* Compuware climbs in premarket; near deal to sell itself
* Exelixis tumbles after cancer drug fails study; to cut jobs
* Dollar General ups Family Dollar bid
* Futures up: Dow 12 pts, S&P 1.5 pts, Nasdaq 7.5 pts (Updates prices)
By Chuck Mikolajczak
NEW YORK, Sept 2 (Reuters) - U.S. stocks were poised for a flat open on Tuesday, after the S&P 500 closed out its best month since February, ahead of reports on the manufacturing sector.
* Investors will eye the final August reading on the manufacturing sector from financial data firm Markit at 9:45 a.m. (1345 GMT).
* At 10 a.m. (1400 GMT), the Institute for Supply Management's August reading on manufacturing will be released. Expectations call for manufacturing to dip slightly to 56.8 from 57.1 in July. Also due at 10 a.m. (1400 GMT) is construction spending data for July.
* S&P 500 e-mini futures were up 1.5 points and fair value - a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract - indicated a flat open. Dow Jones industrial average e-mini futures rose 12 points and Nasdaq 100 e-mini futures added 7.5 points.
* The benchmark S&P index gained 3.8 percent in August, its best month since a 4.3 percent climb in February. However, the monthly average volume of 5.24 billion was the lowest of the year, according to data from BATS Global Markets.
* Exelixis shares plunged 52.7 percent to $1.96 before the opening bell. The company said on Monday it would cut about 70 percent of its workforce after its experimental prostate cancer drug cabozantinib failed a late-stage study.
* Dollar General Corp raised its bid for Family Dollar Stores Inc by 2 percent to $80 per share, or $9.1 billion, and warned it may turn hostile and appeal directly to shareholders if the new offer is rejected. Family Dollar shares gained 0.7 percent to $80.37 in premarket.
* Compuware jumped 15.3 percent to $10.78 in premarket after the Wall Street Journal reported the company is near a deal to sell itself.
* Norwegian Cruise Line Holdings Ltd said it would buy Prestige Cruises International Inc in a $3.03 billion deal, including debt. Its shares jumped 16.2 percent to $38.70 before the opening bell.
* Select Income REIT said it would buy office REIT Cole Corporate Income Trust in a $3 billion deal to expand its portfolio in the United States.
* Conn's Inc tumbled 28.1 percent to $32.23 before the opening bell after the retailer posted second-quarter results that missed expectations and gave a full-year outlook below analysts' forecasts.
(Reporting by Chuck Mikolajczak; Editing by Chizu Nomiyama and Nick Zieminski)