Japan's Astellas Pharma Inc offered to buy U.S. drugmaker OSI Pharmaceuticals for $52.00 a share, or about $3.5 billion, in cash to gain access to OSI's cancer drug Tarceva.

Astellas said it was taking its offer directly to OSI shareholders after its bid was rejected by OSI, earlier this month.

The offer represents a premium of over 40 percent to OSI's Friday closing price.

Astellas said it has cash and cash equivalents on hand to complete the deal and plans to nominate directors at OSI's upcoming annual meeting.

The Japanese drugmaker will commence a tender offer on March 2 and is being advised by Citigroup. OSI's Tarceva, which the company co-markets with Swiss drug giant Roche Holding AG, is approved as a second line treatment for patients whose lung cancer has gotten worse following at least one round of chemotherapy.

OSI receives royalties on sales of the blockbuster drug, which is also approved for pancreatic cancer. OSI shares were up 38 percent to $51 in premarket trade. They closed at $37.02 Friday on Nasdaq. (Reporting by Esha Dey in Bangalore; Editing by Aradhana Aravindan)

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