A device being developed at Draper Laboratory in Cambridge, MA, can deliver drugs in a controlled and timed manner to the inner ear. In combination with novel therapies capable of halting or repairing damage to the cells in the inner ear, the device could provide a more effective way to treat hearing loss.
Tiny hair-like cells in the inner ear vibrate in response to sound, converting those vibrations into electrical signals that travel to the brain through neural pathways. But these delicate cells die off as people age, and can be destroyed by loud noises and exposure to certain drugs. The loss of a large number of cells results in permanent hearing loss. This form of hearing loss, called sensorineural hearing loss, is extremely common, but cannot be cured with drugs.
Researchers are working on ways to treat hearing loss by engineering regenerated hair cell tissue, or by developing drugs which will stop the hair cells in the inner ear from breaking down. But finding ways to introduce the drugs to the hard-to-reach pocket of the inner ear remains a challenge. Drugs have to be injected into a space behind the eardrum, and diffuse into the inner ear over time. With this method, however, there is no way of controlling the quantities of drug that reach the target site, or administering more than one drug at a time.
“It takes some heroic efforts to get compounds into the inner ear,” says Sharon Kujawa, director of audiology at the Massachusetts Eye and Ear Infirmary (MEEI) and associate professor at Harvard Medical School, and part of the team that developed the implantable device. “It’s our view that with all of the effort going on in drug discovery around the world, some attention needs to paid to how those compounds are going to get to the inner ear.”
“There’s really no treatment except hearing aids, and in severe cases cochlear implants,” says Albert Edge, associate professor at Harvard Medical School and an investigator at MEEI, who was unconnected with the study. Hearing aids can be bulky, and cochlear implants destroy all residual hearing remaining in the ear, and neither device receives sound as well as the hair cells.
“A device that will deliver this compound into the fluid filled chambers is exactly what we need to deliver these drugs,” says Edge, whose lab is working on ways to regenerate inner ear hair cells. The device will be remotely controlled and could deliver a variety of drugs, in a preprogrammed sequence, without damaging the delicate environment of the inner ear.
The device being developed at Draper Laboratory is no larger than an AA battery. It consists of a microfluidics pump, a drug reservoir, and a small tube. The pump and drug reservoir are surgically implanted in the temporal bone of the ear, with the tube injecting drugs into the cochlea.
The Draper-MEEI team tested a prototype on guinea pigs, and demonstrated the first instance of precise and timed delivery of drugs to the cochlea, with no damage to the animal’s hearing apparatus. The team is working on miniaturizing the device so it can be implanted into the human ear. “We’re hoping to have the system ready for clinical trials in less than five years–that’s the goal,” says Jeffrey Borenstein, a researcher at Draper Laboratory.
One potential application of timed drug delivery would be stem-cell-induced growth of hair cells in the inner ear. “A potential scenario would be that it would deliver one drug for a couple of days, and then another,” says Edge. “The first drug [would] help prime the cell types and help them divide and the other [would] help them differentiate.”
Recent advances in microfluidics technology have been combined with miniaturized electronics and to make this tiny pump a reality. The work was supported by the National Institute on Deafness and Other Communication Disorders.
While the team is working on better prototypes, researchers like Edge are racing to develop the compounds that will regenerate or stop the death of hair cells. “In a perfect world, they both would be ready at the same time,” says Edge.