No abstract

SummaryImprogan, a chemical congener of cimetidine, is a highly effective non-opioid analgesic when injected into the CNS. Despite extensive characterization, neither the improgan receptor, nor a pharmacological antagonist of improgan has been previously described. Presently, the specific binding of 3 H-cimetidine (3HCIM) in brain fractions was used to discover 4(5)-((4-iodobenzyl) thiomethyl)-1H-imidazole, which behaved in vivo as the first improgan antagonist. The synthesis and pharmacological properties of this drug (named CC12) are described herein. In rats, CC12 (50 -500 nmol, icv) produced dose-dependent inhibition of improgan (200 -400 nmol) antinociception on the tail flick and hot plate tests. When given alone to rats, CC12 had no effects on nociceptive latencies, or on other observable behavioral or motor functions. Maximal inhibitory effects of CC12 (500 nmol) were fully surmounted with a large icv dose of improgan (800 nmol), demonstrating competitive antagonism. In mice, CC12 (200-400 nmol, icv) behaved as a partial agonist, producing incomplete improgan antagonism, but also limited antinociception when given alone. Radioligand binding, receptor autoradiography, and electrophysiology experiments showed that CC12's antagonist properties are not explained by activity at 25 sites relevant to analgesia, including known receptors for cannabinoids, opioids or histamine. The use of CC12 as an improgan antagonist will facilitate the characterization of improgan analgesia. Furthermore, because CC12 was also found presently to inhibit opioid and cannabinoid antinociception, it is suggested that this drug modifies a biochemical mechanism shared by several classes of analgesics. Elucidation of this mechanism will enhance understanding of the biochemistry of pain relief.

J. Neurochem. (2011) 117, 1–18. Abstract The cannabinoid type‐1 (CB1) receptor is a G protein‐coupled receptor that binds the main active ingredient of marijuana, Δ9‐tetrahydrocannabinol, and has been implicated in several disease states, including drug addiction, anxiety, depression, obesity, and chronic pain. In the two decades since the discovery of CB1, studies at the molecular level have centered on the transmembrane core. This interest has now expanded as we discover that other regions of CB1, including the CB1 carboxyl‐terminus, have critical structures that are important for CB1 activity and regulation. Following the recent description of the three dimensional structure of the full‐length CB1 carboxyl‐terminal tail [Biopolymers (2009) vol. 91, pp. 565–573], several residues and structural motifs including two α‐helices (termed H8 and H9) have been postulated to interact with common G protein‐coupled receptor accessory proteins, such as G‐proteins and β‐arrestins. This discourse will focus on the CB1 carboxyl‐terminus; our current understanding of the structural features of this region, evidence for its interaction with proteins, and the impact of structure on the binding and regulatory function of CB1 accessory proteins. The involvement of the carboxyl‐terminus in the receptor life cycle including activation, desensitization, and internalization will be highlighted.

Improgan, a nonopioid antinociceptive agent, activates descending, pain-relieving mechanisms in the brain stem, but the receptor for this compound has not been identified. Because cannabinoids also activate nonopioid analgesia by a brain stem action, experiments were performed to assess the significance of cannabinoid mechanisms in improgan antinociception. The cannabinoid CB 1 antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (SR141716A) induced dose-dependent inhibition of improgan antinociception on the tail-flick test after i.c.v. administration in rats. The same treatments yielded comparable inhibition of cannabinoid {R-(ϩ)-(2,3-dihydro-5-methyl-3-[(4-mor pholinyl)methyl]pyrol[1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl)methanone monomethanesulfonate, WIN 55,212-2} analgesia. Inhibition of improgan and WIN 55,212-2 antinociception by SR141716A was also observed in Swiss-Webster mice. Radioligand binding studies showed no appreciable affinity of improgan on rat brain, mouse brain, and human recombinant CB 1 receptors, ruling out a direct action at these sites. To test the hypothesis that CB 1 receptors indirectly participate in improgan signaling, the effects of improgan were assessed in mice with a null mutation of the CB 1 gene with and without SR141716A pretreatment. Surprisingly, improgan induced complete antinociception in both CB 1 (Ϫ/Ϫ) and wild-type control [CB 1 (ϩ/ϩ)] mice. Furthermore, SR141716A inhibited improgan antinociception in CB 1 (ϩ/ϩ) mice, but not in CB 1 (Ϫ/Ϫ) mice. Taken together, the results show that SR141716A reduces improgan antinociception, but neither cannabinoids nor CB 1 receptors seem to play an obligatory role in improgan signaling. Present and previous studies suggest that ⌬ 9 -tetrahydrocannabinol may act at both CB 1 and other receptors to relieve pain, but no evidence was found indicating that improgan uses either of these mechanisms. SR141716A will facilitate the study of improgan-like analgesics.

ABSTRACT:[ 3 H]Cimetidine (3HCIM) specifically binds to an unidentified site in the rat brain. Because recently described ligands for this site have pharmacological activity, 3HCIM binding was characterized. 3HCIM binding was saturable, heat-labile, and distinct from the histamine H 2 receptor. To test the hypothesis that 3HCIM binds to a cytochrome P450 (P450), the effects of nonselective and isoform-selective P450 inhibitors were studied. The heme inhibitor KCN and the nonselective P450 inhibitor metyrapone both produced complete, concentrationdependent inhibition of 3HCIM binding (K i ‫؍‬ 1.3 mM and 11.9 M, respectively).