Description
Summary Abstract
TB-500 (Thymosin β4; Tβ4; Thymosin Beta 4; TMSB4X peptide product; Ac-SDKP precursor) is a synthetic 43-amino acid polypeptide pharmacologically identical to the endogenous human Thymosin Beta-4 (Tβ4), encoded by the TMSB4X gene and representing one of the most abundant intracellular peptides in mammalian cells. TB-500 is best characterized as a G-actin sequestrant: the core LKKTETQ domain (residues 17–23) binds monomeric actin with a Kd of approximately 0.5 µM, modulating cytoskeletal dynamics that govern cell motility, migration, and tissue remodeling. Beyond cytoskeletal regulation, Tβ4 activates multiple signaling pathways relevant to wound healing, angiogenesis, cardiac repair, and anti-fibrosis. Clinical development by RegeneRx Biopharmaceuticals has produced Orphan Drug Designation and Phase II/III data for ophthalmic (RGN-259) and dermal (RGN-137) indications. TB-500 is classified WADA S2 and injectable Tβ4 appears on the FDA’s 503B difficult-to-compound list.
Clinical Indications
TB-500 has generated controlled clinical and preclinical evidence across ophthalmology, dermatology, cardiology, and neuroscience:
- Neurotrophic Keratopathy (Ophthalmic): RGN-259 (Tβ4 ophthalmic solution) holds FDA Orphan Drug Designation; Phase III data demonstrated accelerated corneal healing and nerve density restoration versus vehicle control, with topical route avoiding systemic exposure concerns.
- Chronic Wound Healing: Phase II of RGN-137 (topical Tβ4) showed healing acceleration in chronic non-healing wounds, including pressure ulcers and epidermolysis bullosa lesions.
- Cardiac Regeneration: The REGENERATIVE-IHD trial showed elevated endogenous Tβ4 levels correlated with improved cardiac outcomes in patients receiving intracoronary stem cell therapy, supporting a cardioprotective role.
- Neuroregeneration: Preclinical data in spinal cord injury and TBI models demonstrate Tβ4 promotes axonal outgrowth, oligodendrocyte differentiation, and reduced lesion volume.
- Systemic IV Safety: Phase I IV study confirmed no dose-limiting toxicity at doses up to 1,260 mg, establishing a favorable safety profile for systemic administration.
Contraindications
- Active Malignancy: Tβ4 is overexpressed in colon, pancreatic, breast, and lung carcinomas, where it promotes tumor cell migration and metastasis via actin-remodeling pathways; use in patients with established active cancer warrants careful evaluation.
- WADA-Governed Athletics: TB-500 is prohibited under WADA S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), in- and out-of-competition; incompatible with competitive sport under WADA code.
- Concurrent Immunosuppressive Regimens: Tβ4’s NF-κB suppression and broad anti-inflammatory activity may interact with immunosuppressive protocols; research designs involving concurrent immunosuppressants should account for additive or synergistic effects.
Mechanism of Action (MOA)
Tβ4 mediates its biological activity through at least four mechanistically distinct but overlapping pathways operating across different cellular compartments:
G-Actin Sequestration & Cell Migration
The LKKTETQ motif (residues 17–23) binds monomeric G-actin with Kd ~0.5 µM, reducing free actin available for F-actin polymerization. This shifts the actin equilibrium toward monomer, promoting lamellipodia formation, cell migration, and re-epithelialization — essential for wound healing and tissue repair.
PI3K/AKT Anti-Apoptosis & NF-κB Suppression
The N-terminal domain (AA 1–15) activates PI3K/AKT, driving cell survival and inhibiting apoptosis under ischemic or cytotoxic stress. Concurrently, Tβ4 downregulates NF-κB transcriptional activity, reducing pro-inflammatory cytokines (IL-1β, TNF-α, IL-6) and COX-2 expression — the mechanistic basis for its anti-inflammatory profile.
Angiogenesis & Anti-Fibrosis
Tβ4 upregulates VEGF expression and activates Notch signaling in endothelial cells, supporting new vessel formation in ischemic and injured tissues. Matrix metalloproteinase (MMP) induction promotes extracellular matrix remodeling and collagen turnover, opposing fibrotic deposition. The N-terminal tetrapeptide Ac-SDKP (cleavable by prolyl oligopeptidase) independently inhibits TGF-β1-driven fibrosis.
Key Features & Specifications
TB-500 combines the full-length Thymosin Beta-4 sequence with multiple functionally active domains in a single lyophilized preparation:
Chemical Analysis
| Property | Specification Reference Data |
|---|---|
| Sequence | Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES |
| CAS Number | 77591-33-4 |
| Molecular Formula | C212H352N56O78S (approximate) |
| Molecular Weight | ~4,921 Da (4.9 kDa) |
| PubChem CID | 16132229 |
| Synonyms | Thymosin β4; Tβ4; TB-500; TB500; Thymosin Beta 4; TMSB4X peptide product; Ac-SDKP precursor |
| Form / Variation | 5 MG Lyophilized (P-041) / 10 MG Lyophilized (P10-040) |
Storage, Safety, and Handling
Storage Protocol
Store lyophilized TB-500 at −20°C, protected from moisture and light; properly sealed material is stable up to 24 months. Reconstituted solution should be refrigerated at 2–8°C and used within 14–21 days; do not freeze reconstituted material. Allow the lyophilized cake to equilibrate to room temperature before reconstituting with bacteriostatic water (multi-dose) or sterile water for injection. Gently swirl to dissolve; do not shake. Minimize freeze-thaw cycles of reconstituted solution by aliquoting for single-use storage if long-term use is planned.
Handling & Compliance
Prepare reconstituted solutions under sterile technique with gloves and appropriate PPE. Phase I IV safety data (no dose-limiting toxicity to 1,260 mg) supports a favorable systemic tolerability profile; adverse events in published trials have been mild and transient. TB-500 is prohibited under WADA S2 in- and out-of-competition. Injectable Tβ4 appears on the FDA 503B bulk drug substances list requiring additional FDA review; 503A compounding for individual patient prescriptions operates under separate rules. Researchers should verify current compounding regulatory status with applicable state pharmacy boards.