Seres Closing SER-287 Maintenance, Open-Label Studies for Ulcerative Colitis


The company expects to continue to study the potential inflammatory bowel disease treatment.

A lack of efficacy has led to the cancellation of a pair of trials for SER-287 in ulcerative colitis patients.

Seres Therapeutics announced the topline results from the phase 2b ECO-RESET study, showing the treatment did not meet its primary endpoint of improving clinical remission rates compared to placebo and will close both the open-label and maintenance studies of the SER-287.

The trial included 2 dosing cohorts—full induction dosing, and step-down induction dosing.

The induction portion of the study occurred following 10 weeks of induction dosing, following vancomycin pre-conditioning. The randomized, placebo controlled, double-blind, parallel group multicenter study included 203 patients at 104 sites in the US and Canada.

The investigators defined clinical remission by a 3-component modified Mayo Score.


Both dosing regimens was generally well-tolerated, with treatment emergent adverse events found in 67.6%, 46.2%, and 50.7% of the participants in the induction dose, step-down dose, and placebo group, respectively.

Most of the adverse events observed, including worsening ulcerative colitis, diarrhea, nausea, and abdominal distension, were mild or moderate in intensity. There were 4 participants that reported serious treatment emergent adverse events in the active treatment group and 1 individual in the placebo group.

A Lack of Efficacy

There was no meaningful clinical differences and no statistical significance observed in absolute clinical remission rates between the 2 dosing arms and the placebo control group (10.3% for the full induction dose, n = 68 and 10.6% for the step-down induction dose, n = 66 versus 11.6% for placebo, n = 69).

There was also no meaningful differences for endoscopic improvement, endoscopic remission, or symptomatic remission.

Reactions from Seres

“While the efficacy results in this trial did not meet the pre-defined threshold, we believe this data-rich study, including microbiome analyses expected in the second half of 2021, will provide valuable insights to inform continued development of our pipeline, including SER-301, our next generation investigational candidate for UC,” said Lisa von Moltke, MD, Chief Medical Officer at Seres, in a statement.

While expressing disappointment in the results, Seres representatives are confident moving forward new drugs will soon be available to serve ulcerative colitis patients.

“While these outcomes were not what we, nor the UC community, were hoping for, we remain committed to leading the creation of a new class of medicines designed to impact how diseases like ulcerative colitis are treated,” Eric Shaff, Chief Executive Officer at Seres, said in a statement. “As with SER-109, we will again follow the science and the data, conduct a rigorous scientific analysis, and determine the optimal path forward for our UC franchise. We are well resourced and continue to prepare for SER-109 commercialization, in collaboration with Nestlé Health Science, and we are excited about advancing the development of our SER-301 and SER-155 investigational candidates as well as our earlier stage pipeline.”

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