A study found that eye drops made from pig semen could treat a rare, hard-to-treat cancer that develops in babies' eyes. The retina is a barrier to drug penetration and hinders cancer treatment, but animal experiments showed that encasing drugs with semen components eliminates the problem.
A research team led by Professor Yu Zhang of Shenyang Pharmaceutical University in China said in Science Advances on the 28th that "we confirmed in animal experiments that drugs loaded into exosomes from pig semen can treat retinoblastoma, a rare, hard-to-treat cancer that occurs in children."
Retinoblastoma is a malignant tumor that occurs in the retina. The retina is the place inside the eye where light is focused, equivalent to the film where a camera captures an image. Retinoblasts are cells that grow into the retina, and when a gene mutation occurs, they grow uncontrollably and become cancer cells.
◇Targeting only cancer cells while sparing normal cells
Retinoblastoma can be treated by injecting drugs into the eye, radiation, or laser therapy, but there is a risk of damaging normal parts of the eye. Zhang's team believed that delivering drugs only to cancer cells would enable treatment without side effects. The problem is that the barriers that protect the eye also block drugs. The researchers 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 that are secreted by cells and act as couriers carrying signals in and out of cells. In this study, the couriers' job was changed to deliver drugs instead of signals. Exosomes in semen help sperm pass through the female reproductive tract. Zhang's team confirmed that exosomes from pig semen can use the same method to open and close tight junctions, a semipermeable structure, in human corneal cells.
The researchers loaded an "nanoenzyme system," an anticancer drug containing carbon dots, manganese dioxide, and glucose oxidase, into pig semen exosomes. Carbon dots, which are nanoparticles, bind well to anticancer agents and can carry drugs on their surface. Manganese dioxide can also attach anticancer agents to its surface.
Glucose oxidase binds with drug-loaded particles to deliver drugs only to cancer cells. Cancer cells grow rapidly and consume a lot of glucose, a nutrient. Glucose oxidase seeks out cancer cells that are rich in glucose. When the oxidase breaks down glucose, it generates hydrogen peroxide, which harms cancer cells.
The team also attached folate molecules to the exosome surface so they target and administer drugs specifically to retinoblastoma. Retinoblastoma cells have much higher folate levels than healthy cells. It is, in effect, a double- and triple-layered guided missile system.
◇Efficacy in mice, safety in rabbits
When the team administered the 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 failed to work.
The researchers said that repeated administration of the eye drops to rabbit eyes for 30 days caused only mild corneal irritation and posed no safety issues. Rabbit experiments are often used to evaluate the safety of drugs and cosmetics. Compared with the eye, rabbits have large corneas 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 Department of Chemical Engineering at the University of Adelaide in Australia, said in Nature that "this study demonstrates that exosomes can penetrate the retina," and noted, "It is difficult for Alzheimer's disease treatments to cross the blood-brain barrier, but the same method could be used to cross such barriers and deliver drugs."
Clinical trials in humans are needed before exosome anticancer eye drops can be commercialized. The team also said that finding a way to mass-produce exosome eye drops equipped with the nanoenzyme system is a challenge.
References
Science Advances (2026), DOI: https://doi.org/10.1126/sciadv.adw7275