Alka Shrikhande

Inhibition of the striatum-enriched phosphodiesterase PDE10A: a novel approach to the treatment of psychosis.

Phosphodiesterase 10A (PDE10A) is a recently identified cyclic nucleotide phosphodiesterase expressed primarily in dopaminoreceptive medium spiny neurons of the striatum. We report that papaverine is a potent, specific inhibitor of PDE10A and use this compound to explore the role of PDE10A in regulating striatal function. Papaverine administration produces an increase in striatal tissue levels of cGMP and an increase in extracellular cAMP measured by microdialysis. These cyclic nucleotide changes are accompanied by increases in the phosphorylation of CREB and ERK, downstream markers of neuronal activation. In rats, papaverine potentiates haloperidol-induced catalepsy, consistent with the hypothesis that inhibition of PDE10A can increase striatal output and prompting a further evaluation of papaverine in models predictive of antipsychotic activity. Papaverine is found to inhibit conditioned avoidance responding in rats and mice and to inhibit PCP- and amphetamine-stimulated locomotor activity in rats. The effects of papaverine on striatal cGMP and CREB and ERK phosphorylation, as well as on conditioned avoidance responding, were absent in PDE10A knockout mice, indicating that the effects of the compound are the result of PDE10A inhibition. These results indicate that PDE10A regulates the activation of striatal medium spiny neurons through effects on cAMP- and cGMP-dependent signaling cascades. Furthermore, the present results demonstrate that papaverine has efficacy in behavioral models predictive of antipsychotic activity. Thus, inhibition of PDE10A may represent a novel approach to the treatment of psychosis.

Pre-clinical properties of the α4β2 nicotinic acetylcholine receptor partial agonists varenicline, cytisine and dianicline translate to clinical efficacy for nicotine dependence

Background and purpose:  Smoking cessation trials with three high‐affinity partial agonists of α4β2 neuronal nicotinic acetylcholine receptors (nAChRs) have demonstrated differences in their clinical efficacy. This work examines the origin of the differences by taking into account brain exposure and pharmacological effects at human α4β2 nAChRs.

Varenicline has antidepressant-like activity in the forced swim test and augments sertraline's effect.

Varenicline, an alpha4beta2 nicotinic acetylcholine receptor partial agonist developed as a smoking cessation aid, showed antidepressant-like activity in the forced swim test in two mouse strains. In addition, a low varenicline dose significantly enhanced the effects of moderately active doses of the selective serotonin reuptake inhibitor sertraline. These findings are consistent with the notion that reducing alpha4beta2 nicotinic acetylcholine receptor activity either by antagonists or by partial agonists that can partially activate or desensitize acetylcholine receptors is associated with antidepressant-like properties. These data suggest that varenicline may have antidepressant potential and can, when combined, augment antidepressant responses of selective serotonin reuptake inhibitors.

Discovery of 4-(5-Methyloxazolo[4,5-b]pyridin-2-yl)-1,4-diazabicyclo[3.2.2]nonane (CP-810,123), a Novel α7 Nicotinic Acetylcholine Receptor Agonist for the Treatment of Cognitive Disorders in Schizophrenia: Synthesis, SAR Development, and in Vivo Efficacy in Cognition Models

A novel alpha 7 nAChR agonist, 4-(5-methyloxazolo[4,5-b]pyridin-2-yl)-1,4-diazabicyclo[3.2.2]nonane (24, CP-810,123), has been identified as a potential treatment for cognitive deficits associated with psychiatric or neurological conditions including schizophrenia and Alzheimers disease. Compound 24 is a potent and selective compound with excellent pharmaceutical properties. In rodent, the compound displays high oral bioavailability and excellent brain penetration affording high levels of receptor occupancy and in vivo efficacy in auditory sensory gating and novel object recognition. The structural diversity of this compound and its preclinical in vitro and in vivo package support the hypothesis that alpha 7 nAChR agonists may have potential as a pharmacotherapy for the treatment of cognitive deficits in schizophrenia.

High-Content Screening for Compounds That Affect mtDNA-Encoded Protein Levels in Eukaryotic Cells

Compounds that interfere with the synthesis of either mitochondrial DNA or mtDNA-encoded proteins reduce the levels of 13 proteins essential for oxidative phosphorylation, leading to a decrease in mitochondrial adenosine triphosphate (ATP) production. Toxicity caused by these compounds is seldom identified in 24- to 72-h cytotoxicity assays due to the low turnover rates of both mtDNA and mtDNA-encoded proteins. To address this problem, the authors developed a 96-well format, high-content screening (HCS) assay that measures, in eukaryotic cells, the level of Complex IV–subunit 1, an mtDNA-encoded protein synthesized on mitochondrial ribosomes, and the level of Complex V–α subunit, a nuclear DNA-encoded protein synthesized on cytosolic ribosomes. The effect of several antibiotics and antiretrovirals on these 2 proteins was assessed, in transformed human liver epithelial cells, 6 days after compound treatment. The results confirmed effects of drugs known to reduce mtDNA-encoded protein levels and also revealed novel information showing that several fluoroquinolones and a macrolide, josamycin, impaired expression of mtDNA-encoded proteins. The HCS assay was robust with an average Z′ factor of 0.62. The assay enables large-scale screening of compounds to identify those that potentially affect mtDNA-encoded protein levels and can be implemented within a screening paradigm to minimize compound attrition.

Synthesis and SAR studies of 1,4-diazabicyclo[3.2.2]nonane phenyl carbamates – subtype selective, high affinity α7 nicotinic acetylcholine receptor agonists

The synthesis and SAR studies about the bicyclic amine, carbamate linker and aromatic ring of a 1,4-diazabicyclo[3.2.2]nonane phenyl carbamate series of alpha7 nAChR agonists is described. The development of the medicinal chemistry strategy and SAR which led to the identification of 5 and 7aa as subtype selective, high affinity alpha7 agonists as excellent leads for further evaluation is discussed, along with key physicochemical and pharmacokinetic data highlighting their lead potential.

A novel series of [3.2.1] azabicyclic biaryl ethers as α3β4 and α6/4β4 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.