LL-37

Think of LL-37 as a member of your body's own fire brigade: it genuinely puts out fires (kills germs) and helps rebuild afterwards (heals wounds). That is why it earned real clinical trials, unlike most peptides. But the same crew can occasionally turn arsonist, fanning the flames of autoimmune disease like psoriasis. And the bigger, more careful trial showed that bottling this firefighter as a cream did not reliably out-perform a placebo: promising on paper, unproven in practice.

LL-37 is a cationic, amphipathic peptide cleaved from the hCAP18 precursor (CAMP gene product) by serine proteases such as proteinase 3. It kills microbes directly by electrostatically binding and permeabilising negatively charged microbial membranes (broad-spectrum, anti-biofilm) and by neutralising bacterial endotoxin (LPS). Beyond killing microbes it is a host-defence/immunomodulatory peptide: it recruits immune cells via the formyl-peptide receptor FPR2, transactivates EGFR, and promotes keratinocyte and fibroblast migration, angiogenesis and re-epithelialisation, which is the basis of its wound-healing rationale. The same properties cut both ways: complexed with self-DNA/RNA it activates plasmacytoid dendritic cells to produce type-I interferon and acts as a T-cell autoantigen, contributing to psoriasis and lupus.

Research contexts. Not proven uses, and not recommendations.

Genuinely more advanced than most grey-market peptides, but still inconclusive. A dose-ranging Phase I/II randomised, placebo-controlled trial in venous leg ulcers (Gronberg et al., 2014, 34 patients) reported good safety and tolerability and faster healing predictors. However, the larger pivotal Phase IIb HEAL LL-37 trial (Mahlapuu et al., 2021, 148 treated patients) FAILED its primary efficacy endpoint (sustained complete wound closure) across the full population, with a statistically significant benefit only in a post-hoc subgroup of large refractory ulcers. Smaller randomised data also exist for diabetic foot ulcers. There is no approved LL-37 product anywhere, and the development programme has not advanced to a successful Phase III. Separately, robust human immunology data establish LL-37 as a driver and self-antigen in psoriasis and lupus, which is relevant human evidence, but of harm, not benefit. Consumer claims of systemic 'recovery', anti-ageing or performance benefit have essentially no supporting human evidence.

• !No LL-37 medicine is approved or licensed anywhere; topical wound products remain investigational and the pivotal Phase IIb trial missed its primary endpoint.
• !Double-edged biology: LL-37 is a recognised autoantigen that drives inflammation in psoriasis and lupus (via self-DNA/RNA complexes and type-I interferon), so 'made by the body' does not equal 'safe'. Potential to aggravate autoimmune or inflammatory skin disease.
• !Cationic peptides can be cytotoxic and pro-inflammatory to host cells, particularly at high local concentrations.
• !Grey-market LL-37 sold as a 'research chemical' has no guarantee of identity, purity, sterility or endotoxin content; injecting unsterile peptide carries infection and immune-reaction risk.
• !Almost all touted 'recovery', anti-ageing or systemic benefits in consumers rest on in-vitro or animal data, not human trials.
• !Implicated mechanistically in tumour biology in a context-dependent way (can be pro- or anti-tumour), so systemic use is not benign by default.

Not a licensed medicine in the UK. There is no LL-37 (ropocamptide) product authorised by the MHRA and no marketing authorisation for any indication. It is an investigational drug (industry-run clinical wound-healing trials) and, in the consumer/grey market, an unlicensed peptide typically sold as a 'research chemical' labelled 'not for human consumption' to sidestep medicines law. Supplying or selling an unlicensed product for human use as a medicine breaches the Human Medicines Regulations 2012. There is no legitimate UK route to obtain LL-37 for self-administration, and it is not a prescribable medicine.

• · Phase 2b· Completed; primary endpoint not met overall (148 patients treated)

  HEAL LL-37: Phase IIb double-blind, randomised, placebo-controlled trial of topical LL-37 (ropocamptide) with compression in hard-to-heal venous leg ulcers

  Sponsored by Promore Pharma; reported in Mahlapuu et al. 2021.

• · Phase 1/2· Completed; positive on healing predictors (34 patients)

  Dose-ranging Phase I/II randomised, placebo-controlled first-in-man trial of topical LL-37 in venous leg ulcers

  Reported in Gronberg et al. 2014.

1. 01
   Treatment with LL-37 is safe and effective in enhancing healing of hard-to-heal venous leg ulcers: a randomized, placebo-controlled clinical trial — Gronberg A, Mahlapuu M, Stahle M, Whately-Smith C, Rollman O, Wound Repair and Regeneration (2014)

   First-in-man dose-ranging Phase I/II RCT in venous leg ulcers (n=34); safe and positive on healing predictors.

2. 02
   Evaluation of LL-37 in healing of hard-to-heal venous leg ulcers: a multicentric prospective randomized placebo-controlled clinical trial (HEAL LL-37) — Mahlapuu M, et al., Wound Repair and Regeneration (2021)

   Pivotal Phase IIb RCT (148 treated). Did NOT meet its primary efficacy endpoint overall; significance only in a post-hoc large-ulcer subgroup. The key honesty point.

3. 03
   Plasmacytoid dendritic cells sense self-DNA coupled with antimicrobial peptide — Lande R, et al., Nature (2007)

   Landmark paper showing LL-37/self-DNA complexes drive type-I interferon and break immune tolerance; basis of its role in autoimmunity.

4. 04
   The antimicrobial peptide LL37 is a T-cell autoantigen in psoriasis — Lande R, et al., Nature Communications (2014)

   Establishes LL-37 as a CD4+/CD8+ T-cell autoantigen correlating with psoriasis disease activity.

5. 05
   In vitro and in vivo wound healing-promoting activities of human cathelicidin LL-37 — Carretero M, et al., Journal of Investigative Dermatology (2008)

   Preclinical evidence for re-epithelialisation and granulation tissue formation; underpins the wound-healing rationale.