Lisuride Maleate

Dravet syndrome is a severe genetic epilepsy primarily caused by de novo mutations in a voltage-activated sodium channel gene (SCN1A). Patients face life-threatening seizures that are largely resistant to available anti-seizure medications. Preclinical Dravet syndrome animal models are a valuable tool to identify candidate anti-seizure medications for these patients. Among these, scn1lab mutant zebrafish, exhibiting spontaneous seizure-like activity, are particularly amenable to large-scale drug screening. Thus far, we have screened more than 3000 drug candidates in scn1lab zebrafish mutants, identifying valproate, stiripentol, and fenfluramine e.g. Food and Drug Administration-approved drugs, with clinical application in the Dravet syndrome population. Successful phenotypic screening in scn1lab mutant zebrafish is rigorous and consists of two stages: (i) a locomotion-based assay measuring high-velocity convulsive swim behaviour and (ii) an electrophysiology-based assay, using in vivo local field potential recordings, to quantify electrographic seizure-like events. Historically, nearly 90% of drug candidates fail during translation from preclinical models to the clinic. With such a high failure rate, it becomes necessary to address issues of replication and false positive identification. Leveraging our scn1lab zebrafish assays is one approach to address these problems. Here, we curated a list of nine anti-seizure drug candidates recently identified by other groups using preclinical Dravet syndrome models: 1-Ethyl-2-benzimidazolinone, AA43279, chlorzoxazone, donepezil, lisuride, mifepristone, pargyline, soticlestat and vorinostat. First-stage locomotion-based assays in scn1lab mutant zebrafish identified only 1-Ethyl-2-benzimidazolinone, chlorzoxazone and lisuride. However, second-stage local field potential recording assays did not show significant suppression of spontaneous electrographic seizure activity for any of the nine anti-seizure drug candidates. Surprisingly, soticlestat induced frank electrographic seizure-like discharges in wild-type control zebrafish. Taken together, our results failed to replicate clear anti-seizure efficacy for these drug candidates highlighting a necessity for strict scientific standards in preclinical identification of anti-seizure medications.

Lisuride is a non-psychedelic serotonin (5-HT) 2A receptor (5-HT_2A) agonist and analogue of the psychedelic lysergic acid diethylamide (LSD). Lisuride also acts as an agonist at the serotonin 1A receptor (5-HT_1A), 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-HT_2A and (2) potent agonism at 5-HT_1A. The in vitro effects of lisuride, LSD, and related analogues on 5-HT_2A signaling were characterized by using miniGα_q and β-arrestin 2 recruitment assays. The 5-HT_1A- and 5-HT_2A-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-HT_2A, with high efficacy and potency for recruiting miniGα_q and β-arrestin 2. By contrast, lisuride displayed partial efficacy for both functional end points (6-52% of 5-HT or LSD E_max) 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-HT_1A antagonist WAY100635 (3 mg/kg). Blockade of 5-HT_1A 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-HT_1A agonist 8-OH-DPAT (1 mg/kg). Overall, our findings show that lisuride is an ultrapotent 5-HT_1A agonist in C57BL/6J mice, limiting its use as a 5-HT_2A ligand in mouse studies examining acute drug effects. Results also indicate that the 5-HT_2A partial agonist-antagonist activity of lisuride explains its lack of psychedelic effects.