Werewolf Therapeutics jumps 127% as $150M Ambros merger targets pain drug

Werewolf Therapeutics shares surged 127 percent in premarket trading after the company agreed to an all-stock merger with Ambros Therapeutics, valuing the private biotech at $500 million and pivoting toward its Phase 3 pain drug neridronate.

"We are uniquely positioned to be advancing neridronate, a differentiated bisphosphonate with extensive prior clinical experience, in an FDA-aligned single Phase 3 trial supporting potential regulatory approval in patients with CRPS-1, a debilitating orphan disease with no currently FDA-approved therapy," Jay Hagan, chief executive officer of Ambros Therapeutics, said.

The combined company, which will operate as Ambros Therapeutics and trade under the ticker AMBX, will be funded by an oversubscribed $150 million private placement co-led by RA Capital Management and Janus Henderson Investors. Pre-merger Ambros stockholders will own about 71.7 percent of the combined company, Werewolf holders about 6.8 percent, and PIPE investors about 21.5 percent. Werewolf shareholders also receive one contingent value right per share tied to future monetization of the company's legacy INDUKINE assets, WTX-124 and WTX-330.

Neridronate, developed by Abiogen Pharma and already approved in Italy for CRPS, osteogenesis imperfecta, and Paget's disease, has been administered to roughly 600,000 patients. The drug holds FDA Breakthrough Therapy, Fast Track, and Orphan Drug designations, and Ambros expects topline data from the CRPS-RISE Phase 3 trial in 2028, with a planned NDA submission and cash runway into the first half of 2029.

A precision-medicine bet on an orphan pain condition

CRPS-1 affects an estimated 65,000 newly diagnosed people in the United States each year, with no FDA-approved pharmacological therapy. The condition typically follows a limb injury and progresses from a "warm" phase — marked by inflammation, redness, and hypersensitivity — to a chronic "cold" phase with persistent, debilitating pain.

The CRPS-RISE trial enrolls approximately 270 patients with warm-phase CRPS-1 confirmed by positive triple-phase bone scans, a precision-medicine approach that Ambros says aligns with neridronate's mechanism of action. The primary endpoint measures change in pain intensity from baseline to week 12 on an 11-point Numerical Rating Scale. Ambros believes positive results from this single Phase 3 trial could support U.S. approval based on prior FDA interactions.

The drug's clinical pedigree includes two successful Italian Phase 3 trials. In the NERIAS study, 100 mg IV neridronate achieved a 50 percent or greater reduction in pain versus placebo (p=0.0003). The NAIMES study showed 65.9 percent of neridronate-treated patients versus 29.7 percent on placebo achieved at least a 50 percent improvement in pain (p=0.0017), with benefits maintained over 12 months.

What Werewolf shareholders get

The deal leaves legacy Werewolf holders with a single-digit stake in the combined company, but the CVR provides a path to additional value. Werewolf recently sold its preclinical INDUCER platform and certain INDUKINE assets to EMD Serono, a unit of Merck KGaA, for $28 million upfront plus $5 million after technology transfer. The CVR entitles holders to a share of net proceeds from any future disposition of WTX-124 and WTX-330.

Werewolf's stock, which closed at $0.43 on Aug. 20, was trading at $0.9780 in premarket, reflecting investor enthusiasm for the neridronate opportunity. The merger is expected to close by the first quarter of 2027, subject to stockholder approvals from both companies, Nasdaq listing approval, and effectiveness of the Form S-4 registration statement.

Ambros brings roughly $104 million in cash as of June 30, 2026, and the combined company projects full funding through Phase 3 topline results and a planned NDA submission. The company's intellectual property portfolio, combined with Orphan Drug designation, supports potential U.S. market exclusivity through 2045. With no other known late-stage CRPS-1 assets in biopharma pipelines, neridronate could capture a first-mover position in a market with roughly 65,000 new patients annually.

This article is for informational purposes only and does not constitute investment advice.