Elucidation of the GSK3α Structure Informs the Design of Novel, Paralog-Selective Inhibitors

Glycogen synthase kinase 3 (GSK3) remains a therapeutic target of interest for diverse clinical indications. However, one hurdle in the development of small molecule GSK3 inhibitors has been safety concerns related to pan-inhibition of both GSK3 paralogs, leading to activation of the Wnt/β-catenin pathway and potential for aberrant cell proliferation. Development of GSK3α or GSK3β paralog-selective inhibitors that could offer an improved safety profile has been reported but further advancement has been hampered by the lack of structural information for GSK3α. Here we report for the first time the crystal structure for GSK3α, both in apo form and bound to a paralog-selective inhibitor. Taking advantage of this new structural information, we describe the design and in vitro testing of novel compounds with up to ∼37-fold selectivity for GSK3α over GSK3β with favorable drug-like properties. Furthermore, using chemoproteomics, we confirm that acute inhibition of GSK3α can lower tau phosphorylation at disease-relevant sites in vivo, with a high degree of selectivity over GSK3β and other kinases. Altogether, our studies advance prior efforts to develop GSK3 inhibitors by describing GSK3α structure and novel GSK3α inhibitors with improved selectivity, potency, and activity in disease-relevant systems.

Discovery of Potent, Selective, and Brain-Penetrant Apoptosis Signal-Regulating Kinase 1 (ASK1) Inhibitors that Modulate Brain Inflammation In Vivo

Apoptosis signal-regulating kinase 1 (ASK1) is one of the key mediators of the cellular stress response that regulates inflammation and apoptosis. To probe the therapeutic value of modulating this pathway in preclinical models of neurological disease, we further optimized the profile of our previously reported inhibitor 3. This effort led to the discovery of 32, a potent (cell IC₅₀ = 25 nM) and selective ASK1 inhibitor with suitable pharmacokinetic and brain penetration (rat Cl/Cl_u = 1.6/56 L/h/kg and K_p,uu = 0.46) for proof-of-pharmacology studies. Specifically, the ability of 32 to inhibit ASK1 in the central nervous system (CNS) was evaluated in a human tau transgenic (Tg4510) mouse model exhibiting elevated brain inflammation. In this study, transgenic animals treated with 32 (at 3, 10, and 30 mg/kg, BID/PO for 4 days) showed a robust reduction of inflammatory markers (e.g., IL-1β) in the cortex, thus confirming inhibition of ASK1 in the CNS.

Investigating small molecules to inhibit germinal center kinase-like kinase (GLK/MAP4K3) upstream of PKCθ phosphorylation: Potential therapy to modulate T cell dependent immunity

Germinal center kinase-like kinase (GLK, also known as MAP4K3) has been hypothesized to have an effect on key cellular activities, including inflammatory responses. GLK is required for activation of protein kinase C-θ (PKCθ) in T cells. Controlling the activity of T helper cell responses could be valuable for the treatment of autoimmune diseases. This approach circumvents previous unsuccessful approaches to target PKCθ directly. The use of structure based drug design, aided by the first crystal structure of GLK, led to the discovery of several inhibitors that demonstrate potent inhibition of GLK biochemically and in relevant cell lines.

Genetic defects in β-spectrin and tau sensitize C. elegans axons to movement-induced damage via torque-tension coupling

Our bodies are in constant motion and so are the neurons that invade each tissue. Motion-induced neuron deformation and damage are associated with several neurodegenerative conditions. Here, we investigated the question of how the neuronal cytoskeleton protects axons and dendrites from mechanical stress, exploiting mutations in UNC-70 β-spectrin, PTL-1 tau/MAP2-like and MEC-7 β-tubulin proteins in Caenorhabditis elegans. We found that mechanical stress induces supercoils and plectonemes in the sensory axons of spectrin and tau double mutants. Biophysical measurements, super-resolution, and electron microscopy, as well as numerical simulations of neurons as discrete, elastic rods provide evidence that a balance of torque, tension, and elasticity stabilizes neurons against mechanical deformation. We conclude that the spectrin and microtubule cytoskeletons work in combination to protect axons and dendrites from mechanical stress and propose that defects in β-spectrin and tau may sensitize neurons to damage.

DOI:http://dx.doi.org/10.7554/eLife.20172.001

Gene targeting using a promoterless gene trap vector ("targeted trapping") is an efficient method to mutate a large fraction of genes

A powerful tool for postgenomic analysis of mammalian gene function is gene targeting in mouse ES cells. We report that homologous recombination using a promoterless gene trap vector ("targeting trapping") yields targeting frequencies averaging above 50%, a significant increase compared with current approaches. These high frequencies appear to be due to the stringency of selection with promoterless constructs, because most random insertions are silent and eliminated by drug selection. The promoterless design requires that the targeted gene be expressed in ES cells at levels exceeding a certain threshold (which we estimate to be approximately 1% of the transferrin receptor gene expression level, for the secretory trap vector used here). Analysis of 127 genes that had been trapped by random (nontargeted) gene trapping with the same vector shows that virtually all are expressed in ES cells above this threshold, suggesting that targeted and random trapping share similar requirements for expression levels. In a random sampling of 130 genes encoding secretory proteins, about half were expressed above threshold, suggesting that about half of all secretory genes are accessible by either targeted or random gene trapping. The simplicity and high efficiency of the method facilitate systematic targeting of a large fraction of the genome by individual investigators and large-scale consortia alike.

Oxidative stress and an altered methionine metabolism in alcoholism

The exact mechanism of brain atrophy in patients with chronic alcoholism remains unknown. There is growing evidence that chronic alcoholism is associated with oxidative stress and with a derangement in sulphur amino acid metabolism (e.g. ethanol-induced hyperhomocysteinemia). Furthermore, it has been reported that homocysteine induces neuronal cell death by stimulating N-methyl-D-aspartate receptors as well as by producing free radicals. To further evaluate this latter hypothesis we analysed serum levels of both homocysteine and markers of oxidative stress (malondialdehyde) in alcoholic patients who underwent withdrawal from alcohol. Homocysteine and malondialdehyde were quantified by high performance liquid chromatography (HPLC) in serum samples of 35 patients (active drinkers). There was a significant correlation (P<0. 01) between blood alcohol concentration and elevated homocysteine (Spearman's r=0.71) and malondialdehyde (r=0.90) levels on admission. In addition, homocysteine and malondialdehyde levels were found to be significant decreased after 3 days of withdrawal treatment (Wilcoxon test: homocysteine, Z=-5.127; malondialdehyde, Z=-3.120; P<0.01). We postulate that excitatory neurotransmitters and mechanisms of oxidative stress in patients with chronic alcoholism may partly mediate excitotoxic neuronal damage and hereby cause brain shrinkage.