Lab tests indicate a compound can prevent and even reverse resistance to isoniazid, the most widely used antibiotic for treating tuberculosis.
About 1.5 million people died of tuberculosis (TB) in 2017, making it the most lethal infectious disease worldwide. A growing rise in drug-resistant TB is a major obstacle to successfully treating the illness, researchers say.
Scientists conducted the research, which appears in PNAS, in bacteria growing in the lab, setting the stage for future studies in animals and people.
Isoniazid treatment is tough
Using the compound in conjunction with isoniazid potentially could restore the antibiotic’s effectiveness in people with drug-resistant tuberculosis, researchers say. The compound also may bolster the antibiotic’s power to kill TB bacteria—even those sensitive to drugs—which means doctors could start thinking about cutting down the onerous six-month treatment regimen they prescribe today.
“It is very hard for people to comply with such a long regimen,” says co-senior author Christina Stallings, associate professor of molecular microbiology at the Washington University in St. Louis School of Medicine. “It’s four drugs. They have side effects. It’s no fun. The longer people have to be on antibiotics, the more issues with patient compliance you get, and that can lead to drug resistance and treatment failure.
“Here, we’ve found a compound that sensitizes bacteria to an antibiotic, prevents drug resistance from arising, and even reverses drug resistance—at least in the lab. If we can turn this compound into a drug for people, it could make our current therapies more effective and be really beneficial for fighting this pandemic.”
TB biofilms
The bacterium Mycobacterium tuberculosis causes tuberculosis. Once inside the body, the bacteria morph into a tougher form that can withstand more stress and is harder to kill.
“We had no idea we would be able to reverse drug resistance.”
Rather than look for new and better antibiotics, Stallings and co-first authors Kelly Flentie, a former postdoctoral researcher, and graduate student Gregory Harrison decided to look for compounds that prevent the bacteria from toughening up.
When put in a low-oxygen environment to mimic the stressful conditions TB bacteria encounter inside the body, the bacteria come together and form a thin film called a biofilm that is resilient to not only low-oxygen conditions but also to antibiotics and other stressors.
With the help of co-senior author Fredrik Almqvist, professor of chemistry at Umea University in Sweden, they screened 91 compounds that share a core chemical structure that inhibits biofilms in other bacterial species. They found one compound, called C10, that didn’t kill the TB bacteria, but did prevent them from forming a biofilm.
Further experiments showed that blocking biofilm formation with C10 made the bacteria easier to kill with antibiotics and even curbed the development of antibiotic resistance.
The researchers needed only a fraction of the amount of isoniazid to kill the TB bacteria when they included C10 compared to isoniazid alone. In addition, one out of 1 million TB bacteria spontaneously become resistant to isoniazid when grown under typical laboratory conditions. But when the researchers grew TB bacteria with isoniazid and the compound, the drug-resistant mutant bacteria never arose.
“By combining C10, or something like it, with isoniazid we could enhance the potency of the antibiotic and block the TB bacteria from developing drug resistance,” Stallings says. “That means we might be able to shorten the treatment regimen.”
Reversing resistance
Most surprisingly, the compound even reversed drug resistance. TB bacteria with mutations in the gene katG can withstand isoniazid treatment. But such bacteria die when treated with isoniazid plus the compound, the researchers discovered. The bacteria didn’t lose their genetic resistance, but they did lose the ability to survive when exposed to isoniazid, as long as it was given alongside C10.
“This was a totally unexpected finding,” Stallings says. “We had no idea we would be able to reverse drug resistance. But this could mean that with all those millions of isoniazid-resistant TB cases, if we use something like C10, we could give people the option of using isoniazid again.”
Stallings cautions the compound is not ready to be used in people or even tested in animals. Researchers conducted the study on bacteria growing in a lab and are still figuring out whether the compound is safe and how it might be processed by the body.
“We have this great compound, and we’ve shown that it’s possible to prevent and reverse antibiotic resistance,” Stallings says. “But now we have to either improve on the compound itself so we can start testing it in animals, or figure out how it prevents biofilm formation so we can develop other drugs that target the pathway. We have a new strategy to treat TB, but it’s going to take time before it’s a reality.”
Funding for the work came from the National Institutes of Health, the Arnold and Mabel Beckman Foundation, Washington University in St. Louis, the Swedish Research Council, the Knut and Alice Wallenberg Foundation, the Swedish Foundation for Strategic Research, the National Science Foundation, the National Institute of General Medical Sciences, the JC Kempe Foundation, the Potts Memorial Foundation; the National Institute of Allergy and Infectious Diseases, National Institutes of Health, and the Department of Health and Human Services.
