Dive Brief:
- An experimental Duchenne muscular dystrophy gene therapy from Regenxbio has met its main objective in a pivotal trial, positioning the company to seek an accelerated regulatory clearance in the U.S.
- Three months after treatment with Regenxbio’s therapy, RGX-202, 28 of the 30 study participants receiving muscle biopsies produced at least 10% of normal levels of a diminutive protein, “microdystrophin,” believed to help Duchenne patients. That result hit the trial’s main goal and passed a key threshold needed to support an approval. Nine volunteers with at least one year of follow-up also demonstrated statistically significant improvements, from the study’s start, on multiple tests of motor function.
- Regenxbio did report two serious adverse events among treatment recipients — one case of heart inflammation and another of asymptomatic liver injury. Both were “easily managed and resolved within weeks” without further incident, and the average levels of liver inflammation markers in those who got RGX-202 didn’t surpass the “upper limit of normal.” Still, company shares fell by more than 35% as the safety findings “muddy the update,” wrote Leerink Partners’ analyst Mani Foroohar.
Dive Insight:
There is already one gene therapy available to treat Duchenne, a progressive and deadly neuromuscular condition with no cure. Yet that treatment, Sarepta Therapeutics’ Elevidys, was controversially approved after less-than-stellar results and has since been linked to potentially deadly liver complications. Use in the U.S. is now limited, and sales projections once in the billions were ratcheted down significantly.
Regenxbio has been hoping for better with RGX-202. Like Elevidys, the therapy is designed to produce microdystrophin, a tiny form of the muscular shock absorber Duchenne patients lack. But RGX-202 is packaged into a different type of microscopic virus and produces a larger version of that protein. It’s also accompanied by an alternate regimen of immune-suppressing drugs — a combination of distinctions the company has long believed would yield better results.
Earlier trial results hinted at such potential and, since then, the company aligned with the FDA on an abbreviated approval path. Notably, that plan didn’t involve the kind of active placebo comparator other Duchenne gene therapies have struggled to outperform, but instead expanded an existing single-arm study to test whether RGX-202 could boost microdystrophin levels to 10% of normal.
Regenxbio has now hit that mark. Microdysrophin expression averaged about 71% across all treatment recipients, and almost 42% in boys over 8 years of age who are already expected to have begun declining. The company has also drawn a connection between that expression and a statistical impact on disease trajectory, something other developers of similar gene therapies have had difficulty with.
Yet Regenxbio still faces questions about approval prospects. The deal it struck with regulators came before Elevidys’ safety struggles and when different leaders were running the FDA office that oversees gene therapies. Several rare disease drugmakers, including Regenxbio, have since been stunned by a surprise regulatory decision.
The ongoing FDA uncertainty has weighed down Regenxbio’s share price, as it “counterbalances” the potentially large market opportunity ahead for RGX-202, Leerink’s Foroohar wrote in April. And that was before commissioner Marty Makary’s resignation added to an already unusual level of turnover at the agency.
Regenxbio executives have said the company’s regulatory strategy is to show a differentiated safety profile from Elevidys. But the two serious adverse events reported, along with the concerns about the FDA’s viewpoint, render Regenxbio’s update “more mixed than we had hoped,” Foroohar wrote Thursday.
Regenxbio, for its part, is optimistic. It claimed the FDA is open to using microdystrophin expression as a “surrogate” marker if it correlates with the kind of impact on outcomes RGX-202 achieved. On a conference call with analysts, CEO Curran Simpson said the company intends to wait before filing an application given the FDA leadership transition underway, but is banking on an approval in 2027.
“We expect that the new leadership will have a mandate on rare disease flexibility,” Simpson said. “Those are the indications that we're hearing will be more uniformly adopted, and with that environment, we're in great shape with our data to push for accelerated approval.”
