U.S. stocks turned lower in afternoon trading on Wednesday, with major indexes erasing earlier gains as a shooting at the Canadian parliament unnerved investors and Boeing and Biogen sold off following results.

Indexes had traded in positive territory for much of the session, putting the S&P 500 on track for a fifth straight day of gains. Earnings initially drove the move higher, with technology and material shares up on the back of strong results.

Hedge fund manager Dan Loeb's bullish thesis on Amgen (AMGN -1.4%) relies on a break-up of the company into two separate organizations, one that would sell its legacy drugs and one that would focus on developing its pipeline. The idea was originally proposed by Sanford Bernstein's Geoffrey Porges in June.

The FDA accepts Alkermes' (ALKS +1.5%) NDA for aripiprazole lauroxil for the treatment of schizophrenia for review. The PDUFA date is August 22, 2015.Aripiprazole lauroxil is an injectable atypical antipsychotic with one-month and two-month formulations. Once in the body, it converts to aripiprazole.

Nanosphere (NSPH -36.2%) prices its public offering of 40M shares of common stock at $0.50 per share. Underwriters over-allotment is 6M shares plus 400K shares as part of the underwriting fee and an additional 60K shares if the over-allotment is exercised in full.

Biogen Idec (BIIB -10.6%) is under selling pressure after this morning's earnings call. Some observers perceive that Tecfidera sales came in a bit light despite its 98% yoy growth. The company also disclosed the death of one patient who had taken the drug for four years. The death was apparently due to pneumonia and not due to the drug.

Thinly-traded micro cap Regulus Therapeutics (NASDAQ: RGLS) is up a whopping 127% premarket on robust volume in response to its announcement that its experimental microRNA therapeutic, RG-101, demonstrated a mean 4 log reduction in viral load in 14 HCV patients after a single subcutaneous dose of 2 mg/kg as a monotherapy.