Horizon Pharma, a biopharmaceutical company focused on improving patients’ lives by identifying, developing, acquiring and commercializing differentiated and accessible medicines that address unmet medical needs, has agreed to acquire River Vision Development and its development-stage medicine teprotumumab (RV001), a fully human monoclonal antibody (mAb) currently in development for thyroid eye disease (TED), a rare, autoimmune inflammatory disorder.

Under the terms of the agreement, Horizon Pharma will acquire all outstanding equity of River Vision for an upfront cash payment of $145 million, plus potential future milestone and earn-out payments contingent on the satisfaction of certain regulatory milestones and sales thresholds.

“This acquisition is an important step in our strategy of pursuing and acquiring development-stage medicines targeting rare diseases,” said Timothy P. Walbert, chairman, president and chief executive officer, Horizon Pharma. “With no approved medicines to treat thyroid eye disease, there is a significant unmet treatment need among the approximately 10,000 patients in the U.S. with moderate to severe disease and we look forward to beginning the pivotal study with teprotumumab in the second half of this year.”

Horizon anticipates a potential peak annual sales opportunity for teprotumumab, if approved, in excess of $250 million in the U.S.

Teprotumumab is a human mAb inhibitor of insulin-like growth factor type 1 receptor (IGF-1R), which has received Orphan Drug, Fast Track and Breakthrough Therapy designations from the FDA.

On May 4, 2017, The New England Journal of Medicine published phase II study results evaluating the efficacy and safety of teprotumumab in patients with recent onset, moderate-to-severe TED. In the randomized double-blind, placebo controlled study, 88 patients were assigned to receive teprotumumab or placebo in eight intravenous infusions, 10mg/kg for their first infusion followed by 20mg/kg for the remaining seven infusions, every three weeks during the six-month treatment course. The primary endpoint was response in the study eye defined as a reduction in clinical activity score of ≥2 points and reduction of proptosis, which is protrusion of the eyeball from the socket of ≥2 mm at week 24. 

In the intent-to-treat population, 29/42 (69%) patients receiving teprotumumab and 9/45 (20%) patients receiving placebo were responders at week 24 (p˂0.001). Therapeutic effects were rapid with responder rates of 46% for patients treated with teprotumumab and 5% for patients treated with placebo at week six (p<0.001). Treatment with teprotumumab was well tolerated with the majority of adverse events being mild. The only treatment-related adverse event was hyperglycemia in diabetic patients, which was controlled by adjusting diabetes medication.