K4 Elite
K4 Elite
TB-500 is a synthetic 7-amino-acid fragment (Ac-LKKTETQ, residues 17-23) of the 43-amino-acid protein thymosin beta-4 (Tβ4). The two are not interchangeable in the evidence base: every completed human trial has used full-length recombinant or synthetic Tβ4 (RegeneRx/ReGenTree's RGN-259 eye drops and RGN-137 dermal gel) applied topically, whereas the fragment has been studied only in animals (e.g., a 2026 rat Achilles-tendon study at 60 µg/kg/day intraperitoneally). FDA's Category 2 statement on the fragment says it 'has not identified any human exposure data' for it. One Phase 1/2 trial of the fragment (NCT07487363, cardiovascular biomarkers) began recruiting in 2026 and has no results. Adverse-event data below therefore come from full-length Tβ4 trials and are labelled as such.
Each row records what a published study did: who it enrolled, the regimen it administered to those subjects, and what it reported. These are historical study descriptions, not protocols to follow.
| Study | Population | Regimen as reported | Primary findings |
|---|---|---|---|
| Biçer et al., Jt Dis Relat Surg 2026 (rat Achilles tendon repair; TB-500 fragment; preclinical) | 32 male Sprague-Dawley rats after standardised Achilles tendon transection and repair (8 per group) | Rats were administered synthetic TB-500 60 µg/kg/day, BPC-157 10 µg/kg/day, both, or vehicle intraperitoneally for four weeks postoperatively; tendons were tested biomechanically and histologically at four weeks. | The TB-500 group had significantly higher maximum load to failure than controls (p < 0.05) and lower Bonar and Movin histology scores; the BPC-157 + TB-500 combination did not add benefit over either agent alone. |
| TB-500 (Thymosin Beta 4 17-23 Fragment) for Cardiovascular Biomarkers in Stable ASCVD — Hudson Biotech (Phase 1/2, recruiting; fragment) Registry: NCT07487363
|
Adults with stable atherosclerotic cardiovascular disease and endothelial dysfunction (planned n=80) | The registration lists TB-500 versus matching vehicle placebo; dose and schedule are not detailed in the public record. Study start date is listed as 5 February 2026. | No results are available; this is the only registered human trial of the fragment located. |
| ARISE-3 — ReGenTree Phase 3 dry eye (full-length Tβ4, RGN-259 0.1% eye drops; human RCT) Registry: NCT03937882
|
Adults with dry eye syndrome (n=700 randomised; 699 in safety population) | Participants received preservative-free RGN-259 (0.1% thymosin beta 4) or vehicle placebo instilled into each eye four times daily for 14 days, with controlled-adverse-environment challenge. | Registry results report 0 serious adverse events in either arm; non-serious adverse events occurred in 47/350 RGN-259 versus 31/349 placebo participants, with instillation-site pain the most common (23/350 vs 16/349). Efficacy outcomes are posted on the registry. |
| ARISE-2 — ReGenTree Phase 3 dry eye (full-length Tβ4, RGN-259 eye drops; human RCT) Registry: NCT02974907
|
Adults with dry eye syndrome (n=601) | Participants received RGN-259 (Tβ4) or vehicle placebo eye drops four times daily for 28 days. | Registry results list serious adverse events in 3/299 RGN-259 versus 2/302 placebo participants and other adverse events in 19/299 versus 21/302; no deaths occurred. |
| Sosne et al., Int J Mol Sci 2022 — SEER-1 Phase 3 neurotrophic keratopathy (full-length Tβ4, RGN-259 0.1%; human RCT) Registry: NCT02600429
|
18 patients with Stage 2-3 neurotrophic keratopathy and persistent epithelial defects (10 RGN-259, 8 placebo) | Patients received 0.1% RGN-259 ophthalmic solution or placebo for 4 weeks with follow-up to day 43. | Complete healing at 4 weeks occurred in 6/10 RGN-259 versus 1/8 placebo patients (p = 0.0656); the authors reported no significant adverse effects. |
| Sosne, Dunn & Kim, Cornea 2015 — Phase 2 severe dry eye (full-length Tβ4, RGN-259 0.1%; human RCT) Registry: NCT01393132
|
9 patients with severe dry eye (including graft-versus-host-disease-associated) at 2 US sites | Patients received RGN-259 (0.1% Tβ4) or vehicle eye drops six times daily for 28 days, with a 28-day follow-up (56-day trial). | At day 56 the RGN-259 group (12 eyes) showed a 35.1% reduction in ocular discomfort versus vehicle (6 eyes; P = 0.0141) and a 59.1% reduction in total corneal fluorescein staining (P = 0.0108); the drops were reported as safe and well tolerated. |
| Phase 2 Tβ4 ophthalmic solution in dry eye (full-length Tβ4; human RCT, registry results only) Registry: NCT01387347
|
72 adults with dry eye syndrome (36 Tβ4, 36 placebo) | Participants received preservative-free 0.1% (w/w) Tβ4 eye drops or 0.0% vehicle twice daily for 28 days in a controlled-adverse-environment design. | Registry results list no serious adverse events in either arm; instillation-site pain was recorded in 2/36 placebo and 0/36 Tβ4 participants. |
| Guarnera et al., Ann N Y Acad Sci 2010 — RegeneRx Phase 2 venous stasis ulcers (full-length Tβ4 topical gel; human RCT) Registry: NCT00832091
|
73 patients with venous stasis ulcers at eight European sites (five in Italy, three in Poland) | Patients were randomised 3:1 to topical Tβ4 gel at one of three ascending concentrations or placebo gel, applied once daily for up to 84 days alongside compression therapy, with 14 days of follow-up. | The safety profile of all doses was reported as acceptable and comparable to placebo; the authors suggest the 0.03% dose may accelerate wound healing, with complete healing within 3 months in about 25% of patients. Registry results list serious adverse events in 3/55 Tβ4 versus 1/17 placebo participants. |
| RegeneRx Phase 2 pressure ulcers (full-length Tβ4 topical gel; human RCT, registry results only) Registry: NCT00382174
|
72 patients with pressure ulcers (Tβ4 at three doses n=53 in safety population; placebo n=18) | Patients received topical 0.01%, 0.02% or 0.1% Tβ4 gel or placebo gel once daily for up to 84 days, with adverse events collected weekly to day 84 and at day 99. | Registry results list serious adverse events in 13 Tβ4-treated versus 5 placebo participants and other adverse events in 40 versus 13; individual events were each reported in 0-2 participants. |
Effects recorded in the cited reports. Frequencies are those the source reported, in the population that source studied.
| Effect | Frequency / context | Source |
|---|---|---|
| Instillation-site pain (full-length Tβ4 eye drops, not the fragment) | 23/350 (6.6%) RGN-259 vs 16/349 (4.6%) placebo in ARISE-3 (NCT03937882); instillation-site irritation 5/350 vs 2/349 in the same trial. | ARISE-3 results, ClinicalTrials.gov NCT03937882 ↗ |
| Visual acuity reduced (full-length Tβ4 eye drops, not the fragment) | 12/350 RGN-259 vs 7/349 placebo in ARISE-3 (NCT03937882); 1/299 vs 10/302 in ARISE-2 (NCT02974907). | ARISE-3 and ARISE-2 results, ClinicalTrials.gov ↗ |
| Serious adverse events (full-length Tβ4, all routes) | 0/350 vs 0/349 in ARISE-3; 3/299 vs 2/302 in ARISE-2; 3/55 vs 1/17 in the venous-ulcer gel trial (NCT00832091); 13 vs 5 participants in the pressure-ulcer gel trial (NCT00382174, chronic-wound population with comorbidities). Causality is not attributed in the registry records. | ClinicalTrials.gov results records for NCT03937882, NCT02974907, NCT00832091 and NCT00382174 ↗ |
| Laboratory changes in chronic-wound gel trials (full-length Tβ4 topical) | In the venous-ulcer trial (NCT00832091) registry results list red-blood-cell sedimentation rate increased in 6/55 Tβ4 vs 0/17 placebo and creatine phosphokinase increased in 3/55 vs 1/17; single cases of ALT and conjugated bilirubin increases occurred in the Tβ4 arm. The published summary describes the safety profile as comparable to placebo. | Study of Thymosin Beta 4 in Patients With Venous Stasis Ulcers (ClinicalTrials.gov results) and Guarnera et al. 2010 ↗ |
| TB-500 fragment: no human safety data (regulatory assessment) | FDA's Category 2 entry for 'Thymosin beta-4, fragment (LKKTETQ), also known as TB-500' states the agency 'has not identified any human exposure data' and 'lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans'; immunogenicity risk from aggregation and peptide-related impurities is cited. | FDA — Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks ↗ |
No interactions with a verifiable citation have been indexed for this compound.
Exclusions and label contraindications recorded in the cited sources.