IGF-1R Inhibitor IBI311 for the Treatment of Active Thyroid Eye Disease in Chinese Patients

Importance: Thyroid eye disease (TED), a disfiguring and potentially sight-threatening condition with racial phenotypic variations, currently has limited effective treatments. Insulin-like growth factor 1 receptor (IGF-1R) inhibitors therapy has emerged as a promising treatment option, although it remains less accessible and lacks substantial evidence in Asian patients. Objective: To assess efficacy and safety of IBI311, an IGF-1R inhibitor with an identical amino acid sequence to teprotumumab but a different dosage form, in Chinese patients with active TED. Design, Setting, and Participants: This was a randomized, double-masked, placebo-controlled, multicenter, 24-week phase 3 trial with recruitment conducted across 20 tertiary hospitals in China from May to December 2023. Chinese participants with active (clinical activity score [CAS] ≥3) moderate to severe TED were included after excluding individuals with active TED onset over 270 days; sight-threatening TED; or history of steroid pulse therapy, radiotherapy, or surgery for TED. Interventions: Eighty-two participants were randomized 2:1 to receive intravenous infusions of either IBI311 or placebo once every 3 weeks for 21 weeks with follow-up through week 24. Main Outcomes and Measures: The primary outcome was the proptosis response rate (proptosis reduction ≥2 mm) in the study eye at week 24. Results: Participants (mean [SD] age, 39.6 [10.9] years; 56 [68.3%] women) were randomized to receive IBI311 (n = 54) or placebo (n = 28). At week 24, 45 of 52 participants receiving IBI311 (85.8%) and 1 of 26 receiving placebo (3.8%) had proptosis response (difference, 81.9 percentage points; 95% CI, 69.8 to 93.9; P < .001). The secondary outcomes included overall response (proptosis reduction ≥2 mm and CAS reduction ≥2, 80.2% vs 3.6%; difference, 76.3 percentage points; 95% CI, 63.3 to 89.4), CAS of 0 or 1 (83.5% vs 16.6%; difference, 67.1 percentage points; 95% CI, 49.4 to 84.8), least-squares mean (SE) change from baseline in proptosis (-2.85 [0.18] mm vs -0.02 [0.24] mm; difference, -2.83 mm; 95% CI, -3.39 mm to -2.27 mm) in the study eye (all P < .001), and diplopia response (diplopia reduction ≥1 grade, 66.0% vs 53.3%; P = .46). All adverse events of interest (infusion reaction, hearing impairment, hyperglycemia, muscle spasm, and nausea or diarrhea) were mild or moderate in severity. No serious adverse event or death occurred in the IBI311 group. Conclusions and Relevance: In this phase 3 randomized clinical trial, IBI311 demonstrated better and clinically relevant outcomes in proptosis and CAS than placebo with no new safety issues not identified in previous clinical trials. The results suggest that IBI311 represents a viable treatment option for Chinese patients with active TED. Trial Registration: ClinicalTrials.gov Identifier: NCT05795621.