Werewolf Therapeutics’ hunt for strategic alternatives has ended.
Ambros Therapeutics has agreed to merge with Werewolf in an all-stock deal and has also raised $150 million. The move positions Ambros to take its lead rare disease drug to an approval filing.
Massachusetts-based Werewolf began looking for an escape route in February. The company exited stealth with $56 million and raised a $72 million series B round on its way to a $120 million IPO in 2021. Yet by early 2026, Werewolf’s cash runway had shrunk to less than one year, leading the biotech to sell off assets to Jazz Pharmaceuticals and Merck KGaA while seeking a taker for its Nasdaq listing.
The reverse merger will see the resulting company operate under the Ambros branding. Werewolf shareholders will own about 7% of the combined entity, with the remaining 93% divided up between Ambros’ existing backers and participants in a planned $150 million private placement.
RA Capital Management and Janus Henderson Investors will co-lead the private placement. Following the deals, Ambros forecasts that its cash runway will extend into the first half of 2029. By then, the company expects to have reported phase 3 data on its lead program and filed for FDA approval.
Ambros is testing an aminobisphosphonate called neridronate in complex regional pain syndrome type 1 (CRPS-1), a condition formerly known as reflex sympathetic dystrophy. The program builds on the use of neridronate in Italy, where the bisphosphonate is used to treat conditions including osteogenesis imperfecta.
Investigators are enrolling people with CRPS-1, a condition characterized by persistent, debilitating pain, in a phase 3 trial to assess the effects of infusing 400 mg of neridronate four times over 10 days. The study will compare the effect of neridronate and placebo on the change in pain intensity from baseline to Week 12 in about 270 people.
In 2013, Italian researchers reported significant reductions in pain in CRPS-1 patients who received four 100-mg infusions of neridronate over 10 days. Informed by earlier studies, Ambros is limiting enrollment in its phase 3 trial to patients with the warm subtype of CRPS-1 and a positive triple-phase bone scan. The biotech believes the subpopulation includes the patients most likely to benefit from neridronate.
Ambros is scheduled to complete its study around the end of 2027 and the start of 2028, according to the federal trials register. The study could establish neridronate as the first FDA-approved treatment for CRPS-1, a condition that Ambros estimates affects 50,000 to 70,000 people a year in the U.S.