From the ganglioside GQ1ba to glycomimetic antagonists of the myelin-associated glycoprotein (MAG)

The tetrasaccharide 4, a substructure of ganglioside GQ1bα, shows a remarkable affinity for the myelinassociated glycoprotein (MAG) and was therefore selected as starting point for a lead optimization program. In our search for structurally simplified and pharmacokinetically improved mimics of 4, antagonists with modifications of the core disaccharide Galβ(1-3)GalNAc, as well as the terminal α(2-3)- and the internal α(2-6)-linked neuraminic acid were synthesized and tested in target-based binding assays. Compared to the reference tetrasaccharide 4, the most potent antagonist 17 exhibits a 360-fold improved affinity. Furthermore, pharmacokinetic parameters such as stability in the cerebrospinal fluid, logD and permeation through the BBB indicate the drug-like properties of antagonist 17

The PADMET platform - pharmacokinetic characterization of carbohydrate mimetics

More than two decades ago it was realized that drug discovery and development strategies focusing exclusively on affinity enhancement and potency are unsuccessful. Instead, simultaneous optimization of pharmacodynamic and pharmacokinetic properties has been proposed and implemented. As a result, new assays for pharmacokinetic characterization were required and existing assays were modified to fulfill high-throughput requirements. These assays, typically used at early stages of drug discovery and development, were modified and employed during this doctoral thesis to determine pharmacokinetic parameters of carbohydrate mimetics. The project was termed PADMET platform, with PADMET standing for physicochemical properties, absorption, distribution, metabolism, elimination, and toxicity. The aims of the platform were on the one hand the elucidation of the pharmacokinetic behavior of carbohydrate mimetics and on the other hand the development of such compounds with improved drug-likeness. While building up the PADMET platform, the need for an inexpensive and uncomplicated pKa determination method became apparent. A methodology based on 1H-NMR spectroscopy was chosen for this purpose and scope and limitations of this approach were explored. An excellent correlation to reference data was achieved. The components of the platform were used to characterize 93 carbohydrate mimetics regarding several pharmacokinetic parameters. The results were used in different projects of which two are discussed in detail in this thesis. First, one of the primary goals of the FimH antagonist project was the synthesis of orally available compounds with fast renal excretion. By the aid of various assays, molecules with a promising profile could be identified. Indeed, in vivo mouse studies confirmed the intended properties. The permeability values gathered during this project were correlated to calculated descriptors and to experimental lipophilicity values in order to identify the driving force of the permeation of carbohydrate mimetics. Calculated lipophilicity values as single descriptor proved to be superior to other descriptors and to combinations thereof. Second, during the MAG project compounds with maintained local concentrations in the cerebrospinal fluid were envisioned. Permeation through artificial blood-brain barrier and stability in artificial cerebrospinal fluid were thus determined

Transcriptional adaptations of lipid metabolism in tibialis anterior muscle of endurance-trained athletes

It was hypothesized that transcriptional reprogramming is involved in the structural and functional adaptations of lipid metabolism in human tibialis anterior muscle (TA) from endurance-trained male subjects. RT-PCR experiments demonstrated a significant upregulation of the mRNA level of key enzymes involved in 1) lipolytic mobilization of fatty acids (FA) from intramyocellular lipid (IMCL) stores via hormone-sensitive lipase (LIPE), 2) intramyocellular FA transport via muscle fatty acid binding protein (FABP3), and 3) oxidative phosphorylation (cytochrome c oxidase I, COI), in TA of endurance-trained vs. untrained subjects. In contrast, mRNAs for factors involved in glycolysis (muscle 6-phosphofructokinase, PFKM), intramyocellular storage of FA (diacylglycerol O-acyltransferase 1, DGAT), and ß-oxidation (long-chain acyl-coenzyme A dehydrogenase, ACADL) were invariant between TA of trained and untrained subjects. Correlation analysis identified an association of LIPE with FABP3 and LPL (lipoprotein lipase) mRNA levels and indicated coregulation of the transcript level for LIPE, FABP3, and COI with the level of mRNA encoding peroxisome proliferator-activated receptor- (PPAR-), the master regulator of lipid metabolism. Moreover, a significant correlation existed between LPL mRNA and the absolute rate of IMCL repletion determined by magnetic resonance spectroscopy after exhaustive exercise. Additionally, the LIPE mRNA level correlated with ultrastructurally determined IMCL content and mitochondrial volume density. The present data point to a training-induced, selective increase in mRNA levels of enzymes which are involved in metabolization of intramuscular FA, and these data confirm the well-established phenomenon of enhanced lipid utilization during exercise at moderate intensity in muscles of endurance-trained subjects