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These products are for laboratory research only and not intended for medical use. They are not FDA-approved to diagnose, treat, cure, or prevent any disease. By purchasing, you certify they will be used solely for research and not for human or animal consumption.
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...
| Property | Value |
|---|---|
| PubMed Citations Referenced | 29 |
| Contributing Researchers | 3 |
| Storage Conditions | Store lyophilized powder at -20°C for long-term stability. |
| Purity Standard | ≥99% (HPLC verified, 3rd-party COA) |
| Research Use Only | Not for human consumption. RUO only. |
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]
TB-500 emerged from a structural decomposition of full-length Tbeta4 aimed at isolating the minimum sequence required for actin sequestration. The 17–23 LKKTETQ window contains the actin-binding helix identified by NMR and X-ray crystallography of Tbeta4-actin complexes, while the N-terminal Ac-SDKP fragment (residues 1–4) carries the parent's distinct anti-fibrotic and hematopoietic-quiescence activity.[6][7] N-terminal acetylation in TB-500 was retained to mirror the natural Tbeta4 acetylation state and to confer modest exopeptidase resistance.[2]
Within the actin-cytoskeleton-modulating peptide research domain, TB-500 is most often referenced alongside Thymosin alpha-1 for parallel thymic-peptide pharmacology, BPC-157 for shared cytoprotection and tissue-repair signaling, and GHK-Cu for matrix-remodeling crosstalk. The compound is supplied here strictly as a research reference standard for in vitro and animal-model investigation, and is not intended for human or veterinary use.
The fundamental molecular target of TB-500 is monomeric globular actin (G-actin). The LKKTETQ motif binds G-actin in a 1:1 stoichiometric complex, sequestering monomeric actin and preventing its uncontrolled polymerization into filamentous actin (F-actin).[6] By regulating actin polymerization, TB-500 modulates cytoskeletal organization — the prerequisite for cell motility and migration essential for tissue repair.[9]
Tβ4 (and potentially its active fragments) interacts with F1-F0 ATP synthase on the surface of endothelial cells, binding the beta-subunit with a dissociation constant (KD) of approximately 12 nM. This interaction increases cell surface ATP levels, which is necessary for purinergic receptor signaling involved in cell migration.[10]
TB-500 forms a functional complex with Integrin-Linked Kinase (ILK) and PINCH (Particularly Interesting New Cys-His protein). This complex leads to phosphorylation and activation of Akt (Protein Kinase B), specifically Akt2 in endothelial cells, promoting cell survival and cardiomyocyte protection following ischemic injury.[11][12]
TB-500 modulates inflammation by interrupting the NF-κB signal transduction pathway. It blocks phosphorylation and nuclear translocation of the RelA/p65 subunit, suppressing transcription of pro-inflammatory cytokines IL-8, IL-1β, and TNF-α.[13][14]
The peptide increases production of Matrix Metalloproteinases (MMP-2 and MMP-9), enzymes necessary for degrading the basement membrane to facilitate cell migration during angiogenesis and wound repair.[15]
TB-500 upregulates manganese superoxide dismutase (Mn-SOD), copper/zinc SOD, and catalase, providing cytoprotection against oxidative stress.[16]
A critical distinction: the anti-fibrotic properties of Tβ4 are largely attributed to the N-terminal tetrapeptide Ac-SDKP (amino acids 1–4), which is not present in TB-500. Ac-SDKP inhibits hematopoietic stem cell proliferation and reduces fibrosis by interfering with TGF-β signaling. Therefore, TB-500 retains the actin-binding and migratory properties but may lack the specific anti-fibrotic signaling of the full-length protein.[7]
Additionally, recent research (Rahaman et al., 2024) suggests that TB-500's metabolite Ac-LKKTE may be the primary wound-healing driver rather than the parent peptide itself.[17]
In laboratory research, TB-500 and its parent molecule Tβ4 are investigated in multiple experimental paradigms:
TB-500 is most directly compared in the cytoskeletal-peptide research literature with the full-length parent Thymosin beta-4 for the actin-binding versus anti-fibrotic activity split, with BPC-157 for parallel pleiotropic tissue-repair coverage, and with GHK-Cu for matrix-remodeling and angiogenic crosstalk. These cross-comparisons inform research designs investigating whether the LKKTETQ minimal motif suffices to recapitulate the parent's broader regenerative profile.[7]
| Property | Value |
|---|---|
| Molecular Formula | C₃₈H₆₈N₁₀O₁₄ |
| Molecular Weight | 889.018 g/mol |
| CAS Number | 885340-08-9 |
| Sequence (3-Letter) | Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln |
| Sequence (1-Letter) | Ac-LKKTETQ |
| Amino Acids | 7 (N-acetylated heptapeptide) |
| Parent Molecule | Thymosin Beta-4 (fragment 17–23 of 43-aa protein) |
| Structural Type | Linear heptapeptide with N-terminal acetylation |
| Synonyms | Fequesetide, Thymosin β4 fragment (17-23), N-acetylated LKKTETQ |
| Plasma Half-Life | ~2.5–3 hours (subcutaneous) |
| PubChem CID | |
|---|---|
| InChI Key | |
| Isomeric SMILES | |
| IUPAC Name |
| Study | Model | Key Findings | Ref |
|---|---|---|---|
| Rahaman et al. (2024) | Rat / fibroblasts in vitro | Metabolite Ac-LKKTE showed wound-healing activity — parent TB-500 did not. Primary metabolite Ac-LK at 0-6h, Ac-LKK to 72h. No cytotoxicity. | [17] |
| Philp et al. (2003) | db/db diabetic mice, aged mice | LKKTETQ fragment promoted dermal repair comparable to full-length Tβ4. ↑ wound contracture and collagen deposition. | [8] |
| Sosne et al. (2010) | In vitro (LDH assay) | No significant difference between acetylated TB-500 and non-acetylated LKKTETQ on cell injury (LDH release). | [26] |
| Ho et al. / Kwok et al. (2012-2013) | Thoroughbred horses | 10 mg SC single dose; detected at 0.02 ng/mL in plasma, 0.01 ng/mL urine. Detection: 11.3h plasma, 9.7h urine. | [27][28] |
Note: These studies used the 43-amino acid full-length Tβ4 protein, not the TB-500 fragment. Results may not be directly transferable to the 7-amino acid fragment.
| Study | Model | Key Findings | Ref |
|---|---|---|---|
| Bao et al. (2013) | Rat myocardial ischemia | 5.37 mg/kg IP, long-term dosing — 43% infarct volume reduction (p < 0.01) | [21] |
| Bock-Marquette et al. (2004) | Mouse cardiac cells | Tβ4 activates ILK → promotes cardiac cell migration, survival, and cardiac repair (published in Nature) | [11] |
| Smart et al. (2007) | Mouse epicardial progenitors | Tβ4 induces epicardial progenitor mobilization and neovascularization (published in Nature) | [29] |
| Malinda et al. (1999) | Rat dermal wound | Tβ4 increased re-epithelialization by 42% over saline at 4 days post-injury | [18] |
| Shah et al. (2018) | Mouse liver fibrosis | Tβ4 prevented oxidative stress, inflammation, and fibrosis in ethanol/LPS liver injury | [25] |
No registered human clinical data exists specifically for the TB-500 fragment. The following are clinical data for the full-length Thymosin Beta-4 protein.
| Study | Design | n= | Key Outcome | Ref |
|---|---|---|---|---|
| RGN-352 Phase I | IV in healthy volunteers | 40 | Safe, well-tolerated, no dose-limiting toxicities at doses up to 1260 mg cumulative over 14 days | [30] |
| RGN-259 Phase II (Dry Eye) | 0.1% ophthalmic solution | — | Improved signs and symptoms of severe dry eye; no drug-related serious adverse events | [19][20] |
| RGN-137 Phase II (Pressure Ulcers) | Topical gel 0.01-0.1% | — | Accelerated dermal healing; no drug-related SAEs | [31] |
| Parameter | Value | Ref |
|---|---|---|
| G-Actin Binding | 1:1 stoichiometric complex (LKKTETQ motif) | [6] |
| ATP Synthase KD | ~12 nM (endothelial cell surface) | [10] |
| In vitro migration activity | ~50 nM (identical to full-length Tβ4) | [26] |
| Plasma Half-life (SC) | ~2.5–3 hours | [27] |
| Equine Detection | Plasma 11.3h, urine 9.7h (10 mg SC) | [28] |
| Primary Metabolite | Ac-LK (0-6h), Ac-LKK (up to 72h) | [17] |
| Acute Toxicity Threshold | No toxicity observed up to 20 mg/kg | [3] |
| Feature | TB-500 (Ac-LKKTETQ) | Thymosin Beta-4 (Full) |
|---|---|---|
| Length | 7 amino acids (fragment 17–23) | 43 amino acids |
| Actin Binding | ✅ Retains LKKTETQ motif | ✅ Full actin-binding domain |
| Anti-Fibrotic (Ac-SDKP) | ❌ Absent (aa 1–4 not included) | ✅ Present via N-terminal Ac-SDKP |
| Cell Migration | Comparable (~50 nM) | Comparable (~50 nM) |
| Wound Healing | Via metabolite Ac-LKKTE | Direct + via Ac-SDKP |
| Human Clinical Data | None | Phase I/II (RGN-352, 259, 137) |
| FDA Status | Category 2 (prohibited) | IND (clinical development) |
The products offered on this website are furnished for in-vitro studies only. In-vitro studies (Latin: in glass) are performed outside of the body. These products are not medicines or drugs and have not been approved by the FDA to prevent, treat or cure any medical condition, ailment or disease. Bodily introduction of any kind into humans or animals is strictly forbidden by law.
For Laboratory Research Only. Not for human use, medical use, diagnostic use, or veterinary use.
ALL ARTICLES AND PRODUCT INFORMATION PROVIDED ON THIS WEBSITE ARE FOR INFORMATIONAL AND EDUCATIONAL PURPOSES ONLY.
Allan L. Goldstein, Ph.D., is Professor Emeritus at George Washington University, Department of Biochemistry and Molecular Medicine, and Chairman and Chief Scientific Advisor at RegeneRx Biopharmaceuticals, Inc. Dr. Goldstein is the co-discoverer of the thymosins. His research laboratory was instrumental in isolating Thymosin Beta-4 (Tβ4) and identifying its active sites, demonstrating that the specific 7-amino acid actin-binding domain (amino acids 17–23), which corresponds to TB-500, is sufficient to promote wound healing, angiogenesis, and tissue repair in animal models comparable to the full-length molecule. Allan L. Goldstein is being referenced as one of the leading scientists involved in the research and development of TB-500 and Thymosin Beta-4. In no way is this doctor/scientist endorsing or advocating the purchase, sale, or use of this product for any reason. There is no affiliation or relationship, implied or otherwise, between Pure US Peptide and this doctor.
View Full Researcher Profile →Hynda K. Kleinman, Ph.D., is affiliated with George Washington University (Department of Biochemistry and Molecular Biology) and formerly with the National Institutes of Health (NIDCR). Dr. Kleinman conducted foundational research isolating the biological activities of Tβ4 to specific peptide sequences. She co-authored key studies showing that the actin-binding motif LKKTETQ (the sequence of TB-500) is essential and sufficient for angiogenesis and endothelial cell migration, and confirmed this fragment's ability to accelerate dermal wound healing. Hynda K. Kleinman is being referenced as one of the leading scientists involved in the research and development of TB-500 and Thymosin Beta-4. In no way is this doctor/scientist endorsing or advocating the purchase, sale, or use of this product for any reason. There is no affiliation or relationship, implied or otherwise, between Pure US Peptide and this doctor.
View Full Researcher Profile →Dr. Hynda K. Kleinman is being referenced as one of the leading scientists involved in the research and development of TB500. In no way is this doctor/scientist endorsing or advocating the purchase, sale, or use of this product for any reason. There is no affiliation or relationship, implied or otherwise, between Pure US Peptide and this doctor. The purpose of citing the doctor is to acknowledge, recognize, and credit the exhaustive research and development efforts conducted by the scientists studying this peptide.
Gabriel Sosne, M.D., is affiliated with Wayne State University (Kresge Eye Institute). Dr. Sosne has extensively studied the ophthalmic applications of Thymosin Beta-4 and its fragments. He co-authored research defining the biological activities of short peptide sequences — including the 17–23 fragment (TB-500) — involved in cell migration, wound healing, and anti-apoptosis. His work has been critical in translating these findings into clinical trials for corneal repair and dry eye (RGN-259). Gabriel Sosne is being referenced as one of the leading scientists involved in the research and development of TB-500 and Thymosin Beta-4. In no way is this doctor/scientist endorsing or advocating the purchase, sale, or use of this product for any reason. There is no affiliation or relationship, implied or otherwise, between Pure US Peptide and this doctor.
View Full Researcher Profile →Dr. Gabriel Sosne is being referenced as one of the leading scientists involved in the research and development of TB500. In no way is this doctor/scientist endorsing or advocating the purchase, sale, or use of this product for any reason. There is no affiliation or relationship, implied or otherwise, between Pure US Peptide and this doctor. The purpose of citing the doctor is to acknowledge, recognize, and credit the exhaustive research and development efforts conducted by the scientists studying this peptide.
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.
DOIDelcourt 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.
DOIGoldstein 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.
DOIU.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.
FDA.govWorld Anti-Doping Agency. The 2025 Prohibited List. WADA. January 1, 2025.
WADAXing Y, Ye Y, Zuo H, Li Y. Progress on the Function and Application of Thymosin β4. Frontiers in Endocrinology. 2021;12:767785.
DOIBock-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.
DOIPhilp 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.
DOIBelsky 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.
DOIHinkel 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.
DOIBock-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.
DOISmart N, Risebro CA, Melville AA, et al. Thymosin β4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007;445(7124):177-182.
DOISosne 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.
DOIReyes-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.
DOIMalinda KM, Sidhu GS, Mani H, et al. Thymosin beta 4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364-368.
DOIShah 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.
DOIRahaman 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.
DOIMalinda KM, Sidhu GS, Mani H, et al. Thymosin beta 4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364-368.
DOISosne 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.
DOISosne 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.
DOIBao 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.
DOITreadwell 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.
DOINguyen J, Verma S, Vuong VT, et al. Engineered Tandem Thymosin Peptide Promotes Corneal Wound Healing. Investigative Ophthalmology & Visual Science. 2025;66(14):31.
DOISosne 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.
DOIHo 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.
DOIKwok 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.
DOISmart N, Risebro CA, Melville AA, et al. Thymosin β4 induces adult epicardial progenitor mobilization and neovascularization. Nature. 2007;445(7124):177-182.
DOIRegeneRx Biopharmaceuticals. Phase I Safety Trial for RGN-352: Injectable Thymosin Beta 4. 2009.
SourceTreadwell 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.
DOIFor Research Use Only (RUO). Not intended for human consumption, clinical use, or as a drug, food, cosmetic, or medical device. This product has not been evaluated by the FDA and is supplied solely for in-vitro laboratory research by qualified professionals.
Each lot is independently tested by accredited third-party laboratories (ISO 17025) at 99%+ purity.
Store lyophilized powder at -20°C for long-term stability. Reconstituted solution: 2-8°C with limited shelf life.
Lyophilized Powder: Store at -20°C (-4°F) for long-term stability. Stable at room temperature for up to 90 days, but freezer storage is recommended for extended periods.
Reconstituted Solution: Refrigerate at 2–8°C (36–46°F). Use within 8 days for optimal potency. In clinical settings, reconstituted solutions are typically used within 6 hours.
Handling: Protect from intense light and heat. Allow vial to reach room temperature before opening. Do not shake — swirl gently during reconstitution. Discard any solution that appears cloudy or contains particulate matter.
“Preclinical Research Summary Animal Studies (TB-500 Fragment Specifically) Study Model Key Findings Ref Rahaman et al.”
Common research questions about TB500 — purity, handling, COA documentation, and published-research context.
Verified researcher feedback on TB500 — purity, COA accuracy, shipping, and lab support.
We've been sourcing TB-500 from Pure US for over a year. Every lot's HPLC trace lines up with the COA they ship. Endotoxin numbers are consistently clean. Documentation is the most thorough I've evaluated in this market.
Lyophilized cake is uniform, reconstitutes cleanly. Identity confirmation matches expected mono-isotopic mass within tolerance. Excellent product.
Pure US Peptides has been our primary TB-500 supplier for two years. The fact that they ship the actual third-party chromatogram alongside the COA — not just a summary — is what sold us originally and keeps us loyal.
Quality is excellent. Would appreciate seeing residual TFA reporting added by default. Otherwise no complaints.
Vials sealed, labeled correctly, shipped overnight. Customer service responded to a technical question within ninety minutes with the documentation I needed.
Solid TB-500 product. Reconstitutes cleanly, COA matches independently verified HPLC. Pure US is on our short list of approved suppliers.
Reviews submitted by verified research-buyer customers via post-purchase email. Reviewer names are shown with initials and role to protect privacy. All feedback covers product purity, documentation, and shipping — never application methodology.
