Proteostasis Therapeutics Inc. said the combination of its experimental drugs PTI-428, PTI-801 and PTI-808 improved certain cystic fibrosis patients' condition in a mid-stage study.
Cystic fibrosis is a hereditary disease that affects the lungs and digestive system. The body produces thick and sticky mucus that can clog the lungs and obstruct the pancreas.
A person with cystic fibrosis inherits two mutated copies of the cystic fibrosis transmembrane conductance regulator gene. These mutations can either be homozygous, the same, or heterozygous, different mutations. The most common mutation is delta F508, accounting for about 70% of all mutations.
The company's therapies, called cystic fibrosis transmembrane conductance modulators, correct the malfunctioning proteins causing the genetic disease.
A total of 28 F508del homozygous and 40 F508del heterozygous subjects were enrolled into the doublet, triplet or placebo arms of the phase 2 study.
The global 28-day study evaluated the effectiveness of the duo of PTI-801 and PTI-808, known as posenacaftor and dirocaftor respectively, as well as in a triple combination with PTI-428, known as nesolicaftor.
According to the company, 80% of the patients' disease was too serious to make them eligible for trials of currently approved modulators.
The study found nesolicaftor's addition to the duo increased the combination's effectiveness. Homozygous patients receiving the triple combination experienced a mean absolute improvement of 8 percentage points in lung function compared to placebo after 28 days of treatment. Improvements in lung function were the highest in high disease burden subgroups.
Mean changes in lung function were not statistically significant in the heterozygous population.
Based on the results, the company intends to launch a global, late-stage trial dubbed MORE and a personalized medicine-based study called Choices, both expected to start in 2020.
The U.S. Food and Drug Administration gave the Boston, Mass.-based company's triple combination therapy a fast-track designation in April 2018, and a breakthrough-therapy designation in March 2018, while the European Commission granted PTI-428 an orphan drug designation in June.