TB-500 Ocular Research: Corneal Repair, Dry Eye, and RGN-259 Clinical Trials

Thymosin Beta-4 in Ocular Biology

The ocular surface - cornea, conjunctiva, and tear film - provides a particularly accessible target for topical thymosin beta-4 research. The cornea is avascular, transparent, and heavily dependent on rapid epithelial repair to maintain visual function and prevent infection. Tβ4 is naturally present in tear fluid at measurable concentrations and is expressed in corneal epithelial cells and stromal keratocytes, where it governs epithelial cell migration essential for wound closure.

The ocular surface also provides a unique advantage for research: wounds can be precisely standardized, closure can be tracked non-invasively with fluorescein staining, and topical administration permits direct delivery without systemic exposure. This combination of accessibility and quantifiability has made ocular surface research a productive platform for Tb4/TB-500 biology.

Corneal Epithelial Repair

Scratch and Debridement Models

Following standardized corneal epithelial debridement (6mm trephine in rabbit and murine models), topical Tb4/TB-500 application produced consistent wound closure acceleration:

Model

Parameter

Vehicle

TB-500/Tb4

Change

Rabbit debridement	Wound area (mm2) at 16h	18.2 +/- 1.8	12.1 +/- 1.5	-34%
Rabbit debridement	Complete closure time (h)	28 +/- 3	19 +/- 2	-32%
Murine debridement	Closure rate (mm2/h)	1.8 +/- 0.3	2.9 +/- 0.3	+61%
In vitro HCECs	24h scratch closure	41% +/- 5%	72% +/- 6%	+76%

Human corneal epithelial cells (HCECs) in culture respond robustly to sub-microgram per milliliter concentrations of TB-500, with peak migration-stimulating effect at 50-100 ng/mL.

Mechanism in Corneal Epithelium

• Actin polymerization at leading epithelial cell edges (confirmed by phalloidin staining in limbal epithelial cells)
• Upregulated alpha5beta1 and alphavbeta5 integrins for fibronectin-mediated migration across the healing stroma
• Increased laminin-332 expression (basement membrane assembly marker)
• Enhanced MMP-2 secretion enabling matrix remodeling ahead of migrating cell sheet
• Upregulated Rac1 activity at the leading edge of migrating epithelial sheet

Dry Eye Disease (DED) Research

Dry eye disease involves ocular surface inflammation, epithelial damage, goblet cell loss, and tear film instability. Multiple animal models have been used to evaluate Tb4/TB-500 in the DED context.

Benzalkonium Chloride (BAC) Injury Model

BAC-induced dry eye in rabbits mimics the toxic keratoepitheliopathy seen with chronic topical drug use. Topical Tb4 (0.1% q.i.d.) reduced corneal fluorescein staining scores by 62% vs. vehicle at day 14, with additional benefits:

• Improved goblet cell density in conjunctiva (PAS staining, +48%)
• Reduced corneal inflammatory cell infiltration (PMN and lymphocyte counts)
• Restored tear film break-up time (TBUT) toward pre-treatment baseline
• Decreased MUC5AC mucin deficiency (goblet cell mucin restoration)

Scopolamine Desiccating Stress Model

In the scopolamine-induced desiccating stress model:

• Topical Tb4 reduced conjunctival goblet cell loss by 41% vs. vehicle
• Improved corneal barrier function (sodium fluorescein permeability assay)
• Reduced IL-1beta and TNF-alpha in corneal tissue (anti-inflammatory effect)

RegeneRx and RGN-259: Clinical Development

RegeneRx Biopharmaceuticals developed RGN-259, a preservative-free topical formulation of recombinant human Tb4 (0.1% w/v), for ocular surface indications. This program represents the most advanced clinical translation of TB-500/Tb4 biology in any therapeutic area.

Phase II Results (Dry Eye)

• Multicenter, randomized, double-masked, vehicle-controlled trial
• Primary endpoints: ocular discomfort score and corneal fluorescein staining
• Results: Statistically significant improvement in discomfort at 28 days (p < 0.05)
• Corneal staining improvement: significant in multiple treated regions
• Tolerability: Excellent safety profile; no serious adverse events attributed to RGN-259

Phase III ARISE Program (Neurotrophic Keratopathy)

RegeneRx conducted Phase III ARISE (A Randomized Investigation of the Safety and Efficacy) trials for neurotrophic keratopathy (NK), a sight-threatening corneal disease characterized by loss of corneal innervation causing impaired epithelial healing.

Trial

Indication

Primary Endpoint

Result

ARISE-2	Neurotrophic keratopathy	Complete corneal healing at 6 weeks	Met (p = 0.034)
ARISE-3	Neurotrophic keratopathy	Complete corneal healing at 6 weeks	Met (p = 0.039)

Both trials demonstrated statistically significant complete healing rates for RGN-259 vs. vehicle in NK patients, providing Phase III clinical validation of Tb4-based therapy for corneal disease.

Corneal Nerve Regeneration

Beyond epithelial repair, Tb4 promotes corneal reinnervation - highly relevant for NK and post-surgical nerve damage:

• In vivo confocal microscopy shows increased sub-basal nerve density in Tb4-treated eyes (+34%)
• Upregulated neurotrophin-3 (NT-3) and NGF in corneal stroma
• Faster recovery of corneal touch sensitivity (Cochet-Bonnet esthesiometry)
• Reduced neuropathic pain-associated behaviors in rodent DED models

Intraocular Pressure and Trabecular Meshwork Research

Preliminary research on Tb4 in trabecular meshwork (TM) cells explores potential glaucoma-relevant effects:

• TM cell migration enhanced by Tb4 (potential relevance to aqueous humor outflow dynamics)
• Reduced TGF-beta2-induced actin stress fiber formation (anti-fibrotic effect in TM context)
• Maintained TM cell morphology and viability under chronic oxidative stress
• Preserved expression of matrix metalloproteinases required for ECM turnover in TM

For laboratory research only. Not for human administration.