Biogen Inc. said Thursday it has entered an exclusive option agreement with TMS Co. Ltd. to acquire its TMS-007 treatment for acute stroke. The company said it will pay $4 million upfront and an additional $18 million once the option is exercised, as well as milestone payments of up to $355 million and tiered royalties. “TMS-007 is a plasminogen activator with a novel mechanism of action associated with breaking down blood clots, and is believed to inhibit local inflammation at the site of thrombosis,” Biogen said in a statement. The drug has the potential to extend the treatment window compared with current thrombolytic agents, it said. Stroke is the fifth leading cause of death in the U.S. TMS-007 has demonstrated an adequate safety profile in an early stage trial and is being evaluated in a phase 2 study in Japan. Biogen shares were slightly higher premarket, but are down 3.7% in 2018, while the S&P 500 has gained 3.7%.