Combative Chemist
Patients With Drug-Resistant Bugs
In his research, Scott Singleton has boosted the bacteria-killing power of several antibiotics.
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Harmful bacteria don’t fight fair. Each year, 2 million patients contract bacterial infections in U.S. hospitals – and 90,000 of them die. These lethal bugs have developed a resistance to the drugs that used to kill them – antibiotics. But Scott Singleton knows how to fix this fight. “Antibiotics versus bacteria is a one-on-one fight, and bacteria are getting bigger and stronger,” says Singleton, an associate professor in the medicinal chemistry and natural products division of the Eshelman School of Pharmacy. “Adding a RecA inhibitor makes it two on one. The inhibitor holds the bacterium down while the antibiotic beats it up.”
As the incidence of drug-resistant bacteria increase, so does the number of emergency room visits, hospitalizations and deaths.
Singleton didn’t set out to bully bacteria. But in studying how bacteria become resistant to antibiotics so quickly, Singleton discovered something singular about bacteria. “They don’t wait on luck” to evolve, he said, and they change even quicker under stress. The stress also triggers an emergency response in certain enzymes that protect and repair the organism’s DNA. So antibiotics, since they cause stress to bacteria, actually trigger the process that speeds up bacteria’s evolutionary resistance.
How are bacteria able to evolve so quickly? “Life finds a way,” Singleton said.
A particular enzyme called RecA both controls the emergency response and repairs DNA damage caused by antibiotics. “It’s astounding the diversity of roles played by RecA,” Singleton said. “It’s like an employee for a small, regional airline who does every job in the airport: taking your ticket, loading your luggage, and serving drinks. RecA is like that for bacteria.” But if bacteria can turn on the RecA switch, then chemists should be able to turn it off. “If we can inhibit RecA, we can make the bacteria much more sensitive to an antibiotic,” Singleton said. “Perhaps more importantly, we can suppress bacteria’s ability to develop resistance to drugs."
E. coli bacteria cells (red) fluoresce green when RecA triggers their SOS response. Tim Wigle, Jonathan Sexton (c)2009 Endeavors
Singleton’s next step was to determine which chemical compounds would actually disable RecA. Then he had to figure out which of those compounds would stop RecA in specific disease-causing bacteria. To do that, he puts 96 different molecules that are RecA inhibitors into a grid-like stock plate and tests each against live bacteria from notoriously resistant diseases like E. coli and staph infections.
Scott Singleton and research specialist Demet A. Guntas prepare 96 different RecA inhibitors for testing against live bacteria.
Once Singleton determines that a certain molecule can inhibit RecA in disease-causing bacteria, it’s time to pair up the inhibitor with an antibiotic. He sets up an Epsilometer test (or E-test) in a dish by inoculating a plate with the bacterium and placing a strip with the antibiotic and the RecA inhibitor on top of it. The drug diffuses into the bacterium and after 24 hours of incubation, Singleton can see how effective the antibiotic-RecA inhibitor one-two punch has been.
Scott Singleton points to an antibiotic E-test strip in a dish growing E. coli bacteria.
For example, this graph illustrates the synergy between an antibiotic and a RecA inhibitor in killing E. coli bacteria. The black line shows how the bacterial community multiplies in a test tube, growing from 100,000 organisms to approximately 100 trillion in eight hours. Introducing the inhibitor alone (red line, open circles) has no effect on the bacteria’s growth. Introducing the antibiotic ciprofloxacin at half a killing dose holds the bacteria in check. Combining the RecA inhibitor with the antibiotic at the same strength nearly wipes out the population of E. coli: only one in a million bacteria survive.
To be able to partner with companies to develop new, more effective antibiotic compounds and bring them to market, Singleton started Synereca Pharmaceuticals (note that RecA is part of the name) in July 2009. He is the company’s president and chief scientific officer. In March 2010, Synereca became the first UNC research spinoff company to use the Carolina Express License. Carolina Express is designed to make starting a company based on technology invented at the University easier and faster by offering a standard set of terms. The company also won a competitive Small Business Research Loan from the state-funded North Carolina Biotechnology Center.
Notice that “RecA” and ribbons of DNA are part of the Synereca logo.
On the business side, Synereca benefited from the new Carolina KickStart program, part of the North Carolina Translational and Clinical Sciences Institute at UNC. Carolina KickStart connected the company’s leaders with an Entrepreneur in Residence, Joel Shaffer, and provided funds to hire Womble Carlyle law firm to sort out intellectual property rights and patents. “Synereca is off to a great start thanks to entrepreneurship empowered by the University and the strong support of the local RTP community,” Singleton said. “We look forward to re-arming antibiotics to help save lives.”
Scott Singleton is one combative chemist who’s ready to take up the fight against disease.