It works by interfering with a bacterium’s ability to make its outer lipid layer, its skin, so to speak.

“If you disrupt the synthesis of the bacterial outer membrane, the bacteria cannot survive without it,” said lead investigator Pei Zhou, a professor of biochemistry in the Duke School of Medicine. “Our compound is very good and very potent.”

The compound, called LPC-233, is a small molecule that has proven effective at wrecking the outer membrane lipid biosynthesis in every gram-negative bacterium it was tested against. Co-authors at the University of Lille in France tested it against a collection of 285 bacterial strains, including some that were highly resistant to commercial antibiotics, and it killed them all.

And it works fast. “LPC-233 can reduce bacterial viability by 100,000-fold within four hours,” Zhou said.

The compound is also tenacious enough to survive all the way to the urinary tract after oral administration, which may make it a vital tool against stubborn urinary tract infections (UTIs).

Tests run at high concentrations of the compound showed “exceedingly low rates of spontaneous resistance mutations in these bacteria,” according to a paper describing the findings, which appears Aug. 9 in Science Translational Medicine.

In animal studies, the compound was successful when administered orally and intravenously or injected into the abdomen. In one experiment, mice given what should have been a fatal dose of multidrug-resistant bacteria were rescued by the new compound.

The search for this compound took decades because of the specificity and safety required of the synthetic molecule.

Zhou credits his late colleague, former Duke Biochemistry Chair Christian Raetz, for starting the search decades ago. “He spent his entire career working on this pathway,” Zhou said. “Dr. Raetz proposed a conceptual blueprint for this pathway in the 1980s, and it took him over two decades to identify all of the players,” Zhou said.

The new drug’s target is an enzyme called LpxC that is the second enzyme in the “Raetz pathway” and is essential to making the outer membrane lipid in gram-negative bacteria.

Raetz joined Duke as the chairman of biochemistry in 1993 after his work on this pathway at Merck & Co. had failed to produce a successful clinical candidate. The Merck antibiotic worked, but only against E. coli, so it wasn’t commercially viable and the pharmaceutical company dropped it.

“He actually recruited me to Duke to work on this enzyme, initially just from the structural biology perspective,” said Zhou, who came to Duke in 2001.

Zhou and Raetz had solved the structure of the LpxC enzyme and revealed molecular details of a few potential inhibitors. “We realized that we could tweak the compound to make it better,” Zhou said. Since then, Zhou has been working with his colleague, Duke Chemistry professor Eric Toone, to make more potent LpxC inhibitors.

The first human trial of LpxC inhibitors had failed because of cardiovascular toxicity. The focus of the Duke group’s subsequent work was to avoid cardiovascular effects while maintaining the potency of the compound.

They worked on more than 200 different versions of the enzyme inhibitor, always searching for better safety and more potency. Other compounds worked to varying degrees, but compound number 233 was the winner.

LPC-233 fits a binding spot on the LpxC enzyme and prevents it from doing its work. “It fits in the right way to inhibit formation of the lipid,” Zhou said. “We’re jamming the system.”

Adding to its durability, the compound works by a remarkable two-step process, Zhou said. After the initial binding to LpxC, the enzyme-inhibitor complex changes its shape somewhat to become an even more stable complex.

The lifetime of the inhibitor binding in this more stable complex is longer than the lifetime of the bacteria. “We think that contributes to the potency, as it has a semi-permanent effect on the enzyme,” he said. “Even after the unbound drug is metabolized by the body, the enzyme is still inhibited due to the extremely slow inhibitor dissociation process,” Zhou said.

There are multiple patents being filed on the series of compounds, and Toone and Zhou have co-founded a company called Valanbio Therapeutics, Inc. which will be looking for partners to bring LPC-233 through phase 1 clinical trials to assess safety and efficacy in humans.

“All of these studies were done in animals,” Zhou said. “Ultimately the cardiovascular safety needs to be tested in humans.”

Large scale synthesis of LPC-233 was first accomplished by David Gooden at the Duke Small Molecule Synthesis Facility. Vance Fowler and Joshua Thaden (Duke School of Medicine), Ziqiang Guan (Biochemistry) and Ivan Spasojevic (Duke PK/PD Core) helped with in vivo studies, mass spectrometry and pharmacokinetics analysis.

This work was supported by grants from National Institutes of Health (R01 GM115355, AI094475, AI152896, AI148366), the North Carolina Biotechnology Center (2016-TEG-1501) and a National Cancer Institute Comprehensive Cancer Center Core Grant (P30CA014236).

Acid reflux is when stomach acid flows into the esophagus, usually after a meal or when lying down. People with acid reflux may experience heartburn and ulcers. People with frequent acid reflux may develop gastroesophageal reflux disease, or GERD, which can lead to cancer of the esophagus.

Proton pump inhibitors reduce stomach acid by targeting the enzymes in the stomach lining that produce that acid.

“Proton pump inhibitors are a useful tool to help control acid reflux, however long-term use has been linked in previous studies to a higher risk of stroke, bone fractures and chronic kidney disease,” said study author Kamakshi Lakshminarayan, MBBS, PhD, of the University of Minnesota School of Public Health in Minneapolis, and a member of the American Academy of Neurology. “Still, some people take these drugs regularly, so we examined if they are linked to a higher risk of dementia. While we did not find a link with short-term use, we did find a higher risk of dementia associated with long-term use of these drugs.”

The study included 5,712 people, age 45 and older, who did not have dementia at the start of the study. They had an average age of 75.

Researchers determined if participants took acid reflux drugs by reviewing their medications during study visits and during yearly phone calls. Of the participants, 1,490 people, or 26%, had taken the drugs. Participants were then divided into four groups based on whether they had taken the drugs and for how long, as follows: people who did not take the drugs; those who took the drugs for up to 2.8 years; those who took them for 2.8 to 4.4 years; and people who took them for more than 4.4 years.

Participants were then followed for a median duration of 5.5 years. During this time, 585 people, or 10%, developed dementia.

Of the 4,222 people who did not take the drugs, 415 people developed dementia, or 19 cases per 1,000 person-years. Person-years represent both the number of people in the study and the amount of time each person spends in the study. Of the 497 people who took the drugs for more than 4.4 years, 58 people developed dementia, or 24 cases per 1,000 person years.

After adjusting for factors such as age, sex and race, as well as health-related factors such as high blood pressure and diabetes, researchers found people who had been taking acid reflux drugs for more than 4.4 years had a 33% higher risk of developing dementia than people who never took the drugs.

Researchers did not find a higher risk of dementia for people who took the drugs for fewer than 4.4 years.

“More research is needed to confirm our findings and explore reasons for the possible link between long-term proton pump inhibitor use and a higher risk of dementia,” said Lakshminarayan. “While there are various ways to treat acid reflux, such as taking antacids, maintaining a healthy weight, and avoiding late meals and certain foods, different approaches may not work for everyone. It is important that people taking these medications speak with their doctor before making any changes, to discuss the best treatment for them, and because stopping these drugs abruptly may result in worse symptoms.”

A limitation of the study was that participants were asked once a year about medication use, so researchers estimated use between annual check-ins. If participants stopped and restarted acid reflux drugs in between check-ins, estimation of their use may have been inaccurate. The authors were also unable to assess if participants took over the counter acid reflux drugs.

The study was supported by the National Institutes of Health, including the National Heart, Lung, and Blood Institute.

“These exciting observations of mature mud cracks are allowing us to fill in some of the missing history of water on Mars. How did Mars go from a warm, wet planet to the cold, dry place we know today? These mud cracks show us that transitional time, when liquid water was less abundant but still active on the Martian surface,” said Nina Lanza, principal investigator of the ChemCam instrument onboard the Curiosity rover. “These features also point to the existence of wet-dry environments that on Earth are extremely conducive to the development of organic molecules and potentially life. Taken as a whole, these results a giving us a clearer picture of Mars as a habitable world.”

The presence of long-term wet environments, such as evidence of ancient lakes on Mars, is well-documented, but far less is known about short-term climate fluctuations.

After years of exploring terrain largely composed of silicates, the rover entered a new area filled with sulfates, marking a major environment transition. In this new environment, the research team found a change in mud crack patterns, signifying a change in the way the surface would have dried. This indicates that water was still present on the surface of Mars episodically, meaning water could have been present for a time, evaporated, and repeated until polygons, or mud cracks, formed.

“A major focus of the Curiosity mission, and one of the main reasons for selecting Gale Crater, is to understand the transition of a ‘warm and wet’ ancient Mars to a ‘cold and dry’ Mars we see today,” said Patrick Gasda of the Laboratory’s Space Remote Sensing and Data Science group and coauthor of the paper. “The rover’s drive from clay lakebed sediments to drier non-lakebed and sulfate-rich sediments is part of this transition.”

On Earth, initial mud cracks in mud form a T-shaped pattern, but subsequent wetting and drying cycles cause the cracks to form more of a Y-shaped pattern, which is what Curiosity observed. Additionally, the rover found evidence that the mud cracks were only a few centimeters deep, which could mean that wet-dry cycles were seasonal, or may have even occurred more quickly, such as in a flash flood.

These findings could mean that Mars once had an Earth-like wet climate, with seasonal or short-term flooding, and that Mars may have been able to support life at some point.

“What’s important about this phenomenon is that it’s the perfect place for the formation of polymeric molecules required for life, including proteins and RNA, if the right organic molecules were present at this location,” Gasda said “Wet periods bring molecules together while dry periods drive reactions to form polymers. When these processes occur repeatedly at the same location, the chance increases that more complex molecules formed there.”