Sorrento Therapeutics, Inc. (SRNE) announced on Monday, after reviewing the latest acquisition proposal in consultation with its advisors, is rejecting a takeover bid.

According to Reuters, the company rejected a proposal by a private equity fund for a majority or all of its outstanding shares that had valued the drug developer at as much as $993 million.

Sorrento’s board of directors determined the offer significantly undervalues the company and is not in the best interest of the company’s stockholders. The board unanimously rejected the acquisition proposal.

Sorrento’s management is also continuing to execute on the core drug development and to pursue multiple potential strategic alliances and transactions.

Sorrento shares are trading down 4.45% at $4.08 in Monday’s pre-market session. The stock has a 52-week high of $6.50 and a 52-week low of $1.39.