ELX-02 Restores CFTR Activity in Organoids With G542X Mutations, Study Finds

ELX-02 restored the levels and function of CFTR — the defective protein in CF — in “mini-organs,” or organoids, derived from patients carrying the most common CF-causing nonsense mutation, a study shows.

“ELX-02 increased CFTR activity in a dose-dependent fashion,” with these functional increases being “similar to those obtained with tezacaftor/ivacaftor [Symdeko]” in organoids carrying the most common CF-causing non-nonsense mutation, Matthew Goddeeris, PhD, the vice president of research at Eloxx Pharmaceuticals, the investigational therapy’s developer, said in a press release.

These findings add to the large body of preclinical evidence highlighting ELX-02’s potential for treating CF caused by nonsense mutations — those that result in a shorter, non-functional protein and that are present in almost 13% of all CF patients.

“These data support our current Phase 2 clinical trial[s] for ELX-02 in cystic fibrosis patients with G542X nonsense [mutations], for whom there are few, if any, treatment options available,” Goddeeris said, noting that top-line results are expected by June.

The study, “Targeting G542X CFTR Nonsense Alleles With ELX-02 Restores CFTR Function in Human-Derived Intestinal Organoids” was published in the Journal of Cystic Fibrosis.

Nonsense mutations in CFTR, the gene mutated in CF, cause an early stop signal in CFTR’s messenger RNA (mRNA) — the molecule derived from DNA and used as a template for protein production — resulting in a shorter, non-functional CFTR protein.

Given that CFTR is involved in water balance by regulating the transport of ions in and out of cells, its lack impairs water and ion transport in cells of the lungs, digestive tract, and reproductive system, affecting how they work.

ELX-02 was designed to target these CFTR nonsense mutations by helping the ribosome — the cells’ protein-building machinery — ignore the mRNA’s premature stop signal (a process called read-through) to generate a full-length, functional CFTR protein.

The therapy was previously shown to effectively restore CFTR activity in several cellular and mouse models of CF caused by nonsense mutations. However, there is limited data of its benefits in patient-derived cells carrying the most common CF-causing nonsense mutation, G542X.

Eloxx researchers, along with colleagues at Hubrecht Organoid Technology in the Netherlands, evaluated the effects of ELX-02 in organoids derived from patients carrying a G542X mutation in one of the two CFTR gene copies (called heterozygous mutations) or in both copies (homozygous mutations).

These patient-derived organoids are 3D “mini-organs” that better mimic diseased tissue, and are considered of value in predicting a therapy’s clinical benefit. The inclusion of cells from patients with heterozygous and homozygous mutations better reflects the genetic diversity of the target patient population, the research team noted.

Data showed that ELX-02 treatment significantly increased the levels of CFTR’s mRNA by fivefold, and improved the molecule’s stability to prevent its degradation in both organoids.

This was accompanied by a raise in CFTR protein levels, which ranged from 1.5% to 5.2% of those found in an organoid derived from a healthy individual.

To assess the therapy’s functional effects, the researchers used a water-uptake swelling assay induced by forskolin, a CFTR activator. In the presence of a working CFTR protein, forskolin activates CFTR, resulting in water uptake and organoid swelling. No such swelling is observed in the absence of working CFTR.

This type of assay has shown potential to differentiate disease severity in CF patients, and to predict which patients may be likely responders to a particular therapy.

Results showed that ELX-02 restored CFTR function in a dose-dependent fashion in G542X homozygous organoids, and in those with a G542X heterozygous mutation and a non-nonsense mutation resulting in a minimally working CFTR protein.

Notably, the levels of CFTR function achieved with ELX-02 in these organoids were comparable to those attained when treating an organoid from a patient carrying a homozygous F508del mutation — the most common CF-causing mutation — with Symdeko (tezacaftor/ivacaftor combo).

Marketed by Vertex Pharmaceuticals, Symdeko is a CFTR modulator approved to treat CF patients carrying the F508del mutation.

“ELX-02 produces significant read-through of the G542X [mutation], leading to increased mRNA[,] protein and protein function across multiple G542X [patient-derived organoids],” the researchers wrote.

They also noted that these findings support the therapy’s clinical development for people with CF caused by G542X mutations, and that future studies are needed to evaluate ELX-02 across other CF-causing nonsense mutations.

ELX-02’s safety, pharmacokinetics (its movement into, through, and out of the body), and pharmacodynamics (its effects on the body) are currently being assessed in the Phase 2 EL-012 (NCT04135495) and EL-004 (NCT04126473) clinical trials, involving CF patients with at least one G542X mutation.