Comparative Pharmacological Effects of Lisuride and Lysergic Acid Diethylamide Revisited

Lisuride is a non-psychedelic serotonin (5-HT) 2A receptor (5-HT2A) agonist and analogue of the psychedelic lysergic acid diethylamide (LSD). Lisuride also acts as an agonist at the serotonin 1A receptor (5-HT1A), a property known to counter psychedelic effects. Here, we tested whether lisuride lacks psychedelic activity due to a dual mechanism: (1) partial agonism at 5-HT2A and (2) potent agonism at 5-HT1A. The in vitro effects of lisuride, LSD, and related analogues on 5-HT2A signaling were characterized by using miniGαq and β-arrestin 2 recruitment assays. The 5-HT1A- and 5-HT2A-mediated effects of lisuride and LSD were also compared in male C57BL/6J mice. The in vitro results confirmed that LSD is an agonist at 5-HT2A, with high efficacy and potency for recruiting miniGαq and β-arrestin 2. By contrast, lisuride displayed partial efficacy for both functional end points (6–52% of 5-HT or LSD Emax) and antagonized the effects of LSD. The mouse experiments demonstrated that LSD induces head twitch responses (HTRs)­(ED50 = 0.039 mg/kg), while lisuride suppresses HTRs (ED50 = 0.006 mg/kg). Lisuride also produced potent hypothermia and hypolocomotion (ED50 = 0.008–0.023 mg/kg) that was blocked by the 5-HT1A antagonist WAY100635 (3 mg/kg). Blockade of 5-HT1A prior to lisuride restored basal HTRs, but it failed to increase HTRs above baseline levels. HTRs induced by LSD were blocked by lisuride (0.03 mg/kg) or the 5-HT1A agonist 8-OH-DPAT (1 mg/kg). Overall, our findings show that lisuride is an ultrapotent 5-HT1A agonist in C57BL/6J mice, limiting its use as a 5-HT2A ligand in mouse studies examining acute drug effects. Results also indicate that the 5-HT2A partial agonist-antagonist activity of lisuride explains its lack of psychedelic effects

Hybrid Dopamine Uptake Blocker–Serotonin Releaser Ligands: A New Twist on Transporter-Focused Therapeutics

As part of our program to study neurotransmitter releasers, we report herein a class of hybrid dopamine reuptake inhibitors that display serotonin releasing activity. Hybrid compounds are interesting since they increase the design potential of transporter related compounds and hence represent a novel and unexplored strategy for therapeutic drug discovery. A series of <i>N</i>-alkylpropiophenones was synthesized and assessed for uptake inhibition and release activity using rat brain synaptosomes. Substitution on the aromatic ring yielded compounds that maintained hybrid activity, with the two disubstituted analogues (<b>PAL-787</b> and <b>PAL-820</b>) having the most potent hybrid activity

Binding of the Amphetamine-like 1-Phenyl-piperazine to Monoamine Transporters

The human serotonin transporter (hSERT), the human dopamine transporter (hDAT), and the human norepinephrine transporter (hNET) facilitate the active uptake of the neurotransmitters serotonin, dopamine, and norepinephrine from the synaptic cleft. Drugs of abuse such as MDMA (streetname “ecstasy”) and certain 1-phenyl-piperazine (PP) analogs such as 1-(3-chlorophenyl)-piperazine (mCPP) elicit their stimulatory effect by elevating the synaptic concentration of serotonin by blocking or reversing the normal transport activity of hSERT. Recent data suggest that certain analogs of PP may be able to counteract the addictive effect of cocaine. Little is still known about the precise mechanism by which MDMA and PP analogs function at hSERT, hDAT, and hNET and even less is known about the specific protein–ligand interactions. In this study, we provide a comprehensive biochemical examination of a repertoire of PP analogs in hSERT, hDAT, and hNET. Combined with induced fit docking models and molecular dynamics simulations of PP and 1-(3-hydroxyphenyl)-piperazine (3-OH-PP) bound to hSERT and hDAT, we present detailed molecular insight into the promiscuous binding of PP analogs in the monoamine transporters. We find that PP analogs inhibit uptake as well as induce release in all three monoamine transporters. We also find that the selectivity of the PP analogs can be adjusted by carefully selecting substituents on the PP skeleton

Synthetic Studies of Neoclerodane Diterpenes from <i>Salvia d</i><i>ivinorum</i>: Preparation and Opioid Receptor Activity of Salvinicin Analogues

Further modification of salvinorin A (1a), the major active component of Salvia divinorum, has resulted in the synthesis of novel neoclerodane diterpenes with opioid receptor affinity and activity. We report in this study that oxadiazole 11a and salvidivin A (12a), a photooxygenation product of 1a, have been identified as the first neoclerodane diterpenes with κ antagonist activity. This indicates that additional structural modifications of 1a may lead to analogues with higher potency and utility as drug abuse medications

Synthetic Studies of Neoclerodane Diterpenes from <i>Salvia d</i><i>ivinorum</i>: Preparation and Opioid Receptor Activity of Salvinicin Analogues

Further modification of salvinorin A (1a), the major active component of Salvia divinorum, has resulted in the synthesis of novel neoclerodane diterpenes with opioid receptor affinity and activity. We report in this study that oxadiazole 11a and salvidivin A (12a), a photooxygenation product of 1a, have been identified as the first neoclerodane diterpenes with κ antagonist activity. This indicates that additional structural modifications of 1a may lead to analogues with higher potency and utility as drug abuse medications

Design and Synthesis of Promiscuous High-Affinity Monoamine Transporter Ligands: Unraveling Transporter Selectivity

A series of 4-[2-[bis(4-fluorophenyl)methoxy]ethyl]-piperidines and 4-[2-[(bisphenyl)methoxy]ethyl]-piperidines with different types of substituents in the phenylpropyl side-chain were synthesized and examined for their ability to bind to the dopamine transporter (DAT), the serotonin transporter (SERT), and the norepinephrine transporter (NET). All of the compounds showed high binding affinities for the DAT in the low to subnanomolar range. Their ability to bind to the SERT and the NET, while maintaining their high affinity for the DAT, could be altered by substitution in positions C2 and C3 of the phenylpropyl side-chain. This approach gave rise to a new set of compounds with selectivity for the DAT, the DAT and the SERT, or the DAT and the NET. Six compounds (7, 9, 11, 12, 14, and 20) with relatively low SERT/DAT ratios were selected for additional study in biogenic amine uptake inhibition assays based on the biogenic amine transporter binding results. Some of the new ligands can serve as pharmacological tools to block DAT or DAT and another transporter simultaneously

Herkinorin Analogues with Differential β-Arrestin-2 Interactions

Salvinorin A is a psychoactive natural product that has been found to be a potent and selective κ opioid receptor agonist in vitro and in vivo. The activity of salvinorin A is unusual compared to other opioids such as morphine in that it mediates potent κ opioid receptor signaling yet leads to less receptor downregulation than observed with other κ agonists. Our initial chemical modifications of salvinorin A have yielded one analogue, herkinorin (1c), with high affinity at the μOR. We recently reported that 1c does not promote the recruitment of β-arrestin-2 to the μOR or receptor internalization. Here we describe three new derivatives of 1c (3c, 3f, and 3i) with similar properties and one, benzamide 7b, that promotes recruitment of β-arrestin-2 to the μOR and receptor internalization. When the important role μ opioid receptor regulation plays in determining physiological responsiveness to opioid narcotics is considered, μ opioids derived from salvinorin A may offer a unique template for the development of functionally selective μ opioid receptor–ligands with the ability to produce analgesia while limiting adverse side effects

N-Substituted 9β-Methyl-5-(3-hydroxyphenyl)morphans Are Opioid Receptor Pure Antagonists

The inhibition of radioligand binding and [35S]GTPγS functional assay data for N-methyl- and N-phenethyl-9β-methyl-5-(3-hydroxyphenyl)morphans (5b and 5c) show that these compounds are pure antagonists at the μ, δ, and κ opioid receptors. Since 5b and 5c have the 5-(3-hydroxyphenyl) group locked in a conformation comparable to an equatorial group of a piperidine chair conformation, this information provides very strong evidence that opioid antagonists can interact with opioid receptors in this conformation. In addition, it suggests that the trans-3,4-dimethyl-4-(3-hydroxyphenyl)piperidine class of antagonist operates via a phenyl equatorial piperidine chair conformation. Importantly, the close relationship between the 4-(3-hydroxyphenyl)piperidines and 5-(3-hydroxyphenyl)morphan antagonists shows that the latter class of compound provides a rigid platform on which to build a novel series of opioid antagonists

Identification of an Opioid κ Receptor Subtype-Selective N-Substituent for (+)-(3<i>R</i>,4<i>R</i>)-Dimethyl-4-(3-hydroxyphenyl)piperidine

A three-component library of compounds was prepared in parallel using multiple simultaneous solution-phase synthetic methodology. The compounds were biased toward opioid receptor antagonist activity by incorporating (+)-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (a potent, nonselective opioid pure antagonist) as one of the monomers. The other two monomers, which included N-substituted or unsubstituted Boc-protected amino acids and a range of substituted aryl carboxylic acids, were selected to add chemical diversity. Screening of these compounds in competitive binding experiments with the κ opioid receptor selective ligand [3H]U69,593 led to the discovery of a novel κ opioid receptor selective ligand, N-{(2‘S)-[3-(4-hydroxyphenyl)propanamido]-3‘-methylbutyl}-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (8, RTI-5989-29). Additional structure−activity relationship studies suggested that 8 possesses lipophilic and hydrogen-bonding sites that are important to its opioid receptor potency and selectivity. These sites appear to exist predominantly within the κ receptor since the selectivity arises from a 530-fold loss of affinity of 8 for the μ receptor and an 18-fold increase in affinity for the κ receptor relative to the μ-selective ligand, (+)-N-[trans-4-phenyl-2-butenyl]-(3R,4R)-dimethyl-4-(3-hydroxyphenyl)piperidine (5a). The degree of selectivity observed in the radioligand binding experiments was not observed in the functional assay. According to its ability to inhibit agonist stimulated binding of [35S]GTPγS at all three opioid receptors, compound 8 behaves as a μ/κ opioid receptor pure antagonist with negligible affinity for the δ receptor

Structure–Activity Relationships for Psilocybin, Baeocystin, Aeruginascin, and Related Analogues to Produce Pharmacological Effects in Mice

4-Phosphoryloxy-N,N-dimethyltryptamine (psilocybin) is a naturally occurring tertiary amine found in many mushroom species. Psilocybin is a prodrug for 4-hydroxy-N,N-dimethyltryptamine (psilocin), which induces psychedelic effects via agonist activity at the serotonin (5-HT) 2A receptor (5-HT2A). Several other 4-position ring-substituted tryptamines are present in psilocybin-containing mushrooms, including the secondary amine 4-phosphoryloxy-N-methyltryptamine (baeocystin) and the quaternary ammonium 4-phosphoryloxy-N,N,N-trimethyltryptamine (aeruginascin), but these compounds are not well studied. Here, we investigated the structure–activity relationships for psilocybin, baeocystin, and aeruginascin, as compared to their 4-acetoxy and 4-hydroxy analogues, using in vitro and in vivo methods. Broad receptor screening using radioligand binding assays in transfected cells revealed that secondary and tertiary tryptamines with either 4-acetoxy or 4-hydroxy substitutions display nanomolar affinity for most human 5-HT receptor subtypes tested, including the 5-HT2A and the serotonin 1A receptor (5-HT1A). The same compounds displayed affinity for 5-HT2A and 5-HT1A in mouse brain tissue in vitro and exhibited agonist efficacy in assays examining 5-HT2A-mediated calcium mobilization and β-arrestin 2 recruitment. In mouse experiments, only the tertiary amines psilocin, psilocybin, and 4-acetoxy-N,N-dimethyltryptamine (psilacetin) induced head twitch responses (ED50 0.11–0.29 mg/kg) indicative of psychedelic-like activity. Head twitches were blocked by 5-HT2A antagonist pretreatment, supporting 5-HT2A involvement. Both secondary and tertiary amines decreased body temperature and locomotor activity at higher doses, the effects of which were blocked by 5-HT1A antagonist pretreatment. Across all assays, the pharmacological effects of 4-acetoxy and 4-hydroxy compounds were similar, and these compounds were more potent than their 4-phosphoryloxy counterparts. Importantly, psilacetin appears to be a prodrug for psilocin that displays substantial serotonin receptor activities of its own