Seres Therapeutics, armed with new safety data, eyes first FDA approval for a microbiome drug

Seres Therapeutics has nabbed the additional safety data for its Clostridium difficile treatment that regulators had called for, teeing up what could be the first-ever approval of a microbiome-based therapy. 

The company says it’s wrapped up the open-label safety trial of its microbiome treatment SER-109 for C. diff, announcing Tuesday that the med had a “favorable safety profile” through 24 weeks. In an interview with Fierce Biotech, CEO Eric Shaff would not dive into details on the data, which the release describes as mirroring previous phase 3 results, but said there were “very few adverse events related to the drug.” 

“We really couldn’t be more pleased with the risk and reward profile associated with the drug in terms of efficacy and safety,” Shaff said. 

It was the final hurdle for the company after the FDA had asked for additional data on at least 300 patients that were dosed in the phase 3 trial. The study also reaffirmed efficacy data seen in the study, with 13.7% of patients experiencing recurrence of infection through 24 weeks. Less than 9% of treated patients experienced recurrence within eight weeks of treatment, the company noted. In comparison, up to a quarter of C. diff patients on currently available treatments can experience recurrence within 30 days.

Now, armed with its full arsenal of data, the company is readying its case for regulators. Seres has initiated its formal approval application to the FDA and is expected to wrap up imminently, with the company estimating that the submission will be completed by “mid-2022.”

While the FDA has not publicly stated its intentions, Shaff said Seres is preparing to go before an agency advisory committee, given the novelty of the therapy mechanism. The drug is an oral capsule comprised of bacteria spores aimed at invigorating the gut microbiome. In the case of SER-109, the capsule is comprised of spores from firmicutes, a type of bacteria that live in the gut. 

Feeling positive about its position, Shaff soaked in the reality that the company had reached the clinical finish line of a drug that at one point seemed near death. In 2016, SER-109 failed a phase 2 trial to treat C. diff, but, rather than abandon the asset, the company doubled down. Shaff credited two critical changes for the phase 3 victory that came four years later: changing the diagnostic protocol and upping the dose. 

“Each of those changes were the result of, or a product of, rigorous scientific analysis that ultimately gave us data that suggested that these two changes could increase our probability of success,” the CEO said. The decision to persist was validated in August 2020 when the med cleared a late-stage trial. 

That success was, naturally, met with external interest that the company welcomed. Last year, Seres granted some rights of the drug to Nestlé Health Sciences, raking in $175 million in upfront cash in exchange for lead commercialization responsibilities. If approved, Seres will be handed over another $125 million in milestone bucks. 

When asked how much the company plans to sell the drug for, Shaff wouldn’t commit, saying the two companies would work together. But he cited a Massachusetts General Hospital study that found the average per-patient cost of recurrent C. diff to the hospital system was $34,000, a finding he called “illustrative” of the costs of these patients. 

“We will work with our partners at Nestlé to find the right balance of ensuring that we have as many people that have access to SER-109 as possible, but also charge a price that’s reflective of the value of the innovation that we’re bringing,” he said.