Fluorescent Probes for Detection of Misfolded Protein Oligomers in Alzheimer's
Disease and Related Disorder
There is significant evidence that the clinical symptoms of Alzheimer’s Disease (AD) and related disorders
are closely linked to the formation and proliferation of small oligomers that precede the emergence of the
prominent late-stage fibrils and plaques. Therefore, amyloid beta oligomers (AßOs) are the most direct
biomarkers for monitoring the onset and progression of AD. Attempts at utilizing this biomarker, however, have
been severely hampered by the dearth of techniques for the reliable detection of AßOs in biological samples and
tissues. While oligomer-selective antibodies have provided important insights into AßOs, their use doesn't extend
to detecting oligomer populations in vivo, let alone monitoring their temporal evolution. The overall objectives
of this proposal are therefore to identify small oligomer-selective dyes for the detection of AßOs and to validate
their specificity for AßOs, and potentially related oligomers, in tissues of animal models of AD and patient tissue.
Multiple laboratories have observed that in vivo Aß assembly displays not only purely sigmoidal but also
biphasic ThT kinetics. We have shown that the onset of biphasic ThT kinetics directly correlates with the onset
and rapid increase in prefibrillar oligomer populations with increases in monomer concentrations. Here we
propose to use this transition from essentially oligomer-free sigmoidal to oligomer-dominated biphasic kinetics
to screen a selection of readily available fluorescent dyes for their selectivity for AßOs over AßFs and monomers.
An initial test of this approach already yielded a highly promising dye candidate. Our preliminary data also
indicate that this dye specifically stains oligomer deposits in animal models of AD.
While very encouraging, the utility of our current oligomer-selective dye requires further validation. In
addition, we seek to identify multiple chemically and structurally distinct oligomer-selective dyes to improve the
chances to develop one of them into a PET probe for in vivo imaging of oligomers. We will therefore extend our
current screen for AßO-selective dyes to a larger set of fluorescent dyes selected from different dye categories. In
parallel, we will scrutinize whether the current dye reliably detects AßOs at various stages of the disease, and
does so in animal models as well as patient tissues. Promising novel AßO-selective dyes identified through our
screening assay will be subjected to the same ex vivo validation of their specificity in tissues.
We anticipate that these experiments will yield multiple promising AßO-selective dyes with application for
fundamental studies of oligomer formation, for the development of new assays for detecting AßOs ex vivo, and,
most importantly, as the detection moiety for a future oligomer-selective PET probe for antemortem in vivo
oligomer imaging in patients.