Take a look at some of the biggest moves.

The company's board of directors adopted a poison pill to prevent Musk from increasing his stake in the company past 15%. Musk made a $54.20 per share bid for the company last week.

The satellite radio operator's stock fell 2% in premarket trading after Morgan Stanley lowered its price target.

The drugmaker's shares plummeted after it halted all trials of its key cancer drug. The desired results were not produced by the experimental treatment.

Bank of America reported a quarterly profit of 80 cents per share, 5 cents higher than expected. Street forecasts were topped by revenue. Bank of America shares were up in the premarket.

The bank beat estimates with quarterly earnings of 86 cents per share. Revenue was in line with predictions. Higher interest rates helped its results.

The financial services company reported a quarterly profit of $1.77 per share, beating the consensus estimate of 1.54 a share. The board of Synchrony approved the addition of $2.8 billion to the company's stock buy back plan as well as a 5% dividend increase.

The board of Southwest Gas authorized the review of a full range or strategic alternatives after receiving an interest in the company well in excess of investor Carl Icahn.

Didi Global posted a loss before the market opened after it reported a drop in revenue. Didi said a shareholder meeting would be held on May 23 to vote on delisting from the New York Stock Exchange.

The restaurant operator's stock fell in the premarket after it was upgraded by a broker.

The insurance company was lowered to an Underweight from a neutral position by the investment firm, which thinks the company is likely to miss earnings estimates. The company fell in the premarket trading.