Karyopharm Therapeutics to cut workforce by 20%; shares fall

** Drugmaker Karyopharm Therapeutics' shares KPTI.O down 15.8% at $4.21 premarket

** Company says in an SEC filing it is reducing its workforce by 20%

** Company expects its one-time expenses in connection with these actions to be immaterial

** Co says board is evaluating financing and strategic alternatives

** As of last close, stock down 50.7% YTD