Scientists have designed the first “living pill” to treat lung infections. Treatment is directed against Pseudomonas aeruginosa, a bacterium that is naturally resistant to many types of antibiotics and is a common source of infections in hospitals.
The treatment consists of using a modified version of the Mycoplasma pneumoniae bacterium, eliminating its pathogenic capacity and adapting it so that it attacks P. aeruginosa instead. The modified bacteria is used in combination with low doses of antibiotics that would not be effective on their own.
The work has been carried out by a team that includes researchers from the Center for Genomic Regulation (CRG) in Barcelona and the International University of Catalonia.
The team found that using the treatment in mice significantly reduced lung infections. The “living pill” doubled the mouse’s survival rate compared to no treatment at all. Administration of a single high dose of the treatment showed no signs of toxicity in the lungs. Once the treatment had run its course, the innate immune system eliminated the modified bacteria over a period of four days.
The company Pulmobiotics (promoted by the CRG), the August Pi i Sunyer Biomedical Research Institute (IDIBAPS) in Barcelona, the Hospital Clínic de Barcelona and the Agrobiotechnology Institute (IdAB), a research institute of the CSIC and the government of Navarra, in Spain.
Infections caused by P. aeruginosa are difficult to treat because the bacteria live in communities that form biofilms. Biofilms can adhere to various surfaces of the body, forming impenetrable bunker-like structures that are beyond the reach of antibiotics.
P. aeruginosa biofilms grow on the surface of endotracheal tubes used by critically ill patients who therefore require mechanical ventilators to breathe. This causes ventilator-associated pneumonia (VAP), a condition that affects up to one in four (9-27%) patients requiring intubation. The incidence exceeds 50% in the case of patients intubated for severe COVID-19. VAP can prolong the stay in the intensive care unit up to a period of thirteen days, and has a mortality rate that reaches one in eight patients (9-13%).
The M. pneumoniae-based living pill was designed to dissolve biofilms. The scientific team modified the bacterium to give it the ability to produce various substances, including pyocins, toxins naturally produced by bacteria to kill or inhibit the growth of various strains of Pseudomonas. To test its efficacy, they collected P. aeruginosa biofilms from the endotracheal tubes of patients in intensive care units. They verified that the treatment crosses the barrier and successfully dissolves the biofilms.
This image shows a cross section of a mouse lung infected with Pseudonomas aeruginosa. The mouse was treated with a version of Mycoplasma pneumoniae that does not produce therapeutic molecules, causing severe pneumonia. This is characterized by massive infiltration of inflammatory cells into the alveolar septa, resulting in air leaking into the alveoli. (Photo: Rocco Mazzolini / CRG. CC BY SA)
“We have developed a battering ram that attacks antibiotic-resistant bacteria. The treatment opens holes in cell walls and creates key entry points for antibiotics to invade and kill the infection at its source. We believe that it is a promising new strategy to address the main cause of hospital mortality”, explains Dr. María Lluch, scientific director of Pulmobiotics, co-author of the study and researcher at the International University of Catalonia.
With the aim of using the “living pill” to treat VAP, more tests will be carried out before reaching the clinical trial phase. Treatment is planned to be administered using a nebulizer, a device that turns liquid medication into a mist that is inhaled through a mouthpiece or mask.
M. pneumoniae is one of the smallest known bacteria species. Dr. Luis Serrano, director of the CRG, had the idea of modifying the bacterium and using it as a “living pill” two decades ago. Dr. Serrano is a specialist in synthetic biology, a field that involves engineering organisms so that they have new and useful abilities. With only 684 genes and no cell wall, the relative simplicity of M. pneumoniae makes it ideal for application-oriented bioengineering.
One of the advantages of using M. pneumoniae to treat respiratory diseases is that it is naturally adapted to lung tissue. After administering the modified bacteria, it travels directly to the source of a respiratory infection, where it sets up a temporary factory, producing a series of therapeutic substances.
By demonstrating that M. pneumoniae can be used against lung infections, the study opens the door to the development of new strains of the bacteria aimed at fighting other types of respiratory diseases such as lung cancer or asthma. “The bacterium can be modified with various different active payloads, be they cytokines, nanobodies or defensins. The goal is to diversify the arsenal of the modified bacterium and unleash its potential in the treatment of a range of complex diseases”, explains ICREA Research Professor Dr. Luis Serrano.
In addition to designing the “living pill,” Dr. Serrano’s lab is also using its expertise in synthetic biology to design new proteins that can be delivered by M. pneumoniae. The team is using these proteins to treat inflammation caused by P. aeruginosa infections.
Although inflammation is a natural response of the body in reaction to infection, excessive or prolonged inflammation can damage lung tissue. The inflammatory response is orchestrated by the immune system, which releases mediator proteins such as cytokines. One type of cytokine, IL-10, has well-known anti-inflammatory properties, thus making it of increasing therapeutic interest.
The study is titled “Engineered live bacterium suppress Pseudomonas aeruginosa infection in mouse lung and dissolve endotracheal-tube biofilms”. And it has been published in the academic journal Nature Biotechnology.
In other research, published in the academic journal Molecular Systems Biology, Dr. Serrano’s research group used ModelX and FoldX, two protein design software, to create new versions of IL-10 optimized for the treatment of inflammation . These new cytokines have new properties that improve their efficiency and affinity.
The scientific team designed strains of M. pneumoniae that express these new cytokines and tested their efficacy in the lungs of mice with acute P. aeruginosa infections. The researchers showed that engineered versions of IL-10 were significantly more effective in reducing inflammation compared to the natural cytokine IL-10.
Ariadna Montero Blay, co-author of that study in Molecular Systems Biology, indicates that “biotherapeutic solutions such as M. pneumoniae provide ideal vehicles to overcome the traditional limitations of cytokines and unlock their enormous potential in the treatment of various human diseases. The engineering of cytokines as therapeutic molecules was essential to combat inflammation. Other lung diseases such as asthma or pulmonary fibrosis could also benefit from this approach.” (Source: CRG)