Functional Coupling of K+-Cl- Cotransporter (KCC) to GABA-Gated Cl- Channels in the Central Nervous System of Drosophila melanogaster Leads to Altered Drug Sensitivities.

GABAergic signaling is the cornerstone for fast synaptic inhibition of neural signaling in arthropods and mammals and is the molecular target for insecticides and pharmaceuticals, respectively. The K+-Cl- cotransporter (KCC) is the primary mechanism by which mature neurons maintain low intracellular Cl- concentration, yet the fundamental physiology, comparative physiology, and toxicological relevance of insect KCC is understudied. Considering this, we employed electrophysiological, genetic, and pharmacological methods to characterize the physiological underpinnings of KCC function to the Drosophila CNS. Our data show that genetic ablation or pharmacological inhibition of KCC results in an increased spike discharge frequency and significantly ( P < 0.05) reduces the CNS sensitivity to γ-aminobutyric acid (GABA). Further, simultaneous inhibition of KCC and ligand-gated chloride channel (LGCC) complex results in a significant ( P < 0.001) increase in CNS spontaneous activity over baseline firing rates that supports functional coupling of KCC to LGCC function. Interestingly, 75% reduction in KCC mRNA did not alter basal neurotransmission levels indicating that only a fraction of the KCC population is required to maintain the Cl- ionic gradient when at rest, but prolonged synaptic activity increases the threshold for GABA-mediated inhibition and reduces nerve sensitivity to GABA. These data expand current knowledge regarding the physiological role of KCC in a model insect and provides the necessary foundation to develop KCC as a novel biochemical target of insecticides, as well as complements existing research to provide a holistic understanding of the plasticity in mammalian health and disease.

Inhibitors of 7-Dehydrocholesterol Reductase: Screening of a Collection of Pharmacologically Active Compounds in Neuro2a Cells.

A small library of pharmacologically active compounds (the NIH Clinical Collection) was assayed in Neuro2a cells to determine their effect on the last step in the biosynthesis of cholesterol, the transformation of 7-dehydrocholesterol (7-DHC) to cholesterol promoted by 7-dehydrocholesterol reductase, DHCR7. Of some 727 compounds in the NIH Clinical Collection, over 30 compounds significantly increased 7-DHC in Neuro2a cells when assayed at 1 µM. Active compounds that increased 7-DHC with a Z-score of +3 or greater generally gave rise to modest decreases in desmosterol and increases in lanosterol levels. Among the most active compounds identified in the library were the antipsychotic, antidepressant, and anxiolytic compounds that included perospirone, nefazodone, haloperidol, aripiprazole, trazodone, and buspirone. Fluoxetine and risperidone were also active at 1 µM, and another 10 compounds in this class of pharmaceuticals were identified in the screen at concentrations of 10 µM. Increased levels of 7-DHC are associated with Smith-Lemli-Opitz syndrome (SLOS), a human condition that results from a mutation in the gene that encodes DHCR7. The SLOS phenotype includes neurological deficits and congenital malformations, and it is linked to a higher incidence of autism spectrum disorder. The significance of the current study is that it identifies common pharmacological compounds that may induce a biochemical presentation similar to SLOS. Little is known about the side effects of elevated 7-DHC postdevelopmentally, and the elevated 7-DHC that results from exposure to these compounds may also be a confounder in the diagnosis of SLOS.

Discovery of potent and selective GIRK1/2 modulators via 'molecular switches' within a series of 1-(3-cyclopropyl-1-phenyl-1H-pyrazol-5-yl)ureas.

This Letter describes the on-going SAR efforts based on ML297, a potent, efficacious and selective GIRK1/2 activator (∼ 10-fold vs GIRK1/4 and inactive on GIRK2/3) via an iterative parallel synthesis approach. The chemical optimization at the 3-position of pyrazole within ML297 indicated that various functionalized 3-cyclopropyl moieties modulated GIRK pharmacology between inhibitor/activator within a series of 1-(3-cyclopropyl-1-phenyl-1H-pyrazol-5-yl)ureas. Importantly, novel 'molecular switches' that modulated the mode of pharmacology from inhibitor to activator was discovered on both the 3-cyclopropyl and N-phenyl moiety of the pyrazole core, providing the first highly selective GIRK1/2 activator.

Development and validation of fluorescence-based and automated patch clamp-based functional assays for the inward rectifier potassium channel Kir4.1.

The inward rectifier potassium (Kir) channel Kir4.1 plays essential roles in modulation of neurotransmission and renal sodium transport and may represent a novel drug target for temporal lobe epilepsy and hypertension. The molecular pharmacology of Kir4.1 is limited to neurological drugs, such as fluoxetine (Prozac(©)), exhibiting weak and nonspecific activity toward the channel. The development of potent and selective small-molecule probes would provide critically needed tools for exploring the integrative physiology and therapeutic potential of Kir4.1. A fluorescence-based thallium (Tl(+)) flux assay that utilizes a tetracycline-inducible T-Rex-HEK293-Kir4.1 cell line to enable high-throughput screening (HTS) of small-molecule libraries was developed. The assay is dimethyl sulfoxide tolerant and exhibits robust screening statistics (Z'=0.75±0.06). A pilot screen of 3,655 small molecules and lipids revealed 16 Kir4.1 inhibitors (0.4% hit rate). 3,3-Diphenyl-N-(1-phenylethyl)propan-1-amine, termed VU717, inhibits Kir4.1-mediated thallium flux with an IC50 of ∼6 µM. An automated patch clamp assay using the IonFlux HT workbench was developed to facilitate compound characterization. Leak-subtracted ensemble "loose patch" recordings revealed robust tetracycline-inducible and Kir4.1 currents that were inhibited by fluoxetine (IC50=10 µM), VU717 (IC50=6 µM), and structurally related calcium channel blocker prenylamine (IC50=6 µM). Finally, we demonstrate that VU717 inhibits Kir4.1 channel activity in cultured rat astrocytes, providing proof-of-concept that the Tl(+) flux and IonFlux HT assays can enable the discovery of antagonists that are active against native Kir4.1 channels.

ML297 (VU0456810), the first potent and selective activator of the GIRK potassium channel, displays antiepileptic properties in mice.

The G-protein activated, inward-rectifying potassium (K(+)) channels, "GIRKs", are a family of ion channels (Kir3.1-Kir3.4) that has been the focus of intense research interest for nearly two decades. GIRKs are comprised of various homo- and heterotetrameric combinations of four different subunits. These subunits are expressed in different combinations in a variety of regions throughout the central nervous system and in the periphery. The body of GIRK research implicates GIRK in processes as diverse as controlling heart rhythm, to effects on reward/addiction, to modulation of response to analgesics. Despite years of GIRK research, very few tools exist to selectively modulate GIRK channels' activity and until now no tools existed that potently and selectively activated GIRKs. Here we report the development and characterization of the first truly potent, effective, and selective GIRK activator, ML297 (VU0456810). We further demonstrate that ML297 is active in two in vivo models of epilepsy, a disease where up to 40% of patients remain with symptoms refractory to present treatments. The development of ML297 represents a truly significant advancement in our ability to selectively probe GIRK's role in physiology as well as providing the first tool for beginning to understand GIRK's potential as a target for a diversity of therapeutic indications.

Development of a high throughput screen for allosteric modulators of melanocortin-4 receptor signaling using a real time cAMP assay.

The melanocortin MC(4) receptor is a potential target for the development of drugs for both obesity and cachexia. Melanocortin MC(4) receptor ligands known thus far are orthosteric agonists or antagonists, however the agonists, in particular, have generally exhibited unwanted side effects. For some receptors, allosteric modulators are expected to reduce side-effect profiles. To identify allosteric modulators of the melanocortin MC(4) receptor, we created HEK293 cell lines coexpressing the human melanocortin MC(4) receptor and a modified luciferase-based cAMP sensor. Monitoring luminescence as a readout of real-time intracellular cAMP concentration, we demonstrate that this cell line is able to report melanocortin agonist responses, as well as inverse agonist response to the physiological AgRP peptide. Based on the MC4R-GLO cell line, we developed an assay that was shown to meet HTS standards (Z'=0.50). A pilot screen run on the Microsource Spectrum compound library (n=2000) successfully identified 62 positive modulators. This screen identified predicted families of compounds: ß(2)AR agonists - the ß(2)AR being endogenously expressed in HEK293 cells, an adenylyl cyclase activator and finally a distribution of phosphodiesterase (PDE) inhibitors well characterized or recently identified. In this last category, we identified a structural family of coumarin-derived compounds (imperatorin, osthol and prenyletin), along with deracoxib, a drug in veterinary use for its COX2 inhibitory properties. This latter finding unveiled a new off-target mechanism of action for deracoxib as a PDE inhibitor. Overall, these data are the first report of a HTS for allosteric modulators for a Gs protein coupled receptor.

Identification and optimization of small molecules that restore E-cadherin expression and reduce invasion in colorectal carcinoma cells.

E-cadherin is a transmembrane protein that maintains intercellular contacts and cell polarity in epithelial tissue. The down-regulation of E-cadherin contributes to the induction of the epithelial-to-mesenchymal transition (EMT), resulting in an increased potential for cellular invasion of surrounding tissues and entry into the bloodstream. Loss of E-cadherin has been observed in a variety of human tumors as a result of somatic mutations, chromosomal deletions, silencing of the CDH1 gene promoter, and proteolytic cleavage. To date, no compounds directly targeting E-cadherin restoration have been developed. Here, we report the development and use of a novel high-throughput immunofluorescent screen to discover lead compounds that restore E-cadherin expression in the SW620 colon adenocarcinoma cell line. We confirmed restoration of E-cadherin using immunofluorescent microscopy and were able to determine the EC(50) for selected compounds using an optimized In-Cell Western assay. The profiled compounds were also shown to have a minimal effect on cell proliferation but did decrease cellular invasion. We have also conducted preliminary investigations to elucidate a discrete molecular target to account for the phenotypic behavior of these small molecules and have noted a modest increase in E-cadherin mRNA transcripts, and RNA-Seq analysis demonstrated that potent analogues elicited a 10-fold increase in CDH1 (E-cadherin) gene expression.

A thallium-sensitive, fluorescence-based assay for detecting and characterizing potassium channel modulators in mammalian cells.

Potassium channels have been identified as targets for a large number of therapeutic indications. The ability to use a high-throughput functional assay for the detection and characterization of small-molecule modulators of potassium channels is very desirable. However, present techniques capable of screening very large chemical libraries are limited in terms of data quality, temporal resolution, ease of use, and requirements for specialized instrumentation. To address these issues, the authors have developed a fluorescence-based thallium flux assay. This assay is capable of detecting modulators of both voltage and ligand-gated potassium channels expressed in mammalian cells. The thallium flux assay can use instruments standard to most high-throughput screening laboratories, and using such equipment has been successfully employed to screen large chemical libraries consisting of hundreds of thousands of compounds.