Sionna Therapeutics is shelving its highly anticipated cystic fibrosis drug candidate, SION-719, after it failed to meet the key endpoint in a proof-of-concept trial.
The biotechnology company said Monday that SION-719 missed the mark in a Phase 2a trial. Adding the drug to standard-of-care therapy failed to yield a meaningful reduction in sweat chloride levels -- a key marker of treatment success -- and instead produced changes that were statistically insignificant.
Furthermore, the drugmaker cited "potential confounders" that may have clouded the trial data, including higher-than-expected variability in individual sweat chloride levels and inconsistent drug exposure between groups.
Shares cratered 92% to $4.08 on Monday, putting Sionna on pace for its largest same-day percentage drop and lowest close on record, according to Dow Jones Market Data.
Sionna was developing SION-719 as an add-on to Vertex Pharmaceuticals' market-leading treatment, Trikafta. The biotech noted that SION-719 was generally well-tolerated in combination with Trikafta over 14 days with no serious side effects -- however, safety alone isn't enough without efficacy.
Following the trial miss, Sionna won't advance SION-719 as a standard-of-care add-on in its current form. CEO Mike Cloonan called the results "unexpected" and disappointing, adding that the company is continuing to evaluate the data to determine next steps.
Sionna spun out of Sanofi in 2019, leveraging science from the biotech's Genzyme unit to develop treatments for cystic fibrosis. Trial outcomes often dictate long-term viability for smaller biotechs, so heavily reliance on a single pipeline candidate leaves them vulnerable. As Sionna has several other assets in its pipeline, the latest trial miss isn't a death sentence.
Still, the setback puts the company on the defensive, forcing it to manage its runway closely. Sionna noted Monday that it ended the second quarter with approximately $268.3 million in cash, cash equivalents, and marketable securities, adding that it intends to "take actions to preserve capital" while evaluating its next steps.
Conversely, Sionna's setback is welcome news for Vertex. Cantor Fitzgerald analysts noted Monday that the trial failure eliminates a persistent overhang on Vertex shares, with RBC Capital Markets framing the outcome as a "clearing event" for the stock.