
Juliane Bubeck Wardenburg (left) and a member of her research laboratory, Naoko Inoshima, PhD
It’s a common catch-22 in the clinical research world that you can’t get funding without preliminary data, but you also can’t get preliminary data without funding. That’s the situation Juliane Bubeck Wardenburg, MD, PhD, Assistant Professor of Pediatrics and Microbiology, found herself in a few years ago when she embarked on a new series of studies of Staphylococcus aureus in 2008.
Bubeck Wardenburg had a long-standing interest in Staphylococcus aureus (S. aureus), and over the years had learned that in cases of pneumonia, the bacteria generated a toxin called a-toxin that targeted lung cells in a very
specific way.
“You can think of the toxin almost like a missile,” Bubeck Wardenburg explained. “It gets sent out from the bacteria, lands on the lung cell, then punctures the membrane of the cell, effectively destroying the cell.”
Bubeck Wardenburg wanted to find out how the toxin was able to so accurately target and injure the lung cells. She had a hunch that it would be a vital part of finding new methods to treat pneumonia, as well as other S. aureus infections. But she knew that in order to develop these ideas, she needed a pilot grant.
“Pilot funding is intended to catapult an idea that’s new, and then hopefully give it some legs so it can get farther in the clinical research process,” Bubeck Wardenburg said.
Bubeck Wardenburg applied for and was awarded a preclinical pilot study grant from University of Chicago’s Institute for Translational Medicine. The ITM provides not only preclinical, but also human subjects, community, and collaborative pilot study funding to clinical researchers at the University of Chicago. The $20,000 grant Bubeck Wardenburg received enabled her to find out just how the a-toxin was able to destroy healthy human lung cells. The key — or rather, the “target” — was a cell surface enzyme known as ADAM10.
“ADAM10 acts as a receptor for the toxin,” said Bubeck Wardenburg. “So if you eliminate ADAM10, the toxin doesn’t act anymore. It can’t locate and bind to the host cells.”
The initial studies from the Bubeck Wardenburg laboratory demonstrated this to be true in lung cells maintained in tissue culture. The discovery was precisely the sort of thing Bubeck Wardenburg hoped to find — an observation that led to other questions and more ideas for preclinical studies.
“We wanted to find an animal model system in which we could eliminate ADAM10, just like you can do in tissue culture,” Bubeck Wardenburg said. “The thought was that if an animal doesn’t have the target for the toxin, it should be resistant to staphylococcal disease.”
Bubeck Wardenburg requested another round of pilot funding, and this time was awarded a grant of $40,000. Once funding was secured, she could work full speed on her second study.
“ADAM10 is required for normal growth and development of an animal,” Bubeck Wardenburg said. “So what we had to do was use a conditional knockout approach, picking ADAM10 as our specific genetic target in the lung cells and skin cells (where the toxin causes injury as well). With this approach, ADAM10 is only eliminated in those tissues.”
Bubeck Wardenburg and her team were able to breed mice in two groups — those without ADAM10 in the lung, and those without ADAM10 in the skin — through an elaborate animal breeding strategy in the first seven months of funding. These mice led to some new potential treatment methods.
“The mice without ADAM10 in the lung were resistant to deadly pneumonia infection, and the mice without ADAM10 in the skin were resistant to severe invasive skin disease,” Bubeck Wardenburg said.
Not only that, but Bubeck Wardenburg noted that the bacteria had an interesting effect on the natural function of ADAM10.
“When the toxin binds to ADAM10, it activates a very specific function,” she explained. “ADAM10 acts like a pair of scissors. Its natural function is to cut proteins that hold cells together so that they can separate and make room for new cells, allowing for normal cell turnover and growth.”
But the toxin seems to accelerate this “scissor function,” causing cells to cleave apart when there are no new cells available to replace them, resulting in further injury to tissue in the lungs or skin. Once Bubeck Wardenburg realized that the ADAM10 enzyme’s role in S. aureus infection was two-fold, it became clear that an enzyme inhibitor, which binds to ADAM10 and decreases its activity, may be a novel way of preventing or treating infection.
“Usually when we think of drugs that we’d use to treat infections, those drugs target the bacteria,” Bubeck Wardenburg said. “This approach has become very problematic, because bacteria can rapidly develop resistance to treatment. Our new method targets the host. The host cells will not be able to resist the effects of the drug. They can’t change at the rate bacteria can. So it’s a very unique strategy.”
It is an exciting discovery, especially when considering treatment for at-risk populations. But as with any new clinical treatment method, development is not without its challenges.
“There is actually an entire group of enzymes in the ADAM family, and they’re all structurally similar,” Bubeck Wardenburg explained. “Not only will the new drug need to have a high potency, it will need to have high specificity as well.”
“A second, very big challenge is that you’re shutting down a process that the host’s body needs to perform,” she continued. “So it begs the question of safety in that, how long can you shut down ADAM10 before you start to see a negative effect on the host?”
The results from Bubeck Wardenburg’s two pilot studies have continued to advance along the translational research spectrum. A vaccine strategy developed as a result of the first pilot study is close to clinical trial phase with a pharmaceutical sponsor company. Bubeck Wardenburg is also in talks with the NIH about drug development for the specific enzyme inhibitor that would shut down ADAM10 activity. Her study on S. aureus bacteria and ADAM10 in lung cells was featured in Nature Medicine in October 2011. A separate study on the bacteria’s interaction with skin cells will be published in the Journal of Investigative Dermatology in early 2012.
Bubeck Wardenburg was insistent that were it not for thepilot funding from the ITM, none of this would have been possible.
“The pilot funding enabled us to do something that was genetically complicated and allowed a new approach to the disease problem,” Bubeck Wardenburg said. “This strategy, used in concert with a traditional course of antibiotics, could make a bigger impact. It could change the duration and severity of infection; it could reduce the number of hospitalizations and surgeries. This could completely change how we treat infections.”