PTC Therapeutics, a New Jersey-based drug company focused on rare diseases, said Wednesday that one of its more advanced experimental medicines succeeded in a late-stage clinical trial meant to support an approval application.
PTC’s medicine is designed to treat phenylketonuria, or “PKU,” an uncommon genetic disorder in which the body can’t properly metabolize an amino acid known as phenylalanine. PKU patients experience a buildup of this amino acid that, without intervention, can lead to intellectual disability, developmental delays and a range of health problems.
The trial results released Wednesday show that patients who were given PTC’s medicine, called sepiapterin, as opposed to a placebo experienced significantly greater reductions in the amount of phenylalanine in their blood. Across the 98 participants who made up the “primary analysis population,” those in the drug arm had an average reduction of 63% during the study’s six-week treatment period, whereas those in the control arm had a 1% increase.
These results “bring us one step closer to providing a therapy that could deliver meaningful benefit to PKU patients," Matthew Klein, PTC’s chief executive, said in a statement. “We look forward to meeting with regulatory authorities to discuss the path to approval."
While estimates vary, PKU is thought to affect roughly 1 in every 15,000 newborns in the U.S. Despite this limited population, the disease has attracted interest from drugmakers both large and small. Homology Medicines, for example, is a Massachusetts-based biotechnology company with two kinds of genetic therapies for PKU in clinical testing. That research caught the attention of Pfizer, which, in 2020, made a $60 million equity investment in Homology.
BioMarin Pharmaceutical is also working on a gene therapy for PKU, though a key clinical trial evaluating it has been delayed due to safety concerns. The company does already have two marketed treatments for the disease, Kuvan and Palynziq, which respectively won approval from the Food and Drug Administration in 2007 and 2018.
Should sepiapterin also secure approval, it would join PTC’s slate of half a dozen commercial products. Last year, the company recorded $535 million in net product revenue.
Danielle Brill, an analyst at the investment firm Raymond James, wrote in a note to clients that PTC’s drug has now demonstrated “an arguably advantageous efficacy profile” compared to Kuvan, its “key competitor.” However, Brill cautioned that her team still thinks it’s difficult to draw definitive conclusions without a head-to-head study of the two drugs.
In his own note, RBC Capital Markets analyst Brian Abrahams wrote that his team believed doctors would start switching their PKU patients onto sepiapterin if PTC’s trial showed the drug could lower phenylalanine levels by more than 40% to 50%.
PTC “met that bar, in our view, with clear and highly statistically significant” results, the analyst wrote, adding that his team expects sepiapterin to capture around one-third of the 4,800 or so U.S. patients who appear to respond to drugs like it. Abrahams estimates that PTC's therapy could generate $400 million or more in annual sales at its peak.
PTC said sepiapterin was well-tolerated and that no serious adverse events were observed. Adverse events occurred at similar frequencies between the drug and placebo arms, according to PTC, and the most common were headache and diarrhea.