Seres Therapeutics has reported that SER-287 failed to meet the primary goal of clinical remission in the Phase IIb ECO-RESET clinical trial in mild-to-moderate ulcerative colitis (UC) patients.

SER-287 is a consortium of bacteria present in the gastrointestinal (GI) tract of healthy people. It is a donor-derived product candidate.

The placebo-controlled, double-blind, parallel-group, multi-centre Phase IIb trial enrolled a total of 203 UC patients at 104 centres across the US and Canada.

Trial subjects were randomised in a 1:1:1 ratio to receive either a full induction dose or step-down induction dose of SER-287 or a placebo.

The primary goal of the induction portion of the trial was the safety and efficacy of SER-287 in reaching clinical remission following ten weeks of dosing after vancomycin pre-conditioning.

As per the trial data, subjects receiving a full induction dose of SER-287 had 10.3% of clinical remission rates while the rates were 10.6% and 11.6% for step-down induction dose and placebo, respectively.

Seres noted that no meaningful clinical differences or statistical significance were reported in absolute clinical remission rates among the three study groups.

Furthermore, no meaningful changes in endoscopic improvement, endoscopic remission or symptomatic remission were demonstrated in the three groups.

Both the tested SER-287 dosing regimens were found to be generally well-tolerated.

Treatment-emergent adverse events (AEs) during the trial were reported in 67.6% and 46.2% of participants on induction dose and step-down dose, respectively, as against 50.7% on placebo.

The severity of most of the AEs was found to be mild or moderate.

As no clinical efficacy signal was detected in the trial, Seres decided to discontinue the open-label and maintenance portions of ECO-RESET.

Seres Therapeutics chief medical officer Lisa von Moltke said: “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 the continued development of our pipeline, including SER-301, our next-generation investigational candidate for UC.”

The company is progressing its SER-301 programme, which is presently in a Phase Ib trial in Australia and New Zealand.

In January, Seres published positive data analyses from its Phase Ib trial of SER-287 in patients with active mild-to-moderate UC.