Improved nanoscale drills kill bacteria directly and revive existing antibiotics

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Molecular machines that kill infectious bacteria have been designed to work with a more clinically useful source of light energy. The latest iteration of these synthetics nanoscale drills, or molecular machines (MM), developed by scientists at Rice University, are activated by visible light rather than ultraviolet (UV), as in previous versions. Testing of burn-related bacterial infections in live preclinical models has confirmed that the new MMS can effectively kill bacteria.

Six variants of molecular machines have been successfully tested by Rice chemist James Tour, PhD, and his team. All were able to punch holes in the membranes of Gram-negative and Gram-positive bacteria in as little as two minutes. And since bacteria have no natural defenses against such mechanical invaders, they are unlikely to develop resistance, the researchers say, offering a strategy that could be used to defeat bacteria that have become resistant to standard antibacterial treatments. “I tell students that when they’re my age, antibiotic-resistant bacteria are going to make COVID-19 look like a walk in the park,” Tour said. “Antibiotics will not be able to prevent 10 million people a year from dying from bacterial infections. But that really stops them.

As with previous versions, the new molecular machines could also help improve the effectiveness of antibacterial drugs. “Drilling through the membranes of microorganisms allows otherwise ineffective drugs to enter cells and overcome the insect’s intrinsic or acquired resistance to antibiotics,” said co-investigator Ann Santos, PhD.

Tour, together with colleagues including Rice alumni and first author Santos and Dongdong Liu, PhD, reported on their development in Scientists progressin an article titled “Light-activated molecular machines are fast-acting broad-spectrum antibacterials that target the membranein which they concluded that at therapeutic doses, synthetic MMs were able to “significantly outperform conventional antibiotics”. The team wrote in conclusion: “Visible light-activated MMs represent a new mode of antibacterial action by mechanical disruption at the molecular scale, which does not exist in nature and to which the development of resistance is unlikely”.

Antimicrobial resistance (AMR) represents one of the greatest challenges facing humans, the authors wrote. “AMR is currently responsible for 700,000 deaths/year. By 2050, 10 million lives a year worldwide will be threatened by drug-resistant infections. The problem is becoming increasingly urgent as drug-resistant bacteria continue to thwart existing antibiotics, while the development of new antimicrobial agents “has nearly stalled”, the team continued. “No new class of antibiotics against Gram-negative bacteria has been approved since the late 1980s, and only one in four antibiotics in clinical development is a new class of drug or works via a new mechanism of stock.” And since most antibiotics in development are potentially susceptible to the same resistance mechanisms that render existing drugs ineffective, there is an “urgent need” to develop new, safe and effective antimicrobials that can help prevent the development of resistance. , while preserving the viability of existing drugs. antibiotics.

The diagrams show two variants of light-activated molecular machines developed at Rice University that drill into and destroy antibiotic-resistant bacteria. The machines could be useful in combating infectious skin diseases. [Tour Research Group/Rice University]

Synthetic molecular motors, or molecular machines, are molecular structures that can rotate in one direction in response to stimuli, resulting in mechanical action, the authors explained. “Among the stimuli that can activate MMs, light is particularly attractive due to its non-chemical and non-invasive nature and its ease of control,” they noted. When irradiated with the correct wavelength, the molecule spins in one direction, resulting in a rapid, drilling-like motion that can propel it through a lipid bilayer.

But while MMs have shown promise for applications ranging from drug delivery to chemotherapy or antimicrobial therapy, the ultraviolet (UV) radiation required to activate them has limited their clinical usefulness because prolonged exposure to UV can be harmful to humans.

The Rice Lab has been refining its MM technology for years. The machines are based on the Nobel Prize-winning work of Bernard Feringa, PhD, who developed the first molecule with a rotor in 1999 and reliably rotated the rotor in one direction. Tour and his team presented their advanced exercises in a 2017 Nature paper.

The new version draws its energy from visible, but still bluish, light at 405 nanometers, spinning the molecules’ rotors at two to three million times per second. The team achieved visible light activation by adding a nitrogen group. “The molecules were then modified with different amines in the (stationary) stator or rotor part of the molecule to promote association between the protonated amines of the machines and the negatively charged bacterial membrane,” said Liu, who is now a scientist. at Arcus Biosciences.

The Rice lab’s first tests with the new molecules in burn infection models confirmed their ability to rapidly kill bacteria, including those resistant to methicillin. Staphylococcus aureusa common cause of skin and soft tissue infections that was responsible for more than 100,000 deaths in 2019.”…at therapeutic levels, MMs attenuated the mortality associated with infection by different bacterial strains (Acinetobacter baumannii and S. aureus) in a burn infection model,” the scientists said.

A transmission electron microscope image shows Escherichia coli bacteria in various stages of degradation after exposure to light-activated molecular drills developed at Rice University. The machines are able to pierce the membranes of antibiotic-resistant bacteria, killing them within minutes. [Image by Matthew Meyer/Rice University]

The researchers also found that the new MMs will effectively break down biofilms and lingering cells that become dormant to ward off antibacterial drugs. “Even if an antibiotic kills most of a colony, there are often a few cells left behind that for some reason don’t die,” Tour said. “But that doesn’t matter for the drills.”

The authors further stated, “Persistent cells are defined as transiently antibiotic-tolerant fractions of metabolically inactive or dormant bacterial populations. MMs were also able to significantly reduce the cell number and biomass of established biofilms of P. aeruginosa and S. aureus.”

It has been suggested by other researchers that light at the wavelength used for new MMs has its own mild antibacterial properties, but the addition of molecular machinery supercharges it, said Tour, who suggested bacterial infections such as those suffered by burn victims and people with gangrene. will be the first targets.

As with previous versions, the new machines could also be used to revive antibacterial drugs that would otherwise be considered ineffective. “…by permeabilizing the membrane, MM at sublethal doses potentiate the action of conventional antibiotics,” the Rice team pointed out. “Drilling through the membranes of microorganisms allows otherwise ineffective drugs to enter cells and overcome the insect’s intrinsic or acquired resistance to antibiotics,” said Santos, who is in his third year of the global postdoctoral fellowship that brought her to Rice for two years and continues at the Balearic Islands Health Research Institute in Palma, Spain.

The lab is working to better target bacteria to minimize damage to mammalian cells by attaching bacteria-specific peptide tags to drill bits to direct them to pathogens of interest. “But even without that, the peptide can be applied to a site of bacterial concentration, such as a burn area,” Santos said.

Summarizing their reported studies, the authors wrote, “Together, these results indicate that, under the experimental conditions examined, MM-induced antibacterial effects can be attributed to the rapid, drill-like unidirectional rotation of MMs after activation of the lumen, by which the rotor part of the molecule rotates around the central olefinic bond, propelling the molecule through the membrane. The subsequent leakage of cell contents and loss of membrane potential ultimately results in the death of bacterial cells.

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