PTI-428 is primarily used in the treatment of cystic fibrosis, a genetic disorder that affects the lungs and digestive system. It functions as a cystic fibrosis transmembrane conductance regulator (CFTR) amplifier, enhancing the production of CFTR protein. This is crucial because mutations in the CFTR gene lead to reduced or dysfunctional CFTR protein, causing the symptoms of cystic fibrosis. By increasing the amount of CFTR protein, PTI-428 helps improve the function of chloride channels in epithelial cells, which can lead to better mucus clearance from the lungs and improved overall lung function. It is often used in combination with other CFTR modulators to maximize therapeutic efficacy, offering a synergistic approach to managing the disease and improving the quality of life for patients with cystic fibrosis.