An FDA-approved drug for hepatitis C can increase bacterial sensitivity to antibiotics and reduce the likelihood of antibiotic resistance, according to the results of research led by New York University (NYU) scientists. The drug, telaprevir, works by blocking the function of chaperones—important proteins that fold other proteins in the cell—in bacteria. When tested in laboratory model strains of Mycobacterium tuberculosis (Mtb) cells—Mtb is the bacterium that causes tuberculosis (TB)—telaprevir boosted the activity of aminoglycoside antibiotics, and reduced resistance to the frontline TB drug, rifampin.

“Telaprevir is the first previously clinically approved compound that has been shown to inhibit chaperone function in bacteria,” said Tania Lupoli, PhD, assistant professor of chemistry at NYU and senior author of the team’s paper, which is published in Cell Chemical Biology. “Our research marks a vital step in developing small molecule chaperone inhibitors that can be used in bacteria to increase the power of antibiotics and slow down the evolution of antibiotic resistance.” The researchers’ paper is titled, “An allosteric inhibitor of bacterial Hsp70 chaperone potentiates antibiotics and mitigates resistance.”

Chaperones exist in almost every cell in every organism, from single-cell bacteria to humans. As the authors noted in their introduction, “The molecular chaperone heat shock protein 70 (Hsp70) is conserved throughout all domains of life and is intimately involved in regulating protein homeostasis for cell survival.”

Due to their critical role in folding other proteins—and what happens when proteins misfold, which can lead to toxicity in the cell—chaperones are the targets of ongoing drug discovery research, but researchers have struggled to find small molecules that can specifically target or bind to chaperones. “Hsp70s have been the targets of ongoing drug discovery campaigns due to their link to protein misfolding-related diseases and certain cancers,” the team continued. And while eukaryotes contain several different Hsp70 isoforms, bacteria typically only have one major protein folding isoform, called DnaK.

For their newly reported study, the researchers sought to identify small molecules that could turn off the function of DnaK chaperones in disease-causing bacteria. “While some existing eukaryotic Hsp70 inhibitors show cross-reactivity against bacterial DnaKs, our goal was to discover chemical scaffolds that directly inhibit Mtb DnaK, since it represents a potential antibiotic target and new TB drugs are in much demand,” they wrote. With this focus on Mtb, the researchers then screened roughly 25,000 compounds—including 1,300 approved drugs—to identify small molecules that could inhibit chaperones in mycobacteria.

The screen highlighted the antiviral drug called telaprevir, which is approved by FDA for treating hepatitis C. In a series of experiments using model mycobacteria in the lab, they demonstrated that the peptidomimetic drug telaprevir binds to mycobacterial chaperones and blocks their ability to fold proteins. “Using in vitro and in vivo chaperone assays, we demonstrate that telaprevir modulates the function of mycobacterial DnaK and its cofactor protein DnaJ2 in cells, which disrupts cellular proteostasis,” the researchers explained. Inhibiting the activity of this chaperone made the mycobacteria more sensitive to antibiotics, including streptomycin, a commonly prescribed aminoglycoside antibiotic drug.

Chaperones can also stabilize proteins in the cell that cause antibiotic resistance, and the studies also showed that using telaprevir to block chaperone function lowered mycobacteria’s resistance against the first-line tuberculosis drug rifampicin (RIF). “In addition, telaprevir combats mycobacterial resistance to the frontline TB drug rifampin, as DnaK-DnaJ2 function is required for stabilization of protein mutants that confer drug tolerance,” the investigators noted. Reducing antibiotic resistance is a major global public health priority, as an increasing number of infections—including tuberculosis—are growing more difficult to treat as antibiotics become less effective.

The authors acknowledged that they don’t expect telaprevir itself to eliminate mycobacterial resistance to RIF. “Since addition of TP does not fully inhibit DnaJ2, we do not expect to eliminate mycobacterial resistance to RIF with this small molecule,” they wrote. However, they added, “… to our knowledge, the work described here provides the first direct evidence that a small-molecule DnaK inhibitor can mitigate antibiotic resistance in bacteria. We anticipate this chemical strategy will be applied to modulating drug resistance in other species, as TP can inhibit DnaKs and Hsp70s from bacteria and humans.” Lupoli added, “In the future, we envision that small molecule chaperone inhibitors could be used in combination with antibiotics to enhance antibiotic potency and lower resistance.”

The researchers are continuing to explore hundreds of telaprevir analogs—compounds that are similar in molecular structure—to determine if others bind more tightly to chaperones, a key factor for moving the research into animal or clinical studies. Future work will also explore how to target chaperone inhibitors to only shut down certain chaperones—for instance, blocking chaperones in bacteria, but not human cells. “Our work contributes to a small but growing list of small molecules that block the function of chaperones and provides a promising avenue for ongoing study of the role that telaprevir and its analogs can play when administered with antibiotics,” said Lupoli.

The authors concluded, “… this work contributes to a small but growing collection of protein chaperone inhibitors, and it demonstrates that these molecules disrupt bacterial mechanisms of survival in the presence of different antibiotic classes.”