Dr. Albert Edge showed in 2013 that a “notch inhibitor” class molecule gives rise to new hair cells in a culture. Each hair cell responds best to a particular frequency of sound—they are arranged in order of frequency along the cochlea—so scientists can pinpoint the effect of these new cells on hearing. When regenerated hair cells were then grown in the cochlea of mice, the pitches corresponding to their placement were better detected by the animals.

Edge and his team first noticed the drug’s potential in a serendipitous report of its side effects in dementia treatment.

“We thought, ‘These side effects in an Alzheimer’s patient are exactly what we’re looking for in treating deafness’,” says Edge. “So we decided to try that idea out in these mice.”

Dutch company Audion Therapeutics, of which Edge is a part, is working on a proof of concept for regeneration of human-ear hair cells. They are using compounds developed by pharmaceutical giant Eli Lilly and applying them locally to the inner ear. With funding from the European Union’s Horizon 2020 fund, which provides extra stimulus to promising but risky investments, animal tests are well under way as part of Project REGAIN. Audion is now planning its first small, human clinical trials.

“Primarily we aim to show that it is safe and well tolerated,” says Rolf Jan Rutten, Audion’s CEO, “And also we will look for an efficacy signal.”

Meanwhile, this year in Farmington, Connecticut, start-up Frequency Therapeutics’ patent filings indicate they have been developing ways to induce supporting cells to multiply, then become hair cells, using a notch inhibitor. The procedure would involve releasing the drug locally, perhaps as a foam or using a tube in the tympanic membrane to send doses into the middle ear.

Unlike drug trials for long-treated ailments like rheumatoid arthritis, there is no development trajectory for something as new and different as hair cell regeneration. It is anyone’s guess how many years or, indeed, decades it will be before hearing-loss patients can benefit from these discoveries. Still, this challenge of bringing a product to market has the atmosphere of a race. Frequency Therapeutics declined an interview on the subject on the basis that they are in “stealth mode” pending a big research announcement.

“It is a competitive field, but everybody has their own approach,” says Ruttan. “Obviously there will be one of us that will be successful first, but it may be that our different approaches are complementary.”

In an organ as complex as the ear, he says, there is a place in the ecosystem for everyone. Perhaps that ecosystem even has room for a mammal that can regenerate its hearing like a songbird.

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