Probing novel 1-aza-9-oxafluorenes as selective GSK-3beta inhibitors

Application of the Meerwein reaction of 1,4-benzoquinone to a metal-free synthesis of benzofuropyridine analogues

Several new heterocyclic systems based on a hydroxybenzofuro[2,3-b]pyridine building block were prepared. This benzofuropyridine is easily available from the Meerwein reaction of benzoquinone and a heterocyclic diazonium salt, followed by reduction and cyclization. Electrophilic substitution and further condensations give polycyclic systems, including oxazolo- and chromeno-fused analogues.

Discovery of novel dual inhibitors of receptor tyrosine kinases EGFR and PDGFR-β related to anticancer drug resistance

With ongoing resistance problems against the marketed EGFR inhibitors having a quinazoline core scaffold there is a need for the development of novel inhibitors having a modified scaffold and, thus, expected lower EGFR resistance problems. An additional problem concerning EGFR inhibitor resistance is an observed heterodimerization of EGFR with PDGFR-β that neutralises the sole inhibitor activity towards EGFR. We developed novel pyrimido[4,5-b]indoles with varied substitution patterns at the 4-anilino residue to evaluate their EGFR and PDGFR-β inhibiting properties. We identified dual inhibitors of both EGFR and PDGFR-β in the nanomolar range which have been initially screened in cancer cell lines to prove a benefit of both EGFR and PDGFR-β inhibition.

Discovery of novel dual inhibitors of receptor tyrosine kinases EGFR and IGF-1R

Novel 4-benzylamino benzo-anellated pyrrolo[2,3-b]pyridines have been synthesized with varied substitution patterns both at the molecular scaffold of the benzo-anellated ring and at the 4-benzylamino residue. With a structural similarity to substituted thieno[2,3-d]pyrimidines as epidermal growth factor receptor (EGFR) inhibitors, we characterized the inhibition of EGFR for our novel compounds. As receptor heterodimerization gained certain interest as mechanism of cancer cells to become resistant against novel protein kinase inhibitors, we additionally measured the inhibition of insulin-like growth factor receptor IGF-1R which is a prominent receptor for such heterodimerizations with EGFR. Structure–activity relationships are discussed for both kinase inhibitions depending on the varied substitution patterns. We discovered novel dual inhibitors of both receptor tyrosine kinases with interest for further studies to reduce inhibitor resistance developments in cancer treatment.

Recent developments of protein kinase inhibitors as potential AD therapeutics

Present Alzheimer’s disease (AD) therapies suffer from inefficient effects on AD symptoms like memory or cognition, especially in later states of the disease. Used acteylcholine esterase inhibitors or the NMDA receptor antagonist memantine address one target structure which is involved in a complex, multifactorial disease progression. So the benefit for patients is presently poor. A more close insight in the AD progression identified more suggested target structures for drug development. Strategies of AD drug development concentrate on novel target structures combined with the established ones dedicated for combined therapy regimes, preferably by the use of one drug which may address two target structures. Protein kinases have been identified as promising target structures because they are involved in AD progression pathways like pathophysiological tau protein phosphorylations and amyloid β toxicity. The review article will shortly view early inhibitors of single protein kinases like glycogen synthase kinase (gsk3) β and cyclin dependent kinase 5. Novel inhibitors will be discussed which address novel AD relevant protein kinases like dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A). Moreover, multitargeting inhibitors will be presented which target several protein kinases and those which are suspected in influencing other AD relevant processes. Such a multitargeting is the most promising strategy to effectively hamper the multifactorial disease progression and thus gives perspective hopes for a future better patient benefit.

Small-Molecule Inhibitors of GSK-3: Structural Insights and Their Application to Alzheimer's Disease Models

The world health organization (WHO) estimated that 18 million people are struck by Alzheimer's disease (AD). The USA, France, Germany, and other countries launched major programmes targeting the identification of risk factors, the improvement of caretaking, and fundamental research aiming to postpone the onset of AD. The glycogen synthase kinase 3 (GSK-3) is implicated in multiple cellular processes and has been linked to the pathogenesis of several diseases including diabetes mellitus, cancer, and AD. Inhibition of GSK-3 leads to neuroprotective effects, decreased β-amyloid production, and a reduction in tau hyperphosphorylation, which are all associated with AD. Various classes of small molecule GSK-3 inhibitors have been published in patents and original publications. Herein, we present a comprehensive summary of small molecules reported to interact with GSK-3. We illustrate the interactions of the inhibitors with the active site. Furthermore, we refer to the biological characterisation in terms of activity and selectivity for GSK-3, elucidate in vivo studies and pre-/clinical trials.

Structure-based optimization of oxadiazole-based GSK-3 inhibitors

Inhibition of glycogen synthase kinase-3 (GSK-3) induces neuroprotective effects, e.g. decreases β-amyloid production and reduces tau hyperphosphorylation, which are both associated with Alzheimer's disease (AD). The two isoforms of GSK-3 in mammalians are GSK-3α and β, which share 98% homology in their catalytic domains. We investigated GSK-3 inhibitors based on 2 different scaffolds in order to elucidate the demands of the ATP-binding pocket [1]. Particularly, the oxadiazole scaffold provided potent and selective GSK-3 inhibitors. For example, the most potent inhibitor of the present series, the acetamide 26d, is characterized by an IC50 of 2 nM for GSK-3α and 17 nM for GSK-3β. In addition, the benzodioxane 8g showed up to 27-fold selectivity for GSK-3α over GSK-3β, with an IC50 of 35 nM for GSK-3α. Two GSK-3 inhibitors were further profiled for efficacy and toxicity in the wild-type (wt) zebrafish embryo assay to evaluate simultaneously permeability and safety.

Discovery of 4-benzylamino-substituted α-carbolines as a novel class of receptor tyrosine kinase inhibitors

Within the last decade, interest in the development of new anticancer drugs increased mainly from emerging resistance against established drugs, which were found to be limited by the multidrug resistance (MDR) phenomenon. Several anticancer targets have been investigated for the development of structurally new drugs which were thought to be unaffected by the MDR phenomenon. Receptor tyrosine kinases (RTKs) make up one interesting group of anticancer targets. The overexpression and mutation of RTKs lead to an ongoing stimulus of cell growth and cancer progression. Early approaches to selective inhibition of single RTKs were generally disappointing in clinical studies, due in part to occurring resistance. Therefore, a new strategy involves the identification of multi-kinase inhibitors to slow the development of potential resistance. Moreover, the expected side effects of the first nonselective inhibitors were less dramatic than had been expected. We have discovered novel 4-benzylamino-α-carbolines as a new class of RTK inhibitors. Docking studies suggest a binding mode to the addressed target structures of the epidermal growth factor receptor (EGFR) and to the vascular endothelial growth factor receptor 2 (VEGFR2). Selectivity profiling against a panel of kinases and antiproliferative studies have highlighted one inhibitor, active in the nanomolar range, as a highly interesting candidate for further clinical studies.

Targeting Cdk5 activity in neuronal degeneration and regeneration

The major priming event in neurodegeneration is loss of neurons. Loss of neurons by apoptotic mechanisms is a theme for studies focused on determining therapeutic strategies. Neurons following an insult, activate a number of signal transduction pathways, of which, kinases are the leading members. Cyclin-dependent kinase 5 (Cdk5) is one of the kinases that have been linked to neurodegeneration. Cdk5 along with its principal activator p35 is involved in multiple cellular functions ranging from neuronal differentiation and migration to synaptic transmission. However, during neurotoxic stress, intracellular rise in Ca(2+) activates calpain, which cleaves p35 to generate p25. The long half-life of Cdk5/p25 results in a hyperactive, aberrant Cdk5 that hyperphosphorylates Tau, neurofilament and other cytoskeletal proteins. These hyperphosphorylated cytoskeletal proteins set the groundwork to forming neurofibrillary tangles and aggregates of phosphorylated proteins, hallmarks of neurodegenerative diseases like Alzheimer's disease, Parkinson's disease and Amyotropic Lateral Sclerosis. Attempts to selectively target Cdk5/p25 activity without affecting Cdk5/p35 have been largely unsuccessful. A polypeptide inhibitor, CIP (Cdk5 inhibitory peptide), developed in our laboratory, successfully inhibits Cdk5/p25 activity in vitro, in cultured primary neurons, and is currently undergoing validation tests in mouse models of neurodegeneration. Here, we discuss the therapeutic potential of CIP in regenerating neurons that are exposed to neurodegenerative stimuli.

2-{3-[4-(Alkylsulfinyl)phenyl]-1-benzofuran-5-yl}-5-methyl-1,3,4-oxadiazole derivatives as novel inhibitors of glycogen synthase kinase-3beta with good brain permeability

Glycogen synthase kinase 3beta (GSK-3beta) inhibition is expected to be a promising therapeutic approach for treating Alzheimer's disease. Previously we reported a series of 1,3,4-oxadiazole derivatives as potent and highly selective GSK-3beta inhibitors, however, the representative compounds 1a,b showed poor pharmacokinetic profiles. Efforts were made to address this issue by reducing molecular weight and lipophilicity, leading to the identification of oxadiazole derivatives containing a sulfinyl group, (S)-9b and (S)-9c. These compounds exhibited not only highly selective and potent inhibitory activity against GSK-3beta but also showed good pharmacokinetic profiles including favorable BBB penetration. In addition, (S)-9b and (S)-9c given orally to mice significantly inhibited cold water stress-induced tau hyperphosphorylation in mouse brain.

Use of molecular modeling, docking, and 3D-QSAR studies for the determination of the binding mode of benzofuran-3-yl-(indol-3-yl)maleimides as GSK-3beta inhibitors

Molecular modeling and docking studies along with three-dimensional quantitative structure relationships (3D-QSAR) studies have been used to determine the correct binding mode of glycogen synthase kinase 3beta (GSK-3beta) inhibitors. The approaches of comparative molecular field analysis (CoMFA) and comparative molecular similarity index analysis (CoMSIA) are used for the 3D-QSAR of 51 substituted benzofuran-3-yl-(indol-3-yl)maleimides as GSK-3beta inhibitors. Two binding modes of the inhibitors to the binding site of GSK-3beta are investigated. The binding mode 1 yielded better 3D-QSAR correlations using both CoMFA and CoMSIA methodologies. The three-component CoMFA model from the steric and electrostatic fields for the experimentally determined pIC(50) values has the following statistics: R(2)(cv) = 0.386 nd SE(cv) = 0.854 for the cross-validation, and R(2) = 0.811 and SE = 0.474 for the fitted correlation. F (3,47) = 67.034, and probability of R(2) = 0 (3,47) = 0.000. The binding mode suggested by the results of this study is consistent with the preliminary results of X-ray crystal structures of inhibitor-bound GSK-3beta. The 3D-QSAR models were used for the estimation of the inhibitory potency of two additional compounds.