Peripheral Administration of a Long-Acting Peptide Oxytocin Receptor Agonist Inhibits Fear-Induced Freezing.

Oxytocin (OT) modulates the expression of social and emotional behaviors and consequently has been proposed as a pharmacologic treatment of psychiatric diseases, including autism spectrum disorders and schizophrenia; however, endogenous OT has a short half-life in plasma and poor permeability across the blood-brain barrier. Recent efforts have focused on the development of novel drug delivery methods to enhance brain penetration, but few efforts have aimed at improving its half-life. To explore the behavioral efficacy of an OT analog with enhanced plasma stability, we developed PF-06655075 (PF1), a novel non-brain-penetrant OT receptor agonist with increased selectivity for the OT receptor and significantly increased pharmacokinetic stability. PF-06478939 was generated with only increased stability to disambiguate changes to selectivity versus stability. The efficacy of these compounds in evoking behavioral effects was tested in a conditioned fear paradigm. Both central and peripheral administration of PF1 inhibited freezing in response to a conditioned fear stimulus. Peripheral administration of PF1 resulted in a sustained level of plasma concentrations for greater than 20 hours but no detectable accumulation in brain tissue, suggesting that plasma or cerebrospinal fluid exposure was sufficient to evoke behavioral effects. Behavioral efficacy of peripherally administered OT receptor agonists on conditioned fear response opens the door to potential peripheral mechanisms in other behavioral paradigms, whether they are mediated by direct peripheral activation or feed-forward responses. Compound PF1 is freely available as a tool compound to further explore the role of peripheral OT in behavioral response.

Phosphodiesterase 9A regulates central cGMP and modulates responses to cholinergic and monoaminergic perturbation in vivo.

Cyclic nucleotides are critical regulators of synaptic plasticity and participate in requisite signaling cascades implicated across multiple neurotransmitter systems. Phosphodiesterase 9A (PDE9A) is a high-affinity, cGMP-specific enzyme widely expressed in the rodent central nervous system. In the current study, we observed neuronal staining with antibodies raised against PDE9A protein in human cortex, cerebellum, and subiculum. We have also developed several potent, selective, and brain-penetrant PDE9A inhibitors and used them to probe the function of PDE9A in vivo. Administration of these compounds to animals led to dose-dependent accumulation of cGMP in brain tissue and cerebrospinal fluid, producing a range of biological effects that implied functional significance for PDE9A-regulated cGMP in dopaminergic, cholinergic, and serotonergic neurotransmission and were consistent with the widespread distribution of PDE9A. In vivo effects of PDE9A inhibition included reversal of the respective disruptions of working memory by ketamine, episodic and spatial memory by scopolamine, and auditory gating by amphetamine, as well as potentiation of risperidone-induced improvements in sensorimotor gating and reversal of the stereotypic scratching response to the hallucinogenic 5-hydroxytryptamine 2A agonist mescaline. The results suggested a role for PDE9A in the regulation of monoaminergic circuitry associated with sensory processing and memory. Thus, PDE9A activity regulates neuronal cGMP signaling downstream of multiple neurotransmitter systems, and inhibition of PDE9A may provide therapeutic benefits in psychiatric and neurodegenerative diseases promoted by the dysfunction of these diverse neurotransmitter systems.

A novel series of [3.2.1] azabicyclic biaryl ethers as alpha3beta4 and alpha6/4beta4 nicotinic receptor agonists.

We report the synthesis of a series of [3.2.1]azabicyclic biaryl ethers as selective agonists of alpha3- and alpha6-containing nicotinic receptors. In particular, compound 17a from this series is a potent alpha3beta4 and alpha6/4beta4 receptor agonist in terms of both binding and functional activity. Compound 17a also shows potent in vivo activity in CNS-mediated animal models that are sensitive to antipsychotic drugs. Compound 17a may thus be a useful tool for studying the role of alpha3beta4 and alpha6/4beta4 nicotinic receptors in CNS pharmacology.

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.

Dopamine D3/D2 Receptor Antagonist PF-4363467 Attenuates Opioid Drug-Seeking Behavior without Concomitant D2 Side Effects.

Dopamine receptor antagonism is a compelling molecular target for the treatment of a range of psychiatric disorders, including substance use disorders. From our corporate compound file, we identified a structurally unique D3 receptor (D3R) antagonist scaffold, 1. Through a hybrid approach, we merged key pharmacophore elements from 1 and D3 agonist 2 to yield the novel D3R/D2R antagonist PF-4363467 (3). Compound 3 was designed to possess CNS drug-like properties as defined by its CNS MPO desirability score (≥4/6). In addition to good physicochemical properties, 3 exhibited low nanomolar affinity for the D3R (D3 Ki = 3.1 nM), good subtype selectivity over D2R (D2 Ki = 692 nM), and high selectivity for D3R versus other biogenic amine receptors. In vivo, 3 dose-dependently attenuated opioid self-administration and opioid drug-seeking behavior in a rat operant reinstatement model using animals trained to self-administer fentanyl. Further, traditional extrapyramidal symptoms (EPS), adverse side effects arising from D2R antagonism, were not observed despite high D2 receptor occupancy (RO) in rodents, suggesting that compound 3 has a unique in vivo profile. Collectively, our data support further investigation of dual D3R and D2R antagonists for the treatment of drug addiction.

Pharmacological disruption of mouse social approach behavior: relevance to negative symptoms of schizophrenia.

Social withdrawal is one of several negative symptoms of schizophrenia, all of which are poorly treated by current therapies. One challenge in developing agents with efficacy against negative symptoms is the lack of suitable preclinical models. The social approach test was used as the basis for developing an assay to test emerging therapies for negative symptoms. NMDA antagonists and dopamine agonists have been used extensively to produce or disrupt behaviors thought to be rodent correlates of positive and cognitive symptoms of schizophrenia. The aim of these studies was to determine whether sociability of mice in the 3-chamber social approach test could be disrupted and whether this paradigm could have utility in predicting efficacy against negative symptoms. The criteria for such a model were: a lack of response to antipsychotics and attenuation by agents such as the glycine agonist, d-cycloserine, which has been shown to possess clinical efficacy against negative symptoms. Administration of the NMDA antagonists MK-801, PCP, or ketamine did not disrupt sociability. In contrast, Grin1 hypomorph mice displayed a social deficit which was not reversed by atypical antipsychotics or d-serine. d-Amphetamine disrupted sociability without stimulating locomotor activity and its effect was not reversed by antipsychotics. The GABAA inverse agonist, FG-7142, reduced sociability and this was reversed by the GABAA antagonist, flumazenil and dcycloserine, but not by clozapine, or the GABAA benzodiazepine anxiolytic, alprazolam. Based on our criteria, the GABAA model warrants further evaluation to confirm that this paradigm has utility as a preclinical model for predicting efficacy against negative symptoms of schizophrenia.

Modulation of NMDA receptor function by inhibition of D-amino acid oxidase in rodent brain.

Observations that N-Methyl-D-Aspartate (NMDA) antagonists produce symptoms in humans that are similar to those seen in schizophrenia have led to the current hypothesis that schizophrenia might result from NMDA receptor hypofunction. Inhibition of D-amino acid oxidase (DAAO), the enzyme responsible for degradation of D-serine, should lead to increased levels of this co-agonist at the NMDA receptor, and thereby provide a therapeutic approach to schizophrenia. We have profiled some of the preclinical biochemical, electrophysiological, and behavioral consequences of administering potent and selective inhibitors of DAAO to rodents to begin to test this hypothesis. Inhibition of DAAO activity resulted in a significant dose and time dependent increase in D-serine only in the cerebellum, although a time delay was observed between peak plasma or brain drug concentration and cerebellum D-serine response. Pharmacokinetic/pharmacodynamic (PK/PD) modeling employing a mechanism-based indirect response model was used to characterize the correlation between free brain drug concentration and D-serine accumulation. DAAO inhibitors had little or no activity in rodent models considered predictive for antipsychotic activity. The inhibitors did, however, affect cortical activity in the Mescaline-Induced Scratching model, produced a modest but significant increase in NMDA receptor-mediated synaptic currents in primary neuronal cultures from rat hippocampus, and resulted in a significant increase in evoked hippocampal theta rhythm, an in vivo electrophysiological model of hippocampal activity. These findings demonstrate that although DAAO inhibition did not cause a measurable increase in D-serine in forebrain, it did affect hippocampal and cortical activity, possibly through augmentation of NMDA receptor-mediated currents.

Preclinical pharmacology of the alpha4beta2 nAChR partial agonist varenicline related to effects on reward, mood and cognition.

The pharmacological properties and pharmacokinetic profile of the alpha4beta2 nicotinic acetylcholine receptor (nAChR) partial agonist varenicline provide an advantageous combination of free brain levels and functional potencies at the target receptor that for a large part explain its efficacy as a smoking cessation aid. Since alpha4beta2 and other nAChR subtypes play important roles in mediating central processes that control reward, mood, cognition and attention, there is interest in examining the effects of selective nAChR ligands such as varenicline in preclinical animal models that assess these behaviors. Here we describe results from studies on varenicline's effects in animal models of addiction, depression, cognition and attention and discuss these in the context of recently published preclinical and preliminary clinical studies that collected data on varenicline's effects on mood, cognition and alcohol abuse disorder. Taken together, the preclinical and the limited clinical data show beneficial effects of varenicline, but further clinical studies are needed to evaluate whether the preclinical effects observed in animal models are translatable to the clinic.