Dual-mechanism antibiotics kill Gram-negative bacteria and avoid drug resistance

Poisons are deadly in themselves — so are arrows — but their combination is greater than the sum of their parts. Weapons that attack from inside and outside at the same time can defeat even the strongest enemies, from E. coli to MRSA (methicillin resistance) Staphylococcus aureus).

Princeton team of researchers reported today In the journal cell They discovered that they have discovered a compound, SCH-79797, that can puncture the bacterial wall and at the same time destroy intracellular folic acid while preserving immunity to antibiotic resistance.

Bacterial infections come in two flavors, Gram-positive and Gram-negative, named after the scientist who discovered how to distinguish them. The main difference is that Gram-negative bacteria have an outer layer that drowns out most antibiotics. In fact, no new class of drugs has been put on the market that kills Gram-negative bacteria in about 30 years.

“This is the first antibiotic that can target Gram-positive and Gram-negative bacteria without resistance,” he said. Zemer Gitai, Professor Edwin Grant Conklin Biology at Princeton and first author of the paper. “It’s important in terms of “why it works,” but the most exciting thing about us as scientists is the discovery of how this antibiotic works. Attacks through two different mechanisms within one molecule: the future.”

The greatest weakness of antibiotics is that bacteria evolve rapidly to resist them, but the Princeton team has found that even with special efforts, they cannot develop resistance to this compound. .. “This is really promising, and that’s why we call the derivative of this compound “iresistin,” said Gitai.

The holy grail of antibiotic research. Antibiotics that are safe against humans but resistant to disease and acquire resistance (unlike disinfecting alcohol and bleach, they are extremely lethal to human and bacterial cells). Target).

For antibiotic researchers, this is like finding a way to convert lead into gold or riding a unicorn. No one really wants what everyone wants, says Dr. James Martin 2019. A graduate who spent most of his graduate career working on this compound. “My first challenge was to convince the lab that it was true,” he said.

However, what is irresistible is a double-edged sword. A typical antibiotic study finds a molecule that can kill a bacterium, crosses multiple generations until the bacterium evolves resistance, finds out exactly how that resistance works, and breaks the molecule down from the beginning. Use it to reverse engineer.

But the SCH-79797 was so attractive that researchers didn’t have to do reverse engineering.

“This was a really technical feat,” Gitai said. “Resistance is a plus in terms of use, but it’s a challenge from a scientific perspective.”

The research team had two major technical challenges. Trying to prove a negative (nothing resisting SCH-79797) and understanding the action of compounds.

To prove resistance to resistance, Martin tried an endless variety of assays and methods, but none revealed particles of resistance to SCH compounds. Finally, he tried brute force. It was “passed continuously” for 25 days. That is, the bacteria were exposed to the drug again and again. Bacteria take about 20 minutes per generation, so they had millions of opportunities to evolve resistance, but not so. To confirm their method, the team serially passaged other antibiotics (Novobiocin, Trimethoprim, Nisin, Gentamicin) and quickly developed resistance to them.

Since it is technically impossible to prove a negative result, researchers have used phrases such as “undetectable low resistance frequency” and “no detectable resistance”. We have come to the conclusion that 79797 is very attractive.

They also tried using against bacterial species known for antibiotic resistance. Neisseria gonorrhoeaeIs in the top 5 list of Urgent threat Published by Center for Disease Control and Prevention.

“Gonorrhea poses a major problem with multidrug resistance,” Gitai said. “We’ve run out of gonorrhea drugs. In the most common infections, older generic drugs still work. Discovered in 1928 when I had streptococcal pharyngitis two years ago. Given Penicillin-G! But N. gonorrhoeae, The standard strain circulating on university campuses is hyperdrug resistant. Breakgrass, the last line of defense of what once was the defense of Neisseria, is now the standard treatment of the forefront, and there is no longer a breakgrass backup. That is why this is a particularly important and exciting thing we can treat. “

Researchers got a sample of the most resistant strains N. gonorrhoeae From the World Health Organization vault-a strain that is resistant to all known antibiotics-“Joe showed that our man still killed this strain,” Gitai is a co-author of the paper. Mentioned one Joseph Sheehan, Lab Manager at Gitai Lab. “We are pretty excited about it.”

Poison tip arrow

Without resisting reverse engineering, researchers have used a vast array of approaches, ranging from the classical methods that have existed since the discovery of penicillin to the state-of-the-art, to find out how molecules can kill bacteria. I spent years trying to decide.

Martin calls it the “everything but the kitchen sink” approach, and finally reveals that SCH-79797 uses two different mechanisms within a single molecule.

“To add poison, you need to sharpen the arrow, but you also have to kill the poison yourself.” Benjamin Bratton, Is a Associate Researcher in Molecular Biology, is a lecturer and another co-author of the Institute for Integrated Genomics at Luis Sigra.

Arrows target the outer membrane — even piercing the thick armor of Gram-negative bacteria — while the venom shreds folic acid, the basic building blocks of RNA and DNA. The researchers were surprised to discover that the two mechanisms act synergistically and bind more than the sum of their parts.

“If you take only these two halves, there are over-the-counter drugs that can attack either of these two pathways, just throw them in the same pot and not kill them as effectively as the molecule they’re bound to” “Same body,” said Bratton.

There was one problem. The original SCH-79797 killed human and bacterial cells at about the same level. So, as a medicine, there was a risk of killing the patient before killing the infection. The derivative Irresistin-16 has fixed it. It is about 1,000 times more potent against bacteria than human cells, making it a promising antibiotic. As a final confirmation, researchers have demonstrated that irresistin-16 can be used to treat infected mice N. gonorrhoeae..

New kibo

The poison arrow paradigm could revolutionize antibiotic development KC Huang, Professor of Biotechnology and Microbiology and Immunology at Stanford University who was not involved in this research.

“What I can’t exaggerate is that antibiotic research has stagnated for decades,” Huang said. “It’s rare to find a scientific field that is very well studied and still needs new energy shocks.”

The poison arrow, a synergistic effect of the two mechanisms that attack bacteria, “can do just that,” said Huang, a postdoctoral fellow at Princeton from 2004 to 2008. Inspired by this, we begin the design of new compounds. That’s why this work was so exciting. “

In particular, two mechanisms, arrows and poisons, target processes that exist in both bacterial and mammalian cells, respectively. Folic acid is essential to mammals (hence the reason pregnant women are told to take folic acid), and of course both bacteria and mammalian cells have membranes. “This gives us a great deal of hope, because people ignore the majority because they thought, “Oh, I can’t target it. That’s why I also kill humans.” Because I was doing it. “.

“Such studies say we can go back and reconsider what we considered to be the limits to the development of new antibiotics,” Huang said. “From a social perspective, it’s great to have new hope for the future.”