Efficacy and safety of a synthetic biotic for treatment of phenylketonuria: a phase 2 clinical trial

Despite available treatment options, many patients with phenylketonuria (PKU) cannot achieve target plasma phenylalanine (Phe) levels ¹. We previously modified Escherichia coli Nissle 1917 to metabolize Phe in the gut after oral administration (SYNB1618) and designed a second strain (SYNB1934) with enhanced activity of phenylalanine ammonia lyase ^2,3. In a 14-day open-label dose-escalation study (Synpheny-1, NCT04534842), we test a primary endpoint of change from baseline in labeled Phe (D5-Phe AUC₀₋₂₄; D5-Phe area under the curve (AUC) over 24 hours after D5-Phe administration) in plasma after D5-Phe challenge in adult participants with screening Phe of greater than 600 µM. Secondary endpoints were the change from baseline in fasting plasma Phe and the incidence of treatment-emergent adverse events. A total of 20 participants (ten male and ten female) were enrolled and 15 completed the study treatment. Here, we show that both strains lower Phe levels in participants with PKU: D5-Phe AUC₀₋₂₄ was reduced by 43% from baseline with SYNB1934 and by 34% from baseline with SYNB1618. SYNB1934 led to a decrease in fasting plasma Phe of 40% (95% CI, −52, −24). There were no serious adverse events or infections. Four participants discontinued because of adverse events, and one withdrew during the baseline period. We show that synthetic biotics can metabolize Phe in the gut, lower post-prandial plasma Phe levels and lower fasting plasma Phe in patients with PKU.