TB-500

What TB-500 Is

TB-500 is a synthetic peptide that reproduces the actin-binding region of Thymosin beta-4 (Tβ4), an endogenous 43-amino-acid protein present throughout human tissue and one of the most abundant intracellular actin-sequestering peptides. Analytical characterization by Esposito and colleagues (Drug Testing and Analysis, 2012) established that the material sold as "TB-500" is the N-terminal acetylated 17-23 fragment of Tβ4, with the sequence Ac-LKKTETQ. This distinction matters: TB-500 is a short seven-residue fragment and a research chemical, not the full protein and not an approved drug. The parent molecule, full-length Tβ4, has been studied for decades and developed clinically by RegeneRx (RGN-259, RGN-137, RGN-352), whereas the fragment sold as TB-500 has a far thinner, largely preclinical evidence base.

Mechanism of Action

The LKKTETQ motif is the core site through which Thymosin beta-4 binds monomeric G-actin. In preclinical models this actin-binding activity supports cytoskeletal remodeling and directed cell migration by maintaining a pool of actin available for polymerization. Philp, Huff, Gho, Hannappel and Kleinman (FASEB Journal, 2003) demonstrated that this seven-amino-acid motif is essential for the angiogenic activity of Tβ4: the isolated peptide stimulated endothelial cell migration, adhesion, and vessel sprouting at nanomolar concentrations, incomplete versions of the sequence were inactive, and adding soluble actin abolished the effect. Repair-associated activity in preclinical studies is attributed to enhanced migration of keratinocytes and endothelial cells, reduced inflammation, and increased collagen deposition.

What Published Research Has Examined

The foundational literature comes largely from the laboratories of Allan Goldstein and Hynda Kleinman. Malinda, Goldstein, Kleinman and colleagues (Journal of Investigative Dermatology, 1999) reported that full-length Tβ4 accelerated dermal wound repair in a rodent model, increasing reepithelialization by roughly 42% at day 4 and up to 61% at day 7, with greater collagen deposition and new vessel formation. The 2003 FASEB J work localized angiogenic activity specifically to the actin-binding motif that TB-500 represents. Beyond skin, preclinical Tβ4 research has extended to corneal, cardiac, vascular, and neural injury models. Human clinical development, however, has used the full-length parent peptide: RegeneRx and its joint venture ReGenTree advanced RGN-259 through Phase 2/3 dry-eye trials and a Phase 3 neurotrophic keratopathy program. No completed, peer-reviewed human randomized controlled trials have evaluated the TB-500 fragment itself.

Key Findings

Across preclinical work, the consistent signal is that the Tβ4 actin-binding region promotes cell migration and angiogenesis, processes that plausibly underlie observed tissue-repair effects in animal models. The strongest mechanistic evidence for the fragment specifically is the 2003 FASEB J study tying angiogenesis to the LKKTETQ motif. The strongest repair evidence (the 1999 wound-healing data) used the full-length protein rather than the fragment. Clinical efficacy signals in humans exist only for full-length Tβ4 in ophthalmic settings, not for TB-500. The appropriate summary is that TB-500 is a mechanistically interesting, preclinically supported fragment whose human evidence base remains limited and indirect.

Regulatory Status

TB-500, described on the docket as the thymosin beta-4 fragment, is currently Category 2 — a substance that 503A compounding pharmacies may not compound — and is one of exactly seven compounds on the FDA Pharmacy Compounding Advisory Committee (PCAC) docket for the July 23-24, 2026 meeting, alongside BPC-157, KPV, MOTS-c, emideltide, epitalon, and semax. The PCAC vote is non-binding and represents roughly the second of about six steps in FDA rulemaking; even a favorable, unanimous vote would not by itself make the compound legally compoundable, with a realistic timeline of at least 12-18 months to any actual compounding availability. TB-500 is not an FDA-approved drug and is otherwise best described as unscheduled / research-use-only.

Safety Considerations and Related Compounds

Human safety data for the TB-500 fragment is limited; most systematic tolerability information relates to full-length Tβ4 (RGN-259) in ophthalmic trials and does not transfer directly to the injectable research-chemical fragment. Because the mechanism promotes angiogenesis and cell migration, the literature notes a theoretical caution regarding tissues where new vessel growth would be undesirable — a preclinical and regulatory discussion point, not an established human finding. TB-500 is also prohibited at all times in sport under the World Anti-Doping Agency prohibited list (S0 non-approved substances), and research-chemical products vary in identity and purity. Closely related compounds include full-length Thymosin beta-4 (RGN-259) as the parent molecule, and other repair-associated peptides studied in overlapping contexts such as BPC-157, GHK-Cu, and KPV. All of the above is research-context information, not medical advice.

Key published studies

Regulatory status

Current status: Category 2 · PCAC July 2026 docket. Category 2 · PCAC July 2026 docket. PepSense tracks FDA filings and updates this record as the regulatory picture changes. See the FDA PCAC tracker for the July 2026 vote and what happens next.

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