Christoffer Bundgaard

Pharmacological effects of Lu AA21004: a novel multimodal compound for the treatment of major depressive disorder.

1-[2-(2,4-Dimethylphenyl-sulfanyl)-phenyl]-piperazine (Lu AA21004) is a human (h) serotonin (5-HT)3A receptor antagonist (Ki = 3.7 nM), h5-HT7 receptor antagonist (Ki = 19 nM), h5-HT1B receptor partial agonist (Ki = 33 nM), h5-HT1A receptor agonist (Ki = 15 nM), and a human 5-HT transporter (SERT) inhibitor (Ki = 1.6 nM) (J Med Chem 54:3206–3221, 2011). Here, we confirm that Lu AA21004 is a partial h5-HT1B receptor agonist [EC50 = 460 nM, intrinsic activity = 22%] using a whole-cell cAMP-based assay and demonstrate that Lu AA21004 is a rat (r) 5-HT7 receptor antagonist (Ki = 200 nM and IC50 = 2080 nM). In vivo, Lu AA21004 occupies the r5-HT1B receptor and rSERT (ED50 = 3.2 and 0.4 mg/kg, respectively) after subcutaneous administration and is a 5-HT3 receptor antagonist in the Bezold-Jarisch reflex assay (ED50 = 0.11 mg/kg s.c.). In rat microdialysis experiments, Lu AA21004 (2.5–10.0 mg/kg s.c.) increased extracellular 5-HT, dopamine, and noradrenaline in the medial prefrontal cortex and ventral hippocampus. Lu AA21004 (5 mg/kg per day for 3 days; minipump subcutaneously), corresponding to 41% rSERT occupancy, significantly increased extracellular 5-HT in the ventral hippocampus. Furthermore, the 5-HT3 receptor antagonist, ondansetron, potentiated the increase in extracellular levels of 5-HT induced by citalopram. Lu AA21004 has antidepressant- and anxiolytic-like effects in the rat forced swim (Flinders Sensitive Line) and social interaction and conditioned fear tests (minimal effective doses: 7.8, 2.0, and 3.9 mg/kg). In conclusion, Lu AA21004 mediates its pharmacological effects via two pharmacological modalities: SERT inhibition and 5-HT receptor modulation. In vivo, this results in enhanced release of several neurotransmitters and antidepressant- and anxiolytic-like profiles at doses for which targets in addition to the SERT are occupied. The multimodal activity profile of Lu AA21004 is distinct from that of current antidepressants.

Brexpiprazole I: In Vitro and In Vivo Characterization of a Novel Serotonin-Dopamine Activity Modulator

Brexpiprazole (OPC-34712, 7-{4-[4-(1-benzothiophen-4-yl)piperazin-1-yl]butoxy}quinolin-2(1H)-one) is a novel drug candidate in clinical development for psychiatric disorders with high affinity for serotonin, dopamine, and noradrenaline receptors. In particular, it bound with high affinity (Ki < 1 nM) to human serotonin 1A (h5-HT1A)-, h5-HT2A-, long form of human D2 (hD2L)-, hα1B-, and hα2C-adrenergic receptors. It displayed partial agonism at h5-HT1A and hD2 receptors in cloned receptor systems and potent antagonism of h5-HT2A receptors and hα1B/2C-adrenoceptors. Brexpiprazole also had affinity (Ki < 5 nM) for hD3-, h5-HT2B-, h5-HT7-, hα1A-, and hα1D-adrenergic receptors, moderate affinity for hH1 (Ki = 19 nM), and low affinity for hM1 receptors (Ki > 1000 nM). Brexpiprazole potently bound to rat 5-HT2A and D2 receptors in vivo, and ex vivo binding studies further confirmed high 5-HT1A receptor binding potency. Brexpiprazole inhibited DOI (2,5-dimethoxy-4-iodoamphetamine)-induced head twitches in rats, suggestive of 5-HT2A antagonism. Furthermore, in vivo D2 partial agonist activity of brexpiprazole was confirmed by its inhibitory effect on reserpine-induced DOPA accumulation in rats. In rat microdialysis studies, brexpiprazole slightly reduced extracellular dopamine in nucleus accumbens but not in prefrontal cortex, whereas moderate increases of the dopamine metabolites, homovanillic acid and DOPAC (3,4-dihydroxy-phenyl-acetic acid), in these areas also suggested in vivo D2 partial agonist activity. In particular, based on a lower intrinsic activity at D2 receptors and higher binding affinities for 5-HT1A/2A receptors than aripiprazole, brexpiprazole would have a favorable antipsychotic potential without D2 receptor agonist- and antagonist-related adverse effects. In conclusion, brexpiprazole is a serotonin-dopamine activity modulator with a unique pharmacology, which may offer novel treatment options across a broad spectrum of central nervous system disorders.

Structure-activity relationship study of first selective inhibitor of excitatory amino acid transporter subtype 1: 2-Amino-4-(4-methoxyphenyl)-7-(naphthalen-1-yl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (UCPH-101).

The excitatory amino acid transporters (EAATs) are expressed throughout the central nervous system, where they are responsible for the reuptake of the excitatory neurotransmitter (S)-glutamate (Glu). (1) Recently, we have reported the discovery of the first subtype selective EAAT1 inhibitor 2-amino-4-(4-methoxyphenyl)-7-(naphthalen-1-yl)-5-oxo-5,6,7,8-tetrahydro-4H-chromene-3-carbonitrile (UCPH-101) (1b) and presented an introductory structure-activity relationship (SAR) study. (2) Here, we present a detailed SAR by the design, synthesis, and pharmacological evaluation of analogues 1g-1t. By comparison of potencies of 1b, 1h, and 1i versus 1j, it is evident that potency is largely influenced by the chemical nature of the R(1) substituent. The study also demonstrates that any chemical change of the functional groups or a change to the parental scaffold results in the complete loss of inhibitory activity of the compounds at EAAT1. Finally, a bioavailability study of UCPH-101 determined the half-life to be 30 min in serum (rats) but also that it was not able to penetrate the blood-brain barrier to any significant degree.

Antipsychotic-Like Effect of Retigabine [N-(2-Amino-4-(fluorobenzylamino)-phenyl)carbamic Acid Ester], a KCNQ Potassium Channel Opener, via Modulation of Mesolimbic Dopaminergic Neurotransmission

Dopaminergic (DAergic) neurons in the ventral tegmental area express both KCNQ2 and KCNQ4 channels, which opening is expected to decrease neuronal excitability via neuronal hyper-polarization. Because psychotic symptoms are believed to be associated with an increased excitability of dopamine (DA) cells in the mesencephalon, KCNQ channels might represent a new potential target for the treatment of psychosis. The aim of our study was to investigate the antipsychotic-like potential of KCNQ channel opening via modulation of neuronal activity within the mesolimbic DAergic system. We report that retigabine [N-(2-amino-4-(fluorobenzylamino)-phenyl)carbamic acid ester], a KCNQ opener, dose-dependently reduced basal DA firing rate and more potently suppressed burst firing activity in the ventral tegmental area, whereas XE-991 [10,10-bis(pyridinylmethyl)-9(10H)-anthracenone], a selective KCNQ blocker, induced opposite effects. In addition, retigabine prevented d-amphetamine-induced DA efflux in the nucleus accumbens and d-amphetamine-induced locomotor hyperactivity. In contrast, XE-991 potentiated both the locomotor hyperactivity and DA efflux evoked by d-amphetamine. These data strongly suggest that the activation of KCNQ channels attenuates DAergic neurotransmission in the mesolimbic system, particularly in conditions of excessive DAergic activity. In a model predictive of antipsychotic activity, the conditioned avoidance response paradigm, retigabine was found to inhibit avoidance responses, an effect blocked by coadministration of XE-991. Furthermore, retigabine was found to significantly inhibit the hyperlocomotor response to a phencyclidine (PCP) challenge in PCP-sensitized animals, considered as a disease model for schizophrenia. Taken together, our studies provide evidence that KCNQ channel openers represent a potential new class of antipsychotics.

Species Comparison of In Vivo P-Glycoprotein-Mediated Brain Efflux Using mdr1a-Deficient Rats and Mice

The experiments described herein compared the extent of in vivo P-glycoprotein (P-gp)-mediated brain efflux between rats and mice for a set of known central nervous system compounds. With use of newly introduced genetically modified mdr1a-deficient rats and their gene-competent counterparts, the brain to plasma distribution was assessed and compared with the distribution pattern in mdr1a-deficient and wild-type mice. Four compounds (aripiprazole, citalopram, risperidone, and venlafaxine) were administered using a continuous subcutaneous osmotic minipump infusion paradigm. Steady-state brain and plasma concentrations of the compounds, including selected metabolites (9-hydroxyrisperidone, O-desmethyl-venlafaxine and N-desmethyl-venlafaxine) were measured in mdr1a-deficient rats and mice and their wild-type counterparts along with their free fractions to determine total and unbound brain to plasma distribution between genotypes within and between species. The results revealed qualitative as well as quantitative similarities between P-gp functionality in vivo at the blood-brain barrier level in rats and mice. All compounds tested were shown to have a significantly higher brain to plasma distribution in both mdr1a-deficient rats and mice compared with that in their wild-type counterparts. Moreover, the relative enhancement in extent of brain penetration between mdr1a-deficient and wild-type rats could be directly correlated to the enhancement ratios obtained in mice. From the unbound brain to unbound plasma distributions, the impact of P-gp on the overall brain penetration capabilities showed minor differences between rats and mice for the compounds tested. In conclusion, a comparable functional role of P-gp between rats and mice with respect to brain efflux mediated by this transporter is suggested.

Triazoloquinazolines as a novel class of phosphodiesterase 10A (PDE10A) inhibitors.

Novel triazoloquinazolines have been found as phosphodiesterase 10A (PDE10A) inhibitors. Structure-activity studies improved the initial micromolar potency which was found in the lead compound by a 100-fold identifying 5-(1H-benzoimidazol-2-ylmethylsulfanyl)-2-methyl-[1,2,4]triazolo[1,5-c]quinazoline, 42 (PDE10A IC(50)=12 nM) as the most potent compound from the series. Two X-ray structures revealed novel binding modes to the catalytic site of the PDE10A enzyme.

Discovery of a potent and brain penetrant mGluR5 positive allosteric modulator.

This Letter describes the discovery of a novel series of mGluR5 positive allosteric modulators (PAMs). The lead compound, 11c, exhibits excellent potency (EC(50)=30 nM) in vitro, and reaches high brain levels in both rats and mice after oral administration.

Discovery and Development of 11C-Lu AE92686 as a Radioligand for PET Imaging of Phosphodiesterase10A in the Brain

Phosphodiesterase 10A (PDE10A) plays a key role in the regulation of brain striatal signaling, and several pharmaceutical companies currently investigate PDE10A inhibitors in clinical trials for various central nervous system diseases. A PDE10A PET ligand may provide evidence that a clinical drug candidate reaches and binds to the target. Here we describe the successful discovery and initial validation of the novel radiolabeled PDE10A ligand 5,8-dimethyl-2-[2-((1-11C-methyl)-4-phenyl-1H-imidazol-2-yl)-ethyl]-[1,2,4]triazolo[1,5-a]pyridine (11C-Lu AE92686) and its tritiated analog 3H-Lu AE92686. Methods: Initial in vitro experiments suggested Lu AE92686 as a promising radioligand, and the corresponding tritiated and 11C-labeled compounds were synthesized. 3H-Lu AE92686 was evaluated as a ligand for in vivo occupancy studies in mice and rats, and 11C-Lu AE92686 was evaluated as a PET tracer candidate in cynomolgus monkeys and in humans. Results: 11C-Lu AE92686 displayed high specificity and selectivity for PDE10A-expressing regions in the brain of cynomolgus monkeys and humans. Similar results were found in rodents using 3H-Lu AE92686. The binding of 11C-Lu AE92686 and 3H-Lu AE92686 to striatum was completely and dose-dependently blocked by the structurally different PDE10A inhibitor 2-[4-(1-methyl-4-pyridin-4-yl-1H-pyrazol-3-yl)-phenoxymethyl]-quinoline (MP-10) in rodents and in monkeys. In all species, specific binding of the radioligand was seen in the striatum but not in the cerebellum, supporting the use of the cerebellum as a reference region. The binding potentials (BPND) of 11C-Lu AE92686 in the striatum of both cynomolgus monkeys and humans were evaluated by the simplified reference tissue model with the cerebellum as the reference tissue, and BPND was found to be high and reproducible—that is, BPNDs were 6.5 ± 0.3 (n = 3) and 7.5 ± 1.0 (n = 12) in monkeys and humans, respectively. Conclusion: Rodent, monkey, and human tests of labeled Lu AE92686 suggest that 11C-Lu AE92686 has great potential as a human PET tracer for the PDE10A enzyme.

Discovery of N-{1-[3-(3-Oxo-2,3-dihydrobenzo[1,4]oxazin-4-yl)propyl]piperidin-4-yl}-2-phenylacetamide (Lu AE51090): An Allosteric Muscarinic M1 Receptor Agonist with Unprecedented Selectivity and Procognitive Potential

The discovery and structure-activity relationship (SAR) of a series of allosteric muscarinic M(1) receptor agonists are described. Compound 17 (Lu AE51090) was identified as a representative compound from the series, based on its high selectivity as an agonist at the muscarinic M(1) receptor across a panel of muscarinic receptor subtypes. Furthermore, 17 displayed a high degree of selectivity when tested in a broad panel of G-protein-coupled receptors, ion channels, transporters, and enzymes, and 17 showed an acceptable pharmacokinetic profile and sufficient brain exposure in rodents in order to characterize the compound in vivo. Hence, in a rodent model of learning and memory, 17 reversed delay-induced natural forgetting, suggesting a procognitive potential of 17.

Asc-1 Transporter Regulation of Synaptic Activity via the Tonic Release of d-Serine in the Forebrain

Abstract d‐Serine is a co‐agonist of NMDA receptors (NMDARs) whose activity is potentially regulated by Asc‐1 (SLC7A10), a transporter that displays high affinity for d‐serine and glycine. Asc‐1 operates as a facilitative transporter and as an antiporter, though the preferred direction of d‐serine transport is uncertain. We developed a selective Asc‐1 blocker, Lu AE00527, that blocks d‐serine release mediated by all the transport modes of Asc‐1 in primary cultures and neocortical slices. Furthermore, d‐serine release is reduced in slices from Asc‐1 knockout (KO) mice, indicating that d‐serine efflux is the preferred direction of Asc‐1. The selectivity of Lu AE00527 is assured by the lack of effect on slices from Asc‐1‐KO mice, and the lack of interaction with the co‐agonist site of NMDARs. Moreover, in vivo injection of Lu AE00527 in P‐glycoprotein‐deficient mice recapitulates a hyperekplexia‐like phenotype similar to that in Asc‐1‐KO mice. In slices, Lu AE00527 decreases the long‐term potentiation at the Schaffer collateral‐CA1 synapses, but does not affect the long‐term depression. Lu AE00527 blocks NMDAR synaptic potentials when typical Asc‐1 extracellular substrates are present, but it does not affect AMPAR transmission. Our data demonstrate that Asc‐1 mediates tonic co‐agonist release, which is required for optimal NMDAR activation and synaptic plasticity.