Combination therapy with GalNAc-siRNA drugs targeting both PCSK9 and APOC3 resulted in enhanced lipid lowering in mice
Authors: Luo H , Zheng S , Cao H , Singh A , Tong C , Zhang H , Liang Z , Gronros J , Wikstrom J , Gao S , Gan L 
Published: October 2024

Abstract

Introduction
Aggressive lowering of both atherogenic low-density lipoprotein cholesterol (LDL-C) and triglyceride-rich lipoproteins (TRLs) could reduce residual atherosclerotic cardiovascular disease (ASCVD) risk. Drugs targeting PCSK9 or APOC3 have shown good lipid-lowering effects in clinic. Here, we have developed GalNAc-conjugated siRNAs, RBD7022 targeting PCSK9 and RBD5044 targeting APOC3, as novel therapeutic agents to lower LDL-C and triglyceride (TG) plasma levels respectively. Each drug shows potent and durable effect in silencing its own target. However, it is unknown whether the combined therapy with siRNA drugs targeting both PCSK9 and APOC3 will generate enhanced effects in lipid lowering.

Purpose
To investigate the effects of fixed-dose combination of RBD7022 and RBD5044 on LDL-C, TG and total cholesterol (TC).

Methods
RBD7022 and RBD5044 completely match the human PCSK9 and APOC3 transcripts respectively. RBD7022 has 2 nucleotide mismatches with mouse pcsk9, but still shows silencing activity in mice, while RBD5044 has no activity due to 5 mismatches with mouse apoc3. Therefore, humanized APOC3 transgenic mice were used in this study, which had serious hypertriglyceridemia with relatively high cholesterol and TG levels. They were randomized into 8 groups with treatment of RBD7022 (1 mg/kg or 3 mg/kg), RBD5044 (3 mg/kg or 6 mg/kg), or 3 different dose combinations of RBD7022 and RBD5044, as well as PBS control. All animals were administrated once on Day 1. Plasma was collected to quantify lipid biomarkers.

Results
RBD7022 showed a robust effect on LDL-C reduction, with inhibition rates of 45% in 3 mg/kg and 43% in 6 mg/kg, indicating 3 mg/kg was a saturated dose for RBD7022 in LDL-C lowering. RBD5044 showed a dose-dependent effect on LDL-C reduction, with inhibition rate of 52% at 1 mg/kg and 59% at 3 mg/kg. Interestingly, significantly enhanced LDL-C reduction was observed in the combination groups, with 67% reduction in LDL-C at RBD5044 1 mg/kg plus RBD7022 3 mg/kg, 73% reduction in LDL-C at RBD5044 3 mg/kg plus RBD7022 3 mg/kg and 78% reduction in LDL-C at RBD5044 3 mg/kg plus RBD7022 6 mg/kg, showing dose-dependent effects (Figure 1A). Enhanced TC reduction was also found in combination at RBD5044 3 mg/kg plus RBD7022 6 mg/kg compared with RBD5044 or RBD7022 alone.
RBD5044 showed a dose dependent effect on TG reduction with inhibition rates of 56% at 1 mg/kg and 83% at 3 mg/kg. RBD7022 treatment alone did not show significant effect on TG reduction. No added effects of RBD7022 on TG levels was found in the combination with RBD5044, indicating the TG lowering was induced by RBD5044.

Conclusions
The combination of RBD7022 targeting PCSK9 and RBD5044 targeting APOC3 simultaneously reduce LDL-C and TC levels. The combination of RBD7022 and RBD5044 could be a better therapeutic option to further reduce LDL-C, particularly for mixed hyperlipidemia patients and other high-risk individuals with both high LDL-C and high TG levels.Figure 1