Astellas Pharma’s bid to buy OSI Pharmaceuticals has turned distinctly hostile now that the Japanese drugmaker has filed a lawsuit against the US firm over its ‘poison pill’ plan to prevent any takeovers.

Astellas has now launched its unsolicited bid and is offering $52.00 per share in cash, which represents a premium of over 40% on OSI’s closing price of $37.02 on February 26. That offer has been rejected and chief executive Colin Goddard wrote to his counterpart at Astellas, Masafumi Nogimori, saying “we are prepared to provide you with certain non-public information…which is fundamental to our view of the value of OSI”.

All reasonably friendly but the tone has changed now that Astellas has filed a lawsuit in Delaware. The suit is seeking to stop the directors from “engaging in any action or inaction, including applying OSI's poison pill rights plan” that has the effect of "improperly impeding, thwarting, frustrating or interfering with the tender offer in a manner inconsistent with the directors' fiduciary duties”.

The suit also claims that Mr Goddard’s offer to provide nonpublic information is “hollow”, as it contained “a two-year standstill agreement that would have prevented Astellas Pharma from, among other things, making a tender offer, or participating in any solicitation of proxies”. The lawsuit also reveals that the Tokyo-headquartered company, which has been pursuing OSI for 13 months, was prepared to negotiate a deal in the range of $55-$57 per share as recently as June last year. However that offer was rejected as too low.

Analysts has suggested that other companies may now have been prompted to make a move for OSI, notably Roche, which co-markets the lung and pancreatic cancer blockbuster Tarceva (erlotinib) with the US group. Pfizer and Celgene Corp have also been mentioned but George Farmer at Canaccord Adams issued a research note saying that “we do not believe any counteroffer, whether from Roche or another party, will come in substantially above current trading levels or will come at all”.

Ranbaxy’s generic Flomax blocked by FDA
Meantime, Ranbaxy Laboratories says that the US Food and Drug Administration has not given final approval to its generic version of Astellas’ benign prostatic hyperplasia drug Flomax (tamsulosin).

The Indian drugmaker issued a statement saying: “We regret that despite our best efforts we were not able to get an approval for the subject product, and hence will not be in a position to launch”. Ranbaxy was due to launch its copycat version in the USA yesterday, eight weeks before the Flomax expires there, following an out-of-court settlement in 2007.

No reason for the deal was given but it is a blow to Ranbaxy, which has 30 of its drugs banned by the FDA in September 2008. The agency also halted fresh approvals for products coming out of two of its Indian facilities for violating US manufacturing rules and early last year, delayed the launch of the company’s generic version of GlaxoSmithKline’s migraine pill Imitrex (sumatriptan).

Even worse news for Ranbaxy is that Impax Laboratories’ version of Flomax was launched in the USA yesterday.