In collaboration with Genzyme, Isis Pharmaceuticals has developed mipomersen sodium (ISIS-310312), a synthetic second-generation 20-base phosphorothioate antisense oligonucleotide (ASO) that targets messenger RNA encoding apolipoprotein B-100 (Apo B-100). Elevated cholesterol levels, in particular low-density lipoprotein cholesterol (LDL-C) which contains a single apolipoprotein B (ApoB) molecule, have been directly correlated with the incidence of cardiovascular events. Preclinical investigations in transgenic mice have demonstrated that lowering LDL-C or ApoB can reduce aortic plaque formation associated with atherosclerosis. Mipomersen pharmacokinetics showed a wide and rapid tissue distribution and a slow prolonged elimination phase of several days in a range of species. Mipomersen displayed dose-dependent efficacy in lowering LDL-C, ApoB, triglycerides, total cholesterol and other low-density lipoproteins in healthy volunteers with mild hyperlipidemia. Similar decreases were observed in patients on stable lipid-lowering therapy for familial hypercholesterolemia with baseline LDL-C levels declining towards clinically desirable concentrations of 70 mg/dL. The efficacy of mipomersen in treating patients with severe heterozygous or homozygous familial hypercholesterolemia with cardiovascular complications has been recently assessed. There have been no serious adverse events noted with treatment and mipomersen can be administered in combination with other lipid-lowering therapies. One concern noted was an elevation in liver transaminase concentrations, although these increases were reversible.