Noribogaine is a G-protein biased κ-opioid receptor agonist.

Noribogaine is the long-lived human metabolite of the anti-addictive substance ibogaine. Noribogaine efficaciously reaches the brain with concentrations up to 20 µM after acute therapeutic dose of 40 mg/kg ibogaine in animals. Noribogaine displays atypical opioid-like components in vivo, anti-addictive effects and potent modulatory properties of the tolerance to opiates for which the mode of action remained uncharacterized thus far. Our binding experiments and computational simulations indicate that noribogaine may bind to the orthosteric morphinan binding site of the opioid receptors. Functional activities of noribogaine at G-protein and non G-protein pathways of the mu and kappa opioid receptors were characterized. Noribogaine was a weak mu antagonist with a functional inhibition constants (Ke) of 20 µM at the G-protein and ß-arrestin signaling pathways. Conversely, noribogaine was a G-protein biased kappa agonist 75% as efficacious as dynorphin A at stimulating GDP-GTP exchange (EC50=9 µM) but only 12% as efficacious at recruiting ß-arrestin, which could contribute to the lack of dysphoric effects of noribogaine. In turn, noribogaine functionally inhibited dynorphin-induced kappa ß-arrestin recruitment and was more potent than its G-protein agonistic activity with an IC50 of 1 µM. This biased agonist/antagonist pharmacology is unique to noribogaine in comparison to various other ligands including ibogaine, 18-MC, nalmefene, and 6'-GNTI. We predict noribogaine to promote certain analgesic effects as well as anti-addictive effects at effective concentrations>1 µM in the brain. Because elevated levels of dynorphins are commonly observed and correlated with anxiety, dysphoric effects, and decreased dopaminergic tone, a therapeutically relevant functional inhibition bias to endogenously released dynorphins by noribogaine might be worthy of consideration for treating anxiety and substance related disorders.

Structure activity relationship study of benzo[d]thiazol-2(3H)one based σ receptor ligands.

Herein we report the SAR study which involved structural modifications to the linker length, aryl substitution and alkylamine ring size of the benzo[d]thiazol-2(3H)one based sigma receptor (σ) ligands. Many compounds in this series displayed low nanomolar affinity for the σ receptor subtypes. In particular, 8a showed high affinity (σ-1 Ki = 4.5 nM) for σ-1 receptors and moderately high selectivity (483-fold) over σ-2 receptors.

New positron emission tomography (PET) radioligand for imaging σ-1 receptors in living subjects.

σ-1 receptor (S1R) radioligands have the potential to detect and monitor various neurological diseases. Herein we report the synthesis, radiofluorination, and evaluation of a new S1R ligand 6-(3-fluoropropyl)-3-(2-(azepan-1-yl)ethyl)benzo[d]thiazol-2(3H)-one ([(18)F]FTC-146, [(18)F]13). [(18)F]13 was synthesized by nucleophilic fluorination, affording a product with >99% radiochemical purity (RCP) and specific activity (SA) of 2.6 ± 1.2 Ci/µmol (n = 13) at end of synthesis (EOS). Positron emission tomography (PET) and ex vivo autoradiography studies of [(18)F]13 in mice showed high uptake of the radioligand in S1R rich regions of the brain. Pretreatment with 1 mg/kg haloperidol (2), nonradioactive 13, or BD1047 (18) reduced the binding of [(18)F]13 in the brain at 60 min by 80%, 82%, and 81%, respectively, suggesting that [(18)F]13 accumulation in mouse brain represents specific binding to S1Rs. These results indicate that [(18)F]13 is a promising candidate radiotracer for further evaluation as a tool for studying S1Rs in living subjects.

A 96-well filtration method for radioligand binding analysis of σ receptor ligands.

σ receptors represent a potential drug target for numerous therapeutic indications including cancer, depression, psychostimulant abuse, and stroke. Most published radioligand binding studies for σ receptors utilize a low throughput method employing a "cell harvester." Higher throughput methods are required to facilitate efficient screening of large numbers of novel compounds. In this study, a series of reference compounds was analyzed with a new medium-throughput 96-well filtration method and the results were compared to those obtained using the conventional cell harvester-based method. The 96-well assay utilized rat liver membranes for the determination of both known σ receptor subtypes (σ(1) and σ(2)) because this tissue contains high densities of both subtypes and fulfills criteria required for reliable use with the 96-well format. The new method gave comparable K(i) values for reference ligands analyzed in parallel with samples prepared in rat brain membranes and processed on the traditional cell harvester. For σ(1) receptors, equivalent affinity values were observed for both methods/tissues. For σ(2) receptors, approximately 2-fold higher affinities were observed for most compounds in liver, as compared to brain membranes, but excellent correlation with brain-derived values was maintained. To further demonstrate the utility of the new method it was used to screen a novel series of 2(3H)-benzothiazolone compounds, resulting in the identification of several analogues with nanomolar affinity and greater than 50-fold specificity for σ(1) versus σ(2) receptors.

Synthesis and characterization of [³H]-SN56, a novel radioligand for the σ1 receptor.

The study of the binding characteristics of σ ligands in vivo and in vitro requires radiolabeled probes with high affinity and selectivity. The radioligand presently used for in vitro studies of the σ1 receptor, [³H](+)-pentazocine, has significant limitations; it is difficult to synthesize, has limited chemical stability, and can be problematic to obtain. Evaluation of a series of novel 2(3H)-benzothiazolone compounds revealed SN56 to have sub-nanomolar and preferential affinity for the σ1 subtype, relative to σ2 and non-sigma, binding sites. The goal of this study was to characterize the binding of [³H]-SN56 to σ1 receptors isolated from rat brain. Standard in vitro binding techniques were utilized to 1) determine the specificity and affinity of binding to σ1 receptors, 2) confirm that[³H]-SN56 labels sites previously identified as σ1 by comparing binding to sites labeled by [³H](+)-pentazocine, and 3) characterize the kinetics of binding. The results indicate that [³H]-SN56 exhibits 1) specific, saturable, and reversible binding to the σ1 receptor, with B(max)=340±10 fmol/mg and K(d)=0.069±0.0074 nM, 2) competitive displacement by classical sigma compounds, yielding σ1 K(i) values consistent with those reported in the literature, and 3) binding kinetics compatible with a 90 min incubation, and filtration for separation of free and bound radioligand. The results of these studies suggest that [(3)H]-SN56 may serve as a viable alternative to [³H](+)-pentazocine in radioligand binding assays.

Sigma receptors: potential targets for a new class of antidepressant drug.

Despite the widespread and devastating impact of depression on society, our current understanding of its pathogenesis is limited. Likewise, existing treatments are inadequate, providing relief to only a subset of people suffering from depression. The search for more effective antidepressant drugs includes the investigation of new molecular targets. Among them, current data suggests that sigma receptors are involved in multiple processes effecting antidepressant-like actions in vivo and in vitro. This review summarizes accumulated evidence supporting a role for sigma receptors in antidepressant effects and provides a conceptual framework for delineating their potential roles over the course of antidepressant treatment.

Synthesis and opioid activity of enantiomeric N-substituted 2,3,4,4a,5,6,7,7a-octahydro-1H-benzofuro[3,2-e]isoquinolines.

A series of enantiomeric N-substituted 2,3,4,4a,5,6,7,7a-octahydro-1H-benzofuro[3,2-e]isoquinolines was synthesized. The (-)-enantiomers had much greater kappa-, mu-, and delta-opioid receptor binding affinity than the corresponding (+)-enantiomers. Compounds (-)-1a, (-)-1b, and (-)-1c displayed subnanomolar binding affinity for the mu-receptor, and (-)-1b had a high affinity for the kappa-receptor. Compound (-)-1a was a mu-partial agonist and kappa-antagonist. Compound (-)-1b was a potent neutral mu-antagonist (K(d) = 0.22 nM) and a kappa-partial agonist.

Relationship between methamphetamine exposure and matrix metalloproteinase 9 expression.

The involvement of matrix metalloproteinase (MMP) 9 in methamphetamine-induced neurotoxicity was evaluated. Injection of mice with stimulant or toxic doses of methamphetamine upregulated MMP9 gene expression in the brain within 5 min. By 24 h, MMP9 gene expression returned to control levels in the stimulant-treated mice, but remained elevated in animals exposed to toxic doses of methamphetamine. Reductions in striatal dopamine levels, a marker of methamphetamine neurotoxicity, developed 1-7 days after methamphetamine exposure, but were not accompanied by concomitant changes in MMP9 gene expression. In MMP9 knockout mice, methamphetamine retained its ability to elicit neurotoxicity. The data suggest that MMP9 expression does not contribute to methamphetamine-induced neurotoxicity, and may instead be involved in remodeling of the nervous system.

Conversion of a highly selective sigma-1 receptor-ligand to sigma-2 receptor preferring ligands with anticocaine activity.

Cocaine's toxicity can be mitigated by blocking its interaction with sigma-1 receptors. The involvement of sigma-2 receptors remains unclear. To investigate their potential role, we have designed compounds through a convergent synthesis utilizing a highly selective sigma-1 ligand and elements of a selective sigma-2 ligand. Among the synthesized compounds was produced a subnanomolar sigma-2 ligand with an 11-fold preference over sigma-1 receptors. These compounds may be useful in developing effective pharmacotherapies for cocaine toxicity.

Sodwanone and yardenone triterpenes from a South African species of the marine sponge Axinella inhibit hypoxia-inducible factor-1 (HIF-1) activation in both breast and prostate tumor cells.

Hypoxia-inducible factor-1 (HIF-1) is a transcription factor that promotes tumor cell adaptation and survival under hypoxic conditions. HIF-1 is currently recognized as an important molecular target for anticancer drug discovery. A T47D breast tumor cell-based reporter assay was used to evaluate the NCI Open Repository of marine invertebrates and algae lipid extracts for HIF-1 inhibitory activity. Bioassay-guided fractionation and isolation of an active extract from Axinella sp. yielded seven new sodwanone triterpenoids [3-epi-sodwanone K (1), 3-epi-sodwanone K 3-acetate (2), 10,11-dihydrosodwanone B (4), sodwanones T-W (3, 7, 8, 9)], the new yardenone triterpene 12R-hydroxyyardenone (10), and the previously reported compounds sodwanone A (5), sodwanone B (6), and yardenone (11). The structures and relative configurations of these Axinella metabolites were determined spectroscopically. The absolute configuration of 1 was determined by the modified Mosher ester procedure. Sodwanone V (8) inhibited both hypoxia-induced and iron chelator (1,10-phenanthroline)-induced HIF-1 activation in T47D breast tumor cells (IC50 15 microM), and 8 was the only sodwanone that inhibited HIF-1 activation in PC-3 prostate tumor cells (IC50 15 microM). Compounds 1, 3, 4, and 5 inhibited hypoxia-induced HIF-1 activation in T47D cells (IC50 values 20-25 microM). Compound 2 was cytotoxic to T47D cells (IC50 22 microM), and 8 showed cytotoxicity to MDA-MB-231 breast tumor cells (IC50 23 microM).