Soleno Therapeutics, a Neurocrine Biosciences (Nasdaq: NBIX) company, today announced late-breaking data at ENDO 2026 showing that resuming treatment with VYKAT^® XR (diazoxide choline) extended-release tablets for two years after a 16-week randomized withdrawal period was associated with durable improvements in hyperphagia and behavioral symptoms characteristic of Prader-Willi syndrome (PWS).

"These compelling data further reinforce our confidence in VYKAT XR as a safe and effective long-term treatment for hyperphagia in individuals four years of age and older living with Prader-Willi syndrome," said Sanjay Keswani, M.D., Chief Medical Officer, Neurocrine Biosciences. "Individuals who resumed treatment following the randomized withdrawal period achieved durable improvements in hyperphagia and other PWS-related behaviors. This completes the presentation of data from our comprehensive Phase 3 development program and further confirms the long-term benefit of VYKAT XR for people living with PWS."

The VYKAT XR Phase 3 development program was conducted sequentially, including:

• A 13-week randomized, double-blind, parallel-arm study (C601) comparing VYKAT XR to placebo in participants four years of age and older with hyperphagia associated with genetically confirmed PWS
• An open-label extension study (C602 OLE) over approximately two to four years
• A 16-week, double-blind, placebo-controlled randomized withdrawal period
• An open-label long-term extension study (C614)

Study C614, the open-label long-term extension study, enrolled 77 participants (mean age, 15.3 years; 55.8% female). The study assessed whether participants who had received placebo during the randomized withdrawal period could regain treatment benefit after restarting VYKAT XR, and whether participants who remained on continuous VYKAT XR maintained benefit over time.

Hyperphagia was assessed using the Hyperphagia Questionnaire for Clinical Trials (HQ-CT) and PWS-related behaviors were assessed using the PWS Profile questionnaire (PWSP). BMI and long-term safety were also assessed. Study results included:

• Participants who restarted VYKAT XR after placebo during the randomized withdrawal showed marked improvements in HQ-CT Total Score by Week 13 (mean [SD], -4.5 [6.3]), with further improvement observed at Week 26 and at two years (-5.5 [7.1] and -6.3 [8.4], respectively).
• Participants who remained on VYKAT XR continuously showed smaller improvements (-2.7 [6.9]) at Week 13 that were sustained at Week 26 and at two years (-3.3 [5.7] and -3.1 [8.0], respectively), underscoring the benefit of uninterrupted therapy.
• Improvements across all six PWSP behavioral domains were observed at two years in participants who restarted VYKAT XR, and BMI remained relatively stable throughout.

These data show that participants who resumed VYKAT XR after randomized withdrawal experienced recovery of treatment benefit, while those who continued therapy maintained durable improvements in hyperphagia and other PWS-related behaviors. Study results were presented as, "Efficacy and Safety of Resuming Diazoxide Choline Extended-Release (DCCR) after 16-week Randomized Withdrawal in Prader-Willi Syndrome (Study C614)," which was authored by Jennifer L. Miller, M.D., University of Florida, Gainesville.

Additional presentations at ENDO 2026:

VYKAT XR Outcomes Compared to Real-World Data from PATH for PWS Natural History Study (PATH):

Long-Term Reductions in Hyperphagia: HQ-CT Analysis
A poster presentation led by Evelien F. Gevers, M.D., Ph.D., Barts Health NHS Trust/Queen Mary University of London, reported three-year data comparing 125 VYKAT XR-treated participants from Studies C601 and C602-OLE to 229 natural history controls from the PATH for PWS Natural History Study. VYKAT XR demonstrated statistically significant and sustained improvements in hyperphagia compared with the PATH cohort at all evaluated time points (p<0.0001), with treatment differences of 6.2 points at Year 1, 6.5 points at Year 2, and 6.2 points at Year 3 on the HQ-CT Total Score.

Long-Term Behavioral Improvements: PWSP Analysis
A second presentation by Dr. Gevers reported PWSP data comparing 105 VYKAT XR-treated participants to 182 PATH controls over three years. Statistically significant improvements favoring VYKAT XR compared with the PATH cohort were observed across all six behavioral domains at Year 1 (p<0.001), Year 2 (p<0.01), and Year 3 (p<0.001). At Year 3, VYKAT XR demonstrated consistent improvements across all assessed behavioral domains versus the PATH cohort, with adjusted mean differences favoring VYKAT XR of -2.5 in anxiety, -2.4 in rigidity/irritability, -2.3 in compulsivity, -2.1 in aggressive behaviors, -1.5 in disordered thinking, and -1.1 in depression.