Xenon Pharmaceuticals (XENE) Provides Update on Additional Positive Data from the XEN1101 Program

Xenon Pharmaceuticals Inc. (Nasdaq: XENE), a neurology-focused biopharmaceutical company, today announced new, compelling efficacy data supporting the late-stage, Phase 3 development of XEN1101.

Mr. Ian Mortimer, Xenon’s President and Chief Executive Officer, stated, “We have generated additional efficacy data from sub-group analyses of our Phase 2b X-TOLE trial, which further support our Phase 3 development plans for XEN1101. A ‘time course to efficacy’ analysis shows that all doses of XEN1101 rapidly reduced the frequency of focal onset seizures within one week compared to placebo, suggesting that XEN1101 may offer a compelling and differentiated option for patients seeking to quickly reduce seizure frequency.”

Dr. Christopher Kenney, Xenon’s Chief Medical Officer, commented, “Based on these Phase 2b efficacy data, we are including the secondary endpoint of ‘Week 1 median percent change in seizure frequency’ within the statistical hierarchy of the Phase 3 focal onset seizure trials to build upon the differentiated profile of XEN1101. Additionally, within our analysis of the open label extension (OLE) population, we are seeing seizure frequency continuing to improve after the double-blind period with patients experiencing increased periods of seizure freedom. At the request of study investigators and based on the potential to continue to provide significant benefit to patients, we are extending the X-TOLE OLE from three to five years.”

Summary of New XEN1101 Data from Phase 2b X-TOLE and Ongoing OLE

• XEN1101 rapidly reduced focal onset seizure (FOS) frequency within one week for all doses compared with placebo. At Week 1, the median percent reduction in monthly focal onset seizure frequency was 55.4% in the 25 mg group (p<0.001), 41.5% in the 20 mg group (p=0.039), and 39.1% in the 10 mg group (p=0.002) compared to 20.2% in the placebo group. Based on the strength of data from this time course to efficacy analysis, a key secondary endpoint in the Phase 3 trials will include the median percent change of weekly FOS at Week 1.
• Approximately 96% of patients who completed the randomized phase of the XEN1101 Phase 2b X-TOLE study rolled over into the OLE, with 231, 193 and 54 patients having now been treated in the trial for at least 6 months, 12 months, and 2 years, respectively.
• Seizure frequency continued to improve for the OLE population during the first month after the 8-week double-blind period (DBP), suggesting that the efficacy signal has the potential to persist, and may potentially improve, in the planned 12-week DBP of the XEN1101 Phase 3 trials.
• Subjects remaining in the X-TOLE OLE for at least 3 months and 12 months experienced a greater than 70% and 80% reduction, respectively, in median monthly seizure frequency when compared to the DBP baseline.
• 54 (19.6%) and 26 (9.5%) of subjects in the OLE experienced a ≥6 and a ≥12 consecutive months of seizure freedom, respectively. This analysis uses the denominator of all patients transitioning to the OLE (N=275) even though not all patients have been in the study long enough to be treated for at least 12 months.
• XEN1101 continues to be generally well-tolerated in the OLE with adverse events (AEs) consistent with other anti-seizure medicines and the X-TOLE double-blind period. There have been no treatment emergent AEs of pigmentary abnormalities reported during the DBP or OLE. As was the case in the DBP, two AEs of urinary retention occurred in the OLE possibly related to study drug; both patients continued in the study without requiring intervention. Weight changes in the OLE were 1.4 ± 4.5 kg at the 6-month visit and 0.9 ± 6.2 kg at the 12-month visit.

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