What is the mechanism of action of inclisiran?

Mechanism of Action of Inclisiran

Inclisiran is a double-stranded small interfering RNA (siRNA) that selectively silences hepatic PCSK9 messenger RNA production, leading to increased LDL receptor expression on hepatocytes and subsequent reduction in circulating LDL cholesterol levels. 1, 2

Molecular Mechanism

Inclisiran works through a sophisticated RNA interference pathway that differs fundamentally from PCSK9 monoclonal antibodies:

Hepatocyte-Specific Targeting:

• The drug is conjugated with triantennary N-acetylgalactosamine (GalNAc) on its sense strand, which specifically directs it to hepatocytes via asialoglycoprotein receptors 1, 2
• This targeted delivery ensures high hepatic uptake and selectivity for the liver, the primary organ for cholesterol metabolism 2

Intracellular PCSK9 Inhibition:

• Once inside hepatocytes, inclisiran binds to the RNA-induced silencing complex (RISC) 3
• This complex catalytically degrades PCSK9 messenger RNA, preventing translation of the PCSK9 protein 1
• Critically, inclisiran inhibits PCSK9 production at the intracellular level, before the protein is even synthesized—unlike PCSK9 monoclonal antibodies (evolocumab, alirocumab) which bind extracellularly to already-produced PCSK9 protein 3

Downstream Effects on LDL Metabolism

By blocking PCSK9 synthesis, inclisiran prevents PCSK9 from binding to LDL receptors on hepatocyte surfaces. This mechanism:

• Increases LDL receptor recycling and expression on the hepatocyte cell surface 1, 2
• Enhances hepatic uptake of LDL cholesterol from circulation 2
• Results in sustained reduction of circulating LDL-C levels 2

Pharmacodynamic Profile

The catalytic nature of RNA interference provides inclisiran's distinctive pharmacodynamic characteristics:

• LDL-C reduction becomes apparent within 14 days of administration 2
• Mean reductions of 38-51% in LDL-C persist from day 30 to 180 post-dose 2
• PCSK9 levels are reduced by approximately 75% at day 120 and 69% at day 180 following the initial two-dose regimen 2
• The effect remains durable for over 6 months, enabling twice-yearly dosing after the loading phase 3, 4

Key Distinguishing Features

Duration of Action: The prolonged pharmacodynamic effect results from several factors 4:

• Sequestration in hepatocyte endosomes
• Enhanced metabolic stability of the modified siRNA
• Slow endosomal release leading to prolonged RISC loading
• The autocatalytic nature of RNA silencing in tissues

Comparison to PCSK9 Monoclonal Antibodies: While both drug classes inhibit PCSK9, their mechanisms differ fundamentally 3:

• Inclisiran: Prevents PCSK9 synthesis (intracellular mechanism)
• PCSK9 mAbs: Bind and neutralize circulating PCSK9 (extracellular mechanism)
• LDL-C lowering with inclisiran appears approximately 10% less than PCSK9 mAbs in similarly designed trials 3

Clinical Implications

The unique mechanism translates to practical advantages:

• Twice-yearly subcutaneous dosing (after initial dose and 3-month dose) versus monthly or biweekly injections for PCSK9 mAbs 3, 1
• Particularly beneficial for patients with medication adherence challenges 1
• Plasma concentrations become undetectable within 24-48 hours, yet pharmacodynamic effects persist for months 2

Important Caveat: While inclisiran effectively lowers LDL-C by approximately 50%, cardiovascular outcomes data from ongoing trials (ORION-4, VICTORION-2P) are still pending to establish effects on morbidity and mortality 3, 1.