Roche has announced that its experimental antibiotic, zosurabalpin, will move into the third and final phase of testing on humans. This marks the first time in 50 years that a new antibiotic showing promise against Acinetobacter baumannii will be tested at this stage. The bacterium is identified by the World Health Organization as a “priority” pathogen and by the U.S. Centers for Disease Control and Prevention as an “urgent threat.”
Acinetobacter baumannii is known to affect patients in hospital settings, causing infections such as pneumonia and sepsis. These infections particularly impact immunocompromised individuals, including those with conditions like cancer. It is estimated that between 40 and 60 percent of infected patients die as a result of the infection.
One of the challenges in treating this pathogen is its protective double-walled membrane, which makes it difficult for drugs to penetrate and remain effective. Zosurabalpin, developed by Roche in collaboration with researchers at Harvard University, targets the mechanism that forms this outer membrane. According to Roche, this mode of action is different from that of existing antibiotics.
Roche stated that the upcoming phase-three trial will involve around 400 patients with carbapenem-resistant Acinetobacter baumannii (CRAB) infections. These patients will receive either zosurabalpin or the current standard of care. The trial is expected to begin later this year or in early 2026. The company hopes the drug will be approved by the end of the decade.
Michael Lobritz, global head of infectious diseases at Roche, stated that the goal is to contribute new innovations to address antimicrobial resistance. Larry Tsai, senior vice president and global head of immunology and product development at Genentech, a unit of Roche, noted that drug-resistant bacteria are present in every country. He also commented that the biology involved in this research may offer new insights into bacterial membrane structures.
Earlier studies on zosurabalpin, including test-tube and mouse models, were published in the journal Nature. These studies reported that the drug performed “extremely well.” Dr. Alistair Farley, scientific lead at the Ineos Oxford Institute, described the development as “exciting” and emphasized the need for new antibiotics to address antimicrobial resistance related to CRAB. He noted that the drug may support future drug development efforts. Professor Laura Piddock, scientific director of the Global Antibiotic Research and Development Partnership, stated that the drug affects one of the building blocks in the outer part of the bacterial cell, and described this aspect as “exciting.”
Antimicrobial resistance was identified as one of the most urgent global health threats during the UN General Assembly earlier this year. A declaration from the assembly committed member states to establish independent panels on antimicrobial resistance and to reduce related deaths by 10 percent by 2030.
Roche acknowledged the broader context in which pharmaceutical companies have previously been reluctant to pursue antibiotic development due to market challenges. The company stated that zosurabalpin is being developed to address a serious hospital infection caused by a common drug-resistant bacterium.
