Multiple-Dose Plasma Pharmacokinetic and Safety Study of LY450108 and LY451395 (AMPA Receptor Potentiators) and Their Concentration in Cerebrospinal Fluid in Healthy Human Subjects

New Insights into Alzheimer’s Disease: Novel Pathogenesis, Drug Target and Delivery

Alzheimer’s disease (AD), the most common type of dementia, is characterized by senile plaques composed of amyloid β protein (Aβ) and neurofilament tangles derived from the hyperphosphorylation of tau protein. However, the developed medicines targeting Aβ and tau have not obtained ideal clinical efficacy, which raises a challenge to the hypothesis that AD is Aβ cascade-induced. A critical problem of AD pathogenesis is which endogenous factor induces Aβ aggregation and tau phosphorylation. Recently, age-associated endogenous formaldehyde has been suggested to be a direct trigger for Aβ- and tau-related pathology. Another key issue is whether or not AD drugs are successfully delivered to the damaged neurons. Both the blood–brain barrier (BBB) and extracellular space (ECS) are the barriers for drug delivery. Unexpectedly, Aβ-related SP deposition in ECS slows down or stops interstitial fluid drainage in AD, which is the direct reason for drug delivery failure. Here, we propose a new pathogenesis and perspectives on the direction of AD drug development and drug delivery: (1) aging-related formaldehyde is a direct trigger for Aβ assembly and tau hyperphosphorylation, and the new target for AD therapy is formaldehyde; (2) nano-packaging and physical therapy may be the promising strategy for increasing BBB permeability and accelerating interstitial fluid drainage.

3,4-Dihydrobenzo[e][1,2,3]oxathiazine 2,2-dioxide analogs act as potential AMPA receptor potentiators with antidepressant activity

Major depressive disorder is a common psychiatric disorder, with ∼30% of patients suffering from treatment-resistant depression. Based on preclinical studies on ketamine, α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor (AMPAR) activation may be a promising therapeutic approach. In this study, we synthesized a series of novel 3,4-dihydrobenzo[e][1,2,3]oxathiazine 2,2-dioxide analogs and analyzed their potential as AMPAR potentiators. Compounds 5aa and 7k exhibited high potentiation with little agonist activity in a high-throughput screen using a calcium influx assay in cultured hippocampal primary neurons. In rats, compound 7k had better pharmacokinetic properties and oral bioavailability (F = 67.19%); it also exhibited an acceptable safety profile in vital internal organs based on hematoxylin and eosin staining. We found that 7k produced a rapid antidepressant-like effect in chronic restraint stress-induced mice 1 h after intraperitoneal administration. Our study presented a series of novel AMPAR potentiators and identified 7k as a promising drug-like candidate against major depressive disorders.

Role of the AMPA receptor in antidepressant effects of ketamine and potential of AMPA receptor potentiators as a novel antidepressant

Ketamine exerts rapid and long-lasting antidepressant effects in patients with treatment-resistant depression. However, its clinical use is limited by its undesirable psychotomimetic side effects. Accumulating evidence from preclinical studies has shown that the antidepressant effects of ketamine are dependent on α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R) activation, which triggers activation of the mechanistic target of rapamycin pathway and brain-derived neurotrophic factor release. Thus, AMPA-R has emerged as a promising new target for novel antidepressants with a rapid onset of action. However, almost all known AMPA-R potentiators carry the risk of a narrow bell-shaped dose-response curve and a poor safety margin against seizures. Our data suggest that agonistic activity is not only related to the risks of bell-shaped dose-response curves and seizures but also to the reduced synaptic transmission and procognitive effects of AMPA-R potentiators. In this review, we describe our original screening approach that led to the discovery of an investigational AMPA-R potentiator with low agonistic activity, TAK-653. We further review the in vitro and in vivo profiles of TAK-653, including its procognitive and antidepressant-like effects, as well as its safety profile, in comparison with known AMPA-R potentiators with agonistic activity and AMPA, an AMPA-R agonist. The low agnostic activity of TAK-653 may overcome limitations of known AMPA-R potentiators. This article is part of the Special Issue on 'Ketamine and its Metabolites'.

Preventive effects of the AMPA receptor potentiator LY450108 in an LPS-induced depressive mouse model

Previous studies have demonstrated a close association between α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid receptors (AMPARs) and depressive disorders, and activation of AMPARs may represent a promising way to treat depression. However, the effects of AMPAR potentiators on depression and the underlying mechanism have not been comprehensively clarified. We used lipopolysaccharide (LPS) to establish a depressive mouse model and an in vitro damage model of SH-SY5Y cells, and the AMPAR potentiator LY450108 was introduced to the study. We found that LY450108 alleviated LPS-induced depressive behavior and abnormal phosphorylation of hippocampal AMPARs in mice. LY450108 also alleviated LPS-induced apoptosis and decreased the viability of SH-SY5Y cells. In addition, LY450108 protected SH-SY5Y cells from LPS-induced abnormal phosphorylation of AMPARs. In conclusion, our findings suggest that LY450108 has antidepressant effects against LPS-induced neuronal damage and depression.

Elevating the Levels of Calcium Ions Exacerbate Alzheimer's Disease via Inducing the Production and Aggregation of β-Amyloid Protein and Phosphorylated Tau

Alzheimer’s disease (AD) is a neurodegenerative disease with a high incidence rate. The main pathological features of AD are β-amyloid plaques (APs), which are formed by β-amyloid protein (Aβ) deposition, and neurofibrillary tangles (NFTs), which are formed by the excessive phosphorylation of the tau protein. Although a series of studies have shown that the accumulation of metal ions, including calcium ions (Ca²⁺), can promote the formation of APs and NFTs, there is no systematic review of the mechanisms by which Ca²⁺ affects the development and progression of AD. In view of this, the current review summarizes the mechanisms by which Ca²⁺ is transported into and out of cells and organelles, such as the cell, endoplasmic reticulum, mitochondrial and lysosomal membranes to affect the balance of intracellular Ca²⁺ levels. In addition, dyshomeostasis of Ca²⁺ plays an important role in modulating the pathogenesis of AD by influencing the production and aggregation of Aβ peptides and tau protein phosphorylation and the ways that disrupting the metabolic balance of Ca²⁺ can affect the learning ability and memory of people with AD. In addition, the effects of these mechanisms on the synaptic plasticity are also discussed. Finally, the molecular network through which Ca²⁺ regulates the pathogenesis of AD is introduced, providing a theoretical basis for improving the clinical treatment of AD.

Preventive and Therapeutic Strategies in Alzheimer's Disease: Focus on Oxidative Stress, Redox Metals, and Ferroptosis

Significance: Alzheimer's disease (AD) is the most common cause of dementia in the elderly. AD is currently ranked as the sixth leading cause of death, but some sources put it as third, after heart disease and cancer. Currently, there are no effective therapeutic approaches to treat or slow the progression of chronic neurodegeneration. In addition to the accumulation of amyloid-β (Aβ) and tau, AD patients show progressive neuronal loss and neuronal death, also high oxidative stress that correlates with abnormal levels or overload of brain metals. Recent Advances: Several promising compounds targeting oxidative stress, redox metals, and neuronal death are under preclinical or clinical evaluation as an alternative or complementary therapeutic strategy in mild cognitive impairment and AD. Here, we present a general analysis and overview, discuss limitations, and suggest potential directions for these treatments for AD and related dementia. Critical Issues: Most of the disease-modifying therapeutic strategies for AD under evaluation in clinical trials have focused on components of the amyloid cascade, including antibodies to reduce levels of Aβ and tau, as well as inhibitors of secretases. Unfortunately, several of the amyloid-focused therapeutics have failed the clinical outcomes or presented side effects, and numerous clinical trials of compounds have been halted, reducing realistic options for the development of effective AD treatments. Future Directions: The focus of research on AD and related dementias is shifting to alternative or innovative areas, such as ApoE, lipids, synapses, oxidative stress, cell death mechanisms, neuroimmunology, and neuroinflammation, as well as brain metabolism and bioenergetics.

Radiosynthesis and preliminary evaluation of 11C-labeled 4-cyclopropyl-7-(3-methoxyphenoxy)-3,4-dihydro-2H-benzo[e] [1,2,4] thiadiazine 1,1-dioxide for PET imaging AMPA receptors

The α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionic acid receptors (AMPARs) belong to the family of ionotropic transmembrane receptors for glutamate (iGluRs) that are implicated in the pathology of neurological disorders and neurodegenerative diseases. Inspired by a recently developed positive allosteric modulator of AMPARs, 4-cyclopropyl-7-(3-methoxyphenoxy)-3,4-dihydro-2H-benzo[ e ][1,2,4]thiadiazine 1,1-dioxide (16; EC₅₀ = 2.0 nM), we designed a new synthetic route for N-protected phenolic precursor 13 and efficiently radiolabeled a PET ligand [¹¹C]AMPA-1905 ([¹¹C]16) using a modified one-pot two-step strategy in high radiochemical yield and high molar activity. Preliminary in vivo evaluation was carried out to investigate the suitability of [¹¹C]16 as a potential PET probe for AMPAR imaging.

Positron Emission Tomography (PET) Ligand Development for Ionotropic Glutamate Receptors: Challenges and Opportunities for Radiotracer Targeting N-Methyl-d-aspartate (NMDA), α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA), and Kainate Receptors

Ionotropic glutamate receptors (iGluRs) mediate excitatory neurotransmission within the mammalian central nervous system. iGluRs exist as three main groups: N-methyl-d-aspartate receptors (NMDARs), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs), and kainate receptors. The past decades have witnessed a remarkable development of PET tracers targeting different iGluRs including NMDARs and AMPARs, and several of the tracers have advanced to clinical imaging studies. Here, we assess the recent development of iGluR PET probes, focusing on tracer design, brain kinetics, and performance in PET imaging studies. Furthermore, this review will not only present challenges in the tracer development but also provide novel approaches in conjunction with most recent drug discovery efforts on these iGluRs, including subtype-selective NMDAR and transmembrane AMPAR regulatory protein modulators and positive allosteric modulators (PAMs) of AMPARs. These approaches, if successful as PET tracers, may provide fundamental knowledge to understand the roles of iGluR receptors under physiological and pathological conditions.

Calcium signaling in Alzheimer's disease & therapies

Alzheimer's disease (AD) is the most common type of dementia and is characterized by the accumulation of amyloid (Aβ) plaques and neurofibrillary tangles in the brain. Much attention has been given to develop AD treatments based on the amyloid cascade hypothesis; however, none of these drugs had good efficacy at improving cognitive functions in AD patients suggesting that Aβ might not be the disease origin. Thus, there are urgent needs for the development of new therapies that target on the proximal cause of AD. Cellular calcium (Ca²⁺) signals regulate important facets of neuronal physiology. An increasing body of evidence suggests that age-related dysregulation of neuronal Ca²⁺ homeostasis may play a proximal role in the pathogenesis of AD as disrupted Ca²⁺ could induce synaptic deficits and promote the accumulation of Aβ plaques and neurofibrillary tangles. Given that Ca²⁺ disruption is ubiquitously involved in all AD pathologies, it is likely that using chemical agents or small molecules specific to Ca²⁺ channels or handling proteins on the plasma membrane and membranes of intracellular organelles to correct neuronal Ca²⁺ dysregulation could open up a new approach to AD prevention and treatment. This review summarizes current knowledge on the molecular mechanisms linking Ca²⁺ dysregulation with AD pathologies and discusses the possibility of correcting neuronal Ca²⁺ disruption as a therapeutic approach for AD.

HBT1, a Novel AMPA Receptor Potentiator with Lower Agonistic Effect, Avoided Bell-Shaped Response in In Vitro BDNF Production

α-Amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor (AMPA-R) potentiators with brain-derived neurotrophic factor (BDNF)-induction potential could be promising as therapeutic drugs for neuropsychiatric and neurologic disorders. However, AMPA-R potentiators such as LY451646 have risks of narrow bell-shaped responses in pharmacological effects, including in vivo BDNF induction. Interestingly, LY451646 and LY451395, other AMPA-R potentiators, showed agonistic effects and exhibited bell-shaped responses in the BDNF production in primary neurons. We hypothesized that the agonistic property is related to the bell-shaped response and endeavored to discover novel AMPA-R potentiators with lower agonistic effects. LY451395 showed an agonistic effect in primary neurons, but not in a cell line expressing AMPA-Rs, in Ca²⁺ influx assays; thus, we used a Ca²⁺ influx assay in primary neurons and, from a chemical library, discovered two AMPA-R potentiators with lower agonistic effects: 2-(((5-methyl-3-(trifluoromethyl)-1H-pyrazol-1-yl)acetyl)amino)-4,5,6,7-tetrahydro-1-benzothiophene-3-carboxamide (HBT1) and (3S)-1-(4-tert-butylphenyl)-N-((1R)-2-(dimethylamino)-1-phenylethyl)-3-isobutyl-2-oxopyrrolidine-3-carboxamide (OXP1). In a patch-clamp study using primary neurons, HBT1 showed little agonistic effect, whereas both LY451395 and OXP1 showed remarkable agonistic effects. HBT1, but not OXP1, did not show remarkable bell-shaped response in BDNF production in primary neurons. HBT1 bound to the ligand-binding domain (LBD) of AMPA-R in a glutamate-dependent manner. The mode of HBT1 and LY451395 binding to a pocket in the LBD of AMPA-R differed: HBT1, but not LY451395, formed hydrogen bonds with S518 in the LBD. OXP1 may bind to a cryptic binding pocket on AMPA-R. Lower agonistic profile of HBT1 may associate with its lower risks of bell-shaped responses in BDNF production in primary neurons.

Discovery of GluN2A-Selective NMDA Receptor Positive Allosteric Modulators (PAMs): Tuning Deactivation Kinetics via Structure-Based Design

The N-methyl-D-aspartate receptor (NMDAR) is a Na(+) and Ca(2+) permeable ionotropic glutamate receptor that is activated by the coagonists glycine and glutamate. NMDARs are critical to synaptic signaling and plasticity, and their dysfunction has been implicated in a number of neurological disorders, including schizophrenia, depression, and Alzheimer's disease. Herein we describe the discovery of potent GluN2A-selective NMDAR positive allosteric modulators (PAMs) starting from a high-throughput screening hit. Using structure-based design, we sought to increase potency at the GluN2A subtype, while improving selectivity against related α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptors (AMPARs). The structure-activity relationship of channel deactivation kinetics was studied using a combination of electrophysiology and protein crystallography. Effective incorporation of these strategies resulted in the discovery of GNE-0723 (46), a highly potent and brain penetrant GluN2A-selective NMDAR PAM suitable for in vivo characterization.

The discovery and characterization of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor potentiator N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242)

A unique tetrahydrofuran ether class of highly potent α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor potentiators has been identified using rational and structure-based drug design. An acyclic lead compound, containing an ether-linked isopropylsulfonamide and biphenyl group, was pharmacologically augmented by converting it to a conformationally constrained tetrahydrofuran to improve key interactions with the human GluA2 ligand-binding domain. Subsequent replacement of the distal phenyl motif with 2-cyanothiophene to enhance its potency, selectivity, and metabolic stability afforded N-{(3S,4S)-4-[4-(5-cyano-2-thienyl)phenoxy]tetrahydrofuran-3-yl}propane-2-sulfonamide (PF-04958242, 3), whose preclinical characterization suggests an adequate therapeutic index, aided by low projected human oral pharmacokinetic variability, for clinical studies exploring its ability to attenuate cognitive deficits in patients with schizophrenia.

Mibampator (LY451395) randomized clinical trial for agitation/aggression in Alzheimer's disease

BACKGROUND

Mibampator, an amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptor potentiator, was evaluated for treatment of agitation and aggression (A/A) in Alzheimer's disease (AD).

METHODS

Outpatients (n = 132) with probable AD and A/A randomized to 12 weeks of double-blind treatment with 3-mg po mibampator or placebo were assessed using the 4-domain A/A subscale of the Neuropsychiatric Inventory (NPI-4-A/A) derived from the Neuropsychiatric Inventory. Secondary measures included the Cohen-Mansfield Agitation Inventory, Cornell Scale for Depression in Dementia, Frontal Systems Behavior Inventory (FrSBe), and Alzheimer's Disease Assessment Scale-Cognitive. Efficacy was analyzed using mixed-effects model repeated measures from baseline to endpoint. Adverse events (AEs), labs, vital signs, and electrocardiograms were monitored.

RESULTS

Baseline characteristics were comparable between groups. Both groups improved on the NPI-4-A/A, but without group differences. Among secondaries, mibampator was significantly better (p = 0.007) than placebo only on the FrSBe. AEs were similar between groups. One death occurred in the placebo group.

CONCLUSION

Possible explanations for no significant group differences include caregiver, drug target engagement, and design issues. This trial is registered on ClinicalTrials.gov; ID: NCT00843518.

Using Simcyp to project human oral pharmacokinetic variability in early drug research to mitigate mechanism-based adverse events

Positive allosteric modulators ('potentiators') of the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) have been shown to display a mechanism-based exposure-response continuum in preclinical species with procognitive electrophysiological and behavioral effects ('efficacy') at low exposures and motor coordination disruptions at progressively higher exposures. Due to the dose-capping nature of such motor coordination deficits, an exposure threshold-mediated adverse event (C(AE) ), the adequacy of separation between the maximal total plasma compound concentration (C(max) ) at a predicted clinically efficacious oral dose and this adverse event (AE) was explored in early drug research with three AMPAR potentiators considered potential candidates for clinical trials. In vitro metabolism studies in human liver microsomes and human hepatocytes demonstrated the metabolic clearance for each compound was predominately due to cytochromes P450 (CYP). Thus, for each compound's anticipated clinically efficacious dose, human C(max) variability following oral administration was assessed using Simcyp software, which combines its virtual human populations database using extensive demographic, physiological and genomic information with routinely collected compound-specific in vitro biochemical data to simulate and predict drug disposition. Using a combination of experimentally determined recombinant human CYP intrinsic clearances for CYP1A2, CYP2C8, CYP2C9, CYP2C19, CYP2D6 and CYP3A4, human binding factors, expected fraction absorbed and estimated steady-state volume of distribution, Simcyp simulations demonstrated that two of the three potentiators had acceptable projected C(max) variability (i.e. the 95th percentile C(max) did not breach C(AE) ). This evaluation aided in the selection of compounds for preclinical progression, and represents a novel application of pharmacologically based pharmacokinetic (PBPK) software approaches to predict interpatient variability.

Delta oscillation and short-term plasticity in the rat medial prefrontal cortex: modelling NMDA hypofunction of schizophrenia

Dysfunction of the prefrontal cortex (PFC) is considered to be an important factor contributing to a decrease in cognitive performance of schizophrenia patients. The medial PFC (mPFC) is innervated by the hippocampus/subiculum, and the subiculum-mPFC pathway is known to be involved in various cognitive processes. Glutamate-containing subicular axons innervate cortical pyramidal neurons and interneurons where AMPA and NMDA receptors are implicated in synaptic transmission. In our experiments, properties of subiculum-mPFC interactions were studied using pathway stimulation and local field potential (LFP) recordings of the mPFC in urethane-anaesthetized rats. Changes in paired-pulse facilitation (PPF) and LFP oscillations, effects of the NMDA receptor antagonist MK-801, and the AMPAkine LY451395 were evaluated. Effects of disruption of the thalamo-cortical loop with local microinjection of lidocaine into the mediodorsal thalamic nucleus (MD) were also studied. Our findings demonstrate that both systemic administration of MK-801 and local MD lidocaine microinjection produce similar changes in LFP oscillations and reduction in PPF. Specifically, it was observed that MK-801 (0.05 mg/kg i.v.) and intra-thalamic lidocaine changed regular, 2 Hz delta oscillation to a less regular 0.5-1.5 Hz delta rhythm. Concurrently, PPF in response to electrical stimulation of the subiculum was significantly attenuated. Administration of the AMPAkine LY451395 (0.01 mg/kg i.v.) reversed the MK-801- and lidocaine-induced changes, and was itself blocked by the AMPA receptor antagonist CP-465022. Analysis of our findings suggests a critical role of cortical interneurons in NMDA/AMPA receptor-mediated changes in thalamo-cortical oscillations and PPF, and contributes to our understanding of the NMDA hypofunction model of schizophrenia.

AMPA receptor potentiation can prevent ethanol-induced intoxication

We present a substantial series of behavioral and imaging experiments, which demonstrate, for the first time, that increasing AMPA receptor-mediated neurotransmission via administration of potent and selective biarylsulfonamide AMPA potentiators LY404187 and LY451395 reverses the central effects of an acutely intoxicating dose of ethanol in the rat. Using pharmacological magnetic resonance imaging (phMRI), we observed that LY404187 attenuated ethanol-induced reductions in blood oxygenation level dependent (BOLD) in the anesthetized rat brain. A similar attenuation was apparent when measuring local cerebral glucose utilization (LCGU) via C14-2-deoxyglucose autoradiography in freely moving conscious rats. Both LY404187 and LY451395 significantly and dose-dependently reversed ethanol-induced deficits in both motor coordination and disruptions in an operant task where animals were trained to press a lever for food reward. Both prophylactic and acute intervention treatment with LY404187 reversed ethanol-induced deficits in motor coordination. Given that LY451395 and related AMPA receptor potentiators/ampakines are tolerated in both healthy volunteers and elderly patients, these data suggest that such compounds may form a potential management strategy for acute alcohol intoxication.