PCSK9 inhibitors: what we know, what we should have understood, and what is to come

Induced alternative splicing an opportunity to study PCSK9 protein isoforms at physiologically relevant concentrations

Splice modulating antisense oligomers (AOs) are increasingly used to modulate RNA processing. While most are investigated for their use as therapeutics, AOs can also be used for basic research. This study examined their use to investigate internally and terminally truncated proprotein convertase subtilisin/kexin type 9 (PCSK9) protein isoforms. Previous studies have used plasmid or viral-vector-mediated protein overexpression to study different PCSK9 protein isoforms, creating an artificial environment within the cell. Here we designed and tested AOs to remove specific exons that encode for PCSK9 protein domains and produced protein isoforms at more physiologically relevant levels. We evaluated the isoforms' expression, secretion, and subsequent impact on the low-density lipoprotein (LDL) receptor and its activity in Huh-7 cells. We found that modifying the Cis-His-rich domain by targeting exons 10 or 11 negatively affected LDL receptor activity and hence did not enhance LDL uptake although the levels of LDL receptor were increased. On the other hand, removing the hinge region encoded by exon 8, or a portion of the prodomain encoded by exon 2, have the potential as therapeutics for hypercholesterolemia. Our findings expand the understanding of PCSK9 isoforms and their impact on the LDL receptor and its activity at physiologically relevant concentrations.

PCSK9 Monoclonal Antibodies: New Developments and Their Relevance in a Nucleic Acid-Based Therapy Era

Purpose of Review

To report on recent data about PCSK9 monoclonal antibodies and to evaluate their relevance in a nucleic acid–based therapy era for lipid lowering and prevention of cardiovascular disease.

Recent Findings

New methods of PCSK9 inhibition based on nucleic acid therapeutics such as antisense oligonucleotides, small interfering RNAs, and CRISPR tools for therapeutic gene editing are reported, and interesting new data regarding the clinical relevance of PCSK9 antibodies are discussed.

Summary

Promising methods of PCSK9 inhibition are in development, and one of them, the siRNA inclisiran targeting PCSK9, has already been approved for clinical use. However, PCSK9-mAb remains the PCSK9-inhibiting tool with the longest safety data and the only one having positive cardiovascular outcome trials. An ongoing cardiovascular outcome trial with inclisiran is planned to be completed in 2026. Other forms of PCSK9 inhibition, such as antisense oligonucleotides targeting PCSK9 and CRISPR base editing of PCSK9, are still in early phases of development, and their potential clinical relevance remains to be established.

The year in cardiovascular medicine 2021: dyslipidaemia

The past year was an exciting time for clinical lipidology when we learnt more about existing therapies as well as therapies targeting novel pathways discovered through genetic studies. LDL cholesterol remained the main target and a variety of drugs to lower LDL cholesterol through different mechanisms were explored. Emerging evidence on the atherogenity of triglyceride-rich lipoproteins led to renewed interest in lowering them with new treatments. Lp(a) was back in focus with evidence on causality and new targeted therapeutics which dramatically lower Lp(a) levels. We will be able to personalise lipid lowering therapy further with this enriched armamentarium once we have the results of the cardiovascular outcome studies with some of these new agents.

What Lessons Have We Learned and What Remains to be Clarified for PCSK9 Inhibitors? A Review of FOURIER and ODYSSEY Outcomes Trials

For more than half a century, low-density lipoprotein cholesterol (LDL-C) has been recognized as a major risk factor for incident atherosclerotic cardiovascular disease. The discovery of proprotein convertase subtilisin-kexin type 9 (PCSK9) in 2003, which prevents LDL-C receptor recycling, identified a new target for drug intervention. Recently, two large-scale randomized clinical outcomes trials involving fully human anti-PCSK9 monoclonal antibodies tested the hypothesis that targeting this pathway would reduce cardiovascular events. Both the FOURIER (Further cardiovascular OUtcomes Research with PCSK9 Inhibition in subjects with Elevated Risk) and ODYSSEY OUTCOMES trials met their primary efficacy endpoints, confirming findings reported earlier that major adverse cardiovascular events can be reduced by a further lowering of LDL-C beyond that achieved with statin therapy. In both trials, there were incremental reductions in LDL-C of > 50% from baseline, with no major safety concerns, over the trials' median follow-up time (2.2 and 2.8 years, respectively). While there were differences in design, lipid management and overall results, key messages from both studies were similar. However, post-publication, additional questions have arisen, especially regarding drug effects over the long-term, including a potential mortality benefit.