Shares of Chimerix Inc. /zigman2/quotes/209385333/composite CMRX +0.98% shot up 14.4% in premarket trading Monday, after the biopharmaceutical company said it will sell exclusive rights to its smallpox treatment, including Tembexa, to Emergent BioSolutions Inc. for up to $337.5 million plus royalties. Emergent BioSolutions shares were still inactive ahead of the open. Under terms of the deal, Chimerix will receive $225 million and up to $100 million in milestone payments. Chimerix could also receive $12.5 million in regulatory milestones, and could also earn a 20% royalty on future gross profit of Tembexa in the U.S. and a 15% royalty on gross profit for Tembexa sales during the exclusivity period. "This transaction significantly enhances Chimerix's balance sheet and allows us to focus and invest in our development pipeline," said Chimerix Chief Executive Mike Sherman. Chimerix shares have tumbled 34.1% year to date through Friday and Emergent's stock has dropped 33.9%, while the S&P 500 /zigman2/quotes/210599714/realtime SPX -0.07% has declined 15.6%.