Xenon Pharmaceuticals Inc. (NASDAQ:XENE) had a busy Friday. The neuroscience-focused biopharmaceutical company submitted a New Drug Application to the U.S. Food and Drug Administration for its investigational drug azetukalner to treat focal seizures. At the same time, it announced a voluntary pause on new patient enrollment in its ongoing depression clinical studies following reports of neuropsychiatric adverse events.
Two headlines, one stock, and a market that decided to focus on the scarier one.
Positive Data Drives FDA Submission
The regulatory filing leans on clinical data from the Phase 2b X-TOLE and the Phase 3 X-TOLE2 studies. Across both trials, treatment with all four evaluated doses of azetukalner demonstrated a statistically significant reduction in monthly seizure frequency from baseline compared to placebo.
Precautionary Pause In Psychiatry Trials
In a parallel development, Xenon temporarily halted new participant recruitment in ongoing studies for major depressive disorder and bipolar depression. The company implemented this voluntary, precautionary measure in consultation with its Data Safety Monitoring Board to analyze observed neuropsychiatric adverse events and evaluate potential dosing modifications.
While these adverse events align with azetukalner's known safety profile and mechanism, researchers did not observe them in the earlier Phase 2 X-NOVA major depressive disorder study. This enrollment pause does not impact any ongoing epilepsy studies.
Updated Timeline For X-NOVA2
Recruitment in the X-NOVA2 study reached approximately 80% of its 450-patient target, providing sufficient statistical power to evaluate the HAM-D17 primary endpoint. Xenon plans to complete six-week dosing for currently enrolled participants and unblind the data, shifting expected topline trial results to the first quarter of 2027.
Wall Street Reaction
William Blair on Friday wrote that the stock reaction is overblown given similar incidence rates of psychosis have been reported on the label of blockbuster antidepressants like Zoloft and Wellbutrin, but no black box warning has been issued.
Analyst Myles Minter also notes that Potiga (ezogabine), a less selective Kv7 potentiator, had a psychosis incidence of around 1% but was still approved as an antiseizure medication with only a segment in the warnings and precautions section of the label on this safety aspect.
Analyst Minter further added that the pause naturally raises concerns about azetukalner's profile in focal onset epilepsy (FOS). However, any read-through should be limited, as psychosis events in FOS were already known as part of the risk/benefit profile in the indication.
William Blair notes that the 42.7% placebo-normalized improvement in median monthly seizure frequency reported in X-TOLE2 is a truly remarkable result in a highly refractory population, and that the single pill, no titration, no drug-drug interaction, and daily dose paradigm will truly turn the impressive profile of azetukalner into a blockbuster product in FOS.
XENE Price Action: Xenon Pharmaceuticals shares were down 29.22% to $40.59 at the time of publication on Friday, according to market data.
