Optimization of N'-(arylsulfonyl)pyrazoline-1-carboxamidines by exploiting a novel interaction site in the 5-HT6 antagonistic binding pocket.

The discovery of non-basic N'-(arylsulfonyl)pyrazoline-1-carboxamidines as 5-HT6 antagonists with unique structural features was recently disclosed. Here we describe how this structural class was further developed by addressing an unexplored interaction site of the 5-HT6 receptor. Compound 13 resulting from this effort is a highly potent and selective 5-HT6 antagonist with improved metabolic stability. It is furthermore devoid of hERG affinity. Despite its modest CNS/plasma ratio, a high brain free fraction ensured substantial exposure to allow for rodent cognition studies.

5-HT6 Receptor Antagonists: Potential Efficacy for the Treatment of Cognitive Impairment in Schizophrenia.

5-hydroxytryptamine6 receptor (5-HT6R) antagonists have shown efficacy in animal models for cognitive impairment in multiple cognitive domains relevant for schizophrenia. Improvements were found with 5-HT6R antagonists in preclinical tests for episodic memory, social cognition, executive function, working memory and several other tests for both learning and memory. In contrast, there is little evidence for efficacy on attention. It will be interesting to further investigate 5-HT6R antagonists in neurodevelopmental animal models which are based on prenatal exposure to specific environmental insults, and are characterized by a high level of face, construct and predictive validity for cognitive impairments associated with schizophrenia. It is also important to do more add-on preclinical studies of 5-HT6 antagonists with antipsychotics. Possible mechanisms of action to improve cognition have been described. 5-HT6R antagonists decrease GABA release and GABAergic interneuron excitability, which subsequently disinhibits glutamate and/or acetylcholine release and results in enhancement of synaptic plasticity. Furthermore, cognition could be improved by 5-HT6R antagonists, because these compounds increase the number of NCAM PSA-immunoreactive neurons in the dendate gyrus, inhibit mTOR and Fyn-tyrosine kinase and interact with DARPP-32. Interestingly, there is increasing preclinical evidence that could support additional benefits of 5-HT6R ligandson comorbid conditions in schizophrenia such as drug abuse, depression, anxiety, obesity andantipsychotic-induced EPS. Finally, we briefly give an overview of the 5-HT6R compounds that are currently in clinical development for the treatment of cognitive impairment in both schizophrenia and Alzheimer's disease.

Biophysical and physicochemical methods differentiate highly ligand-efficient human D-amino acid oxidase inhibitors.

Many early drug research efforts are too reductionist thereby not delivering key parameters such as kinetics and thermodynamics of target-ligand binding. A set of human D-Amino Acid Oxidase (DAAO) inhibitors 1-6 was applied to demonstrate the impact of key biophysical techniques and physicochemical methods in the differentiation of chemical entities that cannot be adequately distinguished on the basis of their normalized potency (ligand efficiency) values. The resulting biophysical and physicochemical data were related to relevant pharmacodynamic and pharmacokinetic properties. Surface Plasmon Resonance data indicated prolonged target-ligand residence times for 5 and 6 as compared to 1-4, based on the observed k(off) values. The Isothermal Titration Calorimetry-derived thermodynamic binding profiles of 1-6 to the DAAO enzyme revealed favorable contributions of both ΔH and ΔS to their ΔG values. Surprisingly, the thermodynamic binding profile of 3 elicited a substantially higher favorable contribution of ΔH to ΔG in comparison with the structurally closely related fused bicyclic acid 4. Molecular dynamics simulations and free energy calculations of 1, 3, and 4 led to novel insights into the thermodynamic properties of the binding process at an atomic level and in the different thermodynamic signatures of 3 and 4. The presented holistic approach is anticipated to facilitate the identification of compounds with best-in-class properties at an early research stage.

N'-(arylsulfonyl)pyrazoline-1-carboxamidines as novel, neutral 5-hydroxytryptamine 6 receptor (5-HT6R) antagonists with unique structural features.

The 5-HT(6) receptor (5-HT(6)R) has been in the spotlight for several years regarding CNS-related diseases. We set out to discover novel, neutral 5-HT(6)R antagonists to improve off-target selectivity compared to basic amine-containing scaffolds dominating the field. High-throughput screening identified the N'-(sulfonyl)pyrazoline-1-carboxamidine scaffold as a promising neutral core for starting hit-to-lead. Medicinal chemistry, molecular modeling, small molecule NMR and X-ray crystallography were subsequently applied to optimize the leads into antagonists (compounds 1-49) displaying high 5-HT(6)R affinity with optimal off-target selectivity. Unique structural features include a pseudoaromatic system and an internal hydrogen bond freezing the bioactive conformation. While physicochemical properties and CNS availability were generally favorable, significant efforts had to be made to improve metabolic stability. The optimized structure 42 is an extremely selective, hERG-free, high-affinity 5-HT(6)R antagonist showing good human in vitro metabolic stability. Rat pharmacokinetic data were sufficiently good to enable further in vivo profiling.

The effects of early maternal deprivation on auditory information processing in adult Wistar rats.

BACKGROUND: There is now ample evidence that schizophrenia is due to an interaction between genetic and (early) environmental factors which disturbs normal development of the central nervous system and ultimately leads to the development of clinical symptoms. Recently, we showed that a single 24-hour period of maternal deprivation of rat pups at postnatal day 9 leads to a disturbance in prepulse inhibition, similar to what is seen in schizophrenia. The present set of experiments was designed to further characterize the information processing deficits of maternally deprived Wistar rats. METHODS: Wistar rats were deprived from their mother for 24 hours on postnatal day 9. At adult age, rats were tested in the acoustic startle paradigm for prepulse inhibition and startle habituation. Rats were also tested in the evoked potentials paradigm for auditory sensory gating. RESULTS: The results show that maternal deprivation led to a reduction in acoustic startle habituation and auditory sensory gating in adult rats. Moreover, maternal deprivation disrupted prepulse inhibition but only when the prepulses were given shortly (50-100 milliseconds) before the startle stimulus. At longer intervals (250-1000 milliseconds), no effect was seen. CONCLUSIONS: The implications for the model and the development of disturbances in information processes are discussed.