U.S. stock index futures pointed to a lower open on Thursday as renewed concerns about Greece's debt woes undercut a strong profit forecast from economic bellwether United Parcel Service Inc.

UPS climbed 4.8 percent to $68.60 in premarket trade after the package delivery company said first-quarter earnings would be much higher than expected and also raised its outlook for the year.

Greek debt worries simmered as the cost of insuring against a Greek default exceeded a record closing high. The euro dropped nearly 1 percent against the dollar and yen.

You've got some disconcerting news out of Greece, and that put a little chink in the armor, said Phil Orlando, chief equity market strategist at Federated Investors in New York.

If we were focused on U.S. corporate earnings, and looking at the U.S. economic news, we would continue to rally.

New U.S. jobless claims soared unexpectedly last week as applications held back from the Easter holiday were processed, but a gauge of manufacturing in New York state rose to a six-month high in April.

S&P 500 futures slipped 2.2 points and were below 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 lost 17 points, and Nasdaq 100 futures shed 3 points.

Investors may be ready to take some profits after U.S. stocks notched a fifth straight day of gains on Wednesday as strong corporate results and March retail sales pushed the S&P 500 past 1,200 for the first time in 18 months.

MGM Mirage slumped 5.6 percent to $14.54 premarket, a day after the casino operator projected a wider-than-expected quarterly loss due to weak Las Vegas results, including its new CityCenter development.

PPG Industries Inc
advanced 1.6 percent to $70.63 after the coatings and glassmaker posted quarterly profit that easily beat expectations although it took an $85 million charge.

Other companies set to report results on Thursday included Google Inc , Advanced Micro Devices Inc and People's United Financial Inc

Economic data expected later included March industrial output, the Philadelphia Fed business index for April, and the April NAHB housing market index.

Mariner Energy Inc shares surged 39.1 percent to $25.16 premarket after Apache Corp said it would acquire the smaller oil and natural gas explorer for $2.7 billion in a bid to extend operations into the deepwater Gulf of Mexico. Apache shares slipped 3.5 percent to $104.25.

(Reporting by Chuck Mikolajczak; editing by Jeffrey Benkoe)