Abstract 12052: Role of Alirocumab (Proprotein Convertase Subtilisin/Kexin Type 9 Antibody) on CD81 Levels and Hepatitis C Virus Entry Into Hepatocytes
Background: Proprotein Convertase Subtilisin/Kexin type 9 (PCSK9) is secreted primarily from the liver, and binds to low-density lipoprotein receptors (LDLRs), leading to increased LDL cholesterol (LDL-C) levels. It has been reported that over-expression of a non-secreted, cell membrane-bound form of PCSK9 reduces surface expression of CD81, a major component of Hepatitis C virus (HCV) entry complex. A subsequent hypothesis that inhibition of PCSK9 may increase CD81 levels and augment HCV entry into hepatocytes, thereby enhancing susceptibility to HCV infection, has been suggested, raising safety concerns for PCSK9-targeting agents. However, ectopically expressing membrane-associated PCSK9 may not be physiologically relevant, as native PCSK9 is a secreted protein. Hence this does not represent an appropriate model for studying effects of PCSK9-targeting, particularly with a PCSK9 blocking antibody. Here, the results of a more suitable approach using native secreted PCSK9 are described.
Methods and Results: LDLR and CD81 protein quantitation using flow cytometry and western blotting of Huh-7 cells (human hepatocytes) showed that while LDLR levels were affected by extracellular PCSK9 levels, there was no correlation between the presence and amount of secreted, soluble PCSK9 and total or surface CD81 levels. Moreover, antibody blockade with the monoclonal antibody targeting PCSK9, alirocumab (SAR236553/REGN727), had no impact on CD81. In an in vitro model of HCV entry, addition of soluble PCSK9 or treatment with alirocumab had no effect on the ability of HCV to enter hepatocytes. Consistent with the in vitro findings, in vivo murine models showed no relation between PCSK9 inhibition and CD81 levels. Specifically, while both significant protection of LDLR from PCSK9-mediated degradation and reduction in circulating LDL-C levels were observed in Pcsk9-/- animals compared with wild-type controls and in hyperlipidemic Pcsk9hum/hum Ldlr+/- mice administered with alirocumab compared with isotype control antibody, no changes were observed in hepatic CD81 levels in either animal model.
Conclusion: Based on these preclinical data, blocking PCSK9 with alirocumab has no effect on CD81 and does not result in increased susceptibility to HCV entry.
- © 2013 by American Heart Association, Inc.