Proteostasis Therapeutics, Inc. announced that the first patient has been dosed in the Company's 28-day, Phase 2 study evaluating its proprietary cystic fibrosis transmembrane conductance regulator (CFTR) modulator combinations in F508del homozygous and heterozygous CF subjects. Initiation of the 28-day Phase 2 study follows the positive results of the 14-day Phase 1 clinical studies of PTI's proprietary doublet (PTI-808 and PTI-801) and triplet (PTI-808, PTI-801 and PTI-428) combinations. The previous studies demonstrated a favorable safety and tolerability profile for the combinations, as well as statistically significant improvement in predicted FEV1 (ppFEV1) and sweat chloride concentration that was superior to the current CFTR modulator standard of care for F508del homozygous patients. The ongoing Phase 2 trial will explore efficacy over a longer duration and in additional genotypes including subjects heterozygous for the F508del mutation with PTI's doublet and triplet combinations. Dose selection (600 mg of PTI-801 and 300 mg or PTI-808, with or without 10 mg PTI-428) was based on the totality of dose range finding data from approximately 250 CF subjects studied thus far. Proteostasis Phase 2, global, multicenter, randomized, placebo-controlled study is expected to enroll up to 30 F508del homozygous patients and up to 30 F508del heterozygous patients. Study endpoints include safety, changes in sweat chloride concentration and changes in ppFEV. Data from the study are expected in the first quarter of 2020.