Japan's No.2 drugmaker Astellas Pharma Inc, which went hostile with its $1-billion bid for CV Therapeutics earlier yesterday, also filed a lawsuit against the US biotech firm to prevent it from applying a recently amended shareholder rights plan to stop the takeover.

CV, saying the offer significantly undervalued the company and its growth potentials, has twice rejected Astellas' $16-a-share bid. However, Astellas had said it would keep pursuing CV and look into all available options.

Astellas first brought its offer for CV Therapeutics' board in November, and made the approach public on 27 January, when it represented a 41 per cent premium to the share price. CV shares were up 2 per cent at $16.18, slightly above the offer price, in yesterday's morning trade on NASDAQ.

The bid may foreshadow a fight to oust Louis Lange as chief executive officer and chairman of CV Therapeutics. Lange is one of two directors whose terms expire at this year's annual meeting, according to a regulatory filing. Astellas needs board support to complete the purchase after CV Therapeutics renewed a so-called ''poison pill'' takeover defense last month.

Last month, CV extended a shareholder rights plan to 1 February 2010. The plan was set to expire on 1 February 2009. The company also said it would review its strategies in view of the Astellas bid.

''Their refusal to negotiate with us regarding our proposal has left us with no alternative but to take our offer directly to CV Therapeutics' stockholders,'' Astellas said, adding it may take action in connection with CV Therapeutics' annual meeting.

Astellas said the lawsuit also seeks to preclude CV from claiming that a 2000 agreement between the two companies has been violated by the Astellas tender offer. Earlier in the day, Astellas commenced a cash tender offer for all outstanding shares of CV Therapeutics.

Astellas was formed by the historical merger of Japan's third and fifth largest pharmaceutical companies - Yamanouchi, founded in 1923, and Fujisawa, founded in 1894. Today, Astellas is one of the largest pharmaceutical companies in Japan with a market capitalisation of approximately $17.7 billion as of January 26, 2009, and, for the fiscal year ended 31 March 2008, net income of approximately $1.8 billion.

In 2007, Astellas signed a $537-million deal  to acquire US biotech firm Agensys as part of its plan to accelerate its antibody research, especially in the field of cancer (See: Astellas acquiring cancer biotech firm Agensys). The purpose of the acquisition was to catapult itself to the forefront of the world's antibody drug research business. The Astellas-Agensys combine is considered to have at least seven potential cancer treatments in the pipeline.

Astellas is on the prowl for new drugs after its best seller, Prograf, a treatment used in organ transplants, lost US patent protection in April 2008. CV Therapeutics in November won US approval to market Ranexa as an initial treatment for chronic chest pain, broadening its potential use.