Shares of BioSpecifics, Wilmington, Del., at last check were up 44% at $88.15. The stock has doubled off its 52-week low of $42, set in late March.
Endo International, headquartered in Dublin, was climbing 8.3% to $5.40.
Under the terms, Endo will begin an all-cash tender offer to acquire all BioSpecifics shares for $88.50 each, or $658 million. The deal's enterprise value net of cash on hand is $540 million, BioSpecifics said.
Both boards have approved the deal, which is expected to close late this year. Endo expects to fund the transaction with cash on hand. The acquisition is subject to conditions including antitrust clearance.
Endo said in a statement that it has had a strategic relationship with BioSpecifics since 2004.
BioSpecifics receives a royalty stream from Endo related to Endo's collagenase-based therapies.
This includes two medications. One is Xiaflex, marketed by Endo, which treats Dupuytren's contracture, a gradual thickening and tightening of tissue under the skin in the hand, and Peyronie's disease, which is fibrous scar tissue inside the penis that causes curved, painful erections.
The other is Qwo, an injectable treatment for cellulite, which is expected to be launched by Endo Aesthetics in the spring.
Endo sees "significant long-term growth potential of both Xiaflex and Qwo - two of our most durable and differentiated products," Blaise Coleman, Endo's president and chief executive, said in the statement.