NEW YORK (TheStreet) -- Merrimack Pharmaceuticals (MACK - Get Report) fell in after-hours trading on Thursday after the company announced it had regained worldwide rights from Sanofi (SNY) to develop and commercialize MM-121.
MM-121 is "a monoclonal antibody designed to block ErbB3 (HER3) activation in patients with heregulin-positive tumors and improve response to standard of care treatments," according to the company's press release.
The rights acquisition ends Merrimack's five-year partnership with Sanofi, which helped Merrimack complete a Phase 2 program for MM-121. Sanofi will continue to fund the program for the next six months.
The stock was down 9.13% to $7.17 at 4:45 p.m.