Otsuka Pharmaceutical Co., Ltd.

September 5, 2013

Otsuka Pharmaceutical to Acquire Astex Pharmaceuticals

Tokyo, Japan - September 5, 2013 - Otsuka Pharmaceutical Co., Ltd. is pleased to announce an agreement with Astex Pharmaceuticals, Inc. ("Astex") to acquire Astex via an all-cash tender offer. The total purchase price of $866 million is based on the treasury stock calculation method and a tender offer of US $8.50 per share for all outstanding common shares.

Objectives of the Acquisition

Otsuka aims to enhance its discovery and development of drugs with novel working mechanisms by combining Astex's fragment-based drug discovery technology with Otsuka's own R&D strengths in areas such as central nervous system diseases. The fragment-based discovery technology, named PYRAMID™, is one of the most significant new drug discovery platforms of the past two decades and holds significant promise to bring new therapies more quickly to awaiting patients and physicians. Otsuka will also strengthen its promising oncology development portfolio and inline oncology offerings.

Dr. Taro Iwamoto, Otsuka Pharmaceutical's President and Representative Director, remarked, "I hope that this acquisition of Astex will strengthen not only our cancer portfolio but also our drug discovery research in the central nervous system field, through the acquisition of Astex's fragment-based drug design technology. Astex's unique fragment-based drug discovery technology and clinical oncology research and development capabilities, born out of the passion of its researchers, exemplify our corporate mottos and belief in "Sozosei (Creativity) and Jissho (Proof through Execution). I would like Otsuka Pharmaceutical to continue to respect Astex's uniqueness and leverage it to bring further growth for Otsuka Pharmaceutical."

About Astex Pharmaceuticals, Inc.

Astex is a bio-venture company established in 1991, with a fragment-based drug discovery research center in Cambridge, England and a clinical research and development function in California. Fragment-based discovery technology enables more rapid discovery and development of compounds for target proteins implicated in diseases than has heretofore been possible with high-throughout screening. Simply described, this technology evaluates binding of target proteins with small molecules via 3D structural analysis. As a result, in the past 8 years Astex has advanced 8 new compounds to the clinical R&D stage in the fields of oncology and the central nervous system. Four of these are in phase-2 clinical trials, including SGI-110 a novel DNA methylation inhibitor and AT13387, an inhibitor of heat shock protein 90 (HSP90) which are involved in the reproduction of cancer cells, and four are in phase-1 trials. Four of these compounds are undergoing clinical trials in several partnerships.

Astex achieved the development and launch of Dacogen®, a drug that treats myelodysplastic syndromes and elderly acute myeloid leukemia. Dacogen® (decitabine) has worldwide sales of approximately $280 million and is presently sold by Eisai Inc. in North America and by Janssen in other regions.