The novel apoE4 therapeutic CS6253 penetrates the blood brain barrier, upregulates the ABCA1 transporter and prevents Alzheimer’s disease pathogenesis Anat Boehm-Cagan1, Jan O. Johansson2, John K. Bielicki3 and Daniel M. Michaelson11The Sagol School of Neuroscience, Tel Aviv University, Israel; 2Artery Therapeutics, Inc.; 3Lawrence Berkeley Laboratory, USBackground: The allele ε4 of apolipoprotein E (apoE4) is the most prevalent genetic risk factor for Alzheimer's disease (AD). No apoE4 specific therapeutic is presently available. ApoE is the natural ligand to the ABCA1 transporter, both proteins found predominantly in astrocytes. The apoE to ABCA1 interaction regulate lipidation of apoE and lipid composition of astrocyte cell membranes with many potentially favorable down-stream effects of relevance for brain pathophysiology. We hypothesized that manipulating the apoE4 to ABCA1 interaction would have AD therapeutic actions. To this purpose we applied a peptide that selectively causes ABCA1 mediated lipid removal from macrophage cells in established apoE4 vs. E3 in vitro and in vivo models. Methods and results: Astrocyte cholesterol efflux is highly responsive to stimulation by exogenous CS6253 peptide. Humanized astrocytes from apoE3 (E3) or apoE4 (E4) targeted replacement mice were labeled for 2 days with [3H]cholesterol (1 mCi/mlL), and treated overnight with 22-hydroxycholesterol/cis retinoic acid (each 10 mM final concentration) to upregulate ABCA1 expression. Time-course showed basal [3H]cholesterol efflux from cells to serum-free medium was compromised in apoE4 astrocytes. Incubating with peptide CS6253 (10 µg/mL) showed 6-fold improvement in [3H]cholesterol efflux to serum-free medium containing in both apoE4 and E3 astrocytes. CS6253 i.p. injection (20 mg/kg/48h for 6 weeks) in apoE4 target replacement mice prevented AD phenotype pathogenesis and cognition decline. CS6253 crossed the BBB providing brain levels higher than the in vitro EC50-value for ABCA1 mediated cholesterol efflux, and was found to co-localize with astrocytes in the brain in both apoE3 and E4 mice. Levels of hippocampus ABCA1 were significantly lower in apoE4 mice compared to apoE3 mice in PBS treated groups and significantly increased by CS6253 treatment in apoE4 mice. Lipidation of apoE in the hippocampus was compromised in apoE4 compared to apoE3 mice. CS6253 treatment increased apoE4 lipidation. Further analysis showed that CS6253 treatment counteracted the apoE4-driven phenotype in the hippocampus resulting in decreased Aβ42 and phosphorylated tau and increased levels of VGluT1 and apoER2. Cognitive decline was fully prevented in apoE4 mice by CS6253 treatment as assessed by novel object recognition and Morris water maze. Conclusion: ABCA1 agonist treatment by CS653 resulted in improved apoE4 lipidation in cells and in mice. Six weeks treatment consistently counteracted apoE4 driven AD with regard to both phenotype and cognition. The data point to the potential therapeutic utility of CS6253 in apoE4 sporadic AD.