Ersodetug: pre-BLA dialogue after an unsuccessful pivotal analysis

October 5 recommendation: what changed

Rezolute announced that FDA recommended requesting a Type B pre-BLA meeting after reviewing additional sunRIZE material. This is a regulatory-discussion milestone, not an accepted application or approval. The company explicitly said FDA had not offered an opinion on approvability. The announcement changes the next procedural step while leaving the failed pivotal primary and key secondary tests intact. Public FDA meeting minutes or an approval review were not available; the account is the sponsor’s description of its correspondence. [1]

Insulin-receptor antagonism and PK–PD

Congenital hyperinsulinism exposes the brain to recurrent glucose deprivation because insulin secretion remains excessive for the prevailing glucose concentration. Some children remain hypoglycemic despite diazoxide, somatostatin analogues, nutritional support or pancreatic surgery. Ersodetug is a fully human antibody that binds an allosteric site on the insulin receptor, aiming to reduce overactivation downstream of insulin or related ligands such as IGF-2. It does not repair the pancreatic genetic defect or remove an insulin-secreting tumor. [2] [3] [4]

The dose-finding program described predictable dose-dependent exposure. sunRIZE used 5 or 10 mg/kg every two weeks for three loading doses, followed by every four weeks over the remainder of 24 weeks. Target concentrations were achieved across studied ages. Target engagement and favorable glucose biomarkers are pharmacological evidence, but they cannot by themselves establish the incremental clinical effect against placebo. Background feeding, monitoring intensity and rescue interventions can alter the measured event rate in both groups.

RIZE before sunRIZE

RIZE was an open-label Phase 2b study of 23 patients across four sequential dose cohorts, with eight weeks of treatment every other week. The May 2022 original tables report 22 in the pooled analysis, with additional measure-specific exclusions: one at 3 mg/kg did not meet minimum glucometer testing and one at 9 mg/kg stopped background treatment. There was no placebo arm. Dose cohorts are not randomized comparators, and the reported p values test within-group baseline changes rather than a controlled causal effect. [6]

Mean pooled CGM time below 70 mg/dL changed from 23.3% to 10.4%, and glucometer events from 15.5 to 7.5 per week. Baseline-to-endpoint changes must remain separate from later presentations using different analysis versions. The original report described no adverse drug reactions, study discontinuations or clinically significant hyperglycemia, but did not provide a complete all-cause TEAE/SAE table by dose. Encouraging uncontrolled changes supported Phase 3 testing; they cannot overrule the subsequent failed placebo comparison.

sunRIZE design and analysis population

sunRIZE enrolled 63 participants across more than a dozen countries, including the United States. The original baseline poster separates eight open-label infants and 55 double-blind participants; the 63 total is not a randomized-arm denominator. The original target was 56 (48 blinded plus eight open-label). Its pivotal comparison was a multicenter randomized double-blind placebo-controlled study of congenital HI with 24 weeks of pivotal treatment and an optional open-label extension. Eligibility in the sponsor’s design deck allowed ages three months to 45 years, persistent hypoglycemia and stable standard care or prior discontinuation for intolerance or failure. Actual enrolled ages were three months to 15 years, mean 3.4 years; 35% were younger than two. Eligibility and observed age range therefore are not interchangeable. [2] [4] [7]

The primary endpoint was change in average weekly self-monitored blood glucose hypoglycemia events; the key secondary endpoint was CGM average daily percentage time in hypoglycemia at the end of pivotal treatment. Actual arm counts, analysis-set exclusions, complete missing-data rules and multiplicity sequence were not supplied in the topline announcement. A planned sample or nominal allocation ratio would not supply these missing denominators. The optional extension adds exposure and durability information but loses the original blinded placebo comparison.

The baseline poster specifies at least three weekly SMBG events below 70 mg/dL and at least 8% daily CGM time below that threshold over at least ten monitored screening days. In the pooled population, 40% used enteral feeding and 13% had previous pancreatectomy. Those baseline supports can modify observed glucose outcomes and need to be considered when interpreting self-monitoring behavior.

December 2025 results remain the pivotal record

At 10 mg/kg, weekly hypoglycemic events fell approximately 45%, versus approximately 40% with placebo; the between-group primary test was not significant. CGM time in hypoglycemia fell approximately 25% at 10 mg/kg while increasing approximately 5% with placebo, but the key secondary test also failed significance. These are relative changes from each group’s baseline, not percentage-point changes in the proportion of a day spent hypoglycemic. Baseline and end-of-treatment absolute arm values were not reported in this announcement. [1] [2] [3]

In March 2026 FDA encouraged submission of comprehensive datasets; in June the company supplied prespecified, post-hoc and sensitivity analyses. The October release discusses continuous CGM and extension experience spanning nine months to more than two years. Those analyses may inform regulatory judgment but remain distinct from the original confirmatory tests. Behavioral confounding of self-monitoring is the company’s explanation, not a proven reason that converts a negative primary result into a positive one.

Hypersensitivity and exposure limitations

Two participants experienced serious hypersensitivity reactions and stopped study drug early. The release does not identify the dose groups, safety denominator by arm or timing of these reactions. Describing the overall profile as favorable cannot erase these events. Hyperglycemia is mechanistically relevant when antagonizing insulin signaling, while infants also require attention to nutrition and growth. The retrieved material is insufficient to compare those risks quantitatively or to establish long-term safety from selected extension participants. [2]

Capital, management and the next decision

At June 30, 2026, the company reported $10.6 million of cash and equivalents and $97.2 million of marketable debt investments; fiscal-year R&D expense was $53.8 million. These dated balances are relevant to completing extensions, manufacturing and a possible submission, rather than a guarantee of runway under every regulatory scenario. Management must clarify what package FDA expects before a BLA can be considered complete. The separately running tumor-HI upLIFT study and its end-2026 guidance do not establish congenital-HI efficacy and are not merged into this event. [1] [5]

Sources / References

1. Rezolute · FDA recommendation · October 5, 2026
2. Rezolute · sunRIZE topline · December 11, 2025
3. Rezolute · Type B meeting · March 24, 2026
4. Rezolute · trial design and RIZE · September 2, 2025 SEC exhibit
5. Rezolute · fiscal 2026 results · September 24, 2026
6. Rezolute · original PES 2022 RIZE tables
7. Rezolute · original sunRIZE baseline poster · 2025