Synthetic antibiotic shows 'potent' efficacy against drug-resistant superbugs

From CRISPR and artificial intelligence to an old, once-rejected drug, the arsenal of potential weapons against antibiotic resistance is, thankfully, growing at last. The latest: a synthetic antibiotic that holds bacteria back by blocking the development of their vital outer membrane.

In the results of a study published Aug. 9 in Science, a research team led by scientists from Duke University School of Medicine showed that a small molecule they developed successfully killed off a wide range of bacteria in experiments on human and animal cells. It also cleared multidrug-resistant bacterial infections in rodents, including serious urinary tract infections.

“Our compound is very good and very potent,” senior author Pei Zhou, Ph.D., said in a press release. Zhou and his team have patented the drug and spun out a startup, Valanbio Therapeutics, to take it to the clinic.

Bacteria fall into two broad categories based on the structure of their cell walls. Gram-negative bacteria such as salmonella and E. coli are encased in a unique outer lipid membrane that’s absent from Gram-positive bacteria, like listeria and Staphylococcus aureus. While both can be deadly and develop resistance to antibiotics, their outer membrane makes gram-negative bacteria harder to kill in the first place.

Given the outer membrane’s importance, it makes sense that it would be a prime target for drug developers. But that’s been easier said than done: While researchers have known for some time that blocking a key enzyme, LpxC, will stop the membrane from developing, some drugs that do so have been marred by reports of cardiovascular toxicity, both in preclinical models and in humans. Others simply had poor or limited efficacy.

To see whether they could come up with a LpxC inhibitor that was both safe and effective, the researchers established a set of structural features that the ideal drug would possess. They then analyzed more than 200 synthetic LpxC inhibitors with those qualities until they came up with one with “outstanding antibiotic activities,” they wrote in the paper.

The winner, LPC-233, binds directly to the enzyme, stopping the membrane formation process. Its shape changes over time, so the binding outlives the bacteria itself and even the very presence of the drug in the body, Zhou noted in the press release.

“We think that contributes to the potency, as it has a semi-permanent effect on the enzyme,” he said.

About that potency: In cell studies, LPC-233 killed off all 285 bacterial strains the researchers tested it against, including multidrug-resistant strains of Neisseria gonorrhoeae—the bacteria that causes the sexually transmitted infection gonorrhea—the pathogen E. coli and Pseudomonas aeruginosa, a superbug notorious for causing sepsis in healthcare settings. It did so rapidly, too: It was able to reduce E. coli and P. aeruginosa by 100,000-fold within just four hours.

The same results bore out in two different mouse models. In one set of experiments, the researchers injected two groups of five male and five female mice with drug-resistant E. coli. Two hours after infection, the researchers gave one group an intravenous dose of LPC-233, while the other received a saline control. Those doses were followed up with either control solution or more LPC-233 in one of two concentrations 12 hours later.

All the mice in the control group died of sepsis within 72 hours. In contrast, 90% of the mice treated with a low dose of LPC-233 and 100% treated with a higher dose survived for the rest of the 10-day observation period.

In the second experiment, the researchers evaluated whether an oral version of LPC-233 could halt a urinary tract infection. In this case, they gave groups of 10 female mice urinary tract infections with drug-resistant E. coli. Six hours later, they gave them twice-daily doses of a vehicle solution, oral ciprofloxacin, or LPC-233, which they gave either intravenously or orally at two different concentrations. Another group was left untreated.

By the end of the three-day study period, the bacteria in the kidneys of mice that received LPC-33 were 1,000-fold lower than mice in the vehicle or control groups. The oral version of the drug eliminated the bacterial load entirely, “suggesting that oral LPC-233 can be an effective therapeutic solution for UTI,” the researchers wrote in the study.

But what about toxicity? After finding that the drug was well tolerated by human embryonic kidney cells, the researchers dosed four groups of three male and female rats with various doses of LPC-233 for seven days. The only noticeable side effects attributable to the drug were that the rats ate a bit less and lost a transient amount of weight. Additional experiments on beagles showed that the drug didn’t have any effects on the heart’s rhythm or rate, nor did it change their blood pressure.

Armed with these findings, the researchers are now seeking partners for their startup who can help take the drug into humans, according to the press release.

“These promising properties render LPC-233 an attractive candidate for further development toward clinical trials,” the scientists wrote in their paper. “Because our studies were conducted in rodents and dogs, future studies will be required to determine the compound efficacy, [pharmacokinetics] and safety, particularly cardiovascular safety, in human patients.”