Engineered Peptide Eye Drop Protects Retinal Nerve Cells for Two Weeks After Last Dose in Rats | Research

The takeaway

An engineered peptide-drug eye drop doubled the neuroprotective window for retinal ganglion cells in a rat model of optic nerve injury, providing up to two weeks of protection after the last dose.

2 weeks of protection
Retinal ganglion cells remained protected for up to two weeks after the last eye drop dose — double the duration without the peptide carrier

What the researchers found

A peptide-drug conjugate called HR97-SunitiGel, delivered as an eye drop in rats, provided up to two weeks of retinal ganglion cell protection after the last dose. This effectively doubled the therapeutic window compared to the drug formulation without the engineered peptide.

The system combined two technologies: a hypotonic gel-forming eye drop and a melanin-binding, cell-penetrating peptide. The peptide component extended how long the drug remained inside the eye, allowing once-daily dosing to achieve sustained therapeutic concentrations of sunitinib in the back of the eye.

Why it matters

Treating diseases at the back of the eye — like glaucoma and optic nerve damage — usually requires injections directly into the eye, which are painful and require clinic visits. Eye drops are far more convenient, but drugs from drops rarely reach the retina in useful amounts. This peptide-conjugate approach could make effective eye drop treatment for posterior eye diseases a reality, dramatically improving how patients manage chronic conditions.

The numbers in context

Up to 2 weeks of neuroprotection after last dose · 2× therapeutic window vs. SunitiGel alone · Once daily topical dosing · Rat optic nerve injury model

How the study worked

Researchers engineered a cell-penetrating and melanin-binding peptide (HR97) and conjugated it to sunitinib, then formulated it in a gel-forming eye drop system. They tested this in a rat model of optic nerve injury, measuring retinal ganglion cell survival and intraocular drug concentrations after once-daily topical dosing.

Who was studied

Sprague-Dawley rats with optic nerve injury

What this study cannot tell us

This was an animal study in rats, which have much smaller eyes than humans — drug penetration dynamics differ significantly. The study used an optic nerve crush injury model, which may not fully replicate chronic human glaucoma. No human safety or efficacy data exist yet for this formulation.

How to read the evidence

This is a preliminary animal study using a rat optic nerve injury model. While the results are promising, no human data exist, and the jump from rat to human eyes involves significant pharmacokinetic differences.

When this study was published

Published in 2023. This is recent preclinical work representing the cutting edge of topical ocular peptide-drug delivery research.

The bigger picture

Getting drugs to the back of the eye via eye drops has been one of ophthalmology's biggest unsolved problems. Most serious retinal diseases currently require intravitreal injections — needles into the eye — every few weeks. Peptide-drug conjugates that bind to melanin and penetrate cells could be the key to making topical eye drops work for posterior segment diseases, which would be a major quality-of-life improvement for millions of patients with glaucoma, macular degeneration, and diabetic eye disease.

Questions still open

Will the melanin-binding peptide strategy work in human eyes, which are significantly larger than rat eyes?
Could this peptide-conjugate approach be adapted for other retinal drugs beyond sunitinib?
What is the long-term safety profile of repeated melanin-binding peptide exposure in ocular tissues?

Common questions

How does the peptide help the eye drop work better?

The engineered peptide (HR97) does two things: it penetrates cells to carry the drug deeper into the eye, and it binds to melanin in eye tissues to anchor the drug in place longer. This combination means the drug stays at therapeutic levels in the retina much longer than it would from a regular eye drop.

Could this replace eye injections for glaucoma patients?

That's the long-term goal, but this is still early-stage animal research. The rat results are promising — showing two weeks of nerve cell protection from daily drops — but human eyes are much larger, and the drug delivery challenges are greater. Clinical trials would be needed before this could become a real alternative to injections.

Read the original research

Engineered peptide-drug conjugate provides sustained protection of retinal ganglion cells with topical administration in rats.

Journal of controlled release : official journal of the Controlled Release Society, 362, 371-380

View on PubMed ↗Publisher’s paper ↗

Citation

Hsueh, Henry T; Chou, Renee Ti; Rai, Usha; Kolodziejski, Patricia; Liyanage, Wathsala; Pejavar, Jahnavi; Mozzer, Ann; Davison, Charlotte; Appell, Matthew B; Kim, Yoo Chun; Leo, Kirby T; Kwon, HyeYoung; Sista, Maanasa; Anders, Nicole M; Hemingway, Avelina; Rompicharla, Sri Vishnu Kiran; Pitha, Ian; Zack, Donald J; Hanes, Justin; Cummings, Michael P; Ensign, Laura M. (2023). Engineered peptide-drug conjugate provides sustained protection of retinal ganglion cells with topical administration in rats.. Journal of controlled release : official journal of the Controlled Release Society, 362, 371-380. https://doi.org/10.1016/j.jconrel.2023.08.058