Identification and characterization of an optimized PI3Kg-derived peptide for the treatment of airway obstructive diseases

Cystic fibrosis (CF), the most common genetic disease among Caucasians, is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene encoding a cAMP-dependent chloride transporter expressed in secretory epithelia. CFTR dysfunction occurs in several obstructive airway disorders and results in defective mucociliary clearance, airway mucus thickening and chronic inflammation, ultimately leading to respiratory failure. Recently, the approval of CFTR-modulating drugs aimed at rescuing the molecular defect of the mutant protein revolutionized CF therapy, but limited efficacy and high costs constitute major drawbacks. Previous studies from our group demonstrated that the phosphoinositide 3-kinase γ (PI3Kγ) exhibits a scaffold function promoting the activation of cAMP-degrading phosphodiesterases through their protein kinase A (PKA)-mediated phosphorylation, and that inhibition of this anchoring activity through a PI3Kγ-derived mimetic peptide (PI3Kγ-MP) induces CFTR activation by enhancing cAMP levels in the lungs. Since thick mucus and proteolytic enzymes represent key barriers to peptide-based drug efficacy in obstructive pulmonary disorders, here we screened a new library of peptides derived from the PI3Kγ-MP lacking a predicted degradation site. By assessing cAMP increases, we identified and further optimized a candidate lead exhibiting higher potency and resistance to enzymatic digestion in vitro, while maintaining selectivity for the PI3Kγ-PKA complex. In mice, intratracheal administration of the optimized peptide locally raised cAMP concentrations, while PAMPA assays showed improved phospholipid bilayer penetration ability compared to the parent molecule. Finally, the candidate lead exhibited increased stability to sputum from CF and bronchiectasis patients, designating this new molecule as a valid candidate for the treatment of obstructive respiratory diseases.