Rezolute, Inc. (NASDAQ:RZLT) experienced a devastating market reaction on December 11, 2025, with shares plummeting 90% after the biotechnology company announced disappointing results from its Phase 3 sunRIZE clinical trial. The study, which evaluated the experimental therapy ersodetug in patients with congenital hyperinsulinism, failed to meet both its primary and key secondary endpoints.
The rare disease drug candidate, which had been granted FDA Breakthrough Therapy Designation, was unable to demonstrate statistically significant improvements over placebo in controlling hypoglycemia events in this ultra-rare pediatric genetic disorder.
Weak Trial Results Drive Nearly $900 Million in Market Cap Loss
The Phase 3 sunRIZE study enrolled 63 patients with congenital hyperinsulinism, a condition where the body produces excessive insulin, leading to severe episodes of low blood sugar that can cause brain damage if not properly managed.
While patients receiving the highest dose of ersodetug (10 mg/kg) showed an approximate 45% reduction in weekly hypoglycemia events, this result was not statistically significant when compared to the placebo group, which demonstrated a 40% improvement.
The key secondary endpoint measuring change in average daily percent time in hypoglycemia by continuous glucose monitoring also failed, showing a 25% reduction at the 10 mg/kg dose compared to a 5% increase in the placebo group, but again without statistical significance.
The market reaction was swift and severe. Rezolute’s stock closed at $10.94 on December 10, 2025, representing an 11.07% gain that day. However, pre-market trading on December 11 saw shares collapse to $1.22, down $9.72 or 88.85% as of 9:21 AM EST.
The company’s market capitalization, which stood at approximately $1.014 billion at the previous close, was decimated by the news. Chief Medical Officer Dr. Brian Roberts expressed disappointment with the results, particularly for patients and families living with congenital hyperinsulinism who urgently need new treatment options.
Safety Signals Emerge as Rezolute Plans FDA Discussions
Despite the efficacy disappointment, Rezolute reported that safety observations for ersodetug were generally favorable throughout the trial. However, two study participants experienced serious hypersensitivity reactions that led to early discontinuation of treatment.
The most common adverse event observed in treated participants was hypertrichosis (excessive hair growth), which was characterized as generally mild and self-limiting. Ersodetug is a monoclonal antibody therapy designed to block excessive insulin activity by targeting insulin receptors to stabilize blood sugar levels in patients with hyperinsulinism.
Rezolute plans to meet with the FDA under its existing Breakthrough Therapy Designation to discuss next steps for the ersodetug development program. The company maintains another Phase 3 clinical trial called upLIFT, which is evaluating ersodetug for tumor hyperinsulinism and remains ongoing with topline results expected in the second half of 2026.
Prior to this setback, analyst price targets for RZLT had ranged from $12.00 to $20.00, with an average target of $16.33, and the stock had shown remarkable year-to-date gains of over 123% before the trial announcement.