Alzheimer’s Disease (AD) is the most common form of dementia, which affects 47 million people
worldwide. There are over five million AD patients over the age of 65 in the U.S., which is predicted to increase
to 16 million by 2050, with a concomitant increase in socioeconomic burden. There are currently no approved
disease-modifying therapies for AD and the few symptomatic treatment agents available have limited impact.
Attempts to prevent or eliminate beta-amyloid plaques have been made by targeting the beta-site amyloid
precursor protein (APP) cleaving enzyme 1 (BACE1) and the gamma-secretase enzyme. However, these
strategies have not yet achieved clinical success. Recent research suggests that indirect modulation of the
function of these enzymes via G-protein coupled receptors (GPCRs) may provide a novel strategy to reduce A-
beta peptide production with potentially less side effects. Among GPCRs that influence amyloidogenesis, the
delta opioid receptor (DOR) in particular has been shown to play an important role in the trafficking and function
of BACE1 and gamma-secretase and in the production of A-beta peptide. Activation of DOR increases BACE1
and gamma-secretase activity in vitro and in a mouse model of AD, and antagonism of DOR specifically blocks
the amyloidogenic pathway and efficaciously prevents AD progression in mice. These effects were demonstrated
using a known DOR antagonist, naltrindole. However, the potential of DOR antagonists as therapeutic agents
for AD is yet to be explored.
The parent grant for the proposed supplement targets mixed function ligands possessing agonist activity
at the mu opioid receptor (MOR) and antagonist activity at DOR. The target libraries of compounds generated
through the parent grant were prepared using a series of DOR antagonists as intermediates. This provides us
with a unique opportunity to characterize their DOR antagonist profile and explore the activity of selected
compounds for their ability to modulate the function of the APP processing enzymes and inhibit A-beta pathology.
To this end, in this supplemental effort, we will pursue the following specific aims: analyze and select a set of
preferred ligands from our library of opioid ligands; resynthesize samples of the selected ligands; evaluate the
selected ligands in vitro for their ability to inhibit enzymatic activity and subcellular localization; further select a
small set of the most promising compounds and evaluate their ability to mitigate AD-like pathology using APP/PS
double-transgenic mice. These evaluations will include behavioral tests (spatial memory by Morris Water Maze;
Novel Object Recognition) as well as assessment of A-beta level, beta-amyloid deposits, and inflammation
(activated astrocytes and microglia) in the brain.
The results from this supplemental effort will provide insight into the novel approach of indirect modulation
via opioid receptors to achieve reduction in A-beta pathology and identify lead compounds for further
development as candidate AD therapeutics.