounting evidence points to the existence of a specific anandamide transport protein; however, no direct evidence for this protein has been provided. Here, we use a potent, competitive small molecule inhibitor of anandamide uptake (LY2318912, IC 50 7.27 ؎ 0.510 nM) to identify a high-affinity, saturable anandamide transporter binding site (LY2318912; K d ‫؍‬ 7.62 ؎ 1.18 nM, Bmax ‫؍‬ 31.6 ؎ 1.80 fmol͞mg protein) that is distinct from fatty acid amide hydrolase. Systemic administration of the inhibitor into rodents elevates anandamide levels 5-fold in the brain and demonstrates efficacy in the formalin paw-licking model of persistent pain with no obvious adverse effects on motor function. Identification of the anandamide transporter binding site resolves a missing mechanistic link in endocannabinoid signaling, and in vivo results suggest that endocannabinoid transporter antagonists may provide a strategy for positive modulation of cannabinoid receptors.anandamide ͉ fatty acid amide hydrolase ͉ cannabinoid ͉ marijuana ͉ transporter E ndocannabinoids are recognized as significant intracellular lipid signaling molecules in the central nervous system with extensive control of physiological and behavioral mood and affect. Increases in endocannabinoid neurotransmission have broad therapeutic potential, including reduction of nausea and emesis (1), appetite stimulation (2), analgesia (3), anxiolytic activity (4), antispasmodic activity (5), and lowering of intraocular pressure in glaucoma (6). Identification of a specific binding site for the phytocannabinoid, ⌬ 9 -tetrahydrocannabinol (⌬ 9 -THC) (7), cloning of the cannabinoid receptors (CB 1 and CB 2 ) (8, 9), and the identification of an endogenous ligand, anandamide (N-arachidonoylethanolamide) (10), provided evidence of an endogenous cannabinoid system. Anandamide represents a class of lipid neurotransmitters that stimulate not only presynaptic and postsynaptic CB 1 receptors but also TRPV1 ion channels (11, 12), 5-hydroxytryptamine receptors (13-16), and possibly other receptors, as well as CB 2 receptors in the periphery (10,(17)(18)(19). More recently, the enzymes that are responsible for anandamide synthesis (phospholipase D) and catabolism (fatty acid amide hydrolase, FAAH) have been identified and characterized (20,21). Unlike typical neurotransmitter molecules, anandamide is synthesized in the membrane bilayer, resulting in the phospholipid precursor of anandamide, Narachidonoylphosphatidylethanolamine (22-25). Calciumacti...

We recently demonstrated that 11 C-MePPEP, a PET ligand for CB 1 receptors, has such high uptake in the human brain that it can be imaged for 210 min and that receptor density can be quantified as distribution volume (V T ) using the gold standard of compartmental modeling. However, 11 C-MePPEP had relatively poor retest and intersubject variabilities, which were likely caused by errors in the measurements of radioligand in plasma at low concentrations by 120 min. We sought to find an analog of 11 C-MePPEP that would provide more accurate plasma measurements. We evaluated several promising analogs in the monkey brain and chose the 18 F-di-deutero fluoromethoxy analog ( 18 F-FMPEP-d 2 ) to evaluate further in the human brain. Methods: 11 C-FMePPEP, 18 F-FEPEP, 18 F-FMPEP, and 18 F-FMPEP-d 2 were studied in 5 monkeys with 10 PET scans. We calculated V T using compartmental modeling with serial measurements of unchanged parent radioligand in arterial plasma and radioactivity in the brain. Nonspecific binding was determined by administering a receptorsaturating dose of rimonabant, an inverse agonist at the CB 1 receptor. Nine healthy human subjects participated in 17 PET scans using 18 F-FMPEP-d 2 , with 8 subjects having 2 PET scans to assess retest variability. To identify sources of error, we compared intersubject and retest variability of brain uptake, arterial plasma measurements, and V T . Results: 18 F-FMPEP-d 2 had high uptake in the monkey brain, with greater than 80% specific binding, and yielded less radioactivity uptake in bone than did 18 F-FMPEP. High brain uptake with 18 F-FMPEP-d 2 was also observed in humans, in whom V T was well identified within approximately 60 min. Retest variability of plasma measurements was good (16%); consequently, V T had a good retest variability (14%), intersubject variability (26%), and intraclass correlation coefficient (0.89). V T increased after 120 min, suggesting an accumulation of radiometabolites in the brain. Radioactivity accumulated in the skull throughout the entire scan but was thought to be an insignificant source of data contamination. Conclusion: Studies in monkeys facilitated our development and selection of 18 F-FMPEP-d 2 , compared with 18 F-FMPEP, as a radioligand demonstrating high brain uptake, high percentage of specific binding, and reduced uptake in bone. Retest analysis in human subjects showed that 18 F-FMPEP-d 2 has greater precision and accuracy than 11 C-MePPEP, allowing smaller sample sizes to detect a significant difference between groups.

Abstract[ 11 C]MePPEP is a high affinity, CB 1 receptor-selective, inverse agonist that has been studied in rodents and monkeys. We examined the ability of [ 11 C]MePPEP to quantify CB 1 receptors in human brain as distribution volume calculated with the "gold standard" method of compartmental modeling and compared results with the simple measure of brain uptake. A total of 17 healthy subjects participated in 26 positron emission tomography (PET) scans, with 8 having two PET scans to assess retest variability. After injection of [ 11 C]MePPEP, brain uptake of radioactivity was high (e.g., 3.6 SUV in putamen region at ~60 minutes) and washed out very slowly. A two-tissue compartment model yielded values of distribution volume (which is proportional to receptor density) that were both well identified (SE 5%) and stable between 60 and 210 minutes. The simple measure of brain uptake (average concentration of radioactivity between 40 and 80 minutes) had good retest variability (~8%) and moderate intersubject variability (16%, coefficient of variation). In contrast, distribution volume had two-fold greater retest variability (~15%) and, thus, less precision. In addition, distribution volume had three-fold greater intersubject variability (~52%). The decreased precision of distribution volume compared to brain uptake was likely due to the slow washout of radioactivity from brain and to noise in measurements of the low concentrations of [ 11 C]MePPEP in plasma. These results suggest that brain uptake can be used for within subject studies (e.g., to measure receptor occupancy by medications) but that distribution volume remains the gold standard for accurate measurements between groups.

Clinical development of catechol-based orthosteric agonists of the dopamine D1 receptor has thus far been unsuccessful due to multiple challenges. To address these issues, we identified LY3154207 (3) as a novel, potent, and subtype selective human D1 positive allosteric modulator (PAM) with minimal allosteric agonist activity. Conformational studies showed LY3154207 adopts an unusual boat conformation, and a binding pose with the human D1 receptor was proposed based on this observation. In contrast to orthosteric agonists, LY3154207 showed a distinct pharmacological profile without a bell-shaped dose-response relationship or tachyphylaxis in preclinical models. Identification of a crystalline form of free LY3154207 from the discovery lots was not successful. Instead, a novel cocrystal form with superior solubility was discovered and determined to be suitable for development. This cocrystal form was advanced to clinical development as a potential first-in-class D1 PAM and is now in phase 2 studies for Lewy body dementia.

The serotonin (5-HT) receptor subtype mediating inhibition of neurogenic dural inflammation in guinea pigs was investigated using a series of serotonin agonists with differing affinities for the 5-HT1B, 5-HT1D and 5-HT1F receptors. When agonist potencies for inhibiting neurogenic inflammation were compared with affinities for these receptor subtypes, a significant positive correlation was seen only with the 5-HT1F receptor. The potency of agonists in inhibiting adenylate cyclase in cells transfected with human 5-HT1F receptor was also highly correlated with their potency in the animal model of migraine. In situ hybridization demonstrated 5-HT1F receptor mRNA in guinea pig trigeminal ganglion neurons. These data suggest that the 5-HT1F receptor is a rational target for migraine therapeutics.