A toxic lifesaver, reconstructed
Fixing a widely used antibiotic’s tendency to cause hearing loss
Seated at his desk in the Edwards Building on the Stanford campus, Tony Ricci, PhD, professor of otolaryngology and a renowned biophysicist, looks more like a mechanic than a scientist.
Routinely dressed in jeans and sneakers with a well-worn New York Yankees cap, Ricci has spent his entire career under hoods, but the kind you find in research labs where he tinkers around with high-tech tools.
Ricci has studied the molecular workings of the inner ear in labs from Cleveland to New Orleans and finally, pushed out by Hurricane Katrina, to Stanford in 2006. It was while working in his New Orleans lab that Ricci experienced an “aha” moment that sent him down a new path — drug design. Ricci, a confirmed lab rat, now working in partnership with Alan Cheng, MD, a physician-scientist at Stanford, is intent on building a safer version of a commonly used class of antibiotic that can cause deafness.
“I never thought I’d be doing something like this,” says Ricci, a familiar sentiment for the Bronx-born son of a taxi driver who once thought school was a waste of time. He grins, pushing back his Yankees cap, and adds, “What do I know about making a drug?”
Aminoglycosides, one of the most commonly prescribed classes of antibiotics in the world, are used to treat a broad spectrum of bacterial infections from peritonitis to sepsis to pneumonia.
They’re used to treat cystic fibrosis and tuberculosis patients, low birthweight babies and many others with an infection of unknown origin. While the drugs save countless lives, they also cause hearing loss in about 20 percent of the patients who take them. Because cystic fibrosis causes chronic lung infections, patients with the condition need repeated doses and are particularly at risk: Up to 56 percent of them suffer from hearing loss.
Developed in the 1940s, the drugs’ popularity has continued to grow, despite the introduction of newer, alternative antibiotics. Among the most widely used are gentamicin and streptomycin. Aminoglycosides are cheap, and don’t need refrigeration, which makes them useful in developing countries. The fact that they attack so many infectious diseases also makes them popular around the globe, particularly at a time when the declining potency of antibiotics is a major public health concern.
For years, scientists have tried to figure out how to inhibit the side effect of hearing loss while still maintaining the drugs’ powerful antibacterial properties that save lives. Ricci’s discovery, about a decade ago in that New Orleans lab, may provide an answer.
“If we can eventually prevent people from going deaf from taking these antibiotics, in my mind, we will be successful,” Ricci says.
It was Ricci’s grandmother who insisted that he get out of New York and be the first in his family to go to college. He worked in construction while he was in high school to help support his family and didn’t consider college a useful option.
“The smartest thing I ever did was listen to my grandma,” Ricci says.
When he landed in Cleveland as a freshman at Case Western Reserve University, he got a job working the night shift in a lab. He never really left one again. No one was more surprised than he when he discovered he liked working in a lab — a lot.
“I never even knew that things like labs existed,” he says. “I started learning about what went on in a lab and thought, ‘Wow, people get paid to do this stuff?’”
Early on, Ricci found his niche in advancing the understanding of the molecular workings of the hard-to-access and little understood world of the inner ear. Ricci, fascinated by how hearing works, has become an expert in mechanotransduction, the process by which mechanical sound waves from the outside world pass through the inner ear and are converted into electrical signals sent to the brain so we can hear.
That “aha” moment in New Orleans came from his deep understanding of hearing and the role played by ion channels that open only in response to sound vibrations.
Irreversible hearing loss
The key cells in the hearing process — known as hair cells because hairlike cilia protrude from them — are hidden deep inside the inner ear in the bony, snail-shaped cochlea. Mammals have a limited number of the cells, and when the cells die off — whether from being damaged or destroyed by loud noises, simple aging or, in this case, a toxic antibiotic — the result is irreversible hearing loss.
The ion channels exist within the membranes of these hair cells. They are proteins that act as pores in the cell membranes and allow selective passing of potassium, sodium and calcium ions, which is how electrical currents pass in and out of a cell.
Ricci discovered that these pores, which open into tunnel-like channels, are bigger than the scientific community previously thought. Rather than measuring 0.8 nanometers, the pores are wider — measuring 1.3 nanometers across. Before his discovery, scientists believed that aminoglycosides worked like corks plugging up these channels. But, in fact, his research indicates that the drug molecules easily pass through the channels, streaming right into the cells.
Exactly how aminoglycosides destroy hair cells once they get inside remains a matter for speculation, but rather than solve this quandary, Ricci came up with this new idea: Why not just make the drug molecules too big to enter through the channels in the first place, keeping hair cells safe and preventing hearing loss?
“To me, what’s cool about this approach is it shows how very fundamental basic science research can actually translate into helping patients.” he says. “This idea came from doing biophysical characterization of an ion channel. You don’t get much more basic than that.”
It took a few years before Ricci got to work on his idea because he had to deal with the loss of his home and his livelihood in the aftermath of Hurricane Katrina. He eventually made his way, with his family, to Stanford. His idea continued to brew until about 2008, when he approached Cheng, associate professor of otolaryngology, at a staff meeting. Cheng had recently come to Stanford from the University of Washington, where he had been studying aminoglycosides. When Ricci brought up his idea of creating a new version of an aminoglycoside that retained its antimicrobial powers, but didn’t cause hearing loss, Cheng was drawn in.
As a physician-scientist who treats children with hearing loss, Cheng knows firsthand about both the lifesaving properties of aminoglycosides and their toxic side effects. So he was quick to get involved.
“When a drug causes hearing loss it is devastating, and it’s especially disturbing when this happens to a young child, as they rely on hearing to acquire speech,” Cheng says. Despite this, aminoglycosides remain the “go to” drug for treating life-threatening infections, a choice made by many physicians worldwide.
“I was skeptical in the beginning,” Cheng says. But after a decade of partnering with Ricci, and building a team of drug development experts, they have now designed three versions of aminoglycosides that, in studies in mice, kill off bacterial diseases without causing hearing loss.
Designing a drug is difficult, especially for two basic scientists with no experience in that arena. So, when Ricci and Cheng first set out, they recruited help from experts both on and off campus. In 2013, they connected with SPARK, a program at Stanford that assists scientists in drug development and in moving their discoveries from the lab into patient care. SPARK helped them create a team capable of designing a new drug, consisting of chemists, microbiologists, crystallographers, FDA advisers and more.
“From its inception the work has involved a broad team of investigators, both basic scientists and clinician scientists,” Ricci says. They recruited chemists like Robert Greenhouse, PhD, adjunct professor for otolaryngology, to help figure out how to change the shape of the compound. Ludmila Alexandrova, a research associate at Stanford, developed a mass spectroscopy assay for aminoglycoside detection. They also recruited clinicians such as Markus Huth, MD, a former postdoctoral scholar in Ricci’s lab, who conducted the first ototoxic testing of the new drug compounds.
More recently, the team has worked with crystallographer Hasan DeMirci, PhD, a research associate at the SLAC National Accelerator Laboratory, whose expertise has helped reveal the intricacies of how aminoglycosides interact with ribosomes, the site of protein synthesis in the cells of bacteria. Newer team members Mary O’Sullivan, PhD, a postdoctoral scholar, and Randy Lin, an undergraduate, are working in Ricci’s lab to help characterize the newly made compounds.
“We needed SPARK to tell us to go ahead and try all this,” Ricci says.
So far, they have completed two rounds of testing on 18 new antibiotic compounds. Of the 18 versions, three successful candidates have emerged for further study.
“During the first round, we were successful at creating drugs that don’t enter the ion channels and don’t kill hair cells,” Ricci says. “With the second round, we made significant progress at keeping more of the drug’s antimicrobial properties intact.”
Still, the three drug candidates are not as effective at killing off a wide range of bacteria as the researchers need for a final product, Ricci says.
The team is preparing for a third round of compound testing. To reach the level where the drugs could be tested in humans, they plan to first move testing into guinea pigs, a larger animal model that more closely resembles humans.
“I think this next round is going to be a big leap in the quality of drug we develop,” Ricci says. “With every round we do, we’re doing the synthesis side much faster, with more knowledge, and things are really speeding up,” he says.
As a basic scientist who remains passionate about his ongoing work in the lab, Ricci says his foray into the foreign world of drug design has proved “super hard and frustrating.”
“Figuring out drug design is a nightmare even when there are people who know what they’re doing helping you along,” Ricci says. “I felt like I was back in grad school learning a whole new set of skills.”
But it’s a journey he’s fully committed to completing alongside Cheng and the rest of the team to produce a new set of lifesaving antibiotics that won’t cause hearing loss.
“It’s not always possible to see your basic science research make a difference in people’s lives,” Ricci says. “It’s nice to be able to give back a little — at least, I hope we can.”