Gene editing for cardiovascular disease prevention

Prof. Ulf Landmesser discusses a new study with Mark Nicholls that paves the way for once-in-a-lifetime treatment for cardiovascular disease (CVD) prevention. A new therapy that could deliver an once-in-a-lifetime treatment to help prevent CVD has taken a significant step closer to human application. A team in the USA has harnessed gene-editing technologies, which include the CRISPR–Cas nucleases and CRISPR base editors, to pave the way to permanently modify disease-causing genes in patients. Prof. Ulf Landmesser (Figure 1), who has been working in the field for two decades and has already made significant advances towards treatments in the field, described the development as ‘very exciting’, with the potential to ‘open the door’ for once-in-a-lifetime treatment for CVD. While he acknowledges that there are still some safety concerns with the gene-editing approach, he believes that it will have enormous benefits for patients. Prof. Ulf Landmesser. The paper, ‘In vivo CRISPR base editing of PCSK9 durably lowers cholesterol in primates’ led by Prof. Kiran Musunuru from the Perelman School of Medicine at the University of Pennsylvania and Prof. Sekar Kathiresan from Verve Therapeutics (Cambridge, USA),1 demonstrated that CRISPR base editors that are delivered in vivo using lipid nanoparticles can efficiently and precisely modify disease-related genes in living cynomolgus monkeys. The study team observed a near-complete knockdown of PCSK9 in the liver after a single infusion of CRISPR base editors in lipid nanoparticles, with concomitant reductions in blood levels of PCSK9 and low-density lipoprotein cholesterol of approximately 90% and about 60%, respectively. The changes remained stable for at least 8 months after a single-dose treatment. ‘In addition to supporting a “once-and-done” approach to the reduction of low-density lipoprotein cholesterol and the prevention and/or treatment of atherosclerotic cardiovascular disease’, stated the authors, ‘the results provide a proof-of-concept for how CRISPR base editors can be productively applied to make precise single-nucleotide changes in therapeutic target genes in the liver, and potentially in other organs’. In examining the paper Prof. Landmesser, who is a chairman of the Department of Cardiology at Charite in Berlin said: ‘Why this paper is in line with what we have seen in recent years is that we have now a very clear understanding of which genes are causal for atherosclerosis—and PCSK9 is one of these genes’. Genetic studies have shown that people who have sequence variations in the PCSK9 gene are protected from atherosclerosis and when patients with atherosclerosis are treated with PCSK9 inhibitors their cardiovascular risk can be reduced, he explained. Within work he is contributing to in small-interfering RNA (siRNA) treatment, which blocks and inhibits mRNA, the approach is set to enter clinical practice this year in Europe to inhibit PCSK9. He is also supporting trials with antisense oligonucleotide RNA against apolipoprotein (a) to lower lipoprotein A. ‘The PCSK9 siRNA treatment needs to be conducted only twice a year, as opposed to daily administration’, he continued, ‘but this paper is going one step further. What the authors are aiming to develop is a treatment where you identify the person at risk and do a once-in-a-lifetime treatment to inhibit the target of interest, which here is PCSK9’. With strong interest in the field of molecular therapies to inhibit atherogenic lipoproteins that are causal for atherosclerotic CVD, Prof. Landmesser has been working on the impact of different lipoproteins on vascular function and disease. ‘Therefore’, he continued, ‘I am very excited about this development for what we call targeted nucleic acid-based therapies to prevent atherosclerotic cardiovascular disease’. The work of Prof. Musunuru and collaborators is based on the CRISPR-Cas technology for which Prof. Landmesser's colleague Prof. Emmanuelle Charpentier from the Max Planck Unit for the Science of Pathogens, Berlin, and Prof. Jennifer A. Doudna from the University of California, Berkeley, were awarded the 2020 Nobel Prize in Chemistry ‘for the development of a method for genome editing’. ‘Now we see this system applied to cardiovascular medicine and so this is an interesting development in once-in-a lifetime treatment option’, said Prof. Landmesser. This had previously been demonstrated in small animal models but the new paper is in a large animal model that is closer to the human setting. 'The way the authors have performed this is they have designed several so-called gRNAs, about 20 base pair RNA molecules that then aligned with the DNA and can initiate this so-called gene editing so they change a nucleotide into a different nucleotide. If you do this in a sensitive space of the gene you can basically induce inhibition of the gene. This is what they impressively demonstrate in this paper,' said Prof. Landmesser. He points out that the once-in-a-lifetime option is different to siRNA, which will also have long-term effectiveness but is not modifying the DNA, whereas the new approach is modifying the genome. The Musunuru team targeted the liver and cells for genome editing as it is regarded as the best target for nucleic acid-based therapies, with atherosclerotic CVD disease to a large extent dependent on atherogenic lipoproteins produced in the liver. With a higher dose, of gRNA, the researchers report <1% of off-target editing. Prof. Landmesser explained: 'They have a very effective editing of PSCK9, which is what you want to achieve, but they see also editing in other genes, which you don’t want. They did tests at a different dose of gRNA and report with a lower dose of 0.5 mg per kg delivered in lipid nanoparticles injected intravenously in the monkeys, that there was no off-target editing.' The avoidance of off-target gene editing is still an important area of research for Prof. Landmesser and needs careful attention to avoid inducing unwanted mutations in a human. He also makes the point that if the gene is inactivated, it may not be able to be activated again, supporting really well-targeted approaches. However, he also noted that there is experience of people who have loss of function mutation in PCSK9, and they are ‘doing fine’, indicating that the gene has no other critical physiological function that is not compensated for by other genes if you knock it out. ‘What we learn from this study is that gene editing of PCSK9 can be very effective, what we still need to learn more about is safety, in particular the avoidance of off-target gene editing and it looks like they get close to an approach where you do not have off-target editing’, he continued. ‘But from my perspective, that is the really critical point that you can be sure once you do that in a human you do not have off-target editing. This will open the door for once-in-a-lifetime treatment for cardiovascular disease and its prevention’. Going forward in terms of application, he envisions in the near future the use of the other nucleic acid-based therapies such as siRNA and antisense oligonucleotide approaches now used in secondary prevention, might move towards primary prevention, and preventing disease before it develops. ‘That would be an important development and would also require that we get even better at identifying people who are at high risk of developing the disease. We would treat them with such an approach in a preventive manner. In the further future, as gene editing is highly-attractive in the first line for people who have a genetic disease, but theoretically you can also envisage if it is very safe can also do this as a preventive strategy in the future. But safety is key’, said Prof. Landmesser, who is also the medical chair of the cardiovascular centre at Charite University Medecine in Berlin and has a BIH (Berlin Institute of Health) professorship for cardiology. ‘I am very excited that these important advances in nucleic-acid based therapies are happening in the cardiovascular space. The PCSK9 siRNA is currently by far the largest siRNA programme in general in medicine’, he said. ‘Also, we have the biggest antisense oligonucleotide treatment programme in cardiovascular disease now targeting atherogenic lipoproteins. And it is also very exciting that we may likely be among the first to do this CRISPR-Cas based gene editing for prevention of CVD’.