Japan's Astellas Pharma has sued OSI Pharmaceuticals Inc and its directors for adopting ''poison pill'' defence and for not acting in the best interests of OSI shareholders by rejecting its $52-a-share takeover bid.

Earlier this week, on 2 March, Tokyo-based Astellas Pharma, Japan's second-largest pharmaceutical company after Takeda Pharmaceuticals, launched a $3.5-billion hostile takeover bid for the US drug company OSI Pharmaceuticals, a researcher and developer in molecular targeted therapies for oncology, diabetes and obesity. (See: Astellas launches $3.5-billion hostile bid for OSI Pharmaceuticals) http://www.domain-b.com/industry/pharma/20100302_astellas.html

Melville, New York-based OSI rejected the unsolicited proposal from Astellas yesterday and said that it was not interested in undertaking a sale of OSI at that price, since it believes Astellas' proposal very significantly undervalues the company.

Astellas yesterday took its offer directly to OSI shareholders and commenced a cash tender offer to acquire all the outstanding common stock of OSI for $52 per share.

The offer and withdrawal rights are scheduled to expire on 31 March 2010 unless Astellas extends the offer.

Astellas, through its US subsidiary Astellas US Holding Inc, filed a suit in the Delaware Court seeking injunction against OSI and its directors from engaging in any action, including applying ''poison pill'' rights plan, which would thwart its tender offer inconsistent with the director's fiduciary duties.

Astellas' want the court to quash OSI's corporate anti-takeover defenses and order OSI's directors to fulfill their fiduciary duties to their stockholders by evaluating Astellas offer and conduct negotiations to realize full value of the deal.

OSI specialises in the discovery and development of molecular targeted therapies for oncology, type 2 diabetes and obesity and its revenues are derived mainly from its non-small cell lung and pancreatic cancer drug Tarceva.

Tarceva, which had US sales of $209 million and global sales of $1.2 billion in 2009, is sold in partnership with Swiss drugmaker Roche, which paid OSI $146 million in royalties from for international sales.