CTX203, a novel apolipoprotein mimetic peptide, increases ABCA1 activity in vitro and reduces sub-RPE neutral lipid deposits in ApoE deficient mice

Abstract

Purpose : The earliest biomarker of age-related macular degeneration (AMD) is the presence of lipid-rich drusen, but to date there are no approved therapies for the treatment of lipid accumulation in patients with AMD. Human genetic evidence supports a link between deficiency in cholesterol transporters such as ABCA1 and increased risk of AMD disease incidence and progression. Through a combination of in silico design and functional screening, an apolipoprotein mimetic peptide, CTX203, was discovered and characterized for ABCA1 stabilization and lipid solubilization properties. CTX203 is being developed as a novel treatment for intermediate AMD.

Methods : Cholesterol efflux was measured in ARPE-19 cells loaded with BODIPY-Cholesterol. LXR agonist, monomeric CRP (mCRP), or siABCA1 treatment was used to modulate ABCA1 levels in ARPE-19 cells. ABCA1 protein was measured in ARPE-19 membrane samples via western blot. Lipid solubilization was determined by measuring A_405nm of DMPC liposome solutions. The in vivo efficacy of CTX203 was measured in an ApoE knockout mouse model; following 10-12 weeks of high cholesterol diet, changes in sub-RPE lipid accumulation following intravitreal (IVT) delivery of CTX203 were assessed by BODIPY staining of retinal tissue sections.

Results : CTX203 treatment induced cholesterol efflux from ARPE-19 cells (EC₅₀= 7 μM) in an ABCA1-dependent manner, as 94% of the cholesterol efflux activity was abolished following ABCA1 knockdown with siRNA. In response to mCRP treatment, CTX203 stabilized plasma membrane localization of ABCA1 and prevented the decrease in ABCA1 protein levels (EC₅₀= 4.6 μM). CTX203 solubilized DMPC liposome solutions in vitro with an EC₅₀ of 3.7 μM. In the ApoE knockout mouse model, a single IVT injection of CTX203 significantly decreased the amount of sub-RPE lipid deposition compared to vehicle-treated animals at 18 and 28 days post injection (p<0.05).

Conclusions : CTX203 is an amphipathic helical peptide that enhances ABCA1-mediated cholesterol efflux activity, has direct lipid solubilization activity and reduces sub-RPE lipid accumulation following IVT injection in vivo. These studies support CTX203 as a novel therapeutic candidate to decrease lipid burden in patients with intermediate AMD.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.