Moving toward genome-editing therapies for cardiovascular diseases

Abstract

The rapid invention of genome-editing technologies over the past decade, which has already been transformative for biomedical research, has raised the tantalizing prospect of an entirely new therapeutic modality. Whereas the treatment of chronic cardiovascular diseases has heretofore entailed the use of chronic therapies that typically must be taken repeatedly and frequently for the remainder of the lifetime, genome editing will enable the development of "one-and-done" therapies with durable effects. This Review summarizes the variety of available genome-editing approaches, including nuclease editing, base editing, epigenome editing, and prime editing; illustrates how these various approaches could be implemented as novel therapies for cardiovascular diseases; and outlines a path from technology development to preclinical studies to clinical trials. Although this Review focuses on PCSK9 as an instructive example of the various genome-editing approaches under active investigation, the lessons learned will be broadly applicable to the treatment of a variety of diseases.

Figure 1. CRISPR/Cas9 nuclease editing.

The protospacer-adjacent motif (PAM) in the DNA and spacer sequence in the guide RNA direct CRISPR/Cas9 to a specific genomic site. There, it generates a double-strand break (indicated by red arrows pointing to DNA strands) that is repaired by one of two repair mechanisms: non-homologous end joining (NHEJ) or homology-directed repair (HDR). In NHEJ, free DNA ends are ligated together, which can restore the original DNA sequence or introduce insertions or deletions. This strategy is suitable for disrupting genes or non-coding elements in the genome. HDR enables more precise changes but requires the addition of a template, which reduces its efficiency. Adapted with permission from the Journal of the American College of Cardiology (58).

Figure 2. Base editing and epigenome editing.

(A) Base-editing strategies offer the advantages of precision editing without the inefficiency that complicates the use of HDR. With base editing, only one strand is cut (or nicked), nucleotides around the site of the nick are replaced, and the nick is repaired. The specific nucleotides that undergo replacement are determined by the selection of the base editor. (B) In epigenome editing, catalytically dead Cas9 (dCas9) can be directed to a gene promoter or transcriptional enhancer to modify gene expression. This strategy can be used to either enhance or repress target gene expression. It does not make a change to the DNA sequence. Adapted with permission from the Journal of the American College of Cardiology (58).

Figure 3. Prime editing.

Prime editing overcomes limitations inherent to base editing and HDR by fusing nickase Cas9 to a reverse transcriptase (RT) that can build a DNA sequence with a desired mutation into an extended guide RNA (referred to as pegRNA). Though its efficiency tends to be lower than NHEJ or base editing, prime editing enables single-nucleotide changes of any kind as well as indel mutations of various sizes. Adapted with permission from the Journal of the American College of Cardiology (58).