Analysts are keeping the faith in Ultragenyx’s brittle bone disease medicines despite the monoclonal antibody failing to score an early outright win in an ongoing phase 3 trial.
Ultragenyx and Mereo BioPharma are evaluating UX143, also known as setrusumab, in the phase 3 Orbit study of 159 pediatric and young patients with osteogenesis imperfecta. The study’s data monitoring committee informed the companies that setrusumab “demonstrates an acceptable safety profile and the company should continue the study to the final analysis,” Ultragenyx explained in a July 9 post-market release.
“Based on the feedback we hear from investigators and families who participated in the studies, we are confident that increasing bone mass leads to stronger bone, less fractures, and improved physical abilities,” Ultragenyx CEO Emil Kakkis, M.D., Ph.D., said in the release. “While we had hoped to be able to stop the study early, we look forward to having results from [Orbit] around the end of this year.”
William Blair analysts said the biopharma’s statement implied that the second interim analysis of the trial had not met the efficacy threshold for ending the study early.
Investors appeared to infer the same meaning, sending Ultragenyx’s stock down 23% to $31.96 in pre-market trading Thursday from a Wednesday closing price of $41.44.
But this market reaction was “severely overdone,” according to William Blair analysts in their same July 10 note.
“While it is unfortunate that the Orbit study did not achieve its statistical significance threshold at the second interim analysis, we … still believe there is a high likelihood that the final analysis in the fourth quarter will be positive given there will be a longer duration of follow-up and a lower threshold for statistical significance,” the analysts added.
Two years ago, phase 2 data from setrusumab showed that the antibody reduced bone fractures by 67% among 24 patients who had at least six months of follow-up.
Ultragenyx paid Mereo $50 million upfront for the ex-Europe rights to the therapy, which inhibits a negative regulator of bone formation called sclerostin, back in 2020.