Emerging models in Alzheimer's Disease (AD) pathophysiology indicate that AB (beta-Amyloid) is rapidly and dynamically exchanging across the blood-brain barrier (BBB) separating CNS and peripheral sources of AB processing. Recently, it has been shown that MDR1 P-glycoprotein (Pgp), located on the luminal surface of capillary endothelial cells, mediates the final step of AB extrusion from the brain, indicating a potential role for Pgp in progression of AD. Additionally, Pgp polymorphisms impacting this transport activity are common in the population. Thus, an imaging method capable of interrogating Pgp-mediated transport at the BBB could provide a valuable diagnostic biomarker for determining a novel risk factor in AD. Using transgenic mice that overexpress human amyloid precursor protein (APP) cross bred to Pgp gene knockout or WT mice, we have also demonstrated that 99mTc-Sestamibi, a FDA approved imaging agent and an efficient transport substrate of MDR1 P-glycoprotein, shows at least 3-fold higher uptake in brains of age-matched APP-Pgp-null mice compared with their APP-PgpWT counterparts. We propose to perform advanced preclinical validation of 99mTc-Sestamibi: a) evaluate the potential of 99mTc-Sestamibi to serve as a diagnostic marker for Pgp-mediated efflux of b-amyloid in AD via pharmacokinetic studies in APP-PgpWT mice in the presence of potent and specific Pgp inhibitors and compare results with APP-Pgp-null mice in the absence of inhibitors;b) evaluate the potential of 99m/94mTc-Sestamibi to serve as a noninvasive probe of Pgp transport at the BBB via nanoSPECT and microPET imaging, respectively, in age-matched APP-Pgp-null mice and APP-PgpWT mice, in the absence or presence of Pgp inhibitors;c) characterize clinically-relevant Pgp point mutations in relation to 99mTc-Sestamibi transport in rat brain endothelial cells;and d) perform a pilot human study of participants (previously characterized via 11C-PIB PET scans as demented or normal subjects) to analyze the potential of 99mTc-Sestamibi imaging to provide a functional assessment of Pgp-mediated transport at the BBB. Successful execution of this strategy could provide a molecular-targeted diagnostic agent for assessment of a novel risk factor in AD, assist patient stratification, and monitor therapeutic efficacy in disease management.
Emerging models in Alzheimer's Disease (AD) pathophysiology indicate that MDR1 P-glycoprotein (Pgp) located on the luminal surface of capillary endothelial cells could mediate Ab (b-Amyloid) extrusion from the brain. Therefore, imaging agents capable of probing Pgp-mediated functional transport at the blood-brain barrier (BBB) could serve as novel diagnostic biomarkers for determining this novel risk factor in AD. The proposed project involves development of a single photon emission computed tomography (SPECT) or positron-emission tomography (PET)-imaging agent, capable of interrogating this critical biochemical process at the BBB, and potentially offering an innovative approach to assess this risk factor in the segment of population susceptible to AD. Successful execution of this strategy could provide a molecular-targeted diagnostic agent for assessment of a novel risk factor in AD and could assist subject stratification in guiding therapeutic choices to benefit disease management of patients in future.
