Regeneron Pharmaceuticals Inc on Monday said it has received notice that Sanofi SA intends to acquire Regeneron's common stock through open market purchases and direct purchases from shareholders.

As a result, Sanofi intends that the value of its ownership of voting securities of Regeneron stock will be above the $500 million Hart-Scott-Rodino Act notification threshold, Regeneron said.

Neither company could immediately be reached for comment

The two companies have a longstanding agreement to develop medicines together, including promising treatments for cholesterol and arthritis.

Regeneron is best known for its blockbuster drug Eylea for macular degeneration, which it owns with Bayer AG .

(Reporting By Debra Sherman; Editing by Gerald E. McCormick)

(This story corrects final paragraph to show Bayer AG co-owns Eylea)