Having stripped back its workforce, antibiotics biotech Spero Therapeutics continues to strip away its remaining pipeline.
The latest program to be discontinued is SPR206, a next-gen polymyxin that has shown antibiotic activity against MDR Gram-negative pathogens in preclinical studies. Spero had been lining up the candidate for a phase 2 trial for hospital- and ventilator-acquired bacterial pneumonia.
However, Spero said it had decided to discontinue the program based on a “review and reprioritization of the company’s pipeline in Q1 2025.”
Development of the drug had previously been funded in part by the U.S. Department of Defense, the National Institute of Allergy and Infectious Diseases, the National Institutes of Health, and the Department of Health and Human Services.
“We are grateful to our partners and the government agencies who helped finance this program and to the Spero team members who have worked diligently on its progression into a phase 2-ready asset,” interim President and CEO Esther Rajavelu said in a full-year earnings report.
The Cambridge, Massachusetts-based company most recently halted work on another candidate in October 2024, after the oral antibiotic SPR720 failed to beat placebo and showed signs of liver toxicity in a phase 2 trial for non-tuberculous mycobacterial pulmonary disease. Those disappointing results also led Spero to trigger its latest round of layoffs.
At the time, Spero said it would focus on an oral carbapenem called tebipenem HBr as well as SPR206, although it was already warning that a phase 2 trial of the latter candidate would be dependent on finding non-dilutive funding.
Tebipenem HBr has also faced tricky clinical development. The FDA rejected an approval filing back in 2022 that would have made tebipenem the first oral carbapenem-class antibiotic used in complicated urinary tract infections.
GSK then swooped in to rescue the program, paying $66 million that enabled Spero to design and start a new phase 3 trial. An interim analysis of that trial is currently expected in the second quarter of this year, according to yesterday’s release.
The biotech said it is also reviewing data from the failed SPR720 program for non-tuberculous mycobacterial pulmonary disease.
“There remains a high unmet need for new, approved therapies for this difficult-to-treat disease, and a complete data analysis would enable us to make an informed decision on the program,” Rajavelu explained.
Spero entered 2025 with $52.9 million to hand. Along with milestone payments from GSK, the biotech expects this money to fund operations into the second quarter of 2026.
The low return on investment means many of the biggest biopharmas have given up working on new antifungals or antibiotics in recent years—although GSK in particular has continued to sign deals and post encouraging clinical results against infections like gonorrhea.