ORKAMBI-Mediated Rescue of Mucociliary Clearance in Cystic Fibrosis Primary Respiratory Cultures Is Enhanced by Arginine Uptake, Arginase Inhibition, and Promotion of Nitric Oxide Signaling to the Cystic Fibrosis Transmembrane Conductance Regulator Channel

ORKAMBI®, a combination of the corrector, lumacaftor, and the potentiator, ivacaftor, partially rescues the defective processing and anion channel activity conferred by the major Cystic Fibrosis causing mutation, F508del, in in vitro studies. Clinically, the improvement in lung function after ORKAMBI® treatment is modest and variable, prompting the search for complementary interventions. As our previous work identified a positive effect of arginine-dependent nitric oxide signaling on residual F508del-Cftr function in murine intestinal epithelium, we were prompted to determine if strategies aimed at increasing arginine would enhance F508del-CFTR channel activity in patient-derived airway epithelia. Now, we show that the addition of arginine together with inhibition of intracellular arginase activity increased cytosolic nitric oxide and enhanced the rescue effect of ORKAMBI® on F508del-CFTR mediated chloride conductance at the cell surface of patient-derived bronchial and nasal epithelial cultures. Interestingly, arginine addition plus arginase inhibition also enhanced ORKAMBI® mediated increases in ciliary beat frequency and mucociliary movement, two in vitro Cystic Fibrosis phenotypes that are downstream of the channel defect. This work suggests that strategies to manipulate arginine metabolism in combination with approved CFTR modulators may lead to better clinical outcomes. SIGNIFICANCE STATEMENT The limited efficacy of the Cystic Fibrosis therapy, ORKAMBI®, in improving patient health prompted the search for additional modulators of the CF causing mutant protein, called F508del-CFTR. We showed that the response to ORKAMBI® can be boosted using a small molecule, called CB1158, that is currently in clinical trials as a therapy for the treatment of solid tumours. CB1158 inhibits arginase activity in patients’ airway cells and boosts the ORKAMBI® response because it increases availability of a positive regulator, nitric oxide. These proof-of-concept studies show that compounds in clinical trials for diseases other than Cystic Fibrosis may be repurposed to augment the therapeutic efficacy of poorly effective CF-specific drugs.