What Is TB-500?
Quick Answer
Overview TB-500 (also known as Fequesetide) is a synthetic heptapeptide corresponding to the N-acetylated amino acid sequence 17–23 of the naturally occurring protein Thymosin Beta-4 (Tβ4). Its sequence is Ac-LKKTETQ.[1][2] The parent molecule, Thymosin Beta-4, is a ubiquitous 43-amino acid polypept...
Overview
TB-500 (also known as Fequesetide) is a synthetic heptapeptide corresponding to the N-acetylated amino acid sequence 17–23 of the naturally occurring protein Thymosin Beta-4 (Tβ4). Its sequence is Ac-LKKTETQ.[1][2]
The parent molecule, Thymosin Beta-4, is a ubiquitous 43-amino acid polypeptide originally isolated from the thymus gland. It is found in high concentrations in blood platelets, white blood cells, and wound fluid, and belongs to the β-thymosin family of actin-sequestering proteins.[3]
TB-500 was developed based on the discovery that the specific seven-amino acid sequence (17–23) within Tβ4 is responsible for its actin-binding properties, which are critical for cell migration and tissue repair. The shorter fragment retains the essential angiogenic and wound-healing activities of the parent molecule while being more economical to synthesize.[6][8]
The U.S. FDA has classified TB-500 as a Category 2 Bulk Drug Substance, citing insufficient safety-related information and immunogenicity risk. It is prohibited from being compounded by outsourcing facilities.[4] TB-500 and Tβ4 are also explicitly prohibited by WADA under Section S2.3 at all times.[5]
References
- Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Testing and Analysis. 2012;4(9):733-738.
- Delcourt V, Garcia P, Chabot B, Bailly-Chouriberry L. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Testing and Analysis. 2022;14(12):1963-1969.
- Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opinion on Biological Therapy. 2012;12(1):37-51.
- U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. FDA.gov. Updated July 8, 2025.
- World Anti-Doping Agency. The 2025 Prohibited List. WADA. January 1, 2025.
- Xing Y, Ye Y, Zuo H, Li Y. Progress on the Function and Application of Thymosin β4. Frontiers in Endocrinology. 2021;12:767785.
- Bock-Marquette I, Maar K, Maar S, et al. Thymosin beta-4 denotes new directions towards developing prosperous anti-aging regenerative therapies. International Immunopharmacology. 2023;116:109741.
- Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK. Thymosin β4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration. 2003;11(1):19-24.
- Belsky JB, Rivers EP, Filbin MR, Lee PJ, Morris DC. Thymosin beta 4 regulation of actin in sepsis. Expert Opinion on Biological Therapy. 2018;18(sup1):193-197.
- Hinkel R, El-Aouni C, Olson T, et al. Thymosin beta4 is an essential paracrine factor of embryonic endothelial progenitor cell-mediated cardioprotection. Circulation. 2008;117(17):2232-2240.
- Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472.
- Smart N, Risebro CA, Melville AA, et al. Thymosin β4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007;445(7124):177-182.
- Sosne G, Kleinman HK. Primary Mechanisms of Thymosin β4 Repair Activity in Dry Eye Disorders and Other Tissue Injuries. Investigative Ophthalmology & Visual Science. 2015;56(9):5110-5117.
- Reyes-Gordillo K, Shah R, Popratiloff A, et al. Thymosin-β4 (Tβ4) Blunts PDGF-Dependent Phosphorylation and Binding of AKT to Actin in Hepatic Stellate Cells. American Journal of Pathology. 2011;178(5):2100-2108.
- Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta 4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364-368.
- Shah R, Reyes-Gordillo K, Cheng Y, et al. Thymosin β4 Prevents Oxidative Stress, Inflammation, and Fibrosis in Ethanol- and LPS-Induced Liver Injury in Mice. Oxidative Medicine and Cellular Longevity. 2018;2018:9630175.
- Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. Journal of Chromatography B. 2024;1235:124033.
- Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta 4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364-368.
- Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial. Clinical Ophthalmology. 2015;9:877-884.
- Sosne G, Dunn SP, Kim C. Thymosin β4 Significantly Improves Signs and Symptoms of Severe Dry Eye in a Phase 2 Randomized Trial. Cornea. 2015;34(5):491-496.
- Bao W, Ballard VL, Needle S, et al. Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury. Frontiers in Pharmacology. 2013;4:149.
- Treadwell T, Kleinman HK, Crockford D, et al. The regenerative peptide thymosin β4 accelerates the rate of dermal healing in preclinical animal models and in patients. Annals of the New York Academy of Sciences. 2012;1270:37-44.
- Nguyen J, Verma S, Vuong VT, et al. Engineered Tandem Thymosin Peptide Promotes Corneal Wound Healing. Investigative Ophthalmology & Visual Science. 2025;66(14):31.
- Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta 4 defined by active sites in short peptide sequences. The FASEB Journal. 2010;24(7):2144-2151.
- Ho EN, Kwok WH, Lau MY, et al. Doping control analysis of TB-500 in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A. 2012;1265:57-69.
- Kwok WH, Leung GN, Wan TS, et al. Doping control analysis of seven peptide hormones in horse plasma and urine by liquid chromatography-mass spectrometry. Analytical and Bioanalytical Chemistry. 2013;405:2653-2667.
- Smart N, Risebro CA, Melville AA, et al. Thymosin β4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007;445(7124):177-182.
- RegeneRx Biopharmaceuticals. Phase I Safety Trial for RGN-352: Injectable Thymosin Beta 4. 2009.
- Treadwell T, Kleinman HK, Crockford D, et al. The regenerative peptide thymosin β4 accelerates dermal healing. Annals of the New York Academy of Sciences. 2012;1270:37-44.
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