Targeting Glial Cholesteryl Ester Accumulation to Treat APOE4 Alzheimer's Disease - PROJECT SUMMARY The apolipoprotein E4 (APOE4) allele is the strongest genetic risk factor for late-onset Alzheimer’s disease (AD). APOE is the brain’s major cholesterol transporter. Multiple independent studies using human iPSCs, APOE4 mouse models, and human post-mortem brain tissue indicate that APOE4 drives lipid accumulation in glial cells. While transient lipid buildup offers short-term protection, chronic and excessive lipid accumulation impairs glial cell function, exacerbates neuroinflammation, and hampers toxic protein clearance. Cholesteryl esters (CEs) are the most consistently dysregulated lipid species in postmortem AD brains, AD mouse models, and APOE4 iPSC- derived glia. Although several FDA-approved therapies target systemic lipid metabolism, none address pathological CE accumulation in the brain. ACAT1/SOAT1, the key enzyme that converts free cholesterol into CEs for storage in lipid droplets, represents a promising therapeutic target for AD. Genetic ablation of ACAT1/SOAT1 in AD models reduces Aβ plaques, phospho-Tau (p-Tau) levels, and cognitive deficits. Several ACAT1/SOAT1 inhibitors have been tested clinically for atherosclerosis but were discontinued due to limited efficacy or safety concerns. Among them, Eflucimibe (F-12511), is one of the most potent ACAT1/SOAT1 inhibitors to reach Phase II trials. However, its poor brain penetration hampers its potential for treating AD. To overcome this challenge, we propose conjugating Eflucimibe to a clinically-validated hydroxyl-dendrimer polymer delivery system that targets the CNS while minimizing systemic exposure. Hydroxyl-dendrimers have been validated in multiple CNS disease models and species, including rodents, dogs, and primates, and were recently used in a Phase II COVID-19 clinical trial where they reduced inflammation, neurological injury markers, and improved clinical outcomes. We hypothesize that conjugating Eflucimibe to brain-penetrant hydroxyl-dendrimers will facilitate glial-specific ACAT1/SOAT1 inhibition, decrease CE accumulation in the CNS, and enhance neuropathology and cognitive function in the P301S/E4 tauopathy mouse model of AD. We will pursue two specific aims: Aim 1: Conjugate the ACAT1/SOAT1 inhibitor Eflucimibe to hydroxyl-PAMAM dendrimers (D- Eflucimibe) and evaluate its pharmacokinetics, glial target engagement, and optimal dosing for efficacy studies. Aim 2: Assess the efficacy and tolerability of D-Eflucimibe in P301S/E4 mice by evaluating glial CE accumulation, CD68+ microglial activation, hippocampal volume, p-Tau levels, and cognitive performance in recognition, spatial, and working memory tasks. Upon the successful completion of these aims, we will have developed a first-in-class brain-penetrant ACAT1/SOAT1 inhibitor that reduces excess CEs in the CNS of an AD murine model, laying the foundation for further therapeutic development.
