Drugmaker SuperGen Inc. said Thursday it agreed to acquire British biotechnology Astex Therapeutics Ltd., forming a company called Astex Pharmaceuticals.

SuperGen, of Dublin, Calif., makes drugs to fight tumors and blood disorders. It helped develop the drug Dacogen for bone marrow disease. Astex is a privately held company studying drugs that treat cancer and viruses. SuperGen said it will acquire Astex for $25 million in cash. Astex Therapeutics shareholders will own 35 percent of the combined company at closing, and SuperGen will pay $30 million in additional cash or stock compensation over a period of 30 months.

Pending approval from shareholders and regulators, the deal is expected to close in July. If the deal is completed, shares of the combined company will trade on the Nasdaq under the ticker symbol "ASTX"

SuperGen said the combined company will have seven drug candidates, including four that are in mid-stage testing or moving into mid-stage development. Three of those four drugs are being developed through partnerships with larger drugmakers. Astex Pharmaceuticals will have partnerships with GlaxoSmithKline PLC, Johnson & Johnson, Novartis AG, AstraZeneca PLC, and Eisai Co., and it will have revenue from sales of Dacogen, which is marketed by Johnson & Johnson and Eisai.

The company will be eligible for close to $2 billion in potential drug development milestone payments.

James Manuso, the president, chairman and CEO of SuperGen, will be chairman and CEO of the combined company. Astex Therapeutics CEO Harren Jhoti will be president and a director.

Shares of SuperGen fell 38 cents, or 11.8 percent, to $2.85 in afternoon trading.