Stocks extended losses on Wednesday, with the S&P briefly falling 1 percent, as investor optimism waned over euro zone leaders' ability to reach a resolution to the region's debt crisis at an upcoming summit.

The Dow Jones industrial average <.DJI> dropped 70.65 points, or 0.58 percent, to 12,079.48. The Standard & Poor's 500 Index <.SPX><.INX> dropped 11.92 points, or 0.95 percent, to 1,246.55. The Nasdaq Composite Index <.IXIC> dropped 33.50 points, or 1.26 percent, to 2,616.06.

(Reporting By Chuck Mikolajczak; Editing by James Dalgleish)