Targeting G542X CFTR nonsense alleles with ELX-02 restores CFTR function in human-derived intestinal organoids

BACKGROUND: Promoting full-length protein production is a requisite step to address some of the remaining unmet medical need for those with Cystic Fibrosis (CF) nonsense alleles. ELX-02 promotes read-through of mRNA transcripts bearing nonsense mutations, including the most common CF nonsense allele G542X, in several different preclinical models including human bronchial epithelial cells. Here we evaluate ELX-02 mediated read-through using the CFTR-dependent Forskolin-induced swelling (FIS) assay across a selection of G542X genotype patient derived organoids (PDOs). METHODS: CFTR functional restoration was evaluated in ELX-02 treated G542X homozygous and heterozygous PDOs in the CFTR-dependent FIS assay. CFTR mRNA abundance and integrity were evaluated by qPCR and Nanostring analysis while PDO protein was detected by capillary based size-exclusion chromatography. RESULTS: PDOs homozygous for G542X or heterozygous with a second minimally functional allele had significantly increased CFTR activity with ELX-02 in a dose-dependent fashion across a variety of forskolin induction concentrations. The functional increases are similar to those obtained with tezacaftor/ivacaftor in F508del homozygous PDOs. Increased CFTR C- and B-band protein was observed in accordance with increased function. In addition, ELX-02 treatment of a G542X/G542X PDO results in a 5-fold increase in CFTR mRNA compared with vehicle treated, resulting in normalization of CFTR mRNA as measured via Nanostring. CONCLUSIONS: These data with ELX-02 in PDOs are consistent with previous G542X model evaluations. These results also support the on-going clinical evaluation of ELX-02 as a read-through agent for CF caused by the G542X allele.