This strategy combines targeted upregulation of LDLR expression in brain endothelial cells with engineered antibodies designed for LRP1-mediated transcytosis and endosomal escape. The approach begins by pharmacologically or genetically upregulating LDLR expression levels in brain capillary endothelium, which primes the cholesterol transport machinery and creates a metabolically active endothelial environment that enhances LRP1 receptor density and trafficking capacity. Therapeutic antibodies are then conjugated to high-affinity APOE-mimetic peptides that specifically target the upregulated LRP1 receptors, facilitating rapid receptor-mediated endocytosis with predictable kinetics independent of variable FcRn transport efficiency. The critical innovation lies in engineering these antibody constructs with pH-responsive fusogenic peptides that remain inactive at physiological pH (7.4) but undergo conformational activation in the acidic endosomal environment (pH 5.5-6.0).

This strategy combines targeted upregulation of LDLR expression in brain endothelial cells with engineered antibodies designed for LRP1-mediated transcytosis and endosomal escape. The approach begins by pharmacologically or genetically upregulating LDLR expression levels in brain capillary endothelium, which primes the cholesterol transport machinery and creates a metabolically active endothelial environment that enhances LRP1 receptor density and trafficking capacity. Therapeutic antibodies are then conjugated to high-affinity APOE-mimetic peptides that specifically target the upregulated LRP1 receptors, facilitating rapid receptor-mediated endocytosis with predictable kinetics independent of variable FcRn transport efficiency. The critical innovation lies in engineering these antibody constructs with pH-responsive fusogenic peptides that remain inactive at physiological pH (7.4) but undergo conformational activation in the acidic endosomal environment (pH 5.5-6.0). Upon LRP1-mediated internalization, the decreasing endosomal pH triggers the fusogenic peptides to disrupt endosomal membranes, allowing therapeutic antibodies to escape into the cytoplasm before lysosomal degradation occurs. This dual mechanism transforms the typically degradative APOE-cholesterol clearance pathway into a productive transcytotic delivery route. The LDLR upregulation creates a metabolically primed state that increases LRP1 expression and enhances the overall capacity for APOE-mediated transcytosis, while the pH-responsive escape mechanism ensures that internalized antibodies avoid lysosomal degradation and successfully traverse the blood-brain barrier. This approach provides quantifiable, consistent CNS penetration that bypasses the stochastic variability of FcRn transport while leveraging the brain's endogenous cholesterol transport infrastructure for therapeutic delivery.