* Ionis shares up 9.5 pct premarket
* Deal to close in second quarter
* Comprises equity investment in Ionis plus upfront payment (Adds background, share movement)
April 20 (Reuters) - U.S. drugmaker Biogen Inc rolled out part of its $37 billion investment warchest on Friday, signing a $1 billion deal that seeks to expand on the strength of an existing partnership with Ionis Pharmaceuticals Inc.
The 10-year agreement, which gives Biogen the option to license and commercialize a range of neurological therapies, pushed shares in California-based Ionis up 9.5 percent to $50.20 before the bell.
Ionis developed Spinraza, a treatment for rare disease spinal muscular atrophy that Biogen has licensed and sells. Analysts say it could replace multiple sclerosis treatment Tecfidera as Biogen's biggest selling drug.
The list price for Spinraza is $750,000 for the first year of therapy, dropping to about $375,000 a year after that.
The deal, which comes ahead of Biogen's first-quarter earnings report on Tuesday, includes a $625 million equity investment in Ionis and a $375 million upfront payment to the smaller drug developer.
Ionis is also eligible to receive further milestone-based payments, license fees and royalties on net sales of the drugs.
The companies said they expect the deal to close in the second quarter.
The deal with Ionis adds to previous investments in brain disorder drugs, including a deal with Pfizer Inc that could near $600 million.
Biogen is also testing aducanumab, a treatment for memory-robbing Alzheimer's, amid increased skepticism over the future of viable treatments for the disease. (Reporting by Tamara Mathias in Bengaluru Editing by Supriya Kurane)