Battered and bruised Seres Therapeutics see shares skyrocket on phase 3 win

Seres Therapeutics has endured a tough few years of trials setbacks, cuts and new management, but the GI biotech is hoping with its new set of broadly positive late-stage data it can finally file for an approval.

The Cambridge, Massachusetts-based biotech said Monday morning that its pivotal phase 3 test, known as ECOSPOR III, which was testing its investigational oral microbiome therapeutic SER-109 for recurrent C. difficile infection (CDI) came through.

Using SER-109 saw a statistically significant absolute decrease of 30.2% in the proportion of patients who experienced a recurrence in CDI within eight weeks of administration versus placebo, the study’s primary endpoint, it said in a release.

The drug met the study’s primary endpoint with a significantly lower recurrence rate of 11.1% in SER-109 patients versus 41.3% in placebo patients at eight weeks (with a p value of 0.001) when tested at the one-sided 0.25 level. Patients administered SER-109 experienced a 30.2% lower rate of recurrence, on an absolute basis, compared to placebo.

The biotech said the ECOSPOR III recurrence rates “translate into a sustained clinical response rate of 88.9% versus 58.7% with SER-109 and placebo, respectively.”

The SER-109 safety results “were favorable” and similar to placebo, it added, with AEs mainly being flatulence, abdominal distention and abdominal pain, which were “generally mild to moderate in nature.”

It plans to ask for a Breakthrough FDA meeting as quickly as possible to submit a new BLA for the drug.  

This comes after a tough time for the biotech: In February last year, Seres cut about 30% of its workforce and said goodbye to its chief scientific officer as it narrowed its clinical efforts, which centered on SER-109, as well as a planned immuno-oncology study.

That move came less than a month after the company announced that its chief financial officer, Eric Shaff, would take over as CEO, and that Seres would look more toward immunological indications as it entered its “next phase of development.”

It also comes four years after the drug failed a phase 2 trial: SER-109 failed to outperform a placebo in terms of cutting the risk of CDI, leaving the biotech at the time scraping through the results in search a path forward for the program.

In the SER-109 arm of the study, 44% of participants experience a recurrence of CDI. A little more than half of subjects who received the placebo saw their CDI recur. When Seres crunched the numbers, this difference fell short of being a statistically significant reduction in relative risk of CDI recurrence, leaving the firm with a midstage trial that failed to meet its primary endpoint.

The phase 3 of SER-109 and its planned recruitment of 320 patients had been slowed because of widespread use of fecal microbiota transplants as an unapproved treatment for C. difficile infections.

The ECOSPOR III study in the end enrolled 182 patients with multiply recurrent CDI; there is also an ongoing SER-109 open-label study. The FDA has previously told Seres it would need to see 300 patients tested with the drug to accept a review.

“We are extremely pleased with these highly clinically meaningful SER-109 phase 3 study results, greatly exceeding the statistical threshold provided by the FDA. Based on our prior discussions with the FDA, we believe this trial should provide the efficacy basis for submitting an application for product approval. We look forward to meeting with the FDA as soon as possible to discuss the regulatory path forward with the goal of bringing SER-109 to patients as a first-in-class microbiome therapeutic,” said Eric Shaff, president and CEO of Seres.

“Our results represent the first-ever positive pivotal clinical study results for a targeted microbiome drug candidate. We believe these Phase 3 data provide strong validation for our underlying microbiome therapeutics platform, which has been the scientific basis for the company, as well as persuasive clinical evidence supporting our other active pipeline programs.”

Seres’ shares jumped more than 200% premarket Monday on the news, but then left the atmosphere hitting 460% late morning.