A study found that eye drops made from pig semen could treat a rare, hard-to-cure cancer that occurs in infants. The retina of the eye is a barrier to drug penetration, hindering cancer treatment, but animal experiments showed there is no problem when drugs are encapsulated with semen components.
A research team led by Professor Yu Zhang of Shenyang Pharmaceutical University in China said in Science Advances on the 28th that animal experiments confirmed that drugs loaded into exosomes from pig semen can treat retinoblastoma, a rare, hard-to-cure cancer that occurs in children.
Retinoblastoma is a malignant tumor that forms in the retina. The retina is the place inside the eye where light is focused, corresponding to the film where a camera captures an image. Retinoblasts are cells that grow into the retina, and when gene mutations occur, they grow out of control and become cancer cells.
◇ Targeting only cancer cells while sparing normal cells
Retinoblastoma can be treated by injecting drugs into the eye, radiation, or lasers, but there is a risk of damaging normal parts of the eye. Zhang's team believed that if drugs are delivered only to cancer cells, treatment could proceed without side effects. The problem is that the barrier protecting the eye also blocks drugs. The team explained that exosomes in pig semen freely pass through the retinal barrier to deliver drugs.
Exosomes are tiny vesicles 50–200 nm (nanometers; one-billionth of a meter) in size secreted by cells, acting like postmen that move in and out of cells to deliver signals. In this case, the postman's job was changed to deliver drugs instead of signals. Exosomes in semen allow sperm to pass through the female reproductive tract. Zhang's team confirmed that exosomes from pig semen could open and close tight junctions—semi-permeable structures—in human corneal cells in the same way.
The team loaded a cancer drug "nanoenzyme system" containing carbon dots, manganese dioxide, and glucose oxidase into pig semen exosomes. Carbon dots, which are nanoparticles, bind well with anticancer agents and can carry drugs on their surface. Manganese dioxide can also attach anticancer agents to its surface.
Glucose oxidase binds with the drug-bearing particles and delivers drugs only to cancer cells. Cancer cells grow rapidly and consume a lot of glucose, a nutrient. Glucose oxidase seeks out cancer cells rich in glucose. When the oxidase breaks down glucose, it produces hydrogen peroxide, which harms cancer cells.
The team also attached folate molecules to the surface of the exosomes so they would administer drugs only to retinoblastoma. That is because retinoblastoma cells have much higher folate levels than healthy cells. It is essentially a double- or triple-targeted missile system.
◇ Efficacy in mice, safety in rabbits
When the team administered exosome eye drops to the eyes of mice with retinoblastoma, the tumors did not grow further even after 30 days. The mice still retained their vision. In contrast, when eye drops containing only the nanoenzyme system components without exosomes were administered, cancer cells continued to grow and spread to surrounding areas. The drugs could not enter the eye and thus had no effect.
The team said that when eye drops were repeatedly administered to rabbit eyes for 30 days, they caused only slight corneal irritation and posed no safety issues. Rabbit ocular tests are often used to evaluate the safety of pharmaceuticals and cosmetics. Rabbits have corneas large relative to their eyes and do not blink, making it easy to apply drugs and observe reactions. They also lack a nasolacrimal duct, so administered drugs are not washed away by tears.
Exosome eye drops could help treat not only retinoblastoma but also other intractable diseases. Chunxia Zhao, a professor in the School of Chemical Engineering at the University of Adelaide in Australia, said in Nature that the study proved exosomes can penetrate the retina and noted that Alzheimer's disease treatments have difficulty crossing the blood-brain barrier in the brain, but the same approach could deliver drugs across such barriers.
To commercialize exosome anticancer eye drops, clinical trials in humans are needed. The team also said that finding a way to mass-produce exosome eye drops equipped with the nanoenzyme system is a task ahead.
References
Science Advances (2026), DOI: https://doi.org/10.1126/sciadv.adw7275