CC12, a high-affinity ligand for [3H]cimetidine binding, is an improgan antagonist

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.

High-Affinity Binding of [3H]Cimetidine to a Heme-Containing Protein in Rat Brain

“…In support of this idea, CC12 (Fig. 1), a new derivative of cimetidine, showed high affinity for 3HCIM-binding sites and behaved in vivo as a competitive antagonist of several antinociceptive agents (Hough et al, 2007). In the present study, we have characterized the pharmacological nature of 3HCIM binding in brain homogenates and tested the hypothesis that this binding site is a member of the P450 superfamily.…”

“…The search for high-affinity ligands led to the study of the cimetidine analogs CC11 (Warrander et al, 1983) and CC12 (Hough et al, 2007) (Fig. 1).…”

“…CC12 [4(5)-((4-iodobenzyl)thiomethyl)-1H-imidazole] (Fig. 1) was synthesized as described recently (Hough et al, 2007).…”

Opioid Analgesia in P450 Gene Cluster Knockout Mice: A Search for Analgesia-Relevant Isoforms

“…Since inhibitors of 3 HCIM binding also block the effects of several types of analgesics, 3 HCIM-binding proteins were suggested to be targets for analgesic drug development (Hough et al, 2007;Stadel et al, 2010). The absence of deficits in 3 HCIM binding in liver homogenates from the genotypes studied (Supplemental Fig.…”

“…Characterization of 3 HCIMbinding proteins in brain suggested a P450 profile, but these were never identified (Stadel et al, 2008). Identification of these proteins is of interest because they could be new analgesic drug targets (Hough et al, 2007). Although this idea has not been confirmed (Stadel et al, 2010), 3 HCIM-binding studies led to the discovery that the painrelieving effects of both nonopioid (Hough et al, 2011) and opioid (Conroy et al, 2010) analgesic drugs require brain P450 activity.…”