Very Short and Stable Lactoferricin-Derived Antimicrobial Peptides: Design Principles and Potential Uses.

The alarming rate at which micro-organisms are developing resistance to conventional antibiotics represents one of the global challenges of our time. There is currently ample space in the antibacterial drug pipeline, and scientists are trying to find innovative and novel strategies to target the microbial enemies. Nature has remained a source of inspiration for most of the antibiotics developed and used, and the immune molecules produced by the innate defense systems, as a first line of defense, have been heralded as the next source of antibiotics. Most living organisms produce an arsenal of antimicrobial peptides (AMPs) to rapidly fend off intruding pathogens, and several different attempts have been made to transform this versatile group of compounds into the next generation of antibiotics. However, faced with the many hurdles of using peptides as drugs, the success of these defense molecules as therapeutics remains to be realized. AMPs derived from the proteolytic degradation of the innate defense protein lactoferrin have been shown to display several favorable antimicrobial properties. In an attempt to investigate the biological and pharmacological properties of these much shorter AMPs, the sequence dependence was investigated, and it was shown, through a series of truncation experiments, that these AMPs in fact can be prepared as tripeptides, with improved antimicrobial activity, via the incorporation of unnatural hydrophobic residues and terminal cappings. In this Account, we describe how this class of promising cationic tripeptides has been developed to specifically address the main challenges limiting the general use of AMPs. This has been made possible through the identification of the antibacterial pharmacophore and via the incorporation of a range of unnatural hydrophobic and cationic amino acids. Incorporation of these residues at selected positions has allowed us to extensively establish how these compounds interact with the major proteolytic enzymes trypsin and chymotrypsin and also the two major drug-binding plasma proteins serum albumin and α-1 glycoprotein. Several of the challenges associated with using AMPs relate to their size, susceptibility to rapid proteolytic degradation, and poor oral bioavailability. Our studies have addressed these issues in detail, and the results have allowed us to effectively design and prepare active and metabolically stable AMPs that have been evaluated in a range of functional settings. The optimized short AMPs display inhibitory activities against a plethora of micro-organisms at low micromolar concentrations, and they have been shown to target resistant strains of both bacteria and fungi alike with a very rapid mode of action. Our Account further describes how these compounds behave in in vivo experiments and highlights both the challenges and possibilities of the intriguing compounds. In several areas, they have been shown to exhibit comparable or superior activity to established antibacterial, antifungal, and antifouling commercial products. This illustrates their ability to effectively target and eradicate various microbes in a variety of settings ranging from the ocean to the clinic.

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.

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.

A synthetic antimicrobial peptidomimetic (LTX 109): stereochemical impact on membrane disruption.

LTX 109 is a synthetic antimicrobial peptidomimetic (SAMP) currently in clinical phase II trials for topical treatment of infections of multiresistant bacterial strains. All possible eight stereoisomers of the peptidomimetic have been synthesized and tested for antimicrobial effect, hemolysis, and hydrophobicity, revealing a strong and unusual dependence on the stereochemistry for a molecule proposed to act on a general membrane mechanism. The three-dimensional structures were assessed using nuclear magnetic resonance spectroscopy (NMR) and molecular dynamics (MD) simulations in aqueous solution and in phospholipid bilayers. The solution structures of the most active stereoisomers are perfectly preorganized for insertion into the membrane, whereas the less active isomers need to pay an energy penalty in order to enter the lipid bilayer. This effect is also found to be reinforced by a significantly improved water solubility of the less active isomers due to a guanidyl-π stacking that helps to solvate the hydrophobic surfaces.