Proteostasis Therapeutics Inc., of Cambridge, Mass., disclosed in a midyear update data from phase I testing in healthy volunteers suggesting a dose-linear pharmacokinetic drug profile that supports once-daily dosing of PTI-428, a modulator of cystic fibrosis transmembrane conductance regulator (CFTR). Data from 24 subjects confirmed the expected and dose-dependent relationship between PTI-428 exposure and the magnitude of CFTR mRNA increase.