"Can anyone explain why Zacks has a strong sell rating"
The way i understand it Zack uses mostly technical analysis and does not ascribe much value to the potential of future products of companies. it mostly looks at the balance sheet and the history of past revenues and earnings.
Its the balance sheet. With no profits or approvals in sight, NKTR cash reserves are rapidly dwindling as management awards themselves a new round of options in a desperate last effort to pad the retirement fund. Followed, of course, by a new pie-in-the-sky mouse study report to get the Nektarphilia buzzing.