AliveGen Inc. in Thousand Oaks has sold its drug candidates to Biogen Inc. in a deal valued at up to $562 million. The portfolio of the fledgling biotech startup, founded in 2014 by a pair of former Amgen Inc. scientists, contains two early-stage drugs that could be used to treat a variety of neuromuscular diseases. Both work by inhibiting the activity of a protein called myostatin, which is thought to contribute to the pathogenesis of diseases that cause low muscle mass. Biogen paid $27.5 million upfront for the compounds, which it plans to study to see if they are effective in treating spinal muscular atrophy and amyotrophic lateral sclerosis. The firm may pay up to $535 million more upon completion of various development and commercialization milestones, according to Biogen. A representative from AliveGen could not be reached for comment by press time.