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TB-500

Also known as: Thymosin Beta-4 Fragment 17–23, Ac-LKKTETQ

Research Only

Molecular Formula

C38 H68 N10 O14 Fr Ba

Molecular Weight

889.01 Da (Free Base; Acetate salt ~949.1 Da)

Half-Life

Unknown in humans (human pharmacokinetics and elimination half-life have not been established; equine SC peak ~1–2 hours)

Sequence

Ac-LKKTETQ-OH (Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH)

Clinical Applications & Evidence

Mechanism of Action

TB-500 contains the central actin-binding sequence (LKKTET) of Thymosin Beta-4. In preclinical models, it is hypothesized to sequester G-actin and influence cell migration and tissue remodeling. A 2024 metabolic study indicated that the N-terminal metabolite Ac-LKKTE contributes to fibroblast scratch-wound closure in vitro. Direct equivalence to full-length Tβ4 signaling cascades (VEGF upregulation, NF-κB modulation) in humans remains unconfirmed.

Investigated Uses

  • Muscle & tendon injury repair (Preclinical models & research interest; no human clinical trials for Ac-LKKTETQ-OH)
  • Post-infarction cardiac repair (Preclinical animal models of full-length Tβ4; unstudied clinically for TB-500)
  • Corneal & dermal wound healing (Mouse models & non-acetylated fragment research; human trials RGN-259 evaluated full-length 43-residue Tβ4)
  • Anti-inflammatory & anti-fibrotic research (Preclinical cell & animal models; metabolic activity under investigation)
Animal Models Only

Regulatory & Safety Status

FDA Status

Research Only

WADA / Athletic Status

Prohibited at All Times (WADA S4.4.1)

Known Side Effects

Human adverse-event frequency and safety profile remain uncharacterized in controlled clinical trialsHuman subcutaneous safety, long-term toxicity, immunogenicity, and carcinogenicity are unstudiedFDA safety assessment notes potential immunogenicity and aggregation risks for compounded injectables

Contraindications

  • WADA-tested athletes (Prohibited at all times under S2 Peptide Hormones and Mimetics)
  • Active malignancy or history of cancer (Precautionary exclusion due to theoretical angiogenesis/cell migration concerns)
  • Pregnancy and lactation (Unstudied safety profile)

Drug Interactions

  • No formal clinical drug-interaction studies exist for TB-500
  • Unregulated gray-market injectable preparations carry risks of peptide impurities, endotoxins, or inconsistent dosing

Citations & Clinical Trials

FDA FDA Briefing Document: TB-500 — PCAC Meeting (July 23, 2026) World Anti-Doping Agency WADA 2026 Prohibited List — S2 Peptide Hormones, Growth Factors, and Mimetics PubMed Chemical Identification of TB-500 and Thymosin Beta-4 Derivatives (2012) Europe PMC Thymosin Beta-4 Active Domain LKKTETQ Encodes Wound Healing (2003) Journal of Chromatography B Metabolite Identification and In Vitro Activity of TB-500 (2024) Sports Medicine Use of Unapproved Peptides in Sports Medicine (2026)