LL-37

What It Is

LL-37 is a 37-amino-acid peptide and the only cathelicidin-derived antimicrobial peptide found in humans. It is produced by neutrophils, macrophages, epithelial cells, and other immune tissues as part of the innate immune response. LL-37 demonstrates broad-spectrum antimicrobial activity against over 38 bacterial species, 16 fungi, and 16 viruses through mechanisms including membrane disruption, intracellular targeting, and biofilm suppression. Beyond its antimicrobial role, LL-37 modulates immune cell recruitment, promotes wound healing, and influences inflammatory signaling. A completed Phase 1 clinical trial of intra-tumoral LL-37 injections in melanoma patients with cutaneous metastases demonstrated significant anti-tumor potency, marking the first human clinical validation of LL-37's cancer applications. A key 2026 advancement is the development of LL-37 derivatives that overcome native limitations: the synthetic peptide CD4-PP, created through dimerization and backbone cyclization of LL-37, shows activity against common uropathogens, prevents new biofilm formation, and dissolves mature biofilm — addressing a critical unmet need in urinary tract infection treatment. A 2025 study published in ACS Biomaterials Science & Engineering reviewed systematic modification strategies for LL-37 derivatives with improved stability, reduced hemolytic activity, and enhanced efficacy under physiological salt concentrations. Current development in 2026 focuses on immobilization techniques, nanocarrier delivery systems, LL-37 derivative optimization, and synergistic combinations with existing antibiotics to combat multidrug-resistant infections. A comprehensive 2024 review in PubMed described LL-37 as 'the master antimicrobial peptide,' highlighting its multifaceted role from combating infections to cancer immunity. As of April 2026, the FDA removed LL-37 from the Category 2 bulk substances list, and it will be reviewed by the Pharmacy Compounding Advisory Committee (PCAC) at the July 2026 meeting.

Regulatory Status

Why Researchers Study It

LL-37 is the only human cathelicidin and represents a key component of innate immunity. Its broad-spectrum antimicrobial activity, combined with immunomodulatory and wound-healing properties, makes it a leading candidate for next-generation anti-infective therapies, particularly against multidrug-resistant biofilm-forming bacteria.

Proposed Mechanisms

• Disrupts bacterial membranes via electrostatic interaction with negatively charged lipid bilayers
• Forms oligomeric channels in membrane mimics, enabling membrane permeabilization
• Suppresses biofilm formation and disrupts established biofilms
• Recruits immune cells (neutrophils, monocytes) to infection sites via chemotactic signaling
• Modulates TLR signaling and NF-κB pathways to influence inflammatory responses
• Promotes angiogenesis and keratinocyte migration in wound healing contexts

Evidence Snapshot

Commonly Discussed Benefits

Safety & Cautions

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Citations

1. [1] Vandamme D. et al. — A comprehensive summary of LL-37, the factotum human cathelicidin peptide. Cell Immunol. 2012 PubMed
2. [2] Ridyard KE. & Bhatt A. — The potential of human peptide LL-37 as an antimicrobial and anti-biofilm agent. PMC. 2021 PubMed
3. [3] Barman S. et al. — Exploring the antimicrobial potential of LL-37 derivatives. ACS Biomater Sci Eng. 2025 PubMed
4. [4] Sánchez-Romero S. et al. — LL-37 is potent against non-growing E. coli. mSphere. 2024 PubMed
5. [5] LL-37, the master antimicrobial peptide: multifaceted role from infections to cancer immunity — PubMed 2024 PubMed
6. [6] A stable cyclized antimicrobial peptide derived from LL-37 with immunomodulatory effects — PMC 2022 PubMed

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