Exploring the Therapeutic Potential of Phosphorylated Cis-Tau Antibody in a Pig Model of Traumatic Brain Injury.

Traumatic brain injury (TBI) results in the generation of tau. As hyperphosphorylated tau (p-tau) is one of the major consequences of TBI, targeting p-tau in TBI may lead to the development of new therapy. Twenty-five pigs underwent a controlled cortical impact. One hour after TBI, pigs were administered either vehicle (n = 13) or PNT001 (n = 12), a monoclonal antibody for the cis conformer of tau phosphorylated at threonine 231. Plasma biomarkers of neural injury were assessed for 14 days. Diffusion tensor imaging was performed at day 1 and 14 after injury, and these were compared to historical control animals (n = 4). The fractional anisotropy data showed significant white matter injury for groups at 1 day after injury in the corona radiata. At 14 days, the vehicle-treated pigs, but not the PNT001-treated animals, exhibited significant white matter injury compared to sham pigs in the ipsilateral corona radiata. The PNT001-treated pigs had significantly lower levels of plasma glial fibrillary acidic protein (GFAP) at day 2 and day 4. These findings demonstrate a subtle reduction in the areas of white matter injury and biomarkers of neurological injury after treatment with PNT001 following TBI. These findings support additional studies for PNT001 as well as the potential use of this agent in clinical trials in the near future.

Preclinical characterization and IND-enabling safety studies for PNT001, an antibody that recognizes cis-pT231 tau.

BACKGROUND: The cis-conformer of tau phosphorylated at threonine-231 (cis-pT231 tau) is hypothesized to contribute to tauopathies. PNT001 is a humanized, monoclonal antibody that recognizes cis-pT231 tau. PNT001 was characterized to assess clinical development readiness. METHODS: Affinity and selectivity were assessed by surface plasmon resonance and enzyme-linked immunosorbent assay. Immunohistochemistry (IHC) was performed with brain sections from human tauopathy patients and controls. Real-time quaking-induced conversion (RT-QuIC) was used to assess whether PNT001 reduced tau seeds from Tg4510 transgenic mouse brain. Murine PNT001 was evaluated in vivo in the Tg4510 mouse. RESULTS: The affinity of PNT001 for a cis-pT231 peptide was 0.3 to 3 nM. IHC revealed neurofibrillary tangle-like structures in tauopathy patients with no detectable staining in controls. Incubation of Tg4510 brain homogenates with PNT001 lowered seeding in RT-QuIC. Multiple endpoints were improved in the Tg4510 mouse. No adverse findings attributable to PNT001 were detected in Good Laboratory Practice safety studies. DISCUSSION: The data support clinical development of PNT001 in human tauopathies.

Synthesis of functionalized derivatives of the gamma-secretase modulator BMS-932481 and identification of its major metabolite.

In an effort to improve physical properties by introducing polar functionality into the bicyclic pyrimidine gamma-secretase modulator (GSM) clinical candidate BMS-932481, we prepared several oxidative products of BMS-932481. Among the analogs that were prepared, the C-5 alcohol 3 was identified as the predominant metabolite of BMS-932481 found in rat and human liver microsomes. Alcohol 3 was determined to be chemically unstable, leading to the hypothesis that 3 may lead to the production of reactive species both in vitro and in vivo.

USP30 sets a trigger threshold for PINK1-PARKIN amplification of mitochondrial ubiquitylation.

The mitochondrial deubiquitylase USP30 negatively regulates the selective autophagy of damaged mitochondria. We present the characterisation of an N-cyano pyrrolidine compound, FT3967385, with high selectivity for USP30. We demonstrate that ubiquitylation of TOM20, a component of the outer mitochondrial membrane import machinery, represents a robust biomarker for both USP30 loss and inhibition. A proteomics analysis, on a SHSY5Y neuroblastoma cell line model, directly compares the effects of genetic loss of USP30 with chemical inhibition. We have thereby identified a subset of ubiquitylation events consequent to mitochondrial depolarisation that are USP30 sensitive. Within responsive elements of the ubiquitylome, several components of the outer mitochondrial membrane transport (TOM) complex are prominent. Thus, our data support a model whereby USP30 can regulate the availability of ubiquitin at the specific site of mitochondrial PINK1 accumulation following membrane depolarisation. USP30 deubiquitylation of TOM complex components dampens the trigger for the Parkin-dependent amplification of mitochondrial ubiquitylation leading to mitophagy. Accordingly, PINK1 generation of phospho-Ser65 ubiquitin proceeds more rapidly in cells either lacking USP30 or subject to USP30 inhibition.

Safety of the tau-directed monoclonal antibody BIIB092 in progressive supranuclear palsy: a randomised, placebo-controlled, multiple ascending dose phase 1b trial.

BACKGROUND: Progressive supranuclear palsy is a rare neurodegenerative disease associated with dysfunctional tau protein. BIIB092 is a humanised monoclonal antibody that binds to N-terminal tau and is thus being assessed as a potential novel treatment for progressive supranuclear palsy. We aimed to investigate the safety and tolerability of BIIB092 in individuals with progressive supranuclear palsy. METHODS: This 12-week, double-blind, randomised, placebo-controlled, multiple ascending dose, phase 1b trial was done at 13 outpatient sites in the USA. Participants aged 41-86 years with probable or possible progressive supranuclear palsy with a score of 20 or greater on the Mini-Mental State Examination (MMSE) were enrolled. Three BIIB092 dose escalation cohorts (150 mg, 700 mg, or 2100 mg; eight participants per cohort) were tested sequentially. For each dose cohort, the first two participants were randomly assigned by a computer-generated scheme to receive either BIIB092 or placebo intravenously every 4 weeks for 57 days. After 2 days, the six remaining participants in each cohort were randomly assigned (5:1) to receive BIIB092 or placebo for 57 days. An additional expansion panel of 24 patients was randomly assigned (3:1) to receive 2100 mg or placebo every 4 weeks for 57 days. All participants were followed up to day 85. The primary outcome was safety, which was analysed in the treated population (all enrolled participants who received at least one dose of the study drug). This trial is registered with ClinicalTrials.gov, NCT02460094. FINDINGS: Between Oct 2, 2015, and Oct 19, 2016, 48 participants were enrolled and randomly assigned to the BIIB092 (n=36) and placebo (n=12) groups. No apparent demographic differences were observed between the two groups at baseline. All 48 participants completed the treatment phase of the study. Adverse events were generally mild to moderate in severity; the most common in the placebo and BIIB092 groups were falls (in two [17%] of 12 patients and in ten [28%] of 36 patients), urinary tract infections (in one [8%] of 12 and in six [17%] of 36), contusions (in one [8%] of 12 and in five [14%] of 36), and headaches (in none and in five [14%] of 36). Four serious adverse events resulting in admission to hospital were reported in three participants who received BIIB092 2100 mg: two severe adverse events of urinary tract infection, one severe adverse event of change in mental status, and one moderate adverse event of aspiration pneumonia. None was considered to be related to the study drug, all were resolved, and no deaths were reported. INTERPRETATION: Repeated administration of the anti-tau monoclonal antibody BIIB092, at doses of up to 2100 mg, appears to be well tolerated in participants with progressive supranuclear palsy. Results of this phase 1b trial have informed the design of the ongoing phase 2 PASSPORT (NCT03068468) study to examine the efficacy and safety of BIIB092. FUNDING: Bristol-Myers Squibb, Biogen.

Identification and Preclinical Evaluation of the Bicyclic Pyrimidine γ-Secretase Modulator BMS-932481.

A triazine hit identified from a screen of the BMS compound collection was optimized for potency, in vivo activity, and off-target profile to produce the bicyclic pyrimidine γ-secretase modulator BMS-932481. The compound showed robust reductions of Aß1-42 and Aß1-40 in the plasma, brain, and cerebrospinal fluid of mice and rats. Consistent with the γ-secretase modulator mechanism, increases in Aß1-37 and Aß1-38 were observed, with no change in the total amount of Aß1-x produced. No Notch-based toxicity was observed, and the overall preclinical profile of BMS-932481 supported its further evaluation in human clinical trials.

A randomized, single ascending dose study of intravenous BIIB092 in healthy participants.

INTRODUCTION: Extracellular tau is hypothesized to mediate the onset and progression of tauopathies, including Alzheimer's disease, progressive supranuclear palsy, and a subset of frontotemporal lobar degenerations. A putative strategy for treating these disorders is to reduce extracellular tau levels using tau-directed immunotherapy. The results of the first-in-human study of BIIB092 (formerly BMS-986168/IPN007), a humanized monoclonal antibody that binds to N-terminal tau, are reported here. This randomized, double-blind, single ascending dose study evaluated the safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity profile of BIIB092 after a single intravenous infusion in healthy participants. METHODS: Sixty-five participants were randomized to receive a single intravenous infusion of placebo or BIIB092 at doses of 21, 70, 210, 700, 2100, or 4200 mg (or 700 or 2100 mg for Japanese participants). Serial blood and cerebrospinal fluid samples were obtained for assessment of pharmacokinetic parameters and unbound N-terminal tau suppression. RESULTS: There were no deaths, serious adverse events (AEs), severe AEs, or discontinuations due to an AE. The majority of AEs were mild. Serum BIIB092 concentrations increased in a dose-proportional manner and suppressed unbound cerebrospinal fluid N-terminal tau by 67%-97% at 28 days after dose, with doses of ≥210 mg producing persistent unbound N-terminal tau suppression over 12 weeks. Levels of cerebrospinal fluid N-terminal tau suppression were similar for Japanese and non-Japanese participants. DISCUSSION: BIIB092 was generally safe and well tolerated after a single dose of up to 4200 mg, and up to 2100 mg in Japanese participants. BIIB092 exhibited a dose-dependent increase in the extent and duration of unbound N-terminal tau suppression.

Probing Conformational Dynamics of Tau Protein by Hydrogen/Deuterium Exchange Mass Spectrometry.

Fibrillization of the microtubule-associated protein tau has been recognized as one of the signature pathologies of the nervous system in Alzheimer's disease, progressive supranuclear palsy, and other tauopathies. The conformational transition of tau in the fibrillization process, tau monomer to soluble aggregates to fibrils in particular, remains unclear. Here we report on the use of hydrogen/deuterium exchange mass spectrometry (HDX-MS) in combination with other biochemical approaches, including Thioflavin S fluorescence measurements, enzyme-linked immunosorbent assay (ELISA), and Western blotting to understand the heparin-induced tau's fibrillization. HDX-MS studies including anti-tau antibody epitope mapping experiments provided molecular level details of the full-length tau's conformational dynamics and its regional solvent accessibility upon soluble aggregates formation. The results demonstrate that R3 region in the full-length tau's microtubule binding repeat region (MTBR) is stabilized in the aggregation process, leaving both N and C terminal regions to be solvent exposed in the soluble aggregates and fibrils. The findings also illustrate the practical utility of orthogonal analytical methodologies for the characterization of protein higher order structure. Graphical Abstract ᅟ.

Synergistic inhibition of Aß production by combinations of γ-secretase modulators.

Alzheimer's disease is associated with the accumulation of amyloid-ß (Aß) in the brain. In particular, the 42-amino acid form, Aß1-42, is thought to play a key role in the disease. It is therefore of interest that diverse compounds, known as γ-secretase modulators (GSM), can selectively decrease Aß1-42 production without inhibiting the production of other forms of Aß. Here we describe the novel discovery of synergistic inhibition of Aß by certain combinations of GSMs. Cell cultures were treated with pairwise combinations of GSMs to determine how Aß peptide production was affected. Analysis of isobolograms and calculation of the combination index showed that BMS-869780 and GSM-2 were highly synergistic. Additional combinations of GSMs revealed that inhibition of Aß occurred only when one GSM was of the "acid GSM" structural class and the other was of the "non-acid GSM" class. A total of 15 representative acid/non-acid GSM combinations were shown to inhibit Aß production, whereas 10 pairwise combinations containing two acid GSMs or containing two non-acid GSMs did not inhibit Aß. We also discovered that lasalocid, a natural product, is a potent GSM. Lasalocid is unique in that it did not synergize with other GSMs. Synergism did not translate in vivo perhaps because of biochemical differences between the cell culture model and brain. These findings reinforce the pharmacological differences between different structural classes of GSMs, and may help to exploit the potential of γ-secretase as a drug target.

A Functional NaV1.7-NaVAb Chimera with a Reconstituted High-Affinity ProTx-II Binding Site.

The NaV1.7 voltage-gated sodium channel is implicated in human pain perception by genetics. Rare gain of function mutations in NaV1.7 lead to spontaneous pain in humans whereas loss of function mutations results in congenital insensitivity to pain. Hence, agents that specifically modulate the function of NaV1.7 have the potential to yield novel therapeutics to treat pain. The complexity of the channel and the challenges to generate recombinant cell lines with high NaV1.7 expression have led to a surrogate target strategy approach employing chimeras with the bacterial channel NaVAb. In this report we describe the design, synthesis, purification, and characterization of a chimera containing part of the voltage sensor domain 2 (VSD2) of NaV1.7. Importantly, this chimera, DII S1-S4, forms functional sodium channels and is potently inhibited by the NaV1.7 VSD2 targeted peptide toxin ProTx-II. Further, we show by [125I]ProTx-II binding and surface plasmon resonance that the purified DII S1-S4 protein retains high affinity ProTx-II binding in detergent. We employed the purified DII S1-S4 protein to create a scintillation proximity assay suitable for high-throughput screening. The creation of a NaV1.7-NaVAb chimera with the VSD2 toxin binding site provides an important tool for the identification of novel NaV1.7 inhibitors and for structural studies to understand the toxin-channel interaction.

Dramatic elevation in urinary amino terminal titin fragment excretion quantified by immunoassay in Duchenne muscular dystrophy patients and in dystrophin deficient rodents.

Enzyme-linked and electrochemiluminescence immunoassays were developed for quantification of amino (N-) terminal fragments of the skeletal muscle protein titin (N-ter titin) and qualified for use in detection of urinary N-ter titin excretion. Urine from normal subjects contained a small but measurable level of N-ter titin (1.0 ± 0.4 ng/ml). A 365-fold increase (365.4 ± 65.0, P = 0.0001) in urinary N-ter titin excretion was seen in Duchene muscular dystrophy (DMD) patients. Urinary N-ter titin was also evaluated in dystrophin deficient rodent models. Mdx mice exhibited low urinary N-ter titin levels at 2 weeks of age followed by a robust and sustained elevation starting at 3 weeks of age, coincident with the development of systemic skeletal muscle damage in this model; fold elevation could not be determined because urinary N-ter titin was not detected in age-matched wild type mice. Levels of serum creatine kinase and serum skeletal muscle troponin I (TnI) were also low at 2 weeks, elevated at later time points and were significantly correlated with urinary N-ter titin excretion in mdx mice. Corticosteroid treatment of mdx mice resulted in improved exercise performance and lowering of both urinary N-ter titin and serum skeletal muscle TnI concentrations. Low urinary N-ter titin levels were detected in wild type rats (3.0 ± 0.6 ng/ml), while Dmdmdx rats exhibited a 556-fold increase (1652.5 ± 405.7 ng/ml, P = 0.002) (both at 5 months of age). These results suggest that urinary N-ter titin is present at low basal concentrations in normal urine and increases dramatically coincident with muscle damage produced by dystrophin deficiency. Urinary N-ter titin has potential as a facile, non-invasive and translational biomarker for DMD.

B-973, a novel piperazine positive allosteric modulator of the α7 nicotinic acetylcholine receptor.

The alpha7 (α7) nicotinic acetylcholine receptor is a therapeutic target for cognitive disorders. Here we describe 3-(3,4-difluorophenyl)-N-(1-(6-(4-(pyridin-2-yl)piperazin-1-yl)pyrazin-2-yl)ethyl)propanamide (B-973), a novel piperazine-containing molecule that acts as a positive allosteric modulator of the α7 receptor. We characterize the action of B-973 on the α7 receptor using electrophysiology and radioligand binding. At 0.1mM acetylcholine, 1µM B-973 potentiated peak acetylcholine-induced currents 6-fold relative to maximal acetylcholine (3mM) and slowed channel desensitization, resulting in a 6900-fold increase in charge transfer. The EC50 of B-973 was approximately 0.3µM at acetylcholine concentrations ranging from 0.03 to 3mM. At a concentration of 1µM, B-973 shifted the acetylcholine EC50 of peak currents from 0.30mM in control to 0.007mM. B-973 slowed channel deactivation upon acetylcholine removal (τ=50s) and increased the affinity of the α7 agonist [3H]A-585539. In the absence of exogenously added acetylcholine, application of B-973 at concentrations >1µM induced large methyllycaconitine-sensitive currents, suggesting B-973 can function as an Ago-PAM at high concentrations. B-973 will be a useful probe for investigating the biological consequences of increasing α7 receptor activity through allosteric modulation.

Discovery of furo[2,3-d][1,3]thiazinamines as beta amyloid cleaving enzyme-1 (BACE1) inhibitors.

This Letter describes the synthesis and structure-activity relationships of a series of furo[2,3-d][1,3]thiazinamine BACE1 inhibitors. The co-crystal structure of a representative thiazinamine 2e bound with the BACE1 active site displayed a binding mode driven by interactions with the catalytic aspartate dyad and engagement of the biaryl amide toward the S1 and S3 pockets. This work indicates that furo[2,3-d]thiazine can serve as a viable bioisostere of the known furo[3,4-d]thiazine.

Discovery of S3-Truncated, C-6 Heteroaryl Substituted Aminothiazine ß-Site APP Cleaving Enzyme-1 (BACE1) Inhibitors.

Truncation of the S3 substituent of the biaryl aminothiazine 2, a potent BACE1 inhibitor, led to a low molecular weight aminothiazine 5 with moderate activity. Despite its moderate activity, compound 5 demonstrated significant brain Aß reduction in rodents. The metabolic instability of 5 was overcome by the replacement of the 6-dimethylisoxazole, a metabolic soft spot, with a pyrimidine ring. Thus, truncation of the S3 substituent represents a viable approach to the discovery of orally bioavailable, brain-penetrant BACE1 inhibitors.

The γ-Secretase Modulator, BMS-932481, Modulates Aß Peptides in the Plasma and Cerebrospinal Fluid of Healthy Volunteers.

The pharmacokinetics, pharmacodynamics, safety, and tolerability of BMS-932481, a γ-secretase modulator (GSM), were tested in healthy young and elderly volunteers after single and multiple doses. BMS-932481 was orally absorbed, showed dose proportionality after a single dose administration, and had approximately 3-fold accumulation after multiple dosing. High-fat/caloric meals doubled the Cmax and area under the curve and prolonged Tmax by 1.5 hours. Consistent with the preclinical pharmacology of GSMs, BMS-932481 decreased cerebrospinal fluid (CSF) Aß39, Aß40, and Aß42 while increasing Aß37 and Aß38, thereby providing evidence of γ-secretase enzyme modulation rather than inhibition. In plasma, reductions in Aß40 and Aß42 were observed with no change in total Aß; in CSF, modest decreases in total Aß were observed at higher dose levels. Increases in liver enzymes were observed at exposures associated with greater than 70% CSF Aß42 lowering after multiple dosing. Although further development was halted due to an insufficient safety margin to test the hypothesis for efficacy of Aß lowering in Alzheimer's disease, this study demonstrates that γ-secretase modulation is achievable in healthy human volunteers and supports further efforts to discover well tolerated GSMs for testing in Alzheimer's disease and other indications.

Robust Translation of γ-Secretase Modulator Pharmacology across Preclinical Species and Human Subjects.

The amyloid-ß peptide (Aß)-in particular, the 42-amino acid form, Aß1-42-is thought to play a key role in the pathogenesis of Alzheimer's disease (AD). Thus, several therapeutic modalities aiming to inhibit Aß synthesis or increase the clearance of Aß have entered clinical trials, including γ-secretase inhibitors, anti-Aß antibodies, and amyloid-ß precursor protein cleaving enzyme inhibitors. A unique class of small molecules, γ-secretase modulators (GSMs), selectively reduce Aß1-42 production, and may also decrease Aß1-40 while simultaneously increasing one or more shorter Aß peptides, such as Aß1-38 and Aß1-37. GSMs are particularly attractive because they do not alter the total amount of Aß peptides produced by γ-secretase activity; they spare the processing of other γ-secretase substrates, such as Notch; and they do not cause accumulation of the potentially toxic processing intermediate, ß-C-terminal fragment. This report describes the translation of pharmacological activity across species for two novel GSMs, (S)-7-(4-fluorophenyl)-N2-(3-methoxy-4-(3-methyl-1H-1,2,4-triazol-1-yl)phenyl)-N4-methyl-6,7-dihydro-5H-cyclopenta[d]pyrimidine-2,4-diamine (BMS-932481) and (S,Z)-17-(4-chloro-2-fluorophenyl)-34-(3-methyl-1H-1,2,4-triazol-1-yl)-16,17-dihydro-15H-4-oxa-2,9-diaza-1(2,4)-cyclopenta[d]pyrimidina-3(1,3)-benzenacyclononaphan-6-ene (BMS-986133). These GSMs are highly potent in vitro, exhibit dose- and time-dependent activity in vivo, and have consistent levels of pharmacological effect across rats, dogs, monkeys, and human subjects. In rats, the two GSMs exhibit similar pharmacokinetics/pharmacodynamics between the brain and cerebrospinal fluid. In all species, GSM treatment decreased Aß1-42 and Aß1-40 levels while increasing Aß1-38 and Aß1-37 by a corresponding amount. Thus, the GSM mechanism and central activity translate across preclinical species and humans, thereby validating this therapeutic modality for potential utility in AD.

Development of a spontaneously active dorsal root ganglia assay using multiwell multielectrode arrays.

In vitro phenotypic assays of sensory neuron activity are important tools for identifying potential analgesic compounds. These assays are typically characterized by hyperexcitable and/or abnormally, spontaneously active cells. Whereas manual electrophysiology experiments provide high-resolution biophysical data to characterize both in vitro models and potential therapeutic modalities (e.g., action potential characteristics, the role of specific ion channels, and receptors), these techniques are hampered by their low throughput. We have established a spontaneously active dorsal root ganglia (DRG) platform using multiwell multielectrode arrays (MEAs) that greatly increase the ability to evaluate the effects of multiple compounds and conditions on DRG excitability within the context of a cellular network. We show that spontaneous DRG firing can be attenuated with selective Na(+) and Ca(2+) channel blockers, as well as enhanced with K(+) channel blockers. In addition, spontaneous activity can be augmented with both the transient receptor potential cation channel subfamily V member 1 agonist capsaicin and the peptide bradykinin and completely blocked with neurokinin receptor antagonists. Finally, we validated the use of this assay by demonstrating that commonly used neuropathic pain therapeutics suppress DRG spontaneous activity. Overall, we have optimized primary rat DRG cells on a multiwell MEA platform to generate and characterize spontaneously active cultures that have the potential to be used as an in vitro phenotypic assay to evaluate potential therapeutics in rodent models of pain.

Targeting the BACE1 Active Site Flap Leads to a Potent Inhibitor That Elicits Robust Brain Aß Reduction in Rodents.

By targeting the flap backbone of the BACE1 active site, we discovered 6-dimethylisoxazole-substituted biaryl aminothiazine 18 with 34-fold improved BACE1 inhibitory activity over the lead compound 1. The cocrystal structure of 18 bound to the active site indicated two hydrogen-bond interactions between the dimethylisoxazole and threonine 72 and glutamine 73 of the flap. Incorporation of the dimethylisoxazole substitution onto the related aminothiazine carboxamide series led to pyrazine-carboxamide 26 as a very potent BACE1 inhibitor (IC50 < 1 nM). This compound demonstrated robust brain Aß reduction in rat dose-response studies. Thus, compound 26 may be useful in testing the amyloid hypothesis of Alzheimer's disease.

40 Hz Auditory Steady-State Response Is a Pharmacodynamic Biomarker for Cortical NMDA Receptors.

Schizophrenia patients exhibit dysfunctional gamma oscillations in response to simple auditory stimuli or more complex cognitive tasks, a phenomenon explained by reduced NMDA transmission within inhibitory/excitatory cortical networks. Indeed, a simple steady-state auditory click stimulation paradigm at gamma frequency (~40 Hz) has been reproducibly shown to reduce entrainment as measured by electroencephalography (EEG) in patients. However, some investigators have reported increased phase locking factor (PLF) and power in response to 40 Hz auditory stimulus in patients. Interestingly, preclinical literature also reflects this contradiction. We investigated whether a graded deficiency in NMDA transmission can account for such disparate findings by administering subanesthetic ketamine (1-30 mg/kg, i.v.) or vehicle to conscious rats (n=12) and testing their EEG entrainment to 40 Hz click stimuli at various time points (~7-62 min after treatment). In separate cohorts, we examined in vivo NMDA channel occupancy and tissue exposure to contextualize ketamine effects. We report a robust inverse relationship between PLF and NMDA occupancy 7 min after dosing. Moreover, ketamine could produce inhibition or disinhibition of the 40 Hz response in a temporally dynamic manner. These results provide for the first time empirical data to understand how cortical NMDA transmission deficit may lead to opposite modulation of the auditory steady-state response (ASSR). Importantly, our findings posit that 40 Hz ASSR is a pharmacodynamic biomarker for cortical NMDA function that is also robustly translatable. Besides schizophrenia, such a functional biomarker may be of value to neuropsychiatric disorders like bipolar and autism spectrum where 40 Hz ASSR deficits have been documented.

Passive immunization with phospho-tau antibodies reduces tau pathology and functional deficits in two distinct mouse tauopathy models.

In Alzheimer's disease (AD), an extensive accumulation of extracellular amyloid plaques and intraneuronal tau tangles, along with neuronal loss, is evident in distinct brain regions. Staging of tau pathology by postmortem analysis of AD subjects suggests a sequence of initiation and subsequent spread of neurofibrillary tau tangles along defined brain anatomical pathways. Further, the severity of cognitive deficits correlates with the degree and extent of tau pathology. In this study, we demonstrate that phospho-tau (p-tau) antibodies, PHF6 and PHF13, can prevent the induction of tau pathology in primary neuron cultures. The impact of passive immunotherapy on the formation and spread of tau pathology, as well as functional deficits, was subsequently evaluated with these antibodies in two distinct transgenic mouse tauopathy models. The rTg4510 transgenic mouse is characterized by inducible over-expression of P301L mutant tau, and exhibits robust age-dependent brain tau pathology. Systemic treatment with PHF6 and PHF13 from 3 to 6 months of age led to a significant decline in brain and CSF p-tau levels. In a second model, injection of preformed tau fibrils (PFFs) comprised of recombinant tau protein encompassing the microtubule-repeat domains into the cortex and hippocampus of young P301S mutant tau over-expressing mice (PS19) led to robust tau pathology on the ipsilateral side with evidence of spread to distant sites, including the contralateral hippocampus and bilateral entorhinal cortex 4 weeks post-injection. Systemic treatment with PHF13 led to a significant decline in the spread of tau pathology in this model. The reduction in tau species after p-tau antibody treatment was associated with an improvement in novel-object recognition memory test in both models. These studies provide evidence supporting the use of tau immunotherapy as a potential treatment option for AD and other tauopathies.