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phase 2Immune & Inflammation

Magainin 2

Also known as: Magainin II, Magainin-2, Pexiganan (synthetic derivative), MSI-78, Locilex

Magainin 2 is a 23-amino acid antimicrobial peptide originally isolated from the skin of the African clawed frog (Xenopus laevis) by Michael Zasloff in 1987. Its discovery was a landmark moment in antimicrobial peptide research, demonstrating that vertebrate skin secretions contain potent broad-spectrum antibiotics. Magainin 2 became the template for pexiganan (MSI-78), a synthetic derivative that advanced to Phase III clinical trials as a topical antibiotic for diabetic foot infections.

3 cited references·6 researched benefits

Quick Answer

Magainin 2 is a 23-amino acid antimicrobial peptide discovered in 1987 from the skin of the African clawed frog. It kills bacteria through membrane disruption via the toroidal pore model and has broad-spectrum activity against bacteria, fungi, and protozoa. Its synthetic derivative pexiganan (MSI-78) reached Phase III clinical trials as a topical treatment for diabetic foot infections. Magainin remains one of the most studied template molecules for developing new antimicrobial peptide therapeutics.

Key Facts

Mechanism
Magainin 2 adopts an amphipathic alpha-helical conformation when it contacts microbial membranes. It binds to the membrane surface through electrostatic attraction to anionic phospholipids, then inserts into the lipid bilayer according to the toroidal pore model — peptide molecules and lipid head groups bend inward together to form a continuous pore with both peptide and lipid lining the channel. These pores (approximately 2-3 nm in diameter) cause rapid leakage of ions and small molecules, membrane depolarization, and cell death. The selectivity for microbial over mammalian membranes arises from the preference for anionic phospholipids (abundant in bacteria) over zwitterionic phospholipids (predominant in mammalian cells).
Research Status
phase 2
Half-Life
~30 minutes (rapidly degraded by serum proteases)
Molecular Formula
C₁₁₄H₁₈₁N₃₁O₃₂S₁
Primary Use
Immune & Inflammation
Table of Contents

Benefits

  • Broad-spectrum antimicrobial activity against gram-positive, gram-negative bacteria, fungi, and protozoastrong
  • Low propensity for bacterial resistance development due to membrane-targeting mechanismstrong
  • Pexiganan derivative showed efficacy in Phase III trials for diabetic foot ulcer infectionsmoderate
  • Selective toxicity for microbial membranes with relatively low mammalian cell toxicitymoderate
  • Anti-biofilm activity disrupts established bacterial communities on wound surfacespreliminary
  • Foundational template molecule for rational design of improved synthetic antimicrobial peptidesstrong

Dosage Protocols

RouteDosage RangeFrequencyNotes
Topical (pexiganan cream)1-2% cream formulationTwice daily for 14-28 daysPexiganan (MSI-78) topical cream for mildly infected diabetic foot ulcers; Phase III dosing
Research use only (magainin 2)1–100 mcg/mL (in vitro)VariableNative magainin 2 used as a research tool; synthetic derivatives preferred for therapeutic development

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Local skin irritation or burning with topical applicationcommon
  • Hemolytic activity at high concentrations (improved in synthetic derivatives)rare
  • Rapid proteolytic degradation limits systemic bioavailabilitycommon
  • Contact dermatitis in sensitive individuals with topical userare

Frequently Asked Questions

How was magainin discovered?
Magainin was discovered in 1987 by Michael Zasloff, a researcher at the NIH, who observed that African clawed frogs (Xenopus laevis) recovering from surgery in non-sterile aquarium water rarely developed wound infections. He isolated the antimicrobial substances from the frog's skin secretions and named them magainins (from the Hebrew word "magain" meaning shield). This discovery was published in the Proceedings of the National Academy of Sciences and catalyzed the entire field of antimicrobial peptide research.
What happened to pexiganan (the magainin drug)?
Pexiganan (MSI-78), a synthetic 22-amino acid analogue of magainin, was developed by Magainin Pharmaceuticals as a topical cream for infected diabetic foot ulcers. It reached Phase III clinical trials in the late 1990s but was not approved by the FDA in 1999 because it failed to demonstrate superiority over oral ofloxacin (a fluoroquinolone). A second company, Dipexium Pharmaceuticals, attempted another Phase III trial in 2015-2016 but also failed to achieve its primary endpoint. The drug demonstrated antimicrobial activity but did not show clinical superiority over standard-of-care antibiotics.
Why is magainin important for antimicrobial peptide research?
Magainin is considered one of the founding molecules of antimicrobial peptide (AMP) therapeutics research. Its discovery demonstrated that vertebrates produce their own antibiotic peptides, its structure is simple enough to modify rationally, and its mechanism of action (toroidal pore formation) became the model for understanding how many AMPs kill bacteria. Hundreds of magainin derivatives and analogues have been synthesized to improve activity, stability, and selectivity, making it the single most important template in AMP drug design.
Can bacteria become resistant to magainin?
Resistance to magainin and similar membrane-active AMPs develops very slowly compared to conventional antibiotics. Because the target is the fundamental physical structure of the bacterial membrane (anionic phospholipids) rather than a specific protein, bacteria would need to completely remodel their membrane composition to become resistant. Laboratory evolution experiments show that it takes many more generations for bacteria to develop resistance to magainin compared to conventional antibiotics, though resistance is not impossible — it has been observed at low levels through lipid modification.

References

  1. 1
    Magainins, a class of antimicrobial peptides from Xenopus skin: isolation, characterization of two active forms, and partial cDNA sequence of a precursor(1987)PubMed ↗
  2. 2
    Pexiganan: a synthetic antimicrobial peptide for the topical treatment of diabetic foot ulcer infections(1999)PubMed ↗
  3. 3
    Antimicrobial peptides: pore formers or metabolic inhibitors in bacteria?(2005)PubMed ↗

Latest Research

Last updated: 2026-02-19