Abstract 4365849: Selective Degradation of Excess Free Cholesterol in the Liver by REP-0003 Regresses Atherosclerotic Plaque in <i> Ldlr ^-/- </i> Mice: A Novel Approach for HoFH

Introduction: Homozygous familial hypercholesterolemia (HoFH) is a rare genetic disorder caused by loss-of-function mutations in the low-density lipoprotein receptor (LDLR ) gene, leading to severe hypercholesterolemia and premature atherosclerotic cardiovascular disease. In HoFH patients, statins and PCSK9 inhibitors are ineffective and, while new lipid-lowering therapies including angiopoietin-like 3 inhibitors and lomitapide offer hope, they have not been shown to effectively regress existing plaque, highlighting a critical unmet medical need. The Cholesterol Degrading Platform (CDP) is a fusion protein that degrades excess intracellular free cholesterol into a non-toxic, excretable catabolite to safely regress cholesterol-rich vulnerable plaque. We propose that excess free cholesterol from hypercholesterolemia impairs mechanisms that can otherwise regress atherosclerotic plaque, and that the selective degradation of this free cholesterol in the liver will restore liver health and promote plaque regression throughout the systemic circulation. Methods: Ldlr -/- mice ( n=96 ) were fed a Western diet for 16 weeks and randomized based on body weight and time to exhaustion on an inclined (10%) treadmill. Mice received either intravenous phosphate buffered saline (PBS; equal volume/kg, qw) or REP-0003 (LNP- CDP mRNA ; 0.05–1.50 mg/kg, qw) for 6 weeks followed by another treadmill exhaustion test. At euthanasia, tissues and blood were harvested and assessed for blood chemistries, serum biomarkers, atherosclerotic plaque burden, and histopathology. Results: Compared with PBS, REP-0003 treatment significantly reduced serum alanine transaminase (ALT) levels by 40.5 ± 3.7% ( P&lt;0.01 , indicating improved liver health), reduced serum ApoB levels by 23.9 ± 1.0% ( P&lt;0.01 ) and increased HDL free cholesterol fraction by 61.2 ± 5.8% ( P&lt;0.01 ). Versus controls, (a) aortic root plaque cross-sectional area and aortic tree plaque count/area were significantly reduced by 27.2 ± 4.8% ( P&lt;0.01 ) and 25.8 ± 1.8% ( P&lt;0.05 ), respectively, (b) plaque macrophage infiltration via CD68 staining significantly decreased by 61.5 ± 11.4% ( P&lt;0.01 ), and (c) treadmill runtime significantly increased by 67.2 ± 6.5% ( P&lt;0.01 ). Conclusion: REP-0003 therapy specifically degrades excess free cholesterol in the liver to safely and effectively reduce atherosclerotic plaque burden and enhance exercise tolerance in Ldlr -/- mice, offering a promising first-in-class therapeutic approach for HoFH-associated atherosclerosis.