Daniel Kieser

Bis(arylvinyl)pyrazines, -pyrimidines, and -pyridazines As Imaging Agents for Tau Fibrils and β-Amyloid Plaques in Alzheimer’s Disease Models

The in vivo diagnosis of Alzheimers disease (AD) is of high socioeconomic interest and remains a demanding field of research. The biopathological hallmarks of the disease are extracellular plaques consisting of aggregated β-amyloid peptides (Aβ) and tau protein derived intracellular tangles. Here we report the synthesis and evaluation of fluorescent pyrazine, pyrimidine,and pyridazine derivatives in vitro and in vivo aiming at a tau-based diagnosis of AD. The probes were pre-evaluated on human brain tissue by fluorescence microscopy and were found to label all known disease-related alterations at high contrast and specificity. To quantify the binding affinity, a new thiazine red displacement assay was developed and selected candidates were toxicologically profiled. The application in transgenic mouse models demonstrated bioavailability and brain permeability for one compound. In the course of histological testing, we discovered an AD-related deposition of tau aggregates in the Bowmans glands of the olfactory epithelium, which holds potential for an endoscopic diagnosis of AD in the olfactory system.

NSAID-derived γ-secretase modulation requires an acidic moiety on the carbazole scaffold

Modulation of γ-secretase activity holds potential for the treatment of Alzheimers disease. Most NSAID-derived γ-secretase modulators feature a carboxylic acid, which may impair blood-brain barrier permeation. The structure activity relationship of 33 carbazoles featuring diverse carboxylic acid isosteres or metabolic precursors thereof was established in a cellular amyloid secretion assay. The modulatory activity was observed for acidic moieties and metabolically labile esters only, which supports our hypothesis of an acid-lysine interaction to be relevant for this type of γ-secretase modulators.

Synthesis of Methoxy-X04 Derivatives and Their Evaluation in Alzheimer's Disease Pathology

Background: Alzheimers disease is characterized by two notorious protein aggregates in the brain: extracellular senile plaques mainly consisting of amyloid-β peptides and tau-protein-derived intracellular paired helical filaments. The diagnosis of Alzheimers disease is impaired by insufficient sensitivity and specificity of diagnostic methods to visualize these pathological hallmarks over all disease stages. Objective: The established fluorescence marker methoxy-X04 stains plaques, tau tangles and amyloid-derived angiopathies with good specificity, yet it is limited by slow elimination in vivo. Since the need for new markers is high, we prepared methoxy-X04 derivatives and evaluated their potential as imaging agents in Alzheimers disease pathology. Methods and Results: In this study, we describe an improved synthesis for methoxy-X04 and its derivatives and their affinity determination for the respective protein targets by immunohistology and a displacement assay. Conclusion: This resulted in the identification of new derivatives of methoxy-X04 with improved binding affinity.

Fluorescent dyes detect Aβ- and Tau-pathology post mortem and in vivo

Background:Due to increasing numbers of patients suffering fromAlzheimer’s Disease (AD) and no effective therapies so far, there is an exigent need for a reliableand inexpensive diagnosis at anearly stageof the disease.Aggregates of amyloid ß and tau protein are the physiological markers of the disease. Therefore inhibition and reversal of this protein-aggregation are subjects of clinical studies. The established PET tracer PIB is so far limited to exclude the AD diagnosis. The outcome of clinical studies can be monitored by the combination of cognitive ability assays and the sampling of biomarkers from cerebrospinal fluid, which is supported by PIB PET imaging. A distinct AD diagnosis is possible postmortem only via the histological examination of brain tissue. Neither of these approaches is suitable for a large cohort survey. Moreover, community physicians fail to diagnose up to 33% ofmild dementia cases. Novel markers are required to establish a reliable, early diagnosis of a pathological accumulation of tau andAß in the living patient. Established radio diagnostic probes allowmonitoring individual disease progress but display restricted ability to differentiate AD patients from healthy controls. Hence an important criterion for the development of novel imaging techniques and probes is their ability to differentiate clearly tau-protein depositions from Aßaggregates. ThereforewedevelopbrainMethods:Thereforewedeveloped brain penetrating, selective fluorescent probes for the in vivo detection of tauPHFandAß-aggregates inADpatients and animalmodels.Results: Iterative cycles of ligand design, synthesis and histology of human AD tissue resulted in the identification of bright-fluorescent binders for amyloid plaques and tauPHF. Conclusions: A biomarker-supported diagnosis is of essential importance for future therapies of ADs both for clinical studies and for awidespread screening of high-risk groups with respect to an early beginning of therapy.