Yelp Inc (NYSE:YELP), Nektar Therapeutics (NASDAQ:NKTR) and TW Telecom Inc (NASDAQ:TWTC) are ending the week on the high note and are today’s top midday gainers. On the losing end are Arrowhead Research Corp (NASDAQ:ARWR), Community Health Systems (NYSE:CYH) and Oclaro, Inc. (NASDAQ:OCLR).

chart_1 (38) Yelp

Priceline – OpenTable Deal Gives Yelp a Boost

Up +14.17% as of midday today, starting off the day especially strong this Friday Yelp Inc (NYSE:YELP). The surge is likely the result of Priceline’s OpenTable purchase announcement – a deal valued at $2.6 billion. Billionaire investment manager George Soros picked up a 50,000-share-position in the urban guide and business review platform in Q1 2014.

Nektar Therapeutics (NASDAQ:NKTR)  rallied +12.72%. The biopharmaceutical company and partner AstraZeneca said after close yesterday that an advisory committee to the FDA recommended that large cardiovascular safety trials for a class of one of its drugs should not be required prior to approval.  The Thomas Steyer pick actually halted trading on Wednesday.

Last on today’s list of midday losers is TW Telecom Inc (NASDAQ:TWTC), the share price of which jumped +10.64%. The long-time Soros bet surged on reports that Level 3 is interested in acquiring the company.

Arrowhead Research Dives on Patent Concerns

Arrowhead Research Corp (NASDAQ:ARWR) fell -11.27% as concerns mount regarding a patent obtained by Alnylam Pharmaceuticals. What’s more, company director Charles McKenney sold 22,000 ARWR shares at the start of the week. The biopharmaceutical firm is a new Q1 buy for George Soros.

The share price of Community Health Systems (NYSE:CYH) slipped -7.14%. Insider William Hussey sold 100,000 shares last Friday, which may have some investors concerned. Billionaire Thomas Steyer initiated a position in the firm in the first quarter of the year.

Oclaro, Inc. (NASDAQ:OCLR), yet another Soros bet, dipped -5.86. The optical and laser company is down -16.06% YTD.