U.S. stock index futures pointed to flat open on Wall Street on Wednesday as a higher earnings outlook from bank State Street Corp offset worries about a slowdown in the global economy.

State Street , the world's second-largest custody bank, forecast its second-quarter operating earnings to beat analysts' expectations, which reinforced hopes of strong earnings from some financials and sent the bank's shares up 7.4 percent in premarket trade.

There is a belief that banks, excluding the banks heavily exposed to trading ... are going to have a very strong quarter, and I think State Street is the first evidence of that, said Tim Ghriskey, chief investment officer of Solaris Asset Management in Bedford Hills, New York.

The news helped to offset pessimism when stocks struggled to make headway on Tuesday, with buyers evaporating in the afternoon in what has become a familiar pattern over the past two months.

Concerns about economic growth in the euro zone had pushed shares lower earlier on Wednesday.

S&P 500 futures rose 0.5 points and were just above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures rose 13 points, but Nasdaq 100 futures lost 4.8 points.

UBS lowered its year-end S&P 500 price target to 1,150 from 1,350 to reflect modestly weaker earnings growth and longer-term secular headwinds.

The S&P 500 index has fallen more than 15 percent since a recent peak on April 23 and is down 7.8 percent since the start of the year.

Family Dollar Stores Inc posted higher quarterly profit as customers sought cheaper products in the face of high unemployment, but the discount chain forecast fourth-quarter earnings below expectations. The shares fell about 5.5 percent in premarket trade to $37.25.

BP Plc Chief Executive Tony Hayward met with officials from Abu Dhabi's investment authority as speculation mounted the sovereign fund would make a fresh investment. BP's New York-traded shares rose 2.5 percent to $32.71 in premarket trade.

(Editing by Padraic Cassidy)