Aktis Oncology Initiates Phase 1B Clinical…

Deal Accelerates Expansion of Oncology Franchise

Berkeley, CA—February 28, 2011 - Plexxikon Inc. today announced it has entered into a merger agreement with Daiichi Sankyo Company, Limited, a Japan‐based global pharmaceutical company. The purchase price for Plexxikon is $805 million up‐front. Near‐term milestone payments associated with the approval of PLX4032 could total an additional $130 million. Closure of the transaction is subject to clearance under the Hart‐Scott‐Rodino (HSR) Antitrust Improvements Act and customary closing conditions.