LL-37: Dosing Protocols

Research Dosing Disclaimer#

The dosing information below is derived from research studies and is provided for educational purposes only. LL-37 is not approved for human use, and no official dosing guidelines exist.

Dose-Response Data#

We compiled in vivo dose–response information for the human cathelicidin LL‑37 across animal disease models. We report routes, doses normalized to body weight, schedules, and outcomes, and we note evidence of dose dependence or toxicity when available. A structured summary table is embedded for quick comparison.

Key findings across models

• Polymicrobial sepsis (mouse, CLP): • Intravenous LL‑37 at 2 µg/mouse (≈0.10 mg/kg for a 20 g mouse) given immediately after CLP improved 7‑day survival (6.7% → 36.4%), reduced peritoneal macrophage caspase‑1 activation and pyroptosis, and lowered IL‑1β, IL‑6, and TNF‑α in serum/peritoneal fluid; peritoneal and blood CFU decreased. A lower 1 µg/mouse dose (≈0.05 mg/kg) was also used in experiments, but detailed comparative survival data were not provided, limiting formal dose–response inference. • A single 3 µg/mouse IV dose (≈0.15 mg/kg) administered just prior to CLP decreased bacterial loads and increased neutrophil‑derived ectosomes in vivo. Ectosome fractions isolated from LL‑37–treated CLP mice exhibited dose‑dependent antibacterial activity in vitro, but in vivo dose ranging beyond 3 µg was not reported; toxicity was not observed in the excerpt.

• Gram‑negative sepsis (rat models): • Adult Wistar rats received LL‑37 1 mg/kg IV once immediately after challenge/surgery across LPS shock, IP E. coli peritonitis, and CLP sepsis models. LL‑37 significantly reduced lethality (e.g., E. coli peritonitis: 100% → 26.6%; CLP ~33.3%), lowered bacterial burdens in blood, peritoneum, spleen, liver, and mesenteric lymph nodes by multiple logs, and reduced plasma endotoxin and TNF‑α. Delayed dosing (360 min post‑CLP) was also tested. Only a single dose level (1 mg/kg) was reported in vivo, precluding a within‑study dose–response curve; no significant adverse effects were noted in the excerpts.

• Impaired cutaneous wound healing (mouse): • Topical LL‑37 applied to full‑thickness dorsal wounds in steroid‑impaired healing: two applications of 10 µg per treatment (20 µg/day total), twice daily for 7 days. Using a 20 g mouse assumption, this is ≈1.0 mg/kg/day. LL‑37 accelerated wound closure and re‑epithelialization (near complete by day 7) and increased microvessel density; a single topical regimen was tested and no in vivo dose ranging or toxicity was reported.

Dose–response considerations and safety

• Sepsis models in mice show efficacy at 0.05–0.15 mg/kg IV single doses, with improved survival and reduced pathogen/cytokine readouts; direct head‑to‑head dose–response between 1 and 2–3 µg/mouse was not fully detailed. Rat models support efficacy at 1 mg/kg IV; cross‑species comparison suggests a therapeutic window across roughly 0.05–1 mg/kg depending on species and model. Topical delivery at ≈1 mg/kg/day improved wound healing without overt toxicity in the reported timeframe.

Evidence table

Notes and gaps

• In vivo toxicity signals were not reported in the provided excerpts; comprehensive safety assessments (hematology, organ histology, repeat‑dose) were not detailed. Many studies used a single dose level; formal dose–response curves are uncommon in vivo, though some in vitro components demonstrated dose dependence. Future work should establish MTD/NOAEL and PK/PD to map exposure–response relationships across routes.

Administration Routes#

Introduction LL-37 is a 37–amino acid human cathelicidin with promising topical activity but challenging systemic pharmacokinetics due to rapid proteolysis and plasma binding. Here, we compare pharmacokinetics and bioavailability across subcutaneous (SC), oral, intramuscular (IM), and topical/local routes, emphasizing formulation-dependent behavior.

Summary comparison

Route-by-route analysis

• Oral: When delivered by an engineered probiotic (Lactococcus lactis expressing LL-37, “cas001”), LL-37 became transiently detectable in circulation. In rats and healthy volunteers, serum LL-37 rose with an approximate Tmax around 2 hours after dosing and returned to baseline by about 6 hours, indicating short systemic exposure; absolute bioavailability and numeric Cmax were not reported. The engineered live-vector approach appears necessary to overcome the very low oral bioavailability of free LL-37 due to gastrointestinal and luminal proteases.

• Topical/local (including intratumoral): Clinical development has focused on topical application for wounds and intratumoral injection for melanoma. Reviews and trials indicate minimal systemic exposure from topical formulations; focus is on high local concentrations with negligible blood levels, so systemic Tmax/Cmax are typically not measured. Formulation strategies such as hyaluronic-acid/alginate nanogels, lipid carriers, hydrogels, and microneedles enhance local penetration and prolong residence while protecting against proteases; microneedles can markedly increase local concentrations with low systemic spillover. Intratumoral LL-37 in melanoma is dosed weekly to achieve high intralesional exposure; systemic PK endpoints were not reported.

• Subcutaneous (SC): No formal human PK data for native LL-37 were identified. Multiple reviews emphasize that LL-37 and related AMPs have poor systemic bioavailability and short in vivo persistence without modification, due to proteolysis and plasma binding. Consequently, SC delivery of unmodified LL-37 would be expected to yield low, transient systemic exposure unless stabilized by formulation (e.g., PEGylation, protease-resistant analogs) or depot/encapsulation approaches.

• Intramuscular (IM): As with SC, direct LL-37 PK data are lacking. By analogy to peptide pharmacology and AMP reviews, IM could provide a depot, but native LL-37 is predicted to have limited and short-lived systemic exposure without protective formulation.

Bioavailability differences and route-specific PK implications

• Oral free peptide: Very low bioavailability. Engineered bacterial expression can yield a short-lived systemic signal (Tmax ~2 h; back to baseline ~6 h), implying limited exposure unless dosing is frequent or controlled-release strategies are used.
• Topical/local: High local “bioavailability” at the application site with minimal systemic absorption. Pharmacokinetics are dominated by local retention; advanced formulations increase residence times from hours to potentially days while maintaining low systemic levels.
• SC/IM: Likely low systemic bioavailability for native LL-37 without modification; PK expected to feature rapid loss to proteolysis and short half-life. Formulation and chemical modification are pivotal to achieve meaningful exposure.

Formulation determinants of PK Key factors governing LL-37 PK across routes include protease stability, plasma/tissue binding, and delivery system design. Strategies shown to improve exposure or local retention include D-amino acid substitution or peptidomimetics, PEGylation, and encapsulation in anionic nanogels (e.g., hyaluronic acid, alginate) which protect from proteolysis and modulate release; microneedles can concentrate drug in epidermis/dermis while minimizing systemic levels. Reviews emphasize that limited bioavailability is the reason clinical use has predominantly been topical to date.

Evidence limitations Direct numerical PK for LL-37 after SC or IM dosing in humans was not located, and absolute bioavailability estimates are not reported for any route. Oral data derive from an engineered live-bacteria platform that produces a transient systemic signal; this cannot be directly generalized to free LL-37. Nonetheless, convergent evidence across reviews and formulation studies supports the comparative conclusions above.

Human-Equivalent Dosing#

1. Body-surface-area (BSA; Km) dose translation. One LL-37 clinical program that delivered LL-37 via engineered Lactococcus lactis explicitly used BSA-based scaling to convert an estimated human dose to rat dose for toxicology/PK. The authors state that, “considering the conversion of body surface area,” the rat dose should be multiplied by 6.17 from the estimated clinical 1×10^8 CFU/kg/day, yielding ~6×10^8 CFU/kg/day for rats; they then tested 100-fold higher (6×10^10 CFU/kg/day) for safety. Methodologically, BSA-based HED scaling uses species-specific Km factors with the standard equation HED (mg/kg) = Animal dose (mg/kg) × (Animal Km / Human Km), which is implemented in tools and guidance used broadly for preclinical-to-clinical translation. Foundational work determining BSA and Km for species (e.g., rabbits; Meeh k and Km measurement) underpins such conversions. Non-LL-37 translational reports also reference Reagan-Shaw-style BSA conversions when contextualizing animal doses versus prospective human doses, reflecting common practice (scharton2014favipiravir(t705)protects pages 1-2).

2. Pharmacokinetic allometric scaling of biologics to project human exposure, supporting first-in-human dose selection. For peptides/proteins and antibodies, interspecies allometry commonly scales clearance using a power-law with body weight (exponent ~0.75) to predict human PK, which is then used to back-calculate initial doses targeting conservative exposures (AUC = Dose/CL). Methods include simple allometry (Y = a·W^b), fixed-exponent (b = 0.75) scaling, and “rule of exponents” approaches that invoke corrections such as multiplying clearance by maximum lifespan potential (MLP) or brain weight when appropriate. Reviews of biologic translation summarize these methods and recommend multi-species scaling and model-informed strategies (population PK, PBPK) for complex or nonlinear behavior. Principles reviews explain when to prefer 0.67 (surface area) versus 0.75 (metabolic) exponents, and emphasize using MABEL/NOAEL when mechanism or PK variability limit simple allometry.

Equations and practical examples.

• BSA/Km-based HED: HED (mg/kg) = Animal dose (mg/kg) × (Animal Km / Human Km). Species-specific Km values (e.g., mouse ~3, rat ~6, dog ~20; adult human ~37) are used; several resources and measurements detail Km derivation and usage. In an LL-37 program, rat dosing was derived from a proposed human LL-37 CFU/kg/day using rat Km ≈ 6.17; a 100× multiple was used for toxicology.
• Allometric PK scaling (biologics): CL_human ≈ a·W_human^0.75 using multi-species fits; projected human exposure (AUC = Dose/CL) supports conservative first-in-human dose selection. Where simple allometry is inadequate, corrections (CL·MLP, CL·brain weight) per the rule of exponents improve predictions.

Peptide-specific considerations for LL-37. LL-37 is a cationic host-defense peptide subject to proteolysis and route-dependent bioavailability. For systemic use, exposure-matching via PK allometry (clearance/exposure targets) is more appropriate than direct mg/kg translation. For local administrations (e.g., intratumoral, topical, GI-delivered via probiotic), investigators have used BSA/Km to contextualize animal doses against proposed human dosing, as seen in the oral LL-37 probiotic study. Reviews of biologics emphasize that species differences in proteolysis, target-mediated disposition, and route (IV/SC vs oral/topical) can break simple dose-per-kg scaling, motivating PK-based and model-informed scaling.

• BSA/Km conversion (Reagan‑Shaw style), explicitly used to derive rat doses from an intended human LL-37 dose in a probiotic delivery study, with a rat factor ≈6.17 and safety multiples applied protects pages 1-2).
• Allometric pharmacokinetic scaling typical for biologics, using body-weight power laws (exponent ~0.75) and, when needed, corrected approaches (MLP, brain weight) to predict human clearance and exposures, thereby informing conservative first-in-human dosing, consistent with general principles weighing 0.67 vs 0.75 and advocating MABEL/NOAEL starts.

Embedded artifact summarizing sources and methods:

Evidence Gaps#

• No human dose-finding studies have been completed
• Allometric scaling from animal models has inherent limitations
• Route-specific bioavailability data in humans is absent
• Optimal treatment duration has not been established

Related Reading#

• LL-37 overview and research guide
• LL-37 side effects profile
• LL-37 research evidence