- A rare disease drug developed by Boston-based Stealth BioTherapeutics missed its goals in a late-stage study, sending shares in the biotech down by about two-thirds Friday and putting at risk a partnership signed in October with Alexion Pharmaceuticals.
- Treatment with Stealth's drug, a peptide called elamipretide, didn't appear to benefit patients with an inherited disease characterized by dysfunctional mitochondria, which cells rely on to produce energy. After eight months, participants in the Phase 3 study weren't able to walk significantly further, nor did they report substantially less fatigue.
- Elamipretide was the focus of a partnering deal Stealth negotiated in October with Alexion, which gained an exclusive option to co-develop and co-commercialize the drug following results from the Phase 3 trial.
Stealth has built its pipeline around treating mitochrondrial dysfunction, which is at the root of several rare genetic diseases as well as involved in more common age-related diseases like macular degeneration.
Elamipretide is Stealth's lead drug candidate, under study in four mid- to late-stage trials. Most advanced is the Phase 3 program in primary mitochondrial myopathy that the company said Friday had failed.
"This was an unanticipated and extremely disappointing result following encouraging data from our Phase 1/2 and Phase 2 clinical trials in this indication," company CEO Reenie McCarthy told investors on a conference call Friday morning.
No detailed data were disclosed, but Stealth did say treatment with elamipretide did not meet either of the trial's primary goals: change from baseline in a functional measure known as the six-minute walk test, and fatigue scores on a symptom assessment scale.
Patients with primary mitochondrial myopathy, or PMM, suffer from skeletal muscle weakness, chronic fatigue and reduced or limited ability to exercise. No therapies are currently approved.
Stealth proposed to treat that by using elamipretide to improve mitochondrial function and lower cell stress, which the company argued could deliver functional benefit.
Stealth plans to continue analyzing data from the 218-person study to better determine why that hypothesis didn't play out as expected.
But the setback could make Alexion think twice about exercising its option to co-develop the drug in PMM and two other mitochondrial-related diseases: Barth syndrome and Leber's hereditary optic neuropathy.
"We have informed Alexion of these data and we will provide further updates regarding discussions on that front as we receive more clarity," McCarthy said on the Friday call. Alexion paid Stealth $30 million in fees, equity investment and development funding when it secured the option right in October.
Stealth plans to meet with the Food and Drug Administration in early 2020 on its Barth syndrome program, and will soon submit its design for a Phase 3 study of elamipretide in Leber's.
But some changes could be forthcoming. On Friday, the biotech said it would "review its operational resources to align them with its near-term priorities" in Barth, macular degeneration and other pipeline programs. An update is planned for next month.
Shares in Stealth were down 65% in late Friday morning trading, while Alexion's stock declined by about 3%.