* Dow futures at session lows, down 159 points; S&P 500 futures off 16 points and below fair value.

* Before DuPont, investor sentiment had already taken a hit from pharmaceutical company Merck & Co Inc's disappointing 2009 profit outlook.

* Besides DuPont and Merck, AT&T , a fellow Dow component, cut its capital expenditure budget and said it will eliminate 12,000 jobs.

(Reporting by Ellis Mnyandu, Editing by Kenneth Barry)