Shares of Ionis Pharmaceuticals Inc. soared 8.4% in premarket trade Friday, after Biogen Inc. said it would pay the company $1 billion as part of a new 10-year collaboration agreement to develop drug candidates to treat neurological diseases. Biogen's stock was still inactive. Part of the payment will include $625 million to buy about 11.5 million Ionis shares, or about 9.2% of the shares outstanding, at $54.34 a share, which is 18.5% above Thursday's closing price of $45.85. Biogen will have the option to license therapies and will be responsible for their development and commercialization, and may make milestone payments, license fees and royalties to Ionis on net sales. The deal is expected to close in the second quarter of 2018. Ionis's stock had lost 8.9% year to date through Thursday, while Biogen shares had tumbled 16.5%, the iShares Nasdaq Biotechnology ETF had slipped 0.8% and the S&P 500 had gained 0.7%.