Analysis of Differential Efficacy and Affinity of GABAA (α1/α2) Selective Modulators.

Selective modulators of the γ-amino butyric acid (GABAA) family of receptors have the potential to treat a range of disease states related to cognition, pain, and anxiety. While the development of various α subunit-selective modulators is currently underway for the treatment of anxiety disorders, a mechanistic understanding of the correlation between their bioactivity and efficacy, based on ligand-target interactions, is currently still lacking. In order to alleviate this situation, in the current study we have analyzed, using ligand- and structure-based methods, a data set of 5440 GABAA modulators. The Spearman correlation (ρ) between binding activity and efficacy of compounds was calculated to be 0.008 and 0.31 against the α1 and α2 subunits of GABA receptor, respectively; in other words, the compounds had little diversity in structure and bioactivity, but they differed significantly in efficacy. Two compounds were selected as a case study for detailed interaction analysis due to the small difference in their structures and affinities (ΔpKi(comp1_α1 - comp2_α1) = 0.45 log units, ΔpKi(comp1_α2 - comp2_α2) = 0 log units) as compared to larger relative efficacies (ΔRE(comp1_α1 - comp2_α1) = 1.03, ΔRE(comp1_α2 - comp2_α2) = 0.21). Docking analysis suggested that His-101 is involved in a characteristic interaction of the α1 receptor with both compounds 1 and 2. Residues such as Phe-77, Thr-142, Asn-60, and Arg-144 of the γ chain of the α1γ2 complex also showed interactions with heterocyclic rings of both compounds 1 and 2, but these interactions were disturbed in the case of α2γ2 complex docking results. Binding pocket stability analysis based on molecular dynamics identified three substitutions in the loop C region of the α2 subunit, namely, G200E, I201T, and V202I, causing a reduction in the flexibility of α2 compared to α1. These amino acids in α2, as compared to α1, were also observed to decrease the vibrational and dihedral entropy and to increase the hydrogen bond content in α2 in the apo state. However, freezing of both α1 and α2 was observed in the ligand-bound state, with an increased number of internal hydrogen bonds and increased entropy. Therefore, we hypothesize that the amino acid differences in the loop C region of α2 are responsible for conformational changes in the protein structure compared to α1, as well as for the binding modes of compounds and hence their functional signaling

Modelling Hepatic Endoderm Development: Highly Efficient Differentiation of Human Embryonic Stem Cells to Functional Hepatic Endoderm Requires ActivinA and Wnt3a Signalling.

Human embryonic stem cells (hESCs) are a valuable source of pluripotential primary cells. However, their homogeneous cellular differentiation to specific cell types _in vitro_ has proven difficult thus far. Wnt signalling has been shown to play important roles in coordinating development and we demonstrate that Wnt3a is differentially expressed at critical stages of human liver development _in vivo_. The essential role of Wnt3a in hepatocyte differentiation from hESCs is paralleled by our _in vitro_ model, demonstrating the importance of a physiological approach to cellular differentiation. Our studies provide compelling evidence that Wnt3a signaling is important for coordinated hepato-cellular function _in vitro_ and _in vivo_. In addition, we demonstrate Wnt3a facilitates clonal plating of hESCs capable of hepatic endoderm differentiation. These studies represent an important step forward toward the use of hESC-derived hepatocytes in biomedical applications and has opened the door to high through-put metabolic analysis of human liver function

Trypanosoma brucei Glycogen Synthase Kinase-3, A Target for Anti-Trypanosomal Drug Development: A Public-Private Partnership to Identify Novel Leads

Over 60 million people in sub-Saharan Africa are at risk of infection with the parasite Trypanosoma brucei which causes Human African Trypanosomiasis (HAT), also known as sleeping sickness. The disease results in systemic and neurological disability to its victims. At present, only four drugs are available for treatment of HAT. However, these drugs are expensive, limited in efficacy and are severely toxic, hence the need to develop new therapies. Previously, the short TbruGSK-3 short has been validated as a potential target for developing new drugs against HAT. Because this enzyme has also been pursued as a drug target for other diseases, several inhibitors are available for screening against the parasite enzyme. Here we present the results of screening over 16,000 inhibitors of human GSK-3β (HsGSK-3) from the Pfizer compound collection against TbruGSK-3 short. The resulting active compounds were tested for selectivity versus HsGSK-3β and a panel of human kinases, as well as their ability to inhibit proliferation of the parasite in vitro. We have identified attractive compounds that now form potential starting points for drug discovery against HAT. This is an example of how a tripartite partnership involving pharmaceutical industries, academic institutions and non-government organisations such as WHO TDR, can stimulate research for neglected diseases

Systematic and Controllable Negative, Zero, and Positive Thermal Expansion in Cubic Zr1–xSnxMo2O8

We describe the synthesis and characterization of a family of materials, Zr1–xSnxMo2O8 (0 < x < 1), whose isotropic thermal expansion coefficient can be systematically varied from negative to zero to positive values. These materials allow tunable expansion in a single phase as opposed to using a composite system. Linear thermal expansion coefficients, αl, ranging from −7.9(2) × 10–6 to +5.9(2) × 10–6 K–1 (12–500 K) can be achieved across the series; contraction and expansion limits are of the same order of magnitude as the expansion of typical ceramics. We also report the various structures and thermal expansion of “cubic” SnMo2O8, and we use time- and temperature-dependent diffraction studies to describe a series of phase transitions between different ordered and disordered states of this material

Alkali-metal mediated zincation of N-heterocyclic substrates using the lithium zincate complex, (THF)Li(TMP)Zn(tBu)(2) and applications in in situ cross coupling reactions

This study investigates the ability of the mixed-metal reagent [Li(TMP)Zn(tBu)(2)] 1 to promote direct Zn-H exchange reactions (zincations) of a wide range of N-heterocyclic molecules. The generated metallated intermediates from these reactions are intercepted with I-2 and some of them are also employed as precursors in Pd-catalysed Negishi cross-coupling applications. A comparison with recent precedents in metallation chemistry reveals that for some of these heterocycles, 1 allows improved conversions, under milder conditions and in certain cases, even gives unique regioselectivities

New lithium-zincate approaches for the selective functionalisation of pyrazine: direct dideprotozincation vs. nucleophilic alkylation

Comparing the reactivity of the related lithium zincates [(THF)LiZn(TMP)Bu-t(2)] (1) and [(PMDETA)(LiZnBu3)-Bu-t] (2) towards pyrazine discloses two new bimetallic approaches for the selective 2,5-dideprotonation and room temperature C-H alkylation of this sensitive heterocycle