CROSSBETA STABLE Aβ OLIGOMERS: DISEASE-RELEVANT DRUG TARGETS AND VERSATILE REFERENCE STANDARDS IN BIOMARKER ASSAYS IN AD

Abstract

There is accumulating evidence that soluble amyloid beta (Aβ) oligomers, rather than the amyloid fibrils, are the principal pathogenic species in Alzheimer disease (AD). Because they exhibit acute synaptic toxicity and induce neurodegenerative processes, and because the Aβ oligomer levels in cerebrospinal fluid appear to correlate with disease severity and progression, these species constitute an optimal drug target and possible useful diagnostic marker in early AD. Unfortunately, the instability and limited characterization of oligomer preparations have seriously impeded research and development in this field. Crossbeta has addressed this problem by developing a technology to reproducibly generate stable soluble Aß1–42 oligomers that are devoid of monomeric or fibrillar Aß and show biophysical properties indistinguishable from the native species. Furthermore, Crossbeta oligomers demonstrate typical functionality of pathological Aβ species such as neurotoxicity, in vivo LTP depression and induction of inflammatory response. The availability of the stable oligomers opens previously inaccessible avenues for R&D. For example, it enabled high throughput screening of drug-like compound libraries. Derived from a 100k compound screening effort, small molecule CBB68 was identified and shown to neutralize oligomer-induced neurotoxicity in rat primary neurons and to rescue the synaptic deficit induced by Aβ oligomers in vivo as well as in vitro. In particular, the in vivo LTP assay demonstrated the efficacy and brain penetration of CBB68 after intravenous administration. In another application, Crossbeta's oligomers have also been used to select shark antibodies that specifically recognize a conformational oligomeric epitope and bind to Aß1–42 oligomers with high affinity (sub-nM), but not to the monomers or fibrils. This antibody provides potential to selectively quantify Aß1–42 oligomers in patient material as part of a high sensitivity biomarker assay together with the stable Crossbeta oligomers as calibrator. Furthermore, the oligomers are excellent research tools, e.g. in disease-relevant bioassays. We show and conclude that the stable oligomers enable multiple applications and constitute optimum drug targets.