Changes in cystic fibrosis transmembrane conductance regulator protein expression prior to and during elexacaftor-tezacaftor-ivacaftor therapy

Abstract

Background: Defects in expression, maturation or function of the epithelial membrane glycoprotein CFTR are causative for the progressive disease cystic fibrosis. Recently, molecular therapeutics that improve CFTR maturation and functional defects have been approved. We aimed to verify whether we could detect an improvement of CFTR protein expression and maturation by triple therapy with elexacaftor-tezacaftor-ivacaftor (ELX/TEZ/IVA).Methods: Rectal suction biopsies of 21 p.Phe508del homozygous or compound heterozygous CF patients obtained pre- and during treatment with ELX/TEZ/IVA were analyzed by CFTR Western blot that was optimized to distinguish CFTR glycoisoforms.Findings: CFTR western immunoblot analysis revealed that—compared to baseline—the levels of CFTR protein increased by at least twofold in eight out of 12 patients upon treatment with ELX/TEZ/IVA compared to baseline (p < 0.02). However, polydispersity of the mutant CFTR protein was lower than that of the fully glycosylated wild type CFTR Golgi isoform, indicating an incompletely glycosylated p.Phe508el CFTR protein isoform C* in patients with CF which persists after ELX/TEZ/IVA treatment.Interpretation: Treatment with ELX/TEZ/IVA increased protein expression by facilitating the posttranslational processing of mutant CFTR but apparently did not succeed in generating the polydisperse spectrum of N-linked oligosaccharides that is characteristic for the wild type CFTR band C glycoisoform. Our results caution that the lower amounts or immature glycosylation of the C* glycoisoform observed in patients’ biomaterial might not translate to fully restored function of mutant CFTR necessary for long-term provision of clinical benefit.

Organic Synthesis and Current Understanding of the Mechanisms of CFTR Modulator Drugs Ivacaftor, Tezacaftor, and Elexacaftor

“…Stanke and co-authors [ 128 ] investigated the effects on CFTR protein expression by the approved triple therapy in rectal biopsies from 21 PwCF p.Phe508del homozygous or compound heterozygous before and during treatment. It was observed that this therapy increased CFTR protein expression and maturation in the majority of samples from PwCF evaluated, which suggested that this combination facilitates the posttranslational processing of some mutant CFTR, although not to the fully-glycosylated levels of WT-CFTR [ 128 ].…”

Post-approval studies with the CFTR modulators Elexacaftor-Tezacaftor—Ivacaftor

“…CFTR Western blot analysis of intestinal epithelium of people with CF with one or two p.Phe508del alleles revealed that treatment with ELX/TEZ/IVA improves posttranslational processing and trafficking of Phe508del CFTR. However, a low-complexity Phe508del CFTR glycoisoform is produced that lacks the polydisperse spectrum of N-linked oligosaccharides of mature complex glycosylated wild type CFTR ( Stanke et al, 2023 ). Hence, triple therapy with ELX/TEZ/IVA generates and stabilizes a novel Phe508del CFTR glycoisoform that is distinct from both the wild type and mutant isoforms.…”

Qualitative and quantitative evaluation of computed tomography changes in adults with cystic fibrosis treated with elexacaftor-tezacaftor-ivacaftor: a retrospective observational study

“…ETI was approved in Europe in late August 2020. CFTR modulators partially restore CFTR protein function with clinical efficacy in terms of lung function, pulmonary exacerbations, nutritional status, quality of life ( Burgel et al, 2020 ; Nichols et al, 2022 ) and lung morphology ( Arnaud et al, 2021 ; Graeber et al, 2022a ; 2022b ; Schütz et al, 2023 ; Stanke et al, 2023 ).…”