Genetic engineering of a strain of E. Coli has successfully passed safety protocols for the treatment of PKU.
Phenylketonuria (PKU) is a rare inherited disease that causes serious digestion malfunction. It is caused by bi-allelic mutations in the PAH gene, which prevents the conversion of phenylalanine (Phe) to tyrosine and thus leads to elevated blood Phe levels. The condition has been linked to severe neurological complications such as intellectual disability, behavioural issues, mental disorders and seizures.
Now, a recent multi-centre study has shown the successful genetic engineering of a strain of E. Coli Nissle 1917, designated SYNB1618, to treat the condition. The team achieved this through the insertion of genes encoding phenylalanine ammonia lyase and L-amino acid deaminase into the genome. This enabled bacterial consumption of Phe within the gastrointestinal tract.
Metabolism of Phe
Phe is available within the lumen of the gastrointestinal tract as a dietary derived amino acid and through entero-recirculation from digestive enzymes and other secreted proteins. E. Coli 1917 was engineered to allow it to metabolise Phe within the gut. SYNB1618 operates to convert Phe to trans-cinnamic acid (TCA), and the L-amino deaminase (LAAD) enzyme converts Phe to phenylpyruvate. These are both non-toxic metabolites in the gut.
The primary aim of these experiments was to observe the safety and patient tolerability of the engineered strain, as well as gain further insight into microbial kinetics. SYNB1618 was studied using healthy volunteers and PKU patients with high levels of blood Phe. The participants were randomised to receive single doses of SYNB1618 or placebo up to 3 times per day for up to 7 days. A tracer was also used to study exploratory pharmacodynamic effects.
The results deemed SYNB1618 safe and well tolerated, showing only some mild to moderate adverse effects. These were mostly gastrointestinal, and all participants cleared the bacteria within 4 days of the last dose. Furthermore, microbial kinetics assessed by qPCR of patient samples showed no evidence of colonisation. On top of this, a dose-responsive increase in strain-specific Phe metabolites in plasma and urine samples was observed. This proved the success of the genetically engineered bacterial strain in digestion of excess Phe in a dose-responsive manner within the human gut. Results also concluded that SYNB1618 was a safe oral treatment, available for use by patients of all ages and PAH genotypes.
Moreover, these results warrant further study of SYNB1618 in larger cohorts of PKU patients to evaluate the reduction of plasma Phe via bacterial metabolism. Nonetheless, this first in-human study demonstrates huge potential in the use of genetically engineered probiotics for the treatment of rare metabolic disorders.
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