Arrowhead Research said this week that it has increased its majority ownership in RNAi drugs developer Calando Pharmaceuticals.

Arrowhead said it exchanged a warrant to purchase approximately 3.9 million shares of its stock for Calando Series A preferred stock with a liquidation preference of approximately $3.9 million.

"The Calando preferred stock is convertible into 2.7 million shares of Calando common stock at the discretion of the holder," Arrowhead said.