KR-12
KRIVQRIKDFLR — the minimal 12-residue bactericidal fragment of LL-37. Retains selective antimicrobial activity while losing LL-37's host-cell toxicity, making it the canonical template for LL-37-derived antimicrobial peptide drug discovery. Research-only.
A 12-residue peptide corresponding to LL-37 residues 18–29 (Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg), characterized by Guangshun Wang's group at the University of Nebraska Medical Center as the smallest LL-37 fragment that retains bactericidal activity against Escherichia coli while showing minimal hemolytic and cytotoxic activity against human erythrocytes and keratinocytes. KR-12 has become the canonical minimal LL-37 template for antimicrobial peptide drug discovery, with multiple groups producing chemically modified, D-amino-acid-substituted, and lipidated analogs intended to overcome the proteolytic-instability limitation of the native L-amino-acid peptide. Not FDA-approved; not in clinical development as a standalone agent.
Mechanism of action
Forms amphipathic α-helix on contact with negatively charged bacterial membrane lipids (particularly phosphatidylglycerol and cardiolipin), producing rapid membrane permeabilization through a carpet-or-toroidal-pore mechanism. The 12-residue size appears to be near the minimum for coherent amphipathic α-helix formation in a membrane environment. Selectivity for bacterial over mammalian membranes arises from the charge difference between bacterial (negatively charged) and mammalian (largely zwitterionic) outer-leaflet phospholipids. Also retains weak LPS-neutralizing activity of the parent LL-37.
Primary uses
- Antimicrobial peptide research (in vitro and preclinical)
- Template for LL-37-derived antibiotic drug discovery
- Wound-healing biomaterial research (peptide-functionalized hydrogels and dressings)
Typical dosing
⚠ No human dosing established. Topical preclinical studies have used μM-to-mM concentrations. Any human use would be unregulated.
Regulatory status
Native KR-12 is not FDA-approved. Various KR-12 derivatives and analogs are in preclinical and early-clinical development for topical antimicrobial and wound-healing applications, but no KR-12-based agent has entered a registered Phase 2 or later clinical trial as of early 2026.
Status as of this entry's last review, October 4, 2026. Approvals, compounding rules and sport rules change; the regulatory tracker is checked more often.
What we checked
KR-12 is the smallest fragment of the human antimicrobial peptide LL-37 reported to keep its bacteria-killing activity. Its literature is laboratory chemistry and microbiology; this section records what can be checked.
Identity, computed
| Sequence | Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg (KRIVQRIKDFLR) |
| Formula | C71H126N24O16 |
| Average mass | 1571.94 g/mol |
| Monoisotopic mass | 1570.9784 Da |
| Isoelectric point | 12.24 (net charge +3.98 at pH 7) |
KR-12 is LL-37 residues 18 to 29, Lys-Arg-Ile-Val-Gln-Arg-Ile-Lys-Asp-Phe-Leu-Arg; the values below are computed for the free acid.
Regulatory status, read October 5, 2026
Drugs@FDA: 0 records for “KR-12”. EMA medicines list: 0 records for “KR-12”. Run for semaglutide, the same queries return 6 and 5 records (and the registry search 84 trials), so a zero here is an absence, not a broken search. Not named on the WADA 2026 and 2027 Prohibited Lists. As a substance with no current approval for human therapeutic use, it falls under section S0 (non-approved substances), which is prohibited at all times; the lists were read on September 27, 2026.
What the maker or sellers claim
Claim, from research-chemical sellers: KR-12 is an antimicrobial or skin-healing peptide for human use. It has been studied in the laboratory, not tested in people.
About LL-37, its parent peptide
LL-37 is the only human cathelicidin, a 37-residue antimicrobial peptide. Structural work in 2008 identified KR-12 as its minimal active core, and later designs built on it; those papers are cited in References. Our LL-37 entry covers the parent peptide.
What we looked for and did not find
No human study, no registry record and no dose from a controlled human study.
| Source | Query | Results, October 5, 2026 | What it was |
|---|---|---|---|
| PubMed | KR-12 LL-37 | 41 | fragment and design papers |
| ClinicalTrials.gov | KR-12 | 0 | |
| Drugs@FDA (openFDA) | KR-12 | 0 | |
| EMA medicines list | KR-12 | 0 |
References
- [pubmed] Wang G. "Structures of human host defense cathelicidin LL-37 and its smallest antimicrobial peptide KR-12 in lipid micelles." J Biol Chem, 2008;283:32637-32643 (KR-12 minimal-fragment characterization). PMID: 18818205.
- [pubmed] Mishra B, Wang G. "Ab initio design of potent anti-MRSA peptides based on database filtering technology." J Am Chem Soc, 2012;134:12426-12429. PMID: 22803960.
- [review] Wang G, Narayana JL, et al. "Human antimicrobial peptides and proteins." Pharmaceuticals (Basel), 2014;7:545-594. PMID: 24828484.
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Guides & tools
This entry is for educational purposes only and does not constitute medical advice. Dosing information reflects published regulatory or research data and is not a recommendation. Many compounds described here are not approved for human use in the United States. Consult a licensed medical professional before considering any peptide therapy.