Spero Therapeutics has ceased the development of its antibiotic candidate, SPR720, following disappointing results from a Phase IIa clinical trial. The trial, which investigated SPR720's efficacy in treating patients with non-tuberculous mycobacterial pulmonary disease (NTM-PD), failed to meet its primary endpoint, leading to the program's termination and a significant workforce reduction.
Phase IIa Trial Results
The Phase IIa trial (NCT05496374) enrolled 25 patients with NTM-PD. Interim analysis of 16 patients revealed that SPR720 did not demonstrate a sufficient antimicrobial effect compared to placebo. The primary endpoint, measured by the rate of change in log10 colony forming units per milliliter (CFU/mL), showed no significant difference between the treatment and placebo groups. Furthermore, the trial raised safety concerns, including three cases of Grade 3 hepatotoxicity in patients receiving the 1,000mg oral daily dose.
Strategic Shift and Pipeline Focus
Faced with these results, Spero Therapeutics is redirecting its resources towards two other antibiotic programs: tebipenem HBr, an oral carbapenem antibiotic, and SPR206, a next-generation polymyxin. Tebipenem HBr has been out-licensed to GSK, granting GSK global marketing rights, excluding specific Asian countries. Spero has received $143.5 million from GSK to date and is eligible for up to $400 million in milestone payments, plus tiered royalties on sales.
The Phase III PIVOT-PO trial (NCT06059846) is set to evaluate oral tebipenem HBr against intravenous imipenem and cilastatin in hospitalized adults with complicated urinary tract infections (cUTI). The study aims to enroll approximately 2,648 patients, with completion expected in the second half of 2025.
SPR206 Development
Spero also intends to advance SPR206 as a potential treatment for multidrug-resistant (MDR) Gram-negative pathogens in patients with hospital-acquired or ventilator-associated bacterial pneumonia (HABP/VABP). The FDA has cleared Spero to initiate a Phase II trial for SPR206; however, the trial's commencement is contingent on securing non-dilutive funding.
Industry Context and Financial Impact
The setback with SPR720 and the subsequent restructuring, including a 39% reduction in staff, have impacted Spero Therapeutics' financial outlook. The company's stock price experienced a decline following the announcement. Spero anticipates its current cash reserves will sustain operations into mid-2026. This strategic shift places Spero among other pharmaceutical companies that have recently undergone workforce reductions to concentrate resources on key clinical development programs.
