Regulatory Approval Recommended for Sepiapterin in PKU Treatment

Recent developments in the management of phenylketonuria (PKU) have led to a recommendation for the approval of Sepiapterin, an innovative treatment option for this rare genetic disorder. PKU is characterized by the inability to metabolize phenylalanine, an essential amino acid, due to a deficiency in the enzyme phenylalanine hydroxylase (PAH). This condition typically manifests when individuals consume protein-containing foods, such as breast milk or infant formula, with diagnosis commonly occurring during newborn screening.

Sepiapterin, marketed under the brand name Sephience(TM) by PTC Therapeutics International, is classified as an orphan drug. It will be available in powder form for oral administration, with dosages of 250 mg and 1000 mg. This compound serves as a precursor that is rapidly absorbed and converted into tetrahydrobiopterin (BH4) within cells. BH4 is a crucial coenzyme for PAH, which can enhance protein tolerance in PKU patients by lowering blood phenylalanine levels. Additionally, it acts as a chaperone, correcting the misfolding of PAH and improving the enzyme's stability and functionality. According to the manufacturer, this dual mechanism positions Sepiapterin as a suitable treatment for many individuals affected by PKU.

A Phase III clinical trial, known as APHENTIY, led by a research team at the German Center for Child and Adolescent Medicine at the University Medical Center Hamburg-Eppendorf, evaluated the efficacy and safety of Sepiapterin in approximately 150 participants across 13 countries. In the first part of the study, 114 patients, representing 73% of the cohort, responded positively to Sepiapterin, showing a reduction of at least 15% in blood phenylalanine levels compared to baseline. In the second part of the trial, 98 responders were randomized to receive either a placebo or Sepiapterin with escalating doses over six weeks (20, 40, and 60 mg/kg daily). Results demonstrated a significant drop in blood phenylalanine levels, with a 63% decrease in the Sepiapterin group compared to a mere 1% reduction observed in the placebo group.

The treatment was generally well tolerated, with mild gastrointestinal issues being the most frequently reported side effects in both groups. Other common adverse events included upper respiratory infections, headaches, low phenylalanine levels, and changes in stool color.

Researchers concluded that Sepiapterin presents a promising and well-tolerated oral therapy for patients with PKU, capable of effectively lowering blood phenylalanine levels across varying degrees of disease severity.