Sionna drops cystic fibrosis program after phase 2 study misses

Sionna Therapeutics said Monday that it will stop developing SION-719 as an add-on treatment for cystic fibrosis after the drug missed the objective set for a phase 2a study. The company is evaluating cost reductions and the next steps for its remaining programs.

The study enrolled 15 adults with two copies of the F508del mutation who were already taking Vertex Pharmaceuticals' Trikafta. SION-719 produced a placebo-adjusted reduction in sweat chloride of 1.0 mmol/L. The result was not statistically significant or clinically meaningful.

The study fell well short of its target

Sionna had said before the readout that a 10 mmol/L improvement in sweat chloride would support the program. Outside specialists cited by analysts had identified a smaller improvement of 5 to 7 mmol/L as potentially meaningful. The observed 1.0 mmol/L change did not reach either threshold.

The crossover study compared SION-719 with placebo on top of Trikafta. Sionna said variability in sweat chloride measurements and differences in Trikafta exposure may have affected the result, but it ended the add-on program without waiting for further analysis.

Sionna still has an earlier combination program

The company also reported phase 1 findings for combinations built around another NBD1 stabilizer, SION-451. Sionna selected SION-451 plus SION-2222 as its preferred dual combination based on drug exposure in healthy volunteers.

That program has not yet shown clinical benefit in people with cystic fibrosis. Management said it is reviewing the phase 2a findings and its translational assumptions before deciding how to proceed.

The failure strengthens Vertex's position

Vertex dominates the cystic fibrosis market through medicines including Trikafta. Sionna had attracted investors by proposing a different way to stabilize the defective CFTR protein and potentially improve on existing modulators.

Sionna shares lost about 92 percent by late Monday morning, while Vertex shares rose. The movements reflect investor expectations and do not provide evidence about future results from Sionna's remaining drug combinations.