Seres Therapeutics Announces Discontinuation of Enrollment in SER-401 Study in Metastatic Melanoma

 - Enrollment meaningfully impacted by COVID-19 -

- The Company reiterates opportunity in oncology and continues advancement of its preclinical efforts -

CAMBRIDGE, MA, USA I March 08, 2021 ISeres Therapeutics, Inc. (Nasdaq: MCRB) announced today that the Company, in collaboration with study partners, The Parker Institute for Cancer Immunotherapy (PICI) and The University of Texas MD Anderson Cancer Center, has voluntarily discontinued further enrollment in the Melanoma Checkpoint and Gut Microbiome Alteration With Microbiome Intervention (MCGRAW) study evaluating the safety and drug activity of SER-401 or fecal microbiota transplant (FMT) in combination with nivolumab in patients with metastatic melanoma.

“While we are disappointed to discontinue enrollment, we are encouraged by the opportunity to apply the learnings from this study towards future development programs at Seres that can directly benefit the oncology community in search of new treatment options,” said Matthew Henn, Ph.D., Chief Scientific Officer at Seres. “We want to thank the patients, their care partners, our collaborators and the medical professionals who participated in this study, despite the COVID-19 pandemic, and helped further advance our understanding of the role microbiome therapeutics play in the treatment of cancer.”

A preliminary analysis of results from 10 subjects who received either SER-401 or placebo in combination with nivolumab indicated that SER-401 was safe and well-tolerated. There were no patients enrolled in the FMT portion of the study. Subjects currently enrolled in the study will complete the study protocol. Given challenges in enrollment due to the COVID-19 pandemic, subsequent anticipated time to study completion, and progress in its preclinical oncology pipeline, Seres has decided to deprioritize further development of SER-401. The Company will continue to advance its research and development efforts in cancer, applying learnings from the SER-401 trial.

Evidence continues to emerge that suggests gut microbiome modulation may augment responses to cancer immunotherapy, including improving responses in PD-1 refractory patients1.

Seres and its collaborators continue to be excited about the opportunity to develop next-generation therapeutics targeting gut microbes for the treatment of individuals living with cancer. Seres will continue to engage with MD Anderson and PICI to advance the development of medicines in this field, and maintains a robust preclinical program in oncology as well as a collaboration with Memorial Sloan Kettering Cancer Center centered on advancing microbiome therapeutics in various settings of oncology. Seres’ immuno-oncology patent portfolio includes the option to exclusively license foundational intellectual property from MD Anderson, based upon the work of Jennifer Wargo, M.D., professor of Surgical Oncology and Genomic Medicine.

About Seres Therapeutics

Seres Therapeutics, Inc., (Nasdaq: MCRB) is a leading microbiome therapeutics platform company developing a novel class of multifunctional bacterial consortia that are designed to functionally interact with host cells and tissues to treat disease. Seres’ SER-109 program achieved the first-ever positive pivotal clinical results for a targeted microbiome drug candidate and has obtained Breakthrough Therapy and Orphan Drug designations from the FDA. The SER-109 program is being advanced for the treatment of recurrent C. difficile infection and has potential to become a first-in-class FDA-approved microbiome therapeutic. Seres’ SER-287 program has obtained Fast Track and Orphan Drug designations from the FDA and is being evaluated in a Phase 2b study in patients with active mild-to-moderate UC. Seres is evaluating SER-401 in a Phase 1b study in patients with metastatic melanoma, SER-301 in a Phase 1b study in patients with ulcerative colitis, and SER-155 to prevent mortality due to gastrointestinal infections, bacteremia and graft versus host disease. For more information, please visit

1 Davar et al. 2021. Fecal microbiota transplant overcomes resistance to anti-PD-1 therapy in melanoma patients. Science, DOI: 10.1126/science.abf3363; Baruch et al. 2021. Fecal microbiota transplant promotes response in immunotherapy-refractory melanoma patients. Science, DOI: 10.1126/science.abb5920

SOURCE: Seres Therapeutics

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