Seres Therapeutics has achieved a breakthrough in the microbiome drug space with the approval of its oral drug, SER-109, by the US Food and Drug Administration (FDA). The drug is designed to adjust gut-bacteria populations and prevent recurring infections of C. difficile bacteria in people who have had previous episodes, while also helping to maintain healthy levels of gut bacteria. The drug is based on a combination of bacteria contained in sterilized and processed fecal material, collected from screened donors. The recipe features bacteria from the Firmicute phylum, one of the dominant populations of human gut bacteria.
Tackling the C. diff infections
According to studies on which the approval was based, SER-109 was successful in preventing the recurrence of C. diff infections in patients. 88% of the participants did not have another infection eight weeks after a single course of treatment, compared to 60% of those who received a placebo. Six months later, 79% of those who took SER-109 remained free of re-infections, while only 53% getting placebos did.
C. diff infections spread easily in hospitals and their treatment is challenging, with many of the bacteria now resistant to antibiotics. The US Centers for Disease Control and Prevention (CDC) estimates that about one in six people who have had a C. difficile infection will have another one in two to eight weeks. Between 15,000 and 16,000 people die from C. diff annually in the US.
How it used to be
Before this, efforts to change the microbiome drug to address specific medical conditions mostly involved fecal transplants, which are tricky to develop and administer. Fecal matter is collected from healthy donors and treated in a series of purifying and sterilizing steps to ensure that only the desired populations of bacteria are transferred from one person to another, and it’s then given rectally.
Seres’ product eliminates rectal administration and could be a game-changer in the field. The approval opens the door to a new class of treatments for the microbiome drug that is easy to take and effective. Shaff says C. diff infections are only the start, and the company is already testing another combination of bacteria, SER-155, that seems to prevent deadly infections in people who receive organ transplants.
Eric Shaff, president, and CEO of Seres Therapeutics, believes that the FDA’s approval of SER-109 is a “tipping point for the field” of microbiome drug research. If the data on SER-109 and SER-155 continue to show benefits in adjusting the gut microbiome drug, then other infections might also be targeted.
The new treatment has been a long time in development. Seres Therapeutics had positive early results with the drug in 2016, but the second phase of testing, completed in 2021, was disappointing, showing that most people did not benefit from the treatment. After adjusting the dose and the way that patients were tested for C. diff, the final phase of human testing produced more encouraging results.