Rusfertide

What is Rusfertide?#

Rusfertide (PTG-300) is a first-in-class synthetic peptide mimetic of hepcidin, the master regulatory hormone of iron metabolism. Developed by Protagonist Therapeutics (now partnered with Takeda), rusfertide is designed to control erythrocytosis in polycythemia vera (PV) by restricting the iron supply needed for excessive red blood cell production.

Polycythemia vera is a chronic myeloproliferative neoplasm driven by JAK2 mutations that cause uncontrolled erythropoiesis. The standard approach to managing erythrocytosis -- therapeutic phlebotomy to maintain hematocrit below 45% -- is burdensome, does not address the underlying iron dysregulation, and often causes iron deficiency with associated symptoms. Rusfertide offers a pharmacological alternative that targets the root iron-regulatory pathway.

Mechanism of Action#

Hepcidin is a 25-amino acid peptide hormone synthesized primarily by the liver that serves as the central regulator of systemic iron homeostasis. It acts by binding to ferroportin, the only known cellular iron exporter, triggering its internalization and lysosomal degradation. This blocks iron efflux from enterocytes (dietary absorption), macrophages (recycled iron), and hepatocytes (stored iron), reducing plasma iron availability.

Rusfertide is a minihepcidins -- an engineered peptide that retains the critical ferroportin-binding pharmacophore of native hepcidin but with improved pharmacological properties:

• Ferroportin degradation: Binds ferroportin with high potency (EC50 ~5 nM), triggering internalization and degradation
• Iron restriction: Reduces serum iron and transferrin saturation, limiting iron availability for erythropoiesis
• Erythrocytosis control: By restricting iron supply to the bone marrow, reduces the excessive red blood cell production characteristic of PV
• Hematocrit maintenance: Achieves and maintains hematocrit below the 45% threshold without phlebotomy

Unlike cytoreductive agents (hydroxyurea, ruxolitinib) that suppress marrow proliferation broadly, rusfertide acts specifically on iron metabolism, offering a mechanism-based approach to erythrocytosis control.

Clinical Development#

Rusfertide has progressed through an extensive clinical program for polycythemia vera:

• REVIVE (Phase 2): Published in NEJM 2024, demonstrated 60% response rate vs 17% placebo in randomized withdrawal design, with near-elimination of phlebotomy need
• VERIFY (Phase 3): Met primary endpoint with 77% clinical response vs 33% placebo (P<0.0001), meeting all key secondary endpoints including hematocrit control and patient-reported outcomes
• FDA Breakthrough Therapy Designation: Granted based on REVIVE data, indicating potential to substantially improve treatment

The drug is also being investigated for hereditary hemochromatosis, another condition of iron excess.

Important Considerations#

Rusfertide is an investigational medication not yet approved by any regulatory authority. Key considerations include:

• Injection site reactions are common but generally mild (grade 1-2) and tend to improve with continued treatment
• Dose titration is required to achieve optimal hematocrit control
• Treatment interruption leads to loss of therapeutic benefit, with hematocrit rising and phlebotomy requirements returning
• Rusfertide does not address the underlying JAK2-driven clonal proliferation and is intended to complement, not replace, cytoreductive therapy where indicated

Key Research Findings#

Rusfertide, a Hepcidin Mimetic, for Control of Erythrocytosis in Polycythemia Vera, published in New England Journal of Medicine (Kremyanskaya M et al., 2024; PMID: 38381675):

• The study showed response rate of 60% rusfertide vs 17% placebo in randomized withdrawal
• The study showed mean maximum hematocrit of 44.5% during treatment vs 50.0% before treatment
• The study demonstrated grade 3 adverse events in of 13% ; no grade 4 or 5 events

Related Reading#

• Rusfertide research studies and evidence
• Rusfertide dosing protocols
• Rusfertide side effects profile
• EPO research guide