St. Jude study yields hope for restoring hearing

Diagnosed with liver cancer at age 6, Delaney Wells fought off the disease with the help of potent chemotherapy drugs that made her hair fall out.

The follicles on her head eventually grew back, but auditory hair cells in her inner-ear — also ravaged by the chemo — did not.

Now 11, the Baton Rouge, Louisiana, girl turns the volume way up while watching TV. And she sometimes has trouble distinguishing similar-sounding words such as "bath" and "back" from one another, says her mom, Mary Wells.

"I had no idea hearing loss was a side effect of medication," she said.

But scientists at St. Jude Children's Research Hospital, where Delaney is a patient, last week reported some apparently unprecedented — but still very early — progress toward restoring hearing in cancer patients. In a study published in the journal Cell Reports, researchers manipulated two genes to regenerate immature auditory hair cells in adult laboratory mice.

Located in the cochlea, the cells — called hair cells because of the rows of extensions that oscillate with noise — are vital to hearing. They transform sound vibrations into neural signals that the brain can interpret.

But these cells often die after chemo drugs such as cisplatin, a widely used medication containing platinum, are injected into cancer patients. As a result, about half of all patients with solid tumors or brain tumors experience some degree of hearing loss, said Jian Zuo, a corresponding author of the study and a member of St. Jude's Department of Developmental Neurobiology.

Auditory hair cells also can die as a result of prolonged exposure to loud noise, accidents, illness or aging.

In making the breakthrough, investigators took cues from the animal world. Although auditory hair cells don't naturally regenerate in humans, they do in fish and chicken, Zuo said.

By activating one gene and deleting another, the researchers essentially replicated in specially bred mice the process that occurs naturally in fish and chicken. The manipulation of the two genes induced cells in the inner ears of the mice to take on the appearance of immature hair cells and to begin producing signature proteins of the sensory cells.

The study findings mean that, theoretically, scientists someday could use a virus to deliver the right genes to cells in the inner ear to instigate the regeneration process.

But that's still a long way off — at least five to 10 years, Zuo said. One problem is that the hair cells regenerated in the mice are immature.

"This is a very long process ..." Zuo said. "We're still missing several factors."

Reach Tom Charlier at thomas.charlier@commercialappeal.com or 901-529-2572 and on Twitter at @thomasrcharlier.