Cathelicidin LL-37

What it is

LL-37 is a 37-amino-acid human cathelicidin peptide. FDA's substance record maps Cathelicidin LL-37, Cathelicidin LL 37 (human), LL-37, and Ropocamptide under UNII 3DD771JO2H. The aliases are broad; the route and finished product still matter.

The source record includes topical synthetic peptide products, intratumoral study material, an engineered Lactococcus lactis product designed to express LL-37, and measurements of endogenous LL-37 as a biomarker. A shared LL-37 name does not make those interchangeable.

Why people care

LL-37 is part of the body's host-defense biology and shows antimicrobial activity in laboratory assays. That makes it unusually easy to jump from “this peptide does something in a dish” to “an LL-37 product treats infection or improves immunity.” The human record is much narrower and highly dependent on route, formulation, population, and outcome.

What humans actually show

• First venous-ulcer study: A randomized double-blind dose-finding study enrolled 34 people with hard-to-heal venous leg ulcers. Two lower-concentration topical groups showed improvement in healing predictors, while the highest-concentration group did not differ from placebo. The study was small, short, and measured healing predictors rather than a definitive general wound-healing outcome.
• Larger venous-ulcer study: A 148-person trial tested topical LL-37 with compression therapy. The full cohort showed no significant healing improvement versus placebo. A post hoc subgroup with larger wounds showed a signal on several related measures; that requires prospective confirmation and does not replace the negative full-cohort result.
• Diabetic-foot-ulcer study: A 25-person trial compared LL-37 cream with placebo cream alongside standard wound care. Granulation index improved more with LL-37, but between-group wound-area changes, aerobic bacterial-colonization reductions, and inflammatory-marker reductions were not significant. Granulation is not complete healing or proof of infection treatment.
• Intratumoral melanoma registry: Four people enrolled in an open-label single-center study; posted results cover three analyzed participants. No deaths or serious adverse events were reported, and all three had at least one non-serious event. Three people cannot establish antitumor efficacy or event frequency.
• Engineered oral product: A 238-person open-label single-center trial studied an engineered Lactococcus lactis product designed to express LL-37 in adults hospitalized with one SARS-CoV-2 variant. It reported a shorter viral-RNA negative-conversion time and no severe adverse events. This is not synthetic LL-37, and the virologic endpoint does not establish broad infection treatment or transfer to another product.

Mechanistic and nonhuman evidence

Synthetic LL-37 showed activity against several bacterial species in defined laboratory assays. Those conditions do not reproduce a clinical infection, define a safe human route, or authenticate a product.

FDA's compounding-risk summary also describes nonclinical findings suggesting detrimental male-reproductive effects and protumorigenic activity in some tissues. That official summary does not quantify human risk or establish an adverse-event frequency, but it is part of the uncertainty that prevents a generalized safety claim.

FDA and U.S. status

FDA's current compounding page places Cathelicidin LL-37 under withdrawn nominations and identifies unresolved safety concerns. A separate FDA page states that an advisory committee meeting before the end of February 2027 will consider Cathelicidin LL-37 and four other substances for the 503A Bulks List. The reviewed page did not yet provide the exact meeting date or materials.

That announcement is not a vote, final list action, drug approval, or product-quality finding. The U.S. melanoma registry describes its LL-37 study material as investigational. Exact Drugs@FDA searches returned no match in the dated review, but PepCurrent does not convert a negative database search into a broader legal conclusion.

Risks and warning limits

FDA says compounded Cathelicidin LL-37 may present immunogenicity, peptide-impurity, and active-ingredient-characterization concerns and that available human safety information is insufficient.

The topical wound trials reported acceptable short-term tolerability in their defined populations. Those small topical studies do not characterize systemic, chronic, reproductive, cancer, pregnancy, contraindication, or interaction risks. The three-participant melanoma result is far too small to estimate frequency or attribution.

What remains unknown

• The exact PCAC meeting date and materials, any vote, and any later final FDA action.
• Whether the post hoc large-wound signal or small diabetic-foot-ulcer granulation result would replicate in prospectively powered trials with complete-healing and infection outcomes.
• Human systemic pharmacokinetics, chronic safety, immunogenicity, contraindications, and interaction frequencies for a defined LL-37 product.
• The clinical meaning of the three-participant melanoma results.
• The identity and quality of any nonstudy product.

Product identity and quality limits

Endogenous LL-37 biology and FDA's UNII record do not establish approval, purity, sterility, concentration, stability, or route suitability for a manufactured product. Topical synthetic peptide products, intratumoral study material, and an engineered LL-37-expressing live product are not interchangeable.

FDA's 2020 warning letter describes one firm's specific compounding facts. It does not authenticate or characterize an unrelated product.

What has been studied together

Topical LL-37 was studied with compression therapy in venous ulcers and with standard wound care in diabetic foot ulcers. These are cointervention records, not pharmacokinetic drug-interaction studies.

No adequate direct human systemic interaction program with other drugs or peptides was identified in the focused search. Missing evidence does not establish compatibility or safety.

What people are hearing

• “LL-37's natural antimicrobial role proves that an LL-37 product treats infection.” In-vitro antimicrobial activity is not clinical infection-treatment evidence.
• “Topical wound research supports injectable immune, recovery, or longevity use.” A topical product used with wound care does not establish systemic exposure, benefit, or safety.
• “Topical synthetic LL-37, intratumoral study material, and an engineered oral LL-37-expressing product are interchangeable.” They are different products, routes, and evidence records.

Questions readers raise

Readers ask whether “antimicrobial” means infection treatment, whether wound results transfer to injections, and whether every LL-37 product is the same material. These are questions to investigate, not evidence of efficacy, safety, approval, route transfer, or product identity. PepCurrent has not published anecdotal theme counts or public user reviews for this profile.

What would change this answer

• Publication of the exact PCAC meeting date and materials, an official vote record, and any later final FDA action.
• A prospectively powered topical trial with complete-healing and infection outcomes.
• A defined systemic product with adequate pharmacokinetic, immunogenicity, safety, and controlled clinical-outcome evidence.
• Product-level analytical and manufacturing evidence for any separately marketed material.

Sources and records

• WADA — 2026 Prohibited List

• FDA UNII record for Ropocamptide / Cathelicidin LL-37
• FDA compounding substances with potential significant safety risks
• FDA page for the planned PCAC meeting
• FDA Tailor Made Compounding warning letter
• Drugs@FDA exact active-ingredient API search
• ClinicalTrials.gov LL-37 intervention search
• First venous-ulcer trial — PMID 25041740
• Larger venous-ulcer trial — PMID 34687253
• Diabetic-foot-ulcer trial — PMID 37480520
• Intratumoral melanoma registry, NCT02225366
• Engineered oral-product trial — PMID 37605995
• In-vitro antimicrobial study — PMID 9736536