Sionna Therapeutics (NASDAQ:SION) shares plunged 92% on Monday after the biotechnology company reported disappointing results from its Phase 2a proof-of-concept study of SION-719 in cystic fibrosis.
The PreciSION CF trial failed to achieve its key activity endpoint, which measured the reduction in sweat chloride when SION-719 was administered alongside the standard-of-care treatment Trikafta.
The study produced a mean placebo-adjusted change in sweat chloride of -1.0 mmol/L, with a p-value of 0.7. Following the result, Sionna said it does not intend to continue developing SION-719 as an add-on therapy to the existing standard of care.
Sionna investigates potential factors behind trial outcome
The company received the topline findings on Friday and is continuing to examine the data to better understand the results.
Sionna identified several potential confounding factors within the study, including greater-than-expected variability in individual sweat chloride measurements.
Researchers also observed differences in exposure to Trikafta between the periods when participants received SION-719 and placebo, creating another factor that could have influenced the findings.
Nevertheless, the failure to demonstrate the targeted activity represents a significant setback for the SION-719 programme and triggered the severe decline in Sionna Therapeutics shares.
SION-719 shows favourable safety profile
Although the trial missed its key activity endpoint, SION-719 was generally well tolerated when administered alongside Trikafta for 14 days.
Most treatment-emergent adverse events were classified as mild to moderate, while the study recorded no serious adverse events and no meaningful patterns of adverse events associated with liver function tests.
The safety findings were therefore relatively encouraging, but they were insufficient to offset investor disappointment surrounding the lack of demonstrated efficacy.
SION-451 combination study meets Phase 1 objectives
Alongside the SION-719 update, Sionna released results from a Phase 1 trial evaluating SION-451 in dual combinations with either SION-2222 or SION-109 in healthy participants.
The study successfully achieved its safety, tolerability and pharmacokinetic objectives.
Following the results, Sionna identified the combination of SION-451 and SION-2222 as its preferred dual therapy.
However, the company is now reviewing the next steps for the broader SION-451 development programme in light of the disappointing Phase 2a findings from SION-719.
Sionna moves to preserve cash after clinical setback
Sionna finished the second quarter with approximately $268.3 million in cash, cash equivalents and marketable securities, providing it with substantial financial resources as management reassesses its development strategy.
The company said it intends to take measures to preserve capital while determining the appropriate path forward for its clinical pipeline.
Investors reacted sharply to the uncertainty created by the failed SION-719 study, sending Sionna Therapeutics (NASDAQ:SION) shares down approximately 92%.
While the Phase 1 results for SION-451 combinations offered some positive clinical evidence and Sionna retains a sizeable cash position, the failure of SION-719 to demonstrate its targeted activity has significantly altered expectations for the company’s cystic fibrosis development strategy.