Beyond Trikafta: new models to assess tissue dependent rescue of N1303K-CFTR

Abstract

Rationale: Respiratory status of people with Cystic Fibrosis (pwCF) carrying N1303K is improved by Elexacaftor/Tezacaftor/Ivacaftor (ETI) but, contrary to other mutations, the impact on sweat test results is limited.

Methods: To explore this discrepancy, we implemented new sweat gland and respiratory cell lines stably expressing Wild type (WT)-, F508del- and N1303K-CFTR. CFTR dependent chloride (Cl^-) and bicarbonate (HCO₃-) transport was measured by short circuit current in these new models and in primary Human Nasal Epithelial Cells (HNECs). CFTR expression was evaluated by Western blot.

Results: In the airway and the sweat gland cells expressing F508del-CFTR, ETI induced maturation of CFTR and increased Cl^- transport. In the respiratory cell lines and HNECs, N1303K-CFTR generated both immature and mature forms of CFTR. Correction by ETI increased CFTR amounts without promoting its maturation and improved Cl^- secretion. N1303K-CFTR channel activity was markedly increased by co-potentiation of IVA with Apigenin. In the sweat gland, N1303K-CFTR was expressed as a globally misfolded protein, non-rescuable by ETI. API treatment to 2 patients improved FEV1 without lowering sweat Cl- content.

Conclusion: N1303K-CFTR shows tissue specific correction and suboptimal response to ETI which can be improved by API.

Keywords: CF; CFTR (cystic fibrosis transmembrane conductance regulator); CFTR modulator; N1303K-CFTR; airway epithelium; cystic fibrosis; elexacaftor/tezacaftor/ivacaftor (ETI); sweat gland.