Olpasiran

Olpasiran (AMG 890; formerly ARO-LPA) is an investigational, first-in-class, synthetic double-stranded small interfering RNA (siRNA) conjugated to a trivalent N-acetylgalactosamine (GalNAc) ligand for selective hepatocyte delivery via the asialoglycoprotein receptor (ASGPR). The compound targets the messenger RNA transcribed from the LPA gene, which encodes apolipoprotein(a), the defining protein component of lipoprotein(a) [Lp(a)]. Elevated Lp(a) is a genetically determined, independent, and causal risk factor for atherosclerotic cardiovascular disease (ASCVD), aortic valve stenosis, and thrombotic events, affecting an estimated 20 to 30 percent of the global population at concentrations associated with increased cardiovascular risk. Prior to the development of RNA-targeted therapies, no pharmacologic intervention produced clinically meaningful reduction in Lp(a) concentration; niacin and PCSK9 inhibitors achieve modest decreases of 20 to 30 percent, insufficient to test the causal hypothesis relating Lp(a) lowering to cardiovascular event reduction.

Following uptake into hepatocytes through ASGPR-mediated endocytosis, the antisense strand of olpasiran incorporates into the RNA-induced silencing complex (RISC), which catalytically cleaves LPA mRNA and suppresses de novo synthesis of apolipoprotein(a). The resulting reduction in hepatic apolipoprotein(a) secretion produces a dose-dependent, sustained, and near-complete lowering of circulating Lp(a) particles. In the Phase 1 single ascending-dose trial (NCT03626662), olpasiran produced dose-dependent Lp(a) reductions of 71 to 97 percent that persisted for several months after a single subcutaneous injection, with effects lasting up to six months at higher doses [1]. In the pivotal Phase 2 OCEAN(a)-DOSE trial (NCT04270760), a randomized, double-blind, placebo-controlled study in 281 patients with established ASCVD and Lp(a) greater than 150 nmol/L, olpasiran at doses of 75 mg or higher administered every 12 weeks produced placebo-adjusted Lp(a) reductions exceeding 95 percent at 36 weeks, with the 225 mg every-12-week regimen achieving a placebo-adjusted reduction of 101.1 percent [2]. The off-treatment extension analysis demonstrated that participants who received doses of 75 mg or higher every 12 weeks sustained approximately 40 to 50 percent Lp(a) reduction close to one year after the last dose, reflecting the durability of RISC-mediated mRNA silencing in hepatocytes [3].

The serum pharmacokinetics of olpasiran are characterized by rapid absorption after subcutaneous injection (time to maximum concentration approximately 3 to 9 hours) and rapid clearance from the systemic circulation (serum half-life approximately 3 to 8 hours), consistent with efficient hepatocyte uptake via the GalNAc-ASGPR pathway. The pharmacodynamic effect is dissociated from serum drug concentrations: the prolonged Lp(a) lowering reflects the intracellular persistence of the active RISC complex in hepatocytes rather than circulating drug exposure. The compound is well tolerated. In the OCEAN(a)-DOSE trial, the overall incidence of adverse events was similar in the olpasiran and placebo arms; the most frequently reported treatment-related adverse event was mild injection-site pain, which resolved without intervention [2]. No clinically significant changes in hepatic, renal, hematologic, or glycemic laboratory parameters were observed.

Olpasiran is currently under evaluation in the Phase 3 OCEAN(a)-Outcomes trial (NCT05581303), a large cardiovascular outcomes study assessing the effect of olpasiran versus placebo on the composite endpoint of coronary heart disease death, myocardial infarction, or urgent coronary revascularization in participants with ASCVD and elevated Lp(a). An additional Phase 3 primary prevention trial, OCEAN(a)-PreEvent (NCT07136012), is evaluating olpasiran for prevention of first major cardiovascular events. The compound is not approved by any regulatory authority as of the date of this monograph. This document reviews the chemistry and structural class of olpasiran; the biology of lipoprotein(a) and the LPA gene target; the GalNAc-siRNA delivery mechanism; the preclinical pharmacology in transgenic mice and cynomolgus monkeys; the comprehensive human pharmacokinetic and pharmacodynamic record; the clinical evidence base from Phase 1 through Phase 3; sourcing and handling considerations for research applications; stack interactions; adverse events and safety signal; and a structured comparative assessment of five Lp(a)-lowering candidates against olpasiran on five competency standards.