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Noel Southall, Ph.D.
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Recent Publications:
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PLoS Biology
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COPI Complex Is a Regulator of Lipid Homeostasis
Beller M, Sztalryd C, Southall N, Bell M, Jäckle H, Auld DS, Oliver B
Lipid droplets are ubiquitous triglyceride and sterol ester storage organelles required for energy storage homeostasis and biosynthesis. Although little is known about lipid droplet formation and regulation, it is clear that members of the PAT (perilipin, adipocyte differentiation related protein, tail interacting protein of 47 kDa) protein family coat the droplet surface and mediate interactions with lipases that remobilize the stored lipids. We identified key Drosophila candidate genes for lipid droplet regulation by RNA interference (RNAi) screening with an image segmentation-based optical read-out system, and show that these regulatory functions are conserved in the mouse. Those include the vesicle-mediated Coat Protein Complex I (COPI) transport complex, which is required for limiting lipid storage. We found that COPI components regulate the PAT protein composition at the lipid droplet surface, and promote the association of adipocyte triglyceride lipase (ATGL) with the lipid droplet surface to mediate lipolysis. Two compounds known to inhibit COPI function, Exo1 and Brefeldin A, phenocopy COPI knockdowns. Furthermore, RNAi inhibition of ATGL and simultaneous drug treatment indicate that COPI and ATGL function in the same pathway. These data indicate that the COPI complex is an evolutionarily conserved regulator of lipid homeostasis, and highlight an interaction between vesicle transport systems and lipid droplets.
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Journal of Biomolecular Screening
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A Cell-Based PDE4 Assay in 1536-Well Plate Format for High-Throughput Screening.
Titus SA, Xiao L, Southall N, Lu J, Inglese J, Brasch M, Austin CP, Zheng W.
The cyclic nucleotide phosphodiesterases (PDEs) are intracellular enzymes that catalyze the hydrolysis of 3,'5'-cyclic nucleotides, such as cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), to their corresponding 5'nucleotide monophosphates. These enzymes play an important role in controlling cellular concentrations of cyclic nucleotides and thus regulate a variety of cellular signaling events. PDEs are emerging as drug targets for several diseases, including asthma, cardiovascular disease, attention-deficit hyperactivity disorder, Parkinson's disease, and Alzheimer's disease. Although biochemical assays with purified recombinant PDE enzymes and cAMP or cGMP substrate are commonly used for compound screening, cell-based assays would provide a better assessment of compound activity in a more physiological context. The authors report the development and validation of a new cell-based PDE4 assay using a constitutively active G-protein-coupled receptor as a driving force for cAMP production and a cyclic nucleotide-gated cation channel as a biosensor in 1536-well plates.
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Current Chemical Genomics
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Comparison on Functional Assays for Gq-Coupled GPCRs by Measuring Inositol Monophospate-1 and Intracellular Calcium in 1536-Well Plate Format
Liu K, Titus SA, Southall N, Zhu P, Inglese J, Austin CP, Zheng w.
Cell-based functional assays used for compound screening and lead optimization play an important role in drug discovery for G-protein coupled receptors (GPCRs). Cell-based assays can define the role of a compound as an agonist, antagonist or inverse agonist and can provide detailed information about the potency and efficacy of a compound. In addition, cell-based screens can be used to identify allosteric modulators that interact with sites other than the binding site of the endogenous ligand. Intracellular calcium assays which use a fluorescent calcium binding dye (such as Fluo-3, Fluo-4 or Fura-2) have been used in compound screening campaigns to measure the activity of Gq-coupled GPCRs. However, such screening methodologies require a special instrumentation to record the rapid change in intracellular free calcium concentration over time. The radioactive inositol 1,4,5- triphosphate (IP3) assay measures 3H-inositol incorporation and is another traditional assay for the assessment of Gq-coupled GPCR activity, but it is not suitable for screening of large size compound collections because it requires a cell wash step and generates radioactive waste. To avoid these limitations, we have optimized and miniaturized a TR-FRET based IP-One assay that measures inositol monophosphate in a 1536-well plate format. This assay is homogenous, non-radioactive and does not require a kinetic readout. It has been tested with the cell lines expressing M1 acetylcholine, FFAR1, vasopressin V1b, or Neuropeptide S receptors. The activities of antagonists determined in the IP-One assay correlated well with these measured in the intracellular calcium assay while the correlation of agonist activities might vary from cell line to cell line. This IP-One assay offers an alternative method for high throughput screening of Gq-coupled GPCRs without using costly kinetic plate readers.
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Bioorganic & Medicinal Chemistry Letters
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Identification of a potent new chemotype for the selective inhibition of PDE4.
Skoumbourdis AP, Huang R, Southall N, Leister W, Guo V, Cho MH, Inglese J, Nirenberg M, Austin CP, Xia M, Thomas CJ.
A series of substituted 3,6-diphenyl-7H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines were prepared and analyzed as inhibitors of phosphodiesterase 4 (PDE4). Synthesis, structure–activity relationships, and the selectivity of a highly potent analogue against related phosphodiesterase isoforms are presented.
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Chemical Research Toxicology
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Characterization of Diversity in Toxicity Mechanism Using In Vitro Cytotoxicity Assays in Quantitative High Throughput Screening.
Huang R, Southall N, Cho MH, Xia M, Inglese J, Austin CP.
Assessing the potential health risks of environmental chemical compounds is an expensive
undertaking which has motivated the development of new alternatives to traditional in vivo
toxicological testing. One approach is to stage the evaluation, beginning with less expensive and
higher throughput in vitro testing before progressing to more definitive trials. In vitro testing can
be used to generate a hypothesis about a compound's mechanism of action, which can then be
used to design an appropriate in vivo experiment. Here we begin to address the question of how
to design such a battery of in vitro cell-based assays by combining data from two different types
of assays, cell viability and caspase activation, with the aim of elucidating mechanism of action.
Because caspase activation is a transient event during apoptosis, it is not possible to design a
single end-point assay protocol that would identify all instances of compound-induced caspase
activation. Nevertheless, useful information about compound mechanism of action can be
obtained from these assays in combination with cell viability data. Unsupervised clustering in
combination with Dunn's cluster validity index is a robust method for identifying mechanisms of
action without requiring any a priori knowledge about mechanisms of toxicity. The performance
of this clustering method is evaluated by comparing the clustering results against literature
annotations of compound mechanisms.
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Journal of Biomolecular Sciences
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Quantitative High-Throughput Screening Using a Live-Cell cAMP Assay Identifies Small-Molecule Agonists of the TSH Receptor.
Titus S, Neumann S, Zheng W, Southall N, Michael S, Klumpp C, Yasgar A, Shinn P, Thomas CJ, Inglese J, Gershengorn MC, Austin CP.
The thyroid-stimulating hormone (TSH; thyrotropin) receptor belongs to the glycoprotein hormone receptor subfamily of 7transmembrane spanning receptors. TSH receptor (TSHR) is expressed mainly in thyroid follicular cells and is activated by TSH, which regulates the growth and function of thyroid follicular cells. Recombinant TSH is used in diagnostic screens for thyroid cancer, especially in patients after thyroid cancer surgery. Currently, no selective small-molecule agonists of the TSHR are available. To screen for novel TSHR agonists, the authors miniaturized a commercially available cell-based cyclic adenosine 3',5' monophosphate (cAMP) assay into a 1536-well plate format. This assay uses an HEK293 cell line stably transfected with the TSHR coupled to a cyclic nucleotide gated ion channel as a biosensor. From a quantitative high-throughput screen of 73,180 compounds in parallel with a parental cell line (without the TSHR), 276 primary active compounds were identified. The activities of the selected active compounds were further confirmed in an orthogonal homogeneous time-resolved fluorescence cAMP-based assay. Forty-nine compounds in several structural classes have been confirmed as the small-molecule TSHR agonists that will serve as a starting point for chemical optimization and studies of thyroid physiology in health and disease.
PMID: 18216391
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Journal of Medicinal Chemistry
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Characterization of Chemical Libraries for Luciferase Inhibitory Activity.
Auld DS, Southall N, Jadhav A, Johnson RL, Diller D, Simeonov S, Austin CP, Inglese J.
To aid in the interpretation of HTS results derived from luciferase-based assays we used quantitative HTS (qHTS), an approach that defines the concentration-response behavior of each library sample, to profile the ATP-dependent luciferase from Photinus pyralis against >70,000 samples. We found approximately 3% of the library was active, containing only compounds with inhibitory concentration-responses of which 681 (0.9%) exhibited IC50s < 10 uM. Representative compounds were shown to inhibit purified P. pyralis as well as several commercial luciferase-based detection reagents but were found to be largely inactive against Renilla reniformis luciferase. Light attenuation by the samples was also examined and found to be more prominent in the blue-shifted bioluminescence produced by R. reniformas luciferase than with bioluminescence produced by P. pyralis luciferase. We describe the SAR of the luciferase inhibitors and discuss the use of this data in the interpretation of HTS results, and configuration of luciferase-based assays.
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Journal of Medicinal Chemistry
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Fluorescence Spectroscopic Profiling of Compound Libraries.
Simeonov S, Jadhav A, Thomas CJ, Wang Y, Huang R, Southall N, Shinn P, Smith J, Austin CP, Inglese J.
Chromo/fluorophoric properties often accompany the conjugated, aromatic and heterocyclic features of many of the scaffolds and impurities that make up library samples used for high throughput screening (HTS). These properties impart highly variable effects on assay outputs employing optical detection, thus complicating the interpretation of data and leading to false positives and negatives. Here, we report the comprehensive fluorescence profile of >70,000 samples across multiple spectral regions commonly utilized in HTS assays. The quantitative HTS (qHTS) paradigm was utilized to test each sample at seven or more concentration points over a 4-log concentration range in 1536-well format, with raw fluorescence response collected using a CCD-based imager. The resulting output was compared with fluorophore standards to compute a normalized fluorescence response (termed fluorophore-equivalent concentration, FEC) for each sample, concentration, and relevant spectral region. The greatest fraction of fluorescent compounds appeared in the UV-end of the light spectrum, where over 5% of library members matched or exceeded 10 nM FEC of 4-methylumbelliferone and AlexaFluor 350, while approximately 1.8% of the library matched or exceeded 100 nM FEC of these standards. Red-shifting the spectral window by as little as 100 nm was accompanied by a dramatic decrease in autofluorescence. Native compound fluorescence, scaffold overlap with known fluorophores, fluorescent impurities, novel fluorescent compounds, and the ability to discriminate generalities of fluorescent interferences and devise strategies to identify them are discussed.
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Environmental Health Perspectives
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Compound Cytotoxicity Profiling Using Quantitative High-Throughput Screening.
Xia M, Huang R, Witt KL, Southall N, Fostel J, Cho MH, Jadhav A, Smith CS, Inglese J, Portier CJ, Tice RR, Austin CP.
Background: The propensity of compounds to produce adverse health effects in humans is
generally evaluated using animal-based test methods. Such methods can be relatively expensive,
low-throughput, and associated with pain suffered by the treated animals. In addition, differences
in species biology may confound extrapolation to human health effects.
Objective: The U.S. National Toxicology Program and the NIH Chemical Genomics Center are
collaborating to identify a battery of cell-based screens to prioritize compounds for further
toxicological evaluation.
Methods: 1,408 compounds previously tested in one or more traditional toxicological assays
were profiled for cytotoxicity using quantitative high-throughput screening (qHTS) in 13 human
and rodent cell types derived from six common targets of xenobiotic toxicity (liver, blood,
kidney, nerve, lung, skin). Selected cytotoxicants were further tested to define response kinetics.
Results: qHTS of these compounds produced robust and reproducible results which allowed
cross-compound, cross-cell type, and cross-species comparisons. Some compounds were
cytotoxic to all cell types at similar concentrations, while others exhibited species- or cell typespecific
cytotoxicity. Closely related cell types and analogous cell types in human and rodent
frequently showed different patterns of cytotoxicity. Some compounds inducing similar levels of
cytotoxicity showed distinct time-dependence in kinetic studies, consistent with known
mechanisms of toxicity.
Conclusions: The generation of high-quality cytotoxicity data on this large library of known
compounds using qHTS demonstrates the potential of this methodology to profile a much
broader array of assays and compounds, which, in aggregate, may be valuable for prioritizing
compounds for further toxicological evaluation, identifying compounds with particular
mechanisms of action, and potentially predicting in vivo biological response
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Bioorganic and Medicinal Chemistry Letters
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Identification of N-(quinolin-8-yl)benzenesulfonamides as agents capable of down-regulating NFkappaB activity within two separate high-throughput screens of NFkappaB activation.
Xie Y, Deng S, Thomas CJ, Liu Y, Zhang YQ, Rinderspacher A, Huang W, Gong G, Wyler M, Cayanis E, Aulner N, Többen U, Chung C, Pampou S, Southall N, Vidovic D, Schürer S, Branden L, Davis RE, Staudt LM, Inglese J, Austin CP, Landry DW, Smith DH, Auld DS.
We describe here a series of N-(quinolin-8-yl)benzenesulfonamides capable of suppressing the NFkappaB pathway identified from two high-throughput screens run at two centers of the NIH Molecular Libraries Initiative. These small molecules were confirmed in both primary and secondary assays of NFkappaB activation and expanded upon through analogue synthesis. The series exhibited potencies in the cell-based assays at as low as 0.6muM, and several indications suggest that the targeted activity lies within a common region of the NFkappaB pathway.
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ASSAY and Drug Development Technologies
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A cell-based assay for IkappaBalpha stabilization using a two-color dual luciferase-based sensor.
Davis RE, Zhang YQ, Southall N, Staudt LM, Austin CP, Inglese J, Auld DS.
A cell-sensor assay for stabilization of IkappaBalpha was developed in the activated B cell-like diffuse large B-cell lymphoma cell line OCI-Ly3. This cell line expresses known nuclear factor kappaB (NFkappaB) target genes due to high constitutive activity of IkappaB kinase (IKK), which phosphorylates the protein IkappaBalpha leading to proteasomal degradation of IkappaBalpha and activation of NFkappaB. The cell-sensor assay uses green and red light-emitting beetle luciferases, with the green luciferase fused to IkappaBalpha (IkappaBalpha-CBG68) and the red luciferase (CBR) present in its native state. The IkappaBalpha-CBG68 reporter functions as a sensor of IKK and proteasome activity, while CBR serves to normalize for cell number and nonspecific effects. Both reporter constructs were stably integrated and placed under the control of an inducible promoter system, which increased fold responsiveness to inhibitors when assay incubations were performed simultaneous to reporter induction by doxycycline. The assay was miniaturized to a 1,536-well plate format and showed a Z' of 0.6; it was then used to panel 2,677 bioactive compounds by a concentration-response-based screening strategy. The concentration-effect curves for the IkappaBalpha-CBG68 and CBR signals were then used to identify specific stabilizers of IkappaBalpha, such as IKK inhibitors or proteasome inhibitors, which increased the doxycycline-induced rise in IkappaBalpha-CBG68 without affecting the rise in CBR. Known and unexpected inhibitors of NFkappaB signaling were identified from the bioactive collection. We describe here the development and performance of this assay, and discuss the merits of its specific features.
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Journal of Medicinal Chemistry
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Kinase patent space visualization using chemical replacements.
Southall NT, Ajay
Here we present a methodology for characterizing the structure of patented chemical space. This approach identifies those chemical replacements that can connect sets of exemplified compounds in individual patents. Chemists can then search these replacements to help them discover the architecture within their patent space of interest. To demonstrate the utility of such an approach, we characterize a set of kinase inhibitors from patents and literature and find that many companies' patents can be understood to be straightforward modifications of competitors' patents. By reapplying these same chemical themes to other related compound series, novel, biologically active compounds can be discovered.
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Biophysical Chemistry
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Potential of mean force between two hydrophobic solutes in water.
Southall NT, Dill KA.
We study the potential of mean force between two nonpolar solutes in the Mercedes Benz model of water. Using NPT Monte Carlo simulations, we find that the solute size determines the relative preference of two solute molecules to come into contact ('contact minimum') or to be separated by a single layer of water ('solvent-separated minimum'). Larger solutes more strongly prefer the contacting state, while smaller solutes have more tendency to become solvent-separated, particularly in cold water. The thermal driving forces oscillate with solute separation. Contacts are stabilized by entropy, whereas solvent-separated solute pairing is stabilized by enthalpy. The free energy of interaction for small solutes is well-approximated by scaled-particle theory. Copyright 2002 Elsevier Science B.V.
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Journal of the American Chemical Society
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How ions affect the structure of water.
Hribar B, Southall NT, Vlachy V, Dill KA.
We model ion solvation in water. We use the MB model of water, a simple two-dimensional statistical mechanical model in which waters are represented as Lennard-Jones disks having Gaussian hydrogen-bonding arms. We introduce a charge dipole into MB waters. We perform (NPT) Monte Carlo simulations to explore how water molecules are organized around ions and around nonpolar solutes in salt solutions. The model gives good qualitative agreement with experiments, including Jones-Dole viscosity B coefficients, Samoilov and Hirata ion hydration activation energies, ion solvation thermodynamics, and Setschenow coefficients for Hofmeister series ions, which describe the salt concentration dependence of the solubilities of hydrophobic solutes. The two main ideas captured here are (1) that charge densities govern the interactions of ions with water, and (2) that a balance of forces determines water structure: electrostatics (water's dipole interacting with ions) and hydrogen bonding (water interacting with neighboring waters). Small ions (kosmotropes) have high charge densities so they cause strong electrostatic ordering of nearby waters, breaking hydrogen bonds. In contrast, large ions (chaotropes) have low charge densities, and surrounding water molecules are largely hydrogen bonded.
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