UK's Circassia buys two asthma-focused firms for up to $377 mln

(Adds CEO comment, shares, background on M&A in biotech sector)

LONDON, May 15 (Reuters) - Circassia Pharmaceuticals , a British company developing allergy therapies, said on Friday it had agreed to buy Sweden's Aerocrine (Other OTC: ACNOF - news) and privately held Prosonix, two companies focused on asthma.

Circassia will pay about 139 million pounds ($219 million) for Aerocrine and up to 100 million pounds for Prosonix, with the deals funded through a 275 million pounds placing and open offer.

The transactions continue a recent surge in acquisitions in the biotech sector in the United States and Europe, which has seen multiple companies buying up rivals with overlapping businesses and products.

Shares (Frankfurt: DI6.F - news) in Aerocrine jumped 14 percent in early trading on news of the agreed takeover, while Circassia fell 7.5 percent.

Circassia, which listed on the London stock market in March 2014 in Britain's largest biotech flotation for decades, is banking on using Aerocrine's established commercial operation to help with the launch of its new cat allergy treatment Cat (Taiwan OTC: 4990.TWO - news) -SPIRE (Stuttgart: SIZ.SG - news) .

Cat-SPIRE is due to report pivotal Phase III clinical trial results in the first half of next year.

Prosonix provides a portfolio of products targeting asthma and other respiratory diseases that complement Circassia's existing pipeline.

Circassia Chief Executive Steve Harris said the two deals would accelerate the British company's ability to be a self-sustaining business focused on allergy and asthma.

"Aerocrine has products that they sell to allergy asthma specialists, the very customers we want to sell our allergy products to, so that's a really good strategic fit," he told Reuters. "Prosonix has near-term products that help us create an allergy-asthma specialist pharmaceutical company."

Circassia's 275 million pounds fundraising is being fully underwritten by J.P. Morgan Cazenove and Peel Hunt.

($1 = 0.6339 pounds) (Reporting by Paul Sandle and Ben Hirschler; editing by David Clarke; editing by James Davey)