Seres Releases Positive SER-109 Phase 3 Results for Recurrent C. Difficile Infection

In ECOSPOR III, the lead therapeutic candidate integrated durably and rapidly into the microbiome to prevent recurrence, the company says.

Seres Therapeutics announced the presentation of data from its Phase 3 ECOSPOR III study which suggests that investigational microbiome-based therapeutic SER-109 prevents recurrent Clostridioides difficile infections (rCDI).

SER-109 prevents infection by rapidly establishing a long-lasting colony of beneficial gut microbes, which can help produce fatty acids that disrupt the It’s hard life cycle, according to data presented at the 2022 Digestive Diseases Week annual meeting.

“These results suggest that our experimental microbiome therapeutic, SER-109, is a potentially rapid-acting intervention that may provide long-lasting relief from rCDI when administered to vulnerable patients,” said Matthew Henn, PhD. scientific director of Seres, in a press release. . “Confirming the multiple mechanisms that SER-109 bacteria use to prevent this notoriously difficult infection at the cellular and molecular level not only increases our confidence in this particular therapeutic, but it has the potential to help guide the design of the next generation. of microbiome. therapies based on .

Data was shared as an oral and poster presentation at the meeting.

The ECOSPOR III study included 182 people with RRCI and was a multicenter, placebo-controlled, randomized clinical trial. The trial previously demonstrated that SER-109 prevented rCDI in around 88% of people treated with the drug at the primary endpoint of 8 weeks, compared with around 60% of those in the placebo group.

Safety was similar in both groups.

Additionally, a pre-planned exploratory analysis of the trial showed that approximately two-thirds of It’s hard recurrences of infection have occurred within the first 2 weeks after antibiotic treatment when the microbiome is still decimated and infection spores are free to germinate vegetative toxin-producing bacteria.

“These results suggest that the first 2 weeks following antibiotic treatment are when microbiome therapeutics have the greatest potential benefit, restoring bacterial diversity and disrupting the cycle of recurrent infections. It’s hardsaid Lisa von Moltke, MD, chief medical officer at Seres, in the statement.

SER-109 introduces bacterial species into the gut in the form of spores, which germinate and integrate into the microbiome and appear in the stool as vegetative bacteria, in a process called grafting.

Within a week of treatment, the number of new bacterial species in the stool increased and remained higher than that of the placebo group throughout the 24-week study period. In the placebo group, bacterial diversity rebounded more slowly and to a lesser extent.

The pattern of outcome was similar regardless of the antibiotic received, including fidaxomicin or vancomycin.

In the poster presentation, the researchers performed a post-hoc analysis to better understand how SER-109 prevents rCDI at the molecular level.

Investigators collected stool samples from individuals involved in the ECOSPOR III trial and analyzed the samples for changes in microbial composition and fatty acid concentrations over the 8 weeks following treatment.

People who received SER-109 had butyrate, hexanoate, and valerate levels that rose rapidly, starting in the 2-week window of vulnerability, and remained higher than the placebo group.

These fatty acids have been shown to inhibit the growth of VS. hard.

In those who were in the placebo group who underwent rCDI, valerate levels tended to be lower than those in the placebo group who did not undergo rCDI.

Seres expects to finalize a biologics license application submission for the drug to the FDA in mid-2022, which would make SER-109 potentially the first FDA-approved microbiome-based therapeutic treatment for rCDI.


Seres Therapeutics Presents Phase III Results of SER-109 for Recurrent C. Difficile Infection at Digestive Disease Week (DDW) Annual Meeting. BusinessWire. Press release. May 22, 2022. Accessed May 23, 2022.

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