Pharmacological manipulation of specific neural circuits to optimize therapeutic index is an unrealized goal in neurology and psychiatry. AMPA receptors are important for excitatory synaptic ...transmission, and their antagonists are antiepileptic. Although efficacious, AMPA-receptor antagonists, including perampanel (Fycompa), the only approved antagonist for epilepsy, induce dizziness and motor impairment. We hypothesized that blockade of forebrain AMPA receptors without blocking cerebellar AMPA receptors would be antiepileptic and devoid of motor impairment. Taking advantage of an AMPA receptor auxiliary protein, TARP γ-8, which is selectively expressed in the forebrain and modulates the pharmacological properties of AMPA receptors, we discovered that LY3130481 selectively antagonized recombinant and native AMPA receptors containing γ-8, but not γ-2 (cerebellum) or other TARP members. Two amino acid residues unique to γ-8 determined this selectivity. We also observed antagonism of AMPA receptors expressed in hippocampal, but not cerebellar, tissue from an patient with epilepsy. Corresponding to this selective activity, LY3130481 prevented multiple seizure types in rats and mice and without motor side effects. These findings demonstrate the first rationally discovered molecule targeting specific neural circuitries for therapeutic advantage.
As part of our ongoing research to identify novel agents acting at metabotropic glutamate 2 (mGlu2) and 3 (mGlu3) receptors, we have previously reported the identification of the C4α-methyl analog of ...mGlu2/3 receptor agonist 1 (LY354740). This molecule, 1S,2S,4R,5R,6S-2-amino-4-methylbicyclo3.1.0hexane-2,6-dicarboxylate 2 (LY541850), exhibited an unexpected mGlu2 agonist/mGlu3 antagonist pharmacological profile, whereas the C4β-methyl diastereomer (3) possessed dual mGlu2/3 receptor agonist activity. We have now further explored this structure–activity relationship through the preparation of cyclic and acyclic C4-disubstituted analogs of 1, leading to the identification of C4-spirocyclopropane 5 (LY2934747), a novel, potent, and systemically bioavailable mGlu2/3 receptor agonist which exhibits both antipsychotic and analgesic properties in vivo. In addition, through the combined use of protein–ligand X-ray crystallography employing recombinant human mGlu2/3 receptor amino terminal domains, molecular modeling, and site-directed mutagenesis, a molecular basis for the observed pharmacological profile of compound 2 is proposed.
Identification of orthosteric mGlu2/3 receptor agonists capable of discriminating between individual mGlu2 and mGlu3 subtypes has been highly challenging owing to the glutamate-site sequence homology ...between these proteins. Herein we detail the preparation and characterization of a series of molecules related to (1S,2S,5R,6S)-2-aminobicyclo3.1.0hexane-2,6-dicarboxylate 1 (LY354740) bearing C4-thiotriazole substituents. On the basis of second messenger responses in cells expressing other recombinant human mGlu2/3 subtypes, a number of high potency and efficacy mGlu2 receptor agonists exhibiting low potency mGlu3 partial agonist/antagonist activity were identified. From this, (1R,2S,4R,5R,6R)-2-amino-4-(1H-1,2,4-triazol-3-ylsulfanyl)bicyclo3.1.0hexane-2,6-dicarboxylic acid 14a (LY2812223) was further characterized. Cocrystallization of 14a with the amino terminal domains of hmGlu2 and hmGlu3 combined with site-directed mutation studies has clarified the underlying molecular basis of this unique pharmacology. Evaluation of 14a in a rat model responsive to mGlu2 receptor activation coupled with a measure of central drug disposition provides evidence that this molecule engages and activates central mGlu2 receptors in vivo.
The role of organic cation transporter 1 (OCT1) in humans is gaining attention as data emerges regarding its role in physiology, drug exposure, and drug response. OCT1 variants with decreased
...function correlate well with altered exposure of multiple OCT1 substrates in variant carriers. In the current research, we investigate mechanisms behind activity of OCT1 variants
by generating cell lines expressing known OCT1 variants and quantifying membrane OCT1 protein expression with corresponding OCT1 activity and kinetics. Oct knockout mice have provided additional insight into the role of Oct1 in the liver and have reproduced effects of altered OCT1 activity observed in the clinic. To assess the complex effect of Oct1 depletion on pharmacokinetics of prodrug proguanil and its active moiety cycloguanil, both of which are OCT1 substrates, Oct1/2
mice were used. Decreased membrane expression of OCT1 was demonstrated for all variant cell lines, although activity was substrate-dependent, as reported previously. Lack of change in activity for OCT1*2 resulted in increased intrinsic activity per pmol of OCT1 protein, particularly for sumatriptan but also for proguanil and cycloguanil. Similar to that reported in humans with decreased OCT1 function, systemic exposure of proguanil was minimally affected in Oct1/2
mice. However, proguanil liver partitioning and exposure decreased. Cycloguanil exposure decreased following proguanil administration in Oct1/2
mice, as did the systemic metabolite:parent ratio. When administered directly, systemic exposure of cycloguanil decreased slightly; however liver partitioning and exposure were decreased in Oct1/2
mice. Unexpectedly, following proguanil administration, the metabolite ratio in the liver changed only minimally, and liver partitioning of cycloguanil was affected in Oct1/2
mice to a lesser extent following proguanil administration than direct administration of cycloguanil. In conclusion, these
and
data offer additional complexity in understanding mechanisms of OCT1 variant activity as well as the effects of these variants
. From cell lines, it is apparent that intrinsic activity is not directly related to OCT1 membrane expression. Additionally, in situations with a more complicated role of OCT1 in drug pharmacokinetics there is difficulty translating
impact simply from intrinsic activity from cellular data.
Conventional antidepressants lack efficacy for many patients (treatmentresistant depression or TRD) and generally take weeks to produce full therapeutic response in others. Emerging data has ...identified certain drugs such as ketamine as rapidly-acting antidepressants for major depressive disorder and TRD. Scopolamine, a drug used to treat motion sickness and nausea, has also been demonstrated to function as a rapidly-acting antidepressant. The mechanisms associated with efficacy in TRD patients and rapid onset of action have been suggested to involve a-Amino-3-hydroxy- 5-methyl-4-isoxazolepropionic acid (AMPA) receptor and mammalian target of rapamycin (mTOR) signaling. Since the work on these mechanisms with scopolamine has been limited, the present set of experiments was designed to further explore these mechanisms of action.
Male, NIH Swiss mice demonstrated a robust and immediate antidepressant signature with ketamine or scopolamine when studied under the forced-swim test.
The AMPA receptor antagonist NBQX prevented this antidepressant-like effect of scopolamine and ketamine. An orally-bioavilable mTOR inhibitor (AZD8055) also attenuated the antidepressant- like effects of scopolamine and ketamine. Scopolamine was also shown to augment the antidepressant- like effect of the selective serotonin reuptake inhibitor citalopram. When given in combination, scopolamine and ketamine acted synergistically to produce antidepressant-like effects. Although drug interaction data suggested that additional mechanisms might be at play, metabolomic analysis of frontal cortex and plasma from muscarinic M1+/+ and M1 -/- mice given scopolamine or vehicle did not reveal any hints as to the nature of these additional mechanisms of action.
Overall, the data substantiate and extend the idea that AMPA and mTOR signaling pathways are necessary for the antidepressant-like effects of scopolamine and ketamine, mechanisms that appear to be of general significance for TRD therapeutic agents.
Multiple therapeutic opportunities have been suggested for compounds capable of selective activation of metabotropic glutamate 3 (mGlu
) receptors, but small molecule tools are lacking. As part of ...our ongoing efforts to identify potent, selective, and systemically bioavailable agonists for mGlu
and mGlu
receptor subtypes, a series of C4
-N-linked variants of (1 S,2 S,5 R,6 S)-2-amino-bicyclo3.1.0hexane-2,6-dicarboxylic acid 1 (LY354740) were prepared and evaluated for both mGlu
and mGlu
receptor binding affinity and functional cellular responses. From this investigation we identified (1 S,2 S,4 S,5 R,6 S)-2-amino-4-(3-methoxybenzoyl)aminobicyclo3.1.0hexane-2,6-dicarboxylic acid 8p (LY2794193), a molecule that demonstrates remarkable mGlu
receptor selectivity. Crystallization of 8p with the amino terminal domain of hmGlu
revealed critical binding interactions for this ligand with residues adjacent to the glutamate binding site, while pharmacokinetic assessment of 8p combined with its effect in an mGlu
receptor-dependent behavioral model provides estimates for doses of this compound that would be expected to selectively engage and activate central mGlu
receptors in vivo.
Hepatocyte growth factor/scatter factor (HGF/SF) has a cofactor requirement for heparan sulfate (HS) and dermatan sulfate (DS) in the optimal activation of its signaling receptor MET. However, these ...two glycosaminoglycans (GAGs) have different sugar backbones and sulfation patterns, with only the presence of iduronate in common. The structural basis for GAG recognition and activation is thus very unclear. We have clarified this by testing a wide array of natural and modified GAGs for both protein binding and activation. Comparisons between Ascidia nigra (2,6-O-sulfated) and mammalian (mainly 4-O-sulfated) DS species, as well as between a panel of specifically desulfated heparins, revealed that no specific sulfate isomer, in either GAG, is vital for interaction and activity. Moreover, different GAGs of similar sulfate density had comparable properties, although affinity and potency notably increase with increasing sulfate density. The weaker interaction with CS-E, compared with DS, shows that GlcA-containing polymers can bind, if highly sulfated, but emphasizes the importance of the flexible IdoA ring. Our data indicate that the preferred binding sites in DS in vivo will be comprised of disulfated, IdoA(2S)-containing motifs. In HS, clustering of N-/2-O-/6-O-sulfation in S-domains will lead to strong reactivity, although binding can also be mediated by the transition zones where sulfates are mainly at the N- and 6-O- positions. GAG recognition of HGF/SF thus appears to be primarily driven by electrostatic interactions and exhibits an interesting interplay between requirements for iduronate and sulfate density that may reflect in part a preference for particular sugar chain conformations.
6-(1S)-1-1-5-(2-hydroxyethoxy)-2-pyridylpyrazol-3-ylethyl- 3H-1,3-benzothiazol-2-one (LY3130481 or CERC-611) is a selective antagonist of AMPA receptors containing transmembrane AMPA receptor ...regulatory protein (TARP) γ-8 that is under development for epilepsy. The present study provided a broad inquiry into its anticonvulsant properties. LY3130481 was anticonvulsant in multiple acute seizure provocation models in mice and rats. In addition, LY3130481 was effective against absence seizures in the GAERS genetic model and in the Frings mouse model. Likewise, LY3130481 attenuated convulsions in mice and rats with long-term induction of seizures (e.g., corneal, pentylenetetrazole, hippocampal, and amygdala kindled seizures). In slices of epileptic human cortex, LY3130481 significantly decreased neuronal firing frequencies. LY3130481 displaced from rat brain a radioligand specific for AMPA receptors associated with TARP γ-8 whereas non-TARP-selective molecules did not. Binding was also observed in hippocampus freshly transected from a patient.
Taken as a whole, the findings reported here establish the broad anticonvulsant efficacy of LY3130481 indicating that blockade of AMPA receptors associated with TARP γ-8 is sufficient for these protective effects.
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