Cholesterol-lowering Action of BNA-based Antisense Oligonucleotides Targeting PCSK9 in Atherogenic Diet-induced Hypercholesterolemic Mice

Abstract

Recent findings in molecular biology implicate the involvement of proprotein convertase subtilisin/kexin type 9 (PCSK9) in low-density lipoprotein receptor (LDLR) protein regulation. The cholesterol-lowering potential of anti-PCSK9 antisense oligonucleotides (AONs) modified with bridged nucleic acids (BNA-AONs) including 2',4'-BNA (also called as locked nucleic acid (LNA)) and 2',4'-BNA(NC) chemistries were demonstrated both in vitro and in vivo. An in vitro transfection study revealed that all of the BNA-AONs induce dose-dependent reductions in PCSK9 messenger RNA (mRNA) levels concomitantly with increases in LDLR protein levels. BNA-AONs were administered to atherogenic diet-fed C57BL/6J mice twice weekly for 6 weeks; 2',4'-BNA-AON that targeted murine PCSK9 induced a dose-dependent reduction in hepatic PCSK9 mRNA and LDL cholesterol (LDL-C); the 43% reduction of serum LDL-C was achieved at a dose of 20 mg/kg/injection with only moderate increases in toxicological indicators. In addition, the serum high-density lipoprotein cholesterol (HDL-C) levels increased. These results support antisense inhibition of PCSK9 as a potential therapeutic approach. When compared with 2',4'-BNA-AON, 2',4'-BNA(NC)-AON showed an earlier LDL-C-lowering effect and was more tolerable in mice. Our results validate the optimization of 2',4'-BNA(NC)-based anti-PCSK9 antisense molecules to produce a promising therapeutic agent for the treatment of hypercholesterolemia.

Figure 1

Structure of bridged nucleic acids (BNA) used in this study. LNA, locked nucleic acid.

Figure 2

In vitro silencing properties of AONs (CR01S, CR01SL, P900S, P900SL, P901SL, and P901SNC). AONs were transfected into NMuLi cells. (a,b) After a 24-hour incubation, cells were collected and the expression levels of PCSK9 mRNA were determined. Data represent means ± SD. (c) PCSK9 and LDLR proteins were also detected by western blotting. AONs (P901S, P901SL, and P901SNC) were transfected into HepG2 cells. (d) After a 24-hour incubation, HepG2 cells were collected and the expression levels of PCSK9 mRNA were determined. Data represent mean values ± SD. (e) PCSK9 and β-actin proteins were detected by western blotting. AON, antisense oligonucleotide; LDLR, low-density lipoprotein receptor; mRNA, messenger RNA.

Figure 3

Single administration of P900SL to normal-chow fed C57BL/6J mice. (a,b) Hepatic PCSK9 messenger RNA (mRNA) level and P900SL content 72 hours after a single intravenous (i.v.) administration were expressed as a function of dose level. (c,d) Liver PCSK9 mRNA expression level was measured and presented for each dose 72 hours after subcutaneous (s.c.) and intraperitoneal (i.p.) injection, respectively. Data represent mean values ± SD. n = 4–7.

Figure 4

Short-term effects of P900S and P900SL. Atherogenic diet-fed mice received intraperitoneal administration of P900S or P900SL at a dose of 10 mg/kg twice during 4 days. (a) Liver PCSK9 mRNA levels 4 days after the first injection. (b) Relative serum LDL-C levels 4 days after the first injection. (c) Hepatic LDLR protein expression levels were estimated by western blotting. (d) Serum liver transaminases (AST, ALT) were analyzed. Data represent mean values (± SD). *P < 0.05. ALT, alanine aminotransferase; AST, aspartate aminotransferase; LDL-C, low-density lipoprotein cholesterol; LDLR, low-density lipoprotein receptor; mRNA, messenger RNA.

Figure 5

Dose-dependent responses of physiological parameters to P900SL dosing. (a) Changes in cholesterol fractions upon administration of P900SL analyzed by HPLC. (b) Ratio of serum LDL-C levels after 4 weeks of treatment to before treatment were arranged in order of doses. (c) Liver PCSK9 mRNA levels were measured at all dose levels after 6 weeks of treatment. (d) Hepatic LDLR protein levels were determined 6 weeks after treatment started. (e) The expression levels of genes regulating lipid homeostasis in liver were analyzed. Data represent mean values ± SD. *P < 0.05. n = 5. HDL, high-density lipoprotein; HPLC, high performance liquid chromatography; LDL, low-density lipoprotein; LDL-C, LDL cholesterol; LDLR, LDL receptor; mRNA, messenger RNA; VLDL, very LDL.

Figure 6

Changes in toxicological parameters upon P900SL dosing. (a) Serum liver transaminases (AST and ALT) and BUN levels were measured. Data represent mean values ± SD. *P < 0.05. (b) Representative H&E stain images of liver of saline- and P900SL-treated mice. Bar indicates 100 µm. AST, aspartate aminotransferase; ALT, alanine aminotransferase; BUN, blood urea nitrogen; CV, central vein; H&E, hematoxylin and eosin; PV, portal vein.

Figure 7

Dose-dependent and chemistry-dependent differences in serum LDL-C levels, hepatic LDLR protein, and PCSK9 mRNA levels after treatment of P901SL and P901SL. (a) Raw values of serum LDL-C were obtained at 4th week of schedule. (b) Hepatic LDLR protein expression levels were measured after the end of the schedule. (c) Liver PCSK9 mRNA levels were measured at all dose levels after 6 weeks of treatment. Data represent mean values ± SD. *P < 0.05, **P < 0.001 (versus a saline-treated control arm). n = 5. LDL-C, low-density lipoprotein cholesterol; LDLR, low-density lipoprotein receptor; mRNA, messenger RNA.