The Dopamine D1 Receptor Positive Allosteric Modulator Mevidalen (LY3154207) Enhances Wakefulness in the Humanized D1 Mouse and in Sleep-Deprived Healthy Male Volunteers.

Dopamine (DA) plays a key role in several central functions including cognition, motor activity, and wakefulness. Although efforts to develop dopamine receptor 1 (D1) agonists have been challenging, a positive allosteric modulator represents an attractive approach with potential better drug-like properties. Our previous study demonstrated an acceptable safety and tolerability profile of the dopamine receptor 1 positive allosteric modulator (D1PAM) mevidalen (LY3154207) in single and multiple ascending dose studies in healthy volunteers (Wilbraham et al., 2021). Herein, we describe the effects of mevidalen on sleep and wakefulness in humanized dopamine receptor 1 (hD1) mice and in sleep-deprived healthy male volunteers. Mevidalen enhanced wakefulness (latency to fall asleep) in the hD1 mouse in a dose dependent [3-100 mg/kg, orally (PO)] fashion when measured during the light (zeitgeber time 5) and predominantly inactive phase. Mevidalen promoted wakefulness in mice after prior sleep deprivation and delayed sleep onset by 5.5- and 15.2-fold compared with vehicle-treated animals, after the 20 and 60 mg/kg PO doses, respectively, when compared with vehicle-treated animals. In humans, mevidalen demonstrated a dose-dependent increase in latency to sleep onset as measured by the multiple sleep latency test and all doses (15, 30, and 75 mg) separated from placebo at the first 2-hour postdose time point with a circadian effect at the 6-hour postdose time point. Sleep wakefulness should be considered a translational biomarker for the dopamine receptor 1 positive allosteric modulator mechanism. SIGNIFICANCE STATEMENT: This is the first translational study describing the effects of a selective dopamine receptor 1 positive allosteric modulator (D1PAM) on sleep and wakefulness in the human dopamine receptor 1 mouse and in sleep-deprived healthy male volunteers. In both species, drug exposure correlated with sleep latency, supporting the use of sleep-wake activity as a translational central biomarker for D1PAM. Wake-promoting effects of D1PAMs may offer therapeutic opportunities in several conditions, including sleep disorders and excessive daytime sleepiness related to neurodegenerative disorders.

Identification of a Safe and Tolerable Carbamazepine Dosing Paradigm that Facilitates Effective Evaluation of CYP3A4 Induction.

Carbamazepine (CBZ) is the recommended alternative to rifampicin as a CYP3A4 inducer in drug-drug interaction studies. However, the traditional CBZ dosing paradigm can lead to several adverse events (AEs). This study tested a shorter CBZ dosing regimen using the CYP3A4-sensitive index substrate midazolam (MDZ). This was a fixed-sequence arm of an open-label, phase I study (NCT04840888). Healthy participants (n = 15) aged 18-63 years received oral doses of 1.2 mg MDZ alone (Day 1), CBZ b.i.d. alone (100 mg Days 2-4; 200 mg Days 5-7; 300 mg Days 8-10 and 12-13), and 300 mg CBZ b.i.d. plus 1.2 mg MDZ (Days 11 and 14). One participant (6.7%) experienced constipation due to treatment with CBZ plus MDZ on Day 11. One participant (6.7%) experienced urticaria (Days 12-13), and two participants (13.3%) experienced somnolence (Days 8-10) due to treatment with 300 mg CBZ b.i.d. alone. All AEs were mild. For MDZ, the geometric mean (90% CI) ratio (vs. Day 1) of the area under the curve (AUC 0-∞) was 0.28 (0.24-0.31) on Day 11 and 0.26 (0.23-0.29) on Day 14. The AUC (0-12 hours) of CBZ was 114,000 ng∙h/mL on Day 11 and 105,000 ng∙h/mL on Day 14. Steady-state concentrations of CBZ and induction of CYP3A4 were achieved on Day 11. The data are consistent with predictions of physiologically-based pharmacokinetic models in Simcyp. The 9-day dosing regimen for CBZ induction was well-tolerated by healthy participants, supporting the use of a shorter CBZ regimen for CYP3A4 induction studies.

Investigating the role of mGluR2 versus mGluR3 in antipsychotic-like effects, sleep-wake architecture and network oscillatory activity using novel Han Wistar rats lacking mGluR2 expression.

Group II metabotropic glutamate receptors (mGluR2 and mGluR3) are implicated in a number of psychiatric disorders. They also control sleep-wake architecture and may offer novel therapeutic targets. However, the roles of the mGluR2 versus mGluR3 subtypes are not well understood. Here, we have taken advantage of the recently described mutant strain of Han Wistar rats, which do not express mGluR2 receptors, to investigate behavioural, sleep and EEG responses to mGluR2/3 ligands. The mGluR2/3 agonist, LY354740 (10 mg/kg), reversed amphetamine- and phencyclidine-induced locomotion and rearing behaviours in control Wistar but not in mGluR2 lacking Han Wistar rats. In control Wistar but not in Han Wistar rats the mGluR2/3 agonist LY379268 (3 & 10 mg/kg) induced REM sleep suppression with dose-dependent effects on wake and NREM sleep. By contrast, the mGluR2/3 antagonist LY3020371 (3 & 10 mg/kg) had wake-promoting effects in both rat strains, albeit smaller in the mGluR2-lacking Han Wistar rats, indicating both mGluR2 and mGluR3-mediated effects on wakefulness. LY3020371 enhanced wake cortical oscillations in the theta (4-9 Hz) and gamma (30-80 Hz) range in both Wistar and Han Wistar rat strains, whereas LY379268 reduced theta and gamma oscillations in control Wistar rats, with minimal effects in Han Wistar rats. Together these studies illustrate the significant contribution of mGluR2 to the antipsychotic-like, sleep and EEG effects of drugs acting on group II mGluRs. However, we also provide evidence of a role for mGluR3 activity in the control of sleep and wake cortical theta and gamma oscillations.

Preclinical profile of a dopamine D1 potentiator suggests therapeutic utility in neurological and psychiatric disorders.

DETQ, an allosteric potentiator of the dopamine D1 receptor, was tested in therapeutic models that were known to respond to D1 agonists. Because of a species difference in affinity for DETQ, all rodent experiments used transgenic mice expressing the human D1 receptor (hD1 mice). When given alone, DETQ reversed the locomotor depression caused by a low dose of reserpine. DETQ also acted synergistically with L-DOPA to reverse the strong hypokinesia seen with a higher dose of reserpine. These results indicate potential as both monotherapy and adjunct treatment in Parkinson's disease. DETQ markedly increased release of both acetylcholine and histamine in the prefrontal cortex, and increased levels of histamine metabolites in the striatum. In the hippocampus, the combination of DETQ and the cholinesterase inhibitor rivastigmine increased ACh to a greater degree than either agent alone. DETQ also increased phosphorylation of the AMPA receptor (GluR1) and the transcription factor CREB in the striatum, consistent with enhanced synaptic plasticity. In the Y-maze, DETQ increased arm entries but (unlike a D1 agonist) did not reduce spontaneous alternation between arms at high doses. DETQ enhanced wakefulness in EEG studies in hD1 mice and decreased immobility in the forced-swim test, a model for antidepressant-like activity. In rhesus monkeys, DETQ increased spontaneous eye-blink rate, a measure that is known to be depressed in Parkinson's disease. Together, these results provide support for potential utility of D1 potentiators in the treatment of several neuropsychiatric disorders, including Parkinson's disease, Alzheimer's disease, cognitive impairment in schizophrenia, and major depressive disorder.

REM sleep homeostasis in the absence of REM sleep: Effects of antidepressants.

Most antidepressants suppress rapid eye movement (REM) sleep, which is thought to be important to brain function, yet the resulting REM sleep restriction is well tolerated. This study investigated the impact of antidepressants with different mechanisms of action, such as selective serotonin reuptake inhibitors (SSRIs) and tricyclic antidepressants (TCA), on the regulation of REM sleep in rats. REM sleep was first demonstrated to be homeostatically regulated using 5, 8 and 10 h of REM-sleep specific restriction through EEG-triggered arousals, with an average of 91 ± 10% of lost REM sleep recovered following a 26-29 -hour recovery period. Acute treatment with the antidepressants paroxetine, citalopram and imipramine inhibited REM sleep by 84 ± 8, 84 ± 8 and 69 ± 9% respectively relative to vehicle control. The pharmacologically-induced REM sleep deficits by paroxetine and citalopram were not fully recovered, whereas, after imipramine the REM sleep deficit was fully compensated. Given the marked difference between REM sleep recovery following the administration of paroxetine, citalopram, imipramine and REM sleep restriction, the homeostatic response was further examined by pairing REM sleep specific restriction with the three antidepressants. Surprisingly, the physiologically-induced REM sleep deficits incurred prior to suppression of REM sleep by all antidepressants was consistently recovered. The data indicate that REM sleep homeostasis remains operative following subsequent treatment with antidepressants and is unaffected by additional pharmacological inhibition of REM sleep.

Attenuation of the effects of fluoxetine on serotonergic neuronal activity by pindolol in rats.

Based on its proposed ability to block the effect of selective serotonin reuptake inhibitors (SSRIs) on the firing rate of serotonergic neurons, the 5-HT1A partial agonist/beta-adrenergic antagonist pindolol has been examined in clinical trials for its ability to enhance the efficacy of SSRIs. However, varying results have been obtained in these clinical trials. To explore this issue, we examined the effects of pindolol alone and in combination with fluoxetine on the electrophysiological activity of serotonergic neurons in the dorsal raphe nucleus of anesthetized rats. Administration of pindolol (1, 5, and 20 mg/kg, s.c.) alone decreased the number of spontaneously active serotonergic neurons. Administration of fluoxetine (10 mg/kg, i.p.) alone also decreased the number of spontaneously active serotonergic neurons. However, when administered following fluoxetine, pindolol significantly attenuated, but did not block completely, the inhibitory effects of fluoxetine on the number of spontaneously active serotonergic neurons. These results indicate that pindolol can attenuate the effects of fluoxetine on the firing of serotonergic neurons. These results may help explain the varying efficacy of pindolol in clinical trials with SSRIs.

In vitro characterisation of the novel positive allosteric modulators of the mGlu5 receptor, LSN2463359 and LSN2814617, and their effects on sleep architecture and operant responding in the rat.

The demonstrated functional interaction of metabotropic glutamate 5 (mGlu5) receptors with N-methyl-d-aspartate (NMDA) receptors has prompted speculation that their activation may offer a potential treatment for aspects of schizophrenia. Development of selective mGlu5 agonists has been difficult, but several different positive allosteric modulator (PAM) molecules have now been identified. This study describes two novel mGlu5 PAMs, LSN2463359 (N-(1-methylethyl)-5-(pyridin-4-ylethynyl)pyridine-2-carboxamide) and LSN2814617 [(7S)-3-tert-butyl-7-[3-(4-fluorophenyl)-1,2,4-oxadiazol-5-yl]-5,6,7,8-tetrahydro[1,2,4]triazolo[4,3-A]pyridine], which are useful tools for this field of research. Both compounds are potent and selective potentiators of human and rat mGlu5 receptors in vitro, displaying curve shift ratios of two to three fold in the concentration-response relationship to glutamate or the glutamate receptor agonist, DHPG, with no detectable intrinsic agonist properties. Both compounds displaced the mGlu5 receptor antagonist radioligand, [³H]MPEP in vitro and, following oral administration reached brain concentrations sufficient to occupy hippocampal mGlu5 receptors as measured in vivo by dose-dependent displacement from the hippocampus of intravenously administered MPEPy. In vivo EEG studies demonstrated that these mGlu5 PAMs have marked wake-promoting properties but little in the way of rebound hypersomnolence. In contrast, the previously described mGlu5 PAMs CDPPB and ADX47273 showed relatively poor evidence of in vivo target engagement in either receptor occupancy assays or EEG disturbance. Wake-promoting doses of LSN2463359 and LSN2814617 attenuated deficits in performance induced by the competitive NMDA receptor antagonist SDZ 220,581 in two tests of operant behaviour: the variable interval 30 s task and the DMTP task. These effects were lost if the dose of either compound extended into the range which disrupted performance in the baseline DMTP task. However, the improvements in response accuracy induced by the mGlu5 potentiators in SDZ 220,581-treated rats were not delay-dependent and, therefore, perhaps more likely reflected optimization of general arousal than specific beneficial effects on discrete cognitive processes. The systematic profiling of LSN2463359 and LSN2814617 alongside other previously described molecules will help determine more precisely how mGlu5 potentiator pharmacology might provide therapeutic benefit. This article is part of a Special Issue entitled 'Cognitive Enhancers'.