Novel DYRK1A Inhibitor Rescues Learning and Memory Deficits in a Mouse Model of Down Syndrome.

Down syndrome (DS) is a complex genetic disorder associated with substantial physical, cognitive, and behavioral challenges. Due to better treatment options for the physical co-morbidities of DS, the life expectancy of individuals with DS is beginning to approach that of the general population. However, the cognitive deficits seen in individuals with DS still cannot be addressed pharmacologically. In young individuals with DS, the level of intellectual disability varies from mild to severe, but cognitive ability generally decreases with increasing age, and all individuals with DS have early onset Alzheimer's disease (AD) pathology by the age of 40. The present study introduces a novel inhibitor for the protein kinase DYRK1A, a key controlling kinase whose encoding gene is located on chromosome 21. The novel inhibitor is well characterized for use in mouse models and thus represents a valuable tool compound for further DYRK1A research.

Biofocussed chemoprospecting: An efficient approach for drug discovery.

Drug discovery strategies include from broad random screening to focussed target-based approaches. Structure and substrate information greatly enables target-based design, but this is limited to relatively few targets; cell-based screening can identify new targets but often suffers from low hit rates and difficult hit optimization. Thus, newer approaches are needed that can improve the efficiency of screening and hit optimization. Here, we describe an efficient approach for hit generation, which may be called "biofocussed chemoprospecting." With bio-likeness and ease of synthesis as priority criteria, libraries may be constructed with good optimization potential, physicochemical diversity, drug likeness and low cost. Following this approach, two libraries based on linear and cyclic dipeptide scaffolds were designed, first as virtual libraries comprising of more than 30000 compounds, and after subsequent filtering, as a small library of a total of 51 compounds. These provided good diversity at low cost, and were tested for bioactivities. The discovery of six active compounds demonstrates a hit rate greater than 10%. This is comparable to target-based approaches, but the "chemoprospecting" method described here has the additional potential to identify new targets and mechanisms.

Probing the ATP-Binding Pocket of Protein Kinase DYRK1A with Benzothiazole Fragment Molecules.

DYRK1A has emerged as a potential target for therapies of Alzheimer's disease using small molecules. On the basis of the observation of selective DYRK1A inhibition by firefly d-luciferin, we have explored static and dynamic structural properties of fragment sized variants of the benzothiazole scaffold with respect to DYRK1A using X-ray crystallography and NMR techniques. The compounds have excellent ligand efficiencies and show a remarkable diversity of binding modes in dynamic equilibrium. Binding geometries are determined in part by interactions often considered "weak", including "orthogonal multipolar" types represented by, for example, F-CO, sulfur-aromatic, and halogen-aromatic interactions, together with hydrogen bonds that are modulated by variation of electron withdrawing groups. These studies show how the benzothiazole scaffold is highly promising for the development of therapeutic DYRK1A inhibitors. In addition, the subtleties of the binding interactions, including dynamics, show how full structural studies are required to fully interpret the essential physical determinants of binding.

Bifunctional Ligands for Inhibition of Tight-Binding Protein-Protein Interactions.

The acknowledged potential of small-molecule therapeutics targeting disease-related protein-protein interactions (PPIs) has promoted active research in this field. The strategy of using small molecule inhibitors (SMIs) to fight strong (tight-binding) PPIs tends to fall short due to the flat and wide interfaces of PPIs. Here we propose a biligand approach for disruption of strong PPIs. The potential of this approach was realized for disruption of the tight-binding (KD = 100 pM) tetrameric holoenzyme of cAMP-dependent protein kinase (PKA). Supported by X-ray analysis of cocrystals, bifunctional inhibitors (ARC-inhibitors) were constructed that simultaneously associated with both the ATP-pocket and the PPI interface area of the catalytic subunit of PKA (PKAc). Bifunctional inhibitor ARC-1411, possessing a KD value of 3 pM toward PKAc, induced the dissociation of the PKA holoenzyme with a low-nanomolar IC50, whereas the ATP-competitive inhibitor H89 bound to the PKA holoenzyme without disruption of the protein tetramer.

Diversity of bisubstrate binding modes of adenosine analogue-oligoarginine conjugates in protein kinase a and implications for protein substrate interactions.

Crystal structures of the catalytic subunit α of cAMP-dependent protein kinase (PKAc) with three adenosine analogue-oligoarginine conjugates (ARCs) are presented. The rationally designed ARCs include moieties that, in combination, target both the ATP- and the peptide-substrate-binding sites of PKAc, thereby taking advantage of high-affinity binding interactions offered by the ATP site while utilizing an additional mechanism for target specificity via binding to the peptide substrate site. The crystal structures demonstrate that, in accord with the previously reported bisubstrate character of ARCs, the inhibitors occupy both binding sites of PKAc. Further, they show new binding modes that may also apply to natural protein substrates of PKAc, which have not been revealed by previous crystallographic studies. The crystal structures described here contribute to the understanding of the substrate-binding patterns of PKAc and should also facilitate the design of inhibitors targeting PKAc and related protein kinases.