Theratyping of the Rare CFTR Genotype A559T in Rectal Organoids and Nasal Cells Reveals a Relevant Response to Elexacaftor (VX-445) and Tezacaftor (VX-661) Combination

Abstract

Despite the promising results of new CFTR targeting drugs designed for the recovery of F508del- and class III variants activity, none of them have been approved for individuals with selected rare mutations, because uncharacterized CFTR variants lack information associated with the ability of these compounds in recovering their molecular defects. Here we used both rectal organoids (colonoids) and primary nasal brushed cells (hNEC) derived from a CF patient homozygous for A559T (c.1675G>A) variant to evaluate the responsiveness of this pathogenic variant to available CFTR targeted drugs that include VX-770, VX-809, VX-661 and VX-661 combined with VX-445. A559T is a rare mutation, found in African-Americans people with CF (PwCF) with only 85 patients registered in the CFTR2 database. At present, there is no treatment approved by FDA (U.S. Food and Drug Administration) for this genotype. Short-circuit current (Isc) measurements indicate that A559T-CFTR presents a minimal function. The acute addition of VX-770 following CFTR activation by forskolin had no significant increment of baseline level of anion transport in both colonoids and nasal cells. However, the combined treatment, VX-661-VX-445, significantly increases the chloride secretion in A559T-colonoids monolayers and hNEC, reaching approximately 10% of WT-CFTR function. These results were confirmed by forskolin-induced swelling assay and by western blotting in rectal organoids. Overall, our data show a relevant response to VX-661-VX-445 in rectal organoids and hNEC with CFTR genotype A559T/A559T. This could provide a strong rationale for treating patients carrying this variant with VX-661-VX-445-VX-770 combination.

Proteostasis Landscapes of Selective versus Poorly Responsive CFTR Variants Reveals Structural Vulnerabilities to Correction

“…In stably expressing CF bronchial epithelial cells (CFBEs), variants L558S, A559E/T, and R560T failed to show any response to VX-661/445 combination treatment 17 . A559T only showed 10% WT function after treatment with VX-661/VX-445 in homozygous-derived rectal organoids 18 . Variants V520F, A559T, and Y569D failed to respond to temperature correction in HEK293T cells 16 .…”

“…Previously, research has focused little on these variants because of their low allele frequency (Supplemental Table S1). However, a few previous in vitro studies have also demonstrated no or mild response among these variants 9,[16][17][18][19] . Importantly, small molecules and stabilizing mutations had varying effects on different poor responders, indicating different capacities for correction.…”

One year of treatment with elexacaftor/tezacaftor/ivacaftor in patients with cystic fibrosis homozygous for the F508del mutation causes a significant increase in liver biochemical indexes

“…To date, both homozygous and heterozygous patients with the most frequent F508del mutation have become eligible for treatment. This process has been facilitated by in vitro and in ex vivo models, including organoids ( Kleinfelder et al, 2023 ) and nasal epithelial cells ( Di Lullo et al, 2017 ; Amato et al, 2019 ), that help to predict the responsivity to molecular drugs of each patient with CF. These models allowed for successful treatment of patients with either a rare ( Terlizzi et al, 2021a ) or single unknown CFTR mutation ( Terlizzi et al, 2021b ; Comegna et al, 2021 ).…”