Back to the Future of Neuropsychopharmacology.

Disappointments in translating preclinical findings into clinical efficacy have triggered a number of changes in neuroscience drug discovery ranging from investments diverted to other therapeutic areas to reduced reliance on efficacy claims derived from preclinical models. In this chapter, we argue that there are several existing examples that teach us on what needs to be done to improve the success rate. We advocate the reverse engineering approach that shifts the focus from preclinical efforts to "model" human disease states to pharmacodynamic activity as a common denominator in the journey to translate clinically validated phenomena to preclinical level and then back to humans. Combined with the research rigor, openness, and transparency, this reverse engineering approach is well set to bring new effective and safe medications to patients in need.

Optimized pharmacological control over the AAV-Gene-Switch vector for regulable gene therapy.

Gene therapy in its current design is an irreversible process. It cannot be stopped in case of unwanted side effects, nor can expression levels of therapeutics be adjusted to individual patient's needs. Thus, the Gene-Switch (GS) system for pharmacologically regulable neurotrophic factor expression was established for treatment of parkinsonian patients. Mifepristone, the synthetic steroid used to control transgene expression of the GS vector, is an approved clinical drug. However, pharmacokinetics and -dynamics of mifepristone vary considerably between different experimental animal species and depend on age and gender. In humans, but not in any other species, mifepristone binds to a high-affinity plasma carrier protein. We now demonstrate that the formulation of mifepristone can have robust impact on its ability to activate the GS system. Furthermore, we show that a pharmacological booster, ritonavir (Rtv), robustly enhances the pharmacological effect of mifepristone, and allows it to overcome gender- and species-specific pharmacokinetic and -dynamic issues. Most importantly, we demonstrate that the GS vector can be efficiently controlled by mifepristone in the presence of its human plasma carrier protein, α1-acid glycoprotein, in a "humanized" rat model. Thus, we have substantially improved the applicability of the GS vector toward therapeutic use in patients.

Development of a non-human primate model to support CNS translational research: Demonstration with D-amphetamine exposure and dopamine response.

BACKGROUND: Challenges specific to the discovery and development of candidate CNS drugs have led to implementation of various in silico, in vitro and in vivo approaches to improve the odds for commercialization of novel treatments. NEW METHOD: Advances in analytical methodology and microdialysis probe design have enabled development of a non-human primate model capable of measuring concentrations of drugs or endogenous chemicals in brain extracellular fluid (ECF) and cerebrospinal fluid (CSF). Linking these to population modeling reduces animal numbers to support predictive translational sciences in primates. Application to measure D-amphetamine exposure and dopamine response in ECF and CSF demonstrate the approach. RESULTS: Following a 0.1 mg/kg intravenous bolus dose of D-amphetamine, a population approach was used to build a plasma compartmental-based and brain physiologic-based pharmacokinetic (PK) model linking drug concentrations in plasma to brain ECF and CSF concentrations. Dopamine was also measured in brain ECF. The PK model was used to simulate the relationship between D-amphetamine exposure and dopamine response in ECF over a wide dose range. COMPARISONS WITH EXISTING METHODS: Ability to co-sample and measure drug and endogenous substances in blood, brain ECF and/or CSF, coupled with population modeling, provides an in vivo approach to evaluate CNS drug penetration and effect in non-human primates. CONCLUSIONS: A method to measure drug and endogenous neurochemicals in non-human primate brain fluids is demonstrated. Its basis in non-human primates merits improved confidence regarding predictions of drug exposure and target engagement in human CNS.

Development of a Semimechanistic Pharmacokinetic-Pharmacodynamic Model Describing Dextroamphetamine Exposure and Striatal Dopamine Response in Rats and Nonhuman Primates following a Single Dose of Dextroamphetamine.

Acute central nervous system exposure to dextroamphetamine (d-amphetamine) elicits a multitude of effects, including dual action on the dopamine transporter (DAT) to increase extracellular dopamine, and induction of a negative feedback response to limit the dopamine increase. A semimechanistic pharmacokinetic and pharmacodynamic (PK/PD) model with consideration of these multiple effects as a basis was developed. Integrated pharmacokinetics of d-amphetamine in plasma, brain extracellular fluid (ECF) via microdialysis, and cerebrospinal fluid were characterized using a population approach. This PK model was then linked to an indirect-response pharmacodynamic model using as a basis the measurement of extracellular striatal dopamine, also via microdialysis. In both rats and nonhuman primates (NHPs), d-amphetamine stimulation of dopamine outflow (reverse transport) through DAT was primarily responsible for the dose-linear increase in dopamine. As well, in both species a moderator function was needed to account for loss of the dopamine response in the presence of a relatively sustained d-amphetamine ECF exposure, presumptive of an acute tolerance response. PK/PD model structure was consistent between species; however, there was a 10-fold faster return to baseline dopamine in NHPs in response to an acute d-amphetamine challenge. These results suggest preservation from rodents to NHPs regarding the mechanism by which amphetamine increases extracellular dopamine, but a faster system response in NHPs to tolerate this increase. This microdialysis-based PK/PD model suggests greater value in directing preclinical discovery of novel approaches that modify reverse transport stimulation to treat amphetamine abuse. General value regarding insertion of an NHP model in paradigm rodent-to-human translational research is also suggested.

Novel, potent, selective and brain penetrant vasopressin 1b receptor antagonists.

Herein we report the discovery of a novel oxindole-based series of vasopressin 1b (V1b) receptor antagonists. Introducing a substituted piperazine moiety and optimizing the southern and the northern aromatic rings resulted in potent, selective and brain penetrant V1b receptor antagonists. Compound 9c was found to be efficacious in a rat model of anti-depressant activity (3 mg/kg, ip). Interestingly, both moderate terminal half-life and moderate bioavailability could be achieved despite sub-optimal microsomal stability.

Environmental and Pharmacological Modulation of Amphetamine- Induced 50-kHz Ultrasonic Vocalizations in Rats.

Rats emit high-frequency 50-kHz ultrasonic vocalizations (USV) in appetitive situations like social interactions. Drugs of abuse are probably the most potent non-social elicitors of 50-kHz USV, possibly reflecting their euphorigenic properties. Psychostimulants induce the strongest elevation in 50-kHz USV emission, particularly amphetamine (AMPH), either when applied systemically or locally into the nucleus accumbens (Nacc). Emission of AMPH-induced 50-kHz USV depends on test context, such as the presence of conspecifics, and can be manipulated pharmacologically by targeting major neurotransmitter systems, including dopamine (DA), noradrenaline (NA), and serotonin (5-HT), but also protein kinase C (PKC) signaling. Several D1 and D2 receptor antagonists, as well as typical and atypical antipsychotics block the AMPH-induced elevation in 50-kHz USV. Inhibiting D1 and D2 receptors in the Nacc abolishes AMPH-induced 50-kHz USV, indicating a key role for this brain area. NA neurotransmission also regulates AMPH-induced 50-kHz USV emission given that α 1 receptor antagonists and α 2 receptor agonists exert attenuating effects. Supporting the involvement of the 5-HT system, AMPH-induced 50-kHz USV are attenuated by 5-HT2C receptor activation, whereas 5-HT2C receptor antagonism leads to the opposite effect. Finally, treatment with lithium, tamoxifen, and myricitrin was all found to result in a complete abolishment of the AMPH-induced increase in 50-kHz USV, suggesting the involvement of PKC signaling. Neurotransmitter systems involved in AMPH-induced 50-kHz USV emission only partially overlap with other AMPH-induced behaviors like hyperlocomotion. The validity of AMPHinduced 50-kHz USV as a preclinical model for neuropsychiatric disorders is discussed, particularly with relevance to altered drive and mood seen in bipolar disorder.

Affective communication in rodents: serotonin and its modulating role in ultrasonic vocalizations.

Serotonin (5-hydroxytryptamine, 5-HT) is an important modulatory neurotransmitter and functions as a key neurodevelopmental signal in the mammalian brain. 5-HT plays a prominent role in regulating various types of psychological processes and functions, including mood and emotion, particularly anxiety, but also in regulating social behavior. Consequently, the 5-HT system is implicated in various neuropsychiatric disorders, such as anxiety disorders and depression or autism spectrum disorders (ASD), with selective 5-HT reuptake inhibitors being the frontline medication. Mice and rats perceive and emit ultrasonic vocalizations (USV). It is widely believed that the various distinct USV types reflect the animal's affective state, such as anxiety or pleasure. Furthermore, they serve communicative functions, for instance, as alarm calls or social contact calls. Manipulations targeting the 5-HT system alter affective ultrasonic communication in rodents throughout life, probably because of its important role in regulating anxiety and social behavior. Ample evidence indicates the involvement of the 5-HT system in modulating isolation-induced USV in pups. Later in life, the 5-HT system plays a strong modulatory role in the emission of aversive 22-kHz USV in rats. So far, little is known about the role of 5-HT in the production of interaction-induced USV in mice and appetitive 50-kHz USV in rats, although recent findings also suggest a modulatory effect of the 5-HT system. Assessment of rodent USV is a valuable method to investigate mood and emotion, and to enhance our understanding of, and develop novel pharmacological therapies for neuropsychiatric disorders, such as anxiety disorders and depression or ASD.

The Vasopressin 1b Receptor Antagonist A-988315 Blocks Stress Effects on the Retrieval of Object-Recognition Memory.

Stress-induced activation of the hypothalamo-pituitary-adrenocortical (HPA) axis and high circulating glucocorticoid levels are well known to impair the retrieval of memory. Vasopressin can activate the HPA axis by stimulating vasopressin 1b (V1b) receptors located on the pituitary. In the present study, we investigated the effect of A-988315, a selective and highly potent non-peptidergic V1b-receptor antagonist with good pharmacokinetic properties, in blocking stress effects on HPA-axis activity and memory retrieval. To study cognitive performance, male Sprague-Dawley rats were trained on an object-discrimination task during which they could freely explore two identical objects. Memory for the objects and their location was tested 24 h later. A-988315 (20 or 60 mg/kg) or water was administered orally 90 min before retention testing, followed 60 min later by stress of footshock exposure. A-988315 dose-dependently dampened stress-induced increases in corticosterone plasma levels, but did not significantly alter HPA-axis activity of non-stressed control rats. Most importantly, A-988315 administration prevented stress-induced impairment of memory retrieval on both the object-recognition and the object-location tasks. A-988315 did not alter the retention of non-stressed rats and did not influence the total time spent exploring the objects or experimental context in either stressed or non-stressed rats. Thus, these findings indicate that direct antagonism of V1b receptors is an effective treatment to block stress-induced activation of the HPA axis and the consequent impairment of retrieval of different aspects of recognition memory.

Critical involvement of 5-HT2C receptor function in amphetamine-induced 50-kHz ultrasonic vocalizations in rats.

RATIONALE: Rats emit various distinct types of ultrasonic vocalizations (USV), with high-frequency 50-kHz USV typically occurring in appetitive situations being elicited by administering drugs of abuse, most notably amphetamine (AMPH), possibly reflecting drug wanting/craving and/or liking. OBJECTIVES: Because 50-kHz USV emission is, at least in part, dopamine (DA) dependent and 5-HT2C agonists inhibit DA neurotransmission, we hypothesized that AMPH-induced 50-kHz USV can be attenuated by pretreatment with a 5-HT2C agonist. METHODS: In experiments I and II, a dose-response curve for AMPH-induced 50-kHz USV was established, and the partial dependency of AMPH-induced 50-kHz USV on DA neurotransmission was validated by pretreatment with the D2-antagonist eticlopride. In experiment III, rats were pretreated with the 5-HT2C agonist CP 809,101 (0.0, 0.3, 1.0, 3.0, and 10 mg/kg), while in experiment IV, CP 809,101 (3.0 mg/kg), the 5-HT2C antagonist SB 242084 (1.0 mg/kg), or the combination of the two, was applied before AMPH administration (2.0 mg/kg). Finally, in experiment V, rats were treated with SB 242084 (0.0, 0.1, 0.3, and 1.0 mg/kg) only, i.e., in absence of AMPH. RESULTS: The 5-HT2C agonist CP 809,101 dose-dependently blocked AMPH-induced 50-kHz USV, most notably trills, a call subtype that is considered to exclusively reflect a positive affective state, while the 5-HT2C antagonist SB 242084 induced opposite effects. Moreover, SB 242084 induced 50-kHz USV by its own. CONCLUSIONS: 5-HT2C receptors are critically involved in AMPH-induced 50-kHz USV, with 5-HT2C antagonism resulting in a stimulant-like effect. Attenuation of drug wanting/craving and/or liking by coadministration of a 5-HT2C agonist could be a translational pharmacodynamic biomarker.

NOGO-66 receptor deficient mice show slow acquisition of spatial memory task performance.

The Nogo-66 receptor (NgR1) is part of a co-receptor complex on neurons that transmits a signal for inhibition of neurite outgrowth. In addition, NgR1 function has also been related to other disorders such as schizophrenia and Alzheimer's disease. Here, we studied the effect of life-long deletion of NgR1 (ngr(-/-)) in tests for cognition and positive symptoms of schizophrenia. In the water maze, ngr(-/-) mice learned to locate the hidden platform as well as wild type mice, although with slower acquisition. Deletion of NgR1 did not affect amphetamine- or phencyclidine (PCP)-induced hyperactivity, two models of positive symptoms of schizophrenia. Taken together, ngr(-/-) animals show slower acquisition of a spatial learning and memory task.