Development of a potent epigenetic editor targeting human PCSK9 with durable reduction of cholesterol in mice and non-human primates [twist methylome methyseq]

DNA methylation in gene promoter regions is a conserved, innate epigenetic mechanism to control gene expression. Transient application of epigenetic editors designed to induce DNA methylation has been shown to silence genes in cultured cells and in mice. Here we report the development of a potent, efficacious, and specific human PCSK9-targeting epigenetic editor. A single administration of lipid nanoparticles encapsulating mRNA encoding the epigenetic editor which precisely targets the PCSK9 locus was sufficient to drive near-complete silencing in transgenic mice expressing human PCSK9. Silencing was durable for at least one year and was fully maintained following partial hepatectomy-induced liver regeneration. In addition, we showed reversibility of epigenetic editing in previously silenced mice upon treatment with a targeted epigenetic activator designed to demethylate the PCSK9 locus. Importantly, a single administration of the epigenetic editor robustly, potently, and durably decreased circulating PCSK9 (~90%) in cynomolgus monkeys with concomitant reduction in low-density lipoprotein cholesterol (~70%). These findings support the development of an epigenetic editor targeting PCSK9 for the treatment of hypercholesterolemia and demonstrate the broad therapeutic potential of precise, efficacious, durable, and reversible epigenetic editing in vivo