Stock index futures pointed to a weaker open on Wall Street on Wednesday, extending losses to a sixth straight session, with futures for the S&P 500, for the Dow Jones and for the Nasdaq 100 down 0.4 to 0.6 percent.

U.S. drugmaker Merck & Co is to discontinue a major trial of a key vaccine from Intercell designed to protect against serious hospital infections, the Austrian biotech firm said on Wednesday.

The Mortgage Bankers Association releases its Weekly Mortgage Market Index for the week ended June 3 at 1100 GMT (7 a.m. ET). The mortgage market index read 519.4 and the refinancing index was 2,442.9 in the previous week.

The Federal Reserve issues the Beige Book, a summary of economic conditions in the 12 Federal Reserve districts, at 1800 GMT (2 p.m. ET).

Citigroup Inc will sell a $1.7 billion portfolio of private-equity assets to European buyout firm AXA Private Equity, as the U.S. bank looks to focus on its core businesses, the Wall Street Journal reported, citing people familiar with the matter.

Resource-related shares will be in focus as crude oil fell ahead of an OPEC meeting where members are expected to agree to raise global supplies to rein in high prices. Key base metals prices also fell.

Allowing a brief U.S. debt default to force government spending cuts is a horrible idea that could destabilize the world economy and sour already tense relations with big creditors like China, government officials and investors said on Wednesday.

The Federal Reserve does not need to consider additional monetary policy stimulus as the world's largest economy is likely to pick up in coming quarters due to growth in exports and disposable incomes, IMF acting chief John Lipsky said on Wednesday.

The U.S. Securities and Exchange Commission said it got a court order freezing the proceeds of certain suspicious trade in energy software provider Telvent securities before a $1.36 billion takeover bid by France's Schneider Electric .

Covidien Plc is looking to sell its pharmaceuticals unit for as much as $4 billion, a source familiar with the situation said on Tuesday.

Indian state-run gas firm GAIL (India) and explorer Oil and Natural Gas Corp are interested in buying part of ExxonMobil Corp's stake in Kazakhstan's Kashagan oil field, GAIL Chairman B. C. Tripathi said on Wednesday.

Danisco said on Wednesday its top management would resign later this month following U.S. chemicals group DuPont's takeover of the group for $6.4 billion in May.

China still grapples with elevated inflationary pressures, partly due to higher prices of imported goods, a senior government official said on Wednesday.

Britain is at risk of losing its prized triple-A credit rating if growth remains weak and the government fails to meet its debt-cutting target, a senior analyst at Moody's was quoted as saying on Wednesday.

European shares fell 1.1 percent on Wednesday on weaker miners, while the Nikkei average <.N225> edged higher, holding above key support near the bottom of its post-quake range as foreign investors were lured into buying by cheap valuations.

U.S. stocks extended a losing streak for a fifth day on Tuesday on mounting concerns about the economy after bearish comments from Federal Reserve Chairman Ben Bernanke.

The Dow Jones industrial average <.DJI> slipped 19.15 points, or 0.16 percent, to end at 12,070.81. The Standard & Poor's 500 Index <.SPX> declined 1.23 points, or 0.10 percent, to 1,284.94. The Nasdaq Composite Index <.IXIC> shed 1.00 point, or 0.04 percent, to finish at 2,701.56.

(Reporting by Atul Prakash; Editing by Hans Peters)