Small-molecule inhibitors of Staphylococcus aureus alpha-toxin for severe lung infections
Invasion of a host cell by staphylococci.
Staphylococcus aureus (S. aureus) is a common colonizer of the skin and mucous membranes. In intubated intensive care patients in particular, colonization of the lower respiratory tract is a key risk factor for the development of pneumonia, which is one of the most frequent infections in intensive care units.
A key factor contributing to severe disease is alpha-toxin (also known as alpha-hemolysin), a protein produced by S. aureus. This toxin forms pores in the membranes of human cells, including immune cells and cells lining blood vessels and the respiratory tract. As a result, these cells are damaged or destroyed, weakening the body’s defense against infection. At the same time, the toxin triggers a strong inflammatory response that further damages tissue and worsens disease progression.
„Our strategy does not target the bacterium itself, but neutralizes a toxin it produces—opening up new therapeutic options for critically ill patients at high risk of infection.“
Background
The prevention and treatment of S. aureus infections are becoming increasingly challenging, particularly in intensive care settings. Ventilator-associated pneumonia, in particular, remains a serious and potentially fatal complication despite intensive medical treatment.
Alpha-toxin is considered a key virulence factor of S. aureus, especially in pneumonia. Epidemiological, preclinical, and clinical studies highlight its central role in tissue damage, immune dysregulation, and disease progression. Targeting this toxin therefore represents a novel therapeutic approach: Instead of killing the bacteria, it aims to block their harmful effects.
This strategy is part of a broader concept known as "pathoblockers"—therapeutic agents that inhibit bacterial virulence mechanisms rather than directly targeting bacterial survival. Because such antivirulence approaches exert less selective pressure than conventional antibiotics, they may reduce the risk of resistance development.
Development
Researchers led by Prof. Mark Brönstrup at the Helmholtz Centre for Infection Research, in close collaboration with the Lead Discovery Center in Dortmund, have identified and systematically optimized small-molecule inhibitors of alpha-toxin. Using a miniaturized screening platform, more than 180,000 compounds were tested for their ability to block toxin activity. Compounds from the quinoxalinedione class, in particular the candidate H052, showed strong activity in both cell-based assays and animal models.
In a mouse model of acute lung infection with the highly virulent S. aureus strain USA300, H052 significantly improved survival when administered both prophylactically and therapeutically. In addition, inflammatory markers and bacterial burden in the lungs were reduced. Combination treatment with the antibiotic linezolid also showed beneficial effects.
Pharmacokinetic studies and confirmatory efficacy studies are currently underway to support dose selection for future clinical studies. In parallel, manufacturing processes for preclinical and clinical trial material are being established, and regulatory preclinical safety and toxicology studies are being prepared.
A key component of the project is translational companion research. In collaboration with Hannover Medical School, an observational clinical study in mechanically ventilated intensive care patients is ongoing. Using standardized respiratory sampling and microbiological analyses, methods are being developed to detect alpha-toxin in lung fluid. These data will support the design of a subsequent proof-of-concept clinical study. The goal is to initiate clinical trials in 2027.
Partners
Additional project sponsors
- Combating Antibiotic-Resistant Bacteria Biopharmaceutical Accelerator (CARB-X)
- Institute for Biomedical Translation (IBT)
- Helmholtz Association
