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A study in mice has found that a commonly used antibiotic can be modified to eliminate the risk that it will cause hearing loss.
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.Their popularity is due, in part, to their low cost, lack of need for refrigeration and effectiveness at treating bacterial infections at a time when the declining potency of antibiotics is a major public health concern. They are frequently used in neonatal intensive care units to battle infections, or even the threat of infections, which pose a mortal risk for babies. Exactly how many premature babies from suffer hearing loss as a side effect of treatment with the drug is unknown, Ricci said. “The toxicity of these drugs is something we accept as a necessary evil,” said Daria Mochly-Rosen, PhD, director of SPARK, a program at Stanford that assists scientists in moving their discoveries from bench to bedside. SPARK worked closely with Ricci and Cheng, providing both the funding and the expertise necessary as they entered the new landscape of drug development. “Being an expert on the inner ear put Dr. Ricci in a unique position to help design a better drug — one that would be a huge advantage, especially for premature babies,” Mochly-Rosen said. “This is a project that could make a huge difference in human health.” For decades, researchers have looked for ways of preventing aminoglycosides from killing off the hearing cells of the inner ear, Ricci said. “So many approaches have failed,” Ricci said. “The main problem has been that if you succeeded in stopping the drug from killing hair cells, then you also stopped its antimicrobial effect. The drug just doesn’t work anymore.” The goal, Ricci said, was to keep the antibacterial properties of the drug intact while preventing it from entering the inner-ear cell’s ion channels. He and his fellow researchers used data from structural biologists at Stanford who better understood how the antibiotics fought off infection.
If we can eventually prevent people from going deaf from taking these antibiotics, in my mind, we will have been successful.“We figured, well, let’s not mess with that part of the drug,” Ricci said. “We targeted sites on the drug molecule that were not involved in the antimicrobial activity that kills off infection. This allowed us to reduce toxicity to the ear while retaining antimicrobial action.” The researchers made nine different compounds derived from sisomicin. All nine were significantly less toxic than sisomicin to hair cells when tested in the laboratory. Three of the nine were comparable to sisomicin in inhibiting the growth of and killing E. coli bacteria. Of the three derivatives, however, N1MS was the most effective against the bacteria, and the researchers used it to successfully treat E. coli-caused bladder infection in a mouse model while leaving hearing intact. They also found that, unlike the parent compound, N1MS was nontoxic to the kidneys. “We postulate that entry into kidney cells is also through a channel, and so entry is reduced here as well,” Ricci said. “It is speculation at this point because unlike with the hair cell, we have not measured drug entry into the kidney cells, but it seems reasonable.” Other Stanford co-authors are postdoctoral scholars Markus Huth, MD, Yi-Ju Hsieh, PhD, Thomas Effertz, PhD, Kyu-Hee Han, MD, and Sarah Verhoeven, MD; research assistants Kayvon Sotoudeh and Andrew Vu, MD; Michael Hsieh, MD, PhD, assistant professor of urology; and SPARK chemistry consultant Robert Greenhouse, PhD. The study was funded by the National Institutes of Health (grants P30DC010363, K08DK087895, K08DC011043, R21DC012183, RO1DC003896 and RO1DC013910), the Swiss National Science Foundation, the Jerry Yang Faculty Scholar Fund and SPARK. Information about Stanford’s Department of Otolaryngology-Head and Neck Surgery, which also supported the work, is available at http://med.stanford.edu/ohns/. For information on Stanford’s Hearing Loss Initiative, visit: https://hearinglosscure.stanford.edu/.