Merck & Co. said Monday that it is acquiring San Francisco-based Sirna Therapeutics, in a transaction worth $1.1B. Sirna Therapeutics develops medicines based on RNA interference (RNAi) technology. Merck will acquire 100 percent of the equity of Sirna for $13 per share in cash. Sirna's RNAi therapeutics are aimed at treating cancer and other conditions. The firm was backed by Oxford Bioscience Partners, Sprout Group, Venrock Associates, and others. Sirna's manufacturing operations are based in Boulder, Colorado.