Not content with lining up one potential rival to Amgen’s Tepezza, Viridian Therapeutics has scored a phase 3 win for another thyroid eye disease (TED) prospect. But the candidate’s inability to meet investors’ expectations has cast a shadow over the results.
Viridian evaluated the anti-IGF-1R antibody elegrobart in a late-stage study of 132 patients with TED. Patients received the injected treatment every four weeks or every eight weeks, or placebo.
The study’s primary endpoint was the proptosis responder rate (PRR)—the proportion of people who experienced at least a 2 mm reduction in bulging eye—among participants on the monthly dosing regimen at week 24. The study hit this endpoint, demonstrating a responder rate of 54% compared to 18% for the placebo cohort, according to a March 30 release.
Among the cohort who were dosed every eight weeks, the PRR was 63%.
On the secondary endpoint of the mean change in proptosis at baseline among the monthly dosing cohort, Viridian reported a mean reduction of 2.33 mm compared to 0.81 mm in the placebo group.
Meanwhile, Viridian reported the complete resolution of diplopia, the medical term for double vision, in 51% of patients on monthly elegrobart compared to 16% of their peers in the placebo group.
Viridian CEO Steve Mahoney touted this morning’s results as the “largest pivotal clinical trial conducted in active TED to date.”
“REVEAL-1 met its primary endpoint with high statistical significance,” Mahoney continued. “Elegrobart treatment drove robust proptosis responses in a treatment regimen comprised of as few as three subcutaneous doses.”
Amgen’s Tepezza is already on the market for TED, but Viridian is hoping that it can gain an edge because elegrobart is injected rather than administered as an intravenous infusion.
“Currently, the only marketed treatment for TED requires eight intravenous infusions and, despite low market penetration, annualized in 2025 to approximately $2 billion in revenues,” Mahoney said in the release. “We believe there is a significant opportunity with subcutaneous elegrobart in TED, including the potential to expand the market as an at-home and self-administered treatment option, if approved.”
Related
While Jefferies analysts acknowledged elegrobart hit the trial’s endpoint this morning, they predicted “fierce investor debate on commercial feasibility” based on the drug’s inability to beat Tepezza in a cross-trial comparison. At 36%, elegrobart’s placebo-adjusted PRR was below the 50% bar expected by investors and didn’t reach the 51% seen in a trial of Amgen’s blockbuster, the analysts pointed out in a March 30 note.
Elegrobart’s objective PRR of 54% also fell below the 70% seen by Viridian’s veligrotug, another Tepezza-rivalling anti-IGF-1R antibody. Elegrobart has the same binding domain as veligrotug and was engineered to have a longer half-life.
The FDA is due to decide on whether to approve veligrotug for TED by June 30.
This uncertainty of whether elegrobart can take on Tepezza in a fair fight was reflected in investors’ reaction this morning, with Viridian’s stock opening down 33% at $18.31 in pre-market trading Monday from a Friday closing price of $27.39.
Evercore ISI analysts were more forgiving, however, suggesting today’s readout “meets our base case,” although they acknowledged that the absolute PRR was on the “low end” of their expected range.
When it came to safety, Viridian said elegrobart was generally well-tolerated with “adverse events generally expected from the anti-IGF-1R class, the vast majority of which were mild.” Placebo-adjusted rates of hearing impairment—which has been tied to anti-IGFR drugs—were 11.3% in the monthly dosing cohort and 2.3% in those dosed every eight weeks.
The Massachusetts-based biotech is running another phase 3 trial of elegrobart in chronic TED, with a readout due in the second quarter. The company’s plan is to submit an approval filing for the drug with the FDA in the first quarter of next year.
