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Immune

LL-37 (KR-12) Guide & Dosage Chart

A minimal active fragment of LL-37 studied for antimicrobial action.

Also known asKR-12
Routesubcutaneous
LL-37 (KR-12) — Dosage chart
Every row cited
GoalDoseFrequencyDurationEvidenceSource
Cited dosing data is being compiled for this compound.
For research and educational use only. Not medical advice.

What is LL-37 (KR-12)?

KR-12 is a tiny peptide — just 12 amino acids long — snipped from the larger human antimicrobial peptide LL-37. Scientists describe it as the smallest piece of LL-37 that still keeps antimicrobial activity.[5] Think of LL-37 as a long Swiss Army knife. KR-12 is the single blade that researchers found does a surprising amount of work on its own.

LL-37 itself is part of the body's front-line immune defense system. It belongs to a family called cathelicidins — proteins the body makes to fight off bacteria and regulate inflammation. Interestingly, your body can be nudged to produce more LL-37 simply by exposure to sunlight or vitamin D.[5] KR-12 sits at positions 18–29 of the LL-37 sequence.[4]

Because KR-12 is so small, it is easier and cheaper to manufacture than the full LL-37 molecule. It also shows lower toxicity to healthy mammalian cells than its parent peptide — a combination that has made it attractive for laboratory study.[5]

How LL-37 (KR-12) Works

Picture a bacterial cell as a soap bubble. KR-12 acts like a pin. It is positively charged and shaped like a tiny spiral (an alpha helix). That shape lets it punch into the negatively charged outer membrane of bacteria, causing the membrane to leak and the cell to die.[3]

But KR-12 does more than pop bacterial bubbles. Researchers call it a moonlighting peptide because it also plays roles in calming inflammation, neutralizing bacterial toxins called endotoxins (specifically lipopolysaccharide, or LPS), and even signaling immune cells.[5] In lab studies, KR-12 analogs reduced the release of pro-inflammatory molecules like TNF-α, IL-6, and nitric oxide from immune cells exposed to bacterial toxins.[3]

What the Research Shows

Fighting Drug-Resistant Bacteria

One of the most exciting research angles is antibiotic resistance. Engineered KR-12 analogs showed potent activity against MRSA (methicillin-resistant Staphylococcus aureus), with minimum inhibitory concentrations as low as 4 µM in lab tests.[4] Analogs of KR-12 also outperformed the parent LL-37 peptide against multidrug-resistant Pseudomonas aeruginosa and vancomycin-resistant Enterococcus faecium — and they worked together synergistically with standard antibiotics like ciprofloxacin and chloramphenicol, meaning the combination was more powerful than either agent alone.[3]

Anti-Biofilm Action

Biofilms are slimy bacterial communities that cling to surfaces — including medical implants — and are notoriously hard to kill. Lab research found that KR-12 analogs disrupted preformed biofilms of drug-resistant bacteria more effectively than LL-37 itself.[3] Researchers have even explored bonding KR-12 directly to implant surfaces to prevent biofilm formation.[5]

Tackling a Parasite That Resists Standard Treatment

Trichomoniasis is the world's most common non-viral sexually transmitted infection, and drug-resistant strains are a growing problem. Lab work showed that KR-12 reduced the viability of both a standard strain and a metronidazole-resistant strain of Trichomonas vaginalis. Even at low concentrations, KR-12 boosted the effectiveness of metronidazole against the resistant strain.[2]

Colorectal Cancer Models

In a 2025 mouse study, KR-12 amide was delivered rectally to animals with chemically induced colitis-associated colorectal cancer. It significantly reduced total tumor count and lowered levels of the inflammatory cytokine IL-6 compared to untreated animals. A modified version with a propionyl fatty acid chain reduced both IL-6 and TNF-α.[1] Importantly, in cell culture tests, KR-12 was more toxic to colon cancer cells than to healthy colon cells — a property researchers call selective cytotoxicity.[1]

Skin and Anti-Photoaging Effects

In 2025 lab work on human skin cells, KR-12 analogs showed the ability to reduce UV-radiation-induced inflammation and oxidative stress, promote collagen synthesis, support cell migration, and suppress excess melanin production — all markers of interest in photoaging research.[6]

What LL-37 (KR-12) Is Being Studied For

  • Antimicrobial action against drug-resistant bacteria, including MRSA[4]
  • Anti-biofilm strategies for medical devices[5]
  • Activity against parasites like Trichomonas vaginalis[2]
  • Anti-inflammatory and immune-modulating effects[3]
  • Colorectal cancer models (preclinical, in vivo)[1]
  • Skin photoprotection and anti-aging dermatology applications[6]
  • Neutralizing bacterial endotoxins (LPS)[4]

How LL-37 (KR-12) Is Dosed in Research

Doses used in published studies vary widely depending on the model — cell culture concentrations are typically measured in micromolar (µM) ranges, while animal studies use different routes such as rectal administration.[1] Because no standardized research protocol exists and methods differ across labs, you should refer to the dosage chart on this page for a structured reference summary, and use the calculator to work out specific concentrations for your own research setup. This information is for research reference only and does not constitute medical advice.

Mixing and Storing LL-37 (KR-12)

KR-12 is a peptide, which means it is sensitive to heat, repeated freeze-thaw cycles, and certain solvents. For reconstitution, researchers typically dissolve lyophilized (freeze-dried) KR-12 powder in sterile water or a dilute acetic acid solution, then dilute further in the buffer appropriate for their assay. Once reconstituted, aliquot the solution into single-use portions to avoid repeated freezing and thawing, which degrades peptide quality. Store dry peptide at −20 °C or colder in a sealed, moisture-free container. Reconstituted solution should be kept at −80 °C if not used immediately. Always check the certificate of analysis from your supplier for purity and specific handling notes.

Sources

  1. Synthesis and evaluation of KR-12, an LL-37 fragment, and its short-chain fatty acid derivatives: selective cytotoxicity in colorectal cancer cells and anti-tumor efficacy in an azoxymethane/DSS-induced colitis-associated cancer mouse model. — Pharmacological reports : PR, 2025. PMID 41091413.
  2. The antimicrobial peptides LL-37, KR-20, FK-13 and KR-12 inhibit the growth of a sensitive and a metronidazole-resistant strain of Trichomonas vaginalis. — Parasitology research, 2022. PMID 36171407.
  3. LL-37-derived short antimicrobial peptide KR-12-a5 and its d-amino acid substituted analogs with cell selectivity, anti-biofilm activity, synergistic effect with conventional antibiotics, and anti-inflammatory activity. — European journal of medicinal chemistry, 2017. PMID 28525841.
  4. Short KR-12 analogs designed from human cathelicidin LL-37 possessing both antimicrobial and antiendotoxic activities without mammalian cell toxicity. — Journal of peptide science : an official publication of the European Peptide Society, 2013. PMID 24105706.
  5. Origami of KR-12 Designed Antimicrobial Peptides and Their Potential Applications. — Antibiotics (Basel, Switzerland), 2024. PMID 39334990.
  6. Potential Antiphotoaging Effect of Human Cathelicidin LL-37 Fragments and KR-12 Analogs on UVB-Induced HaCaT Cells and UVA-Induced HDF Cells. — ACS omega, 2025. PMID 40893218.

LL-37 (KR-12) FAQ

What is LL-37 (KR-12)?
KR-12 is the shortest fragment of the human antimicrobial peptide LL-37 that still retains antibacterial activity. It spans positions 18–29 of LL-37's amino acid sequence.[4] Researchers study it because it is small, easier to synthesize than full LL-37, and shows lower toxicity to healthy mammalian cells while keeping useful antimicrobial and immune-modulating properties.[5] It is a research compound, not approved for human use.
How does LL-37 (KR-12) work?
KR-12 folds into a positively charged spiral shape (alpha helix) that inserts into the negatively charged membranes of bacteria, causing them to leak and die.[3] Beyond killing microbes, it also acts as an immune modulator — suppressing pro-inflammatory signals like TNF-α and IL-6, and neutralizing bacterial toxins called endotoxins.[4] Researchers call it a 'moonlighting' peptide because of these multiple roles.[5]
What is LL-37 (KR-12) used for in research?
Lab and preclinical studies have explored KR-12 for fighting drug-resistant bacteria including MRSA,[4] disrupting biofilms on medical devices,[5] killing a metronidazole-resistant parasite,[2] reducing tumor burden in colorectal cancer mouse models,[1] calming inflammation,[3] and protecting skin cells from UV-induced damage.[6] All findings are preclinical — no human clinical applications are established.
How is LL-37 (KR-12) dosed?
Dosing in published research varies significantly by model and administration route. In cell-culture work, effective concentrations are typically in the low micromolar range, with some analogs showing activity at 4 µM against MRSA.[4] Animal studies have used rectal administration at milligram-scale doses.[1] See the dosage chart on this page for a structured reference, and use the calculator for concentration conversions. This is not medical dosing advice.
How do you reconstitute LL-37 (KR-12)?
Dissolve lyophilized KR-12 in sterile water or a dilute acetic acid solution, then dilute to your working concentration in an appropriate research buffer. Divide the reconstituted peptide into single-use aliquots to prevent repeated freeze-thaw cycles, which degrade peptide integrity. Store dry powder at −20 °C or below in a sealed, dry container; store reconstituted aliquots at −80 °C. Always consult the supplier's certificate of analysis for purity-specific guidance.
Is LL-37 (KR-12) safe?
In lab studies, KR-12 shows notably lower toxicity to healthy mammalian cells compared to its parent peptide LL-37, and some analogs demonstrated selective killing of cancer cells over normal cells.[1] However, KR-12 is a research compound only — it has not been evaluated in human clinical trials for safety or efficacy. No conclusions about safety in humans can be drawn from current preclinical data.[5] It should not be used for self-administration.