Effect of an RNA interference drug on the synthesis of proprotein convertase subtilisin/kexin type 9 (PCSK9) and the concentration of serum LDL cholesterol in healthy volunteers: a randomised, single-blind, placebo-controlled, phase 1 trial

Abstract

Background: Proprotein convertase subtilisin/kexin type 9 (PCSK9) binds to LDL receptors, leading to their degradation. Genetics studies have shown that loss-of-function mutations in PCSK9 result in reduced plasma LDL cholesterol and decreased risk of coronary heart disease. We aimed to investigate the safety and efficacy of ALN-PCS, a small interfering RNA that inhibits PCSK9 synthesis, in healthy volunteers with raised cholesterol who were not on lipid-lowering treatment.

Methods: We did a randomised, single-blind, placebo-controlled, phase 1 dose-escalation study in healthy adult volunteers with serum LDL cholesterol of 3·00 mmol/L or higher. Participants were randomly assigned in a 3:1 ratio by computer algorithm to receive one dose of intravenous ALN-PCS (with doses ranging from 0·015 to 0·400 mg/kg) or placebo. The primary endpoint was safety and tolerability of ALN-PCS. Secondary endpoints were the pharmacokinetic characteristics of ALN-PCS and its pharmacodynamic effects on PCSK9 and LDL cholesterol. Study participants were masked to treatment assignment. Analysis was per protocol and we used ANCOVA to analyse pharmacodynamic endpoint data. This trial is registered with ClinicalTrials.gov, number NCT01437059.

Findings: Of 32 participants, 24 were randomly allocated to receive a single dose of ALN-PCS (0·015 mg/kg [n=3], 0·045 mg/kg [n=3], 0·090 mg/kg [n=3], 0·150 mg/kg [n=3], 0·250 mg/kg [n=6], or 0·400 mg/kg [n=6]) and eight to placebo. The proportions of patients affected by treatment-emergent adverse events were similar in the ALN-PCS and placebo groups (19 [79%] vs seven [88%]). ALN-PCS was rapidly distributed, with peak concentration and area under the curve (0 to last measurement) increasing in a roughly dose-proportional way across the dose range tested. In the group given 0·400 mg/kg of ALN-PCS, treatment resulted in a mean 70% reduction in circulating PCSK9 plasma protein (p<0·0001) and a mean 40% reduction in LDL cholesterol from baseline relative to placebo (p<0·0001).

Interpretation: Our results suggest that inhibition of PCSK9 synthesis by RNA interference (RNAi) provides a potentially safe mechanism to reduce LDL cholesterol concentration in healthy individuals with raised cholesterol. These results support the further assessment of ALN-PCS in patients with hypercholesterolaemia, including those being treated with statins. This study is the first to show an RNAi drug being used to affect a clinically validated endpoint (ie, LDL cholesterol) in human beings.

Funding: Alnylam Pharmaceuticals.

Figure 1. PCSK9 pathway and RNA interference synthesis-inhibitor approach

PCSK9 has a role in both intracellular and extracellular degradation of the LDL receptor (LDLR). PCSK9 synthesis inhibitors such as ALN-PCS inhibit PCSK9 synthesis (A) and therefore both intracellular and extracellular functions, whereas PCSK9 blockers (such as anti-PCSK9 antibodies) inhibit only extracellular function (B). mRNA=messenger RNA.

Figure 2

Trial profile

Figure 3. Effect of ALN-PCS treatment on plasma PCSK9 concentration

(A) Mean plasma PCSK9 concentrations relative to baseline and placebo. Error bars are SEs. PCSK9 concentrations were normalised per-individual to baseline and then per-day to placebo group means. For 0·045 mg/kg group at day 10, data from only one of three participants were available; for days 10 and 17, blood samples were only available for the 0·250 mg/kg and 0·400 mg/kg dose groups and their affiliated placebo participants, so values at these days are derived from or normalised to data from two of eight placebo participants. (B) Maximum plasma PCSK9 percentage reduction after treatment with ALN-PCS. Maximum reductions were determined per individual, at lowest PCSK9 value from days 1–28. Data are least-square means and error bars are 95% CIs, determined from analysis of covariance with baseline PCSK9 as covariate. *p<0·05; **p<0·001 (Tukey's post-hoc tests vs placebo). Least-square mean PCSK9 reductions per dose group were estimated via a linear model with dose group as a factor and baseline PCSK9 as a covariate. The overall model was significant (F=8·821; p=2·307x10 ⁵). (C) Mean plasma PCSK9 concentrations relative to baseline. Error bars are SEs. (D) Mean maximum percentage reductions in PCSK9 and LDL cholesterol in participants given 0·150, 0·250, and 0·400 mg/kg ALN-PCS, grouped by low, intermediate, and high baseline PCSK9 concentrations (<0·5, within 0·5, and >0·5 SDs from the mean, respectively). Error bars are SEs.

Figure 4. Effect of ALN-PCS treatment on serum LDL cholesterol

(A) Mean serum LDL cholesterol concentrations relative to baseline and placebo. Error bars are SEs. LDL cholesterol concentrations were normalised per-individual to baseline and then per-day to placebo group means. For 0·045 mg/kg group at day 10, data from only one of three participants were available; for days 10 and 17, blood samples were only available for the 0·250 mg/kg and 0·400 mg/kg dose groups and their affiliated placebo participants, so values at these days are derived from or normalised to data from two of eight placebo participants. (B) Maximum serum LDL cholesterol percentage reductions after treatment with ALN-PCS. Maximum reductions were determined per individual, at nadir LDL cholesterol value from days 1–28. Data are least-square means and error bars are 95% CIs, determined from analysis of covariance with baseline LDL cholesterol as covariate. *p<0·01 (Tukey's post hoc test vs placebo). Least-square mean LDL cholesterol reductions per dose group were estimated via a linear model with dose group as a factor and baseline LDL cholesterol as a covariate. The overall model was significant (F=4·888; p=0·0015). (C) Mean serum LDL cholesterol concentrations relative to baseline and placebo. Error bars are SEs. For days 10 and 17, blood samples were only available for the 0·250 mg/kg and 0·400 mg/kg dose groups and their afliliated placebo participants, so values at these days are derived from or normalised to data from two of eight placebo participants. (D) Mean serum LDL cholesterol concentrations at per-individual nadir from days 1–28. Error bars are SEs.