Early movers: TWTR, CBS, WMT, BA, KMI, PEP, AZN & more

Check out which companies are making headlines before the bell:

Twitter — Twitter was downgraded to "neutral" from "buy" at SunTrust, which said user growth and engagement continue to be "challenged."

CBS — The media giant filed to take its CBS Radio business public. The company currently operates 117 radio stations and preliminary plans indicate that roughly $100 million would be raised in the planned initial public offering.

Zoetis — The pet vaccine business spun off by Pfizer in 2013 saw Bill Ackman's Pershing Square Capital Management cut its stake to 3.8 percent by selling another six million shares in the company. At one time, Pershing had a stake as large as eight percent.

Wal-Mart Stores — The retailer is offering free shipping with no minimum purchase through Friday, as it stages a retail battle against Amazon.com's Prime Day, scheduled for tomorrow.

Boeing — Boeing struck new partnership deals with the U.K. government, involving maritime patrol aircraft as well as new research and development spending.

Comcast — Comcast's Universal Pictures scored a number one hit at the box office over the weekend, with "The Secret Life of Pets" chalking up $103.2 million in North American ticket sales. (Disclosure: Comcast is the parent of NBC Universal and CNBC.)

WellCare Health Plans, Centene Corp. — The two companies have each made offers for the Medicare Advantage plans that insurer Aetna is seeking to sell, according to Reuters. Aetna is selling those plans in its effort to gain approval from regulators for its deal to buy Humana.

Kimberly-Clark — The consumer goods maker is shutting down its operations in Venezuela due to a slumping economy, which has resulted in significant consumer inflation and goods shortages.

Nintendo — The gamemaker's shares continue to surge, on the soaring popularity of its new smartphone game Pokeman Go, launched last Wednesday.

Sagent Pharmaceuticals — Sagent will be acquired by Japan's Nichi-Iko Pharmaceutical for $736 million or $21.75 per share in cash. That compares to a Friday close of $15.50 for the U.S.-based maker of hospital pharmaceuticals.

Kinder Morgan — The pipeline operator sold a 50 percent stake in its southeastern pipeline system to electric and gas utility Southern Co. for $1.47 billion. Kinder Morgan will use the proceeds to pay down debt.

PepsiCo — PepsiCo was interested in buying WhiteWave Foods, according to the New York Post, but thought the price was too high. France's Danone announced a deal to buy WhiteWave last Thursday.

AstraZeneca — AstraZeneca is considering a late bid for drugmaker Medivation, according to a report on London's Sunday Times. Medivation opened its books to Pfizer and Sanofi last week and is reportedly talking to other potential bidders, as well.

Hewlett Packard Enterprise — The Hewlett-Packard spin-off is considering the sale of some software assets, according to a Bloomberg report. The process is said to be in the preliminary stages and may not results in any deals.

WebMD — Mizuho began coverage on the health care information website operator with a "buy" rating, based on valuation and a dominant market share in a growing pharma online ad market, among other factors.

Halliburton — Jefferies added the oilfield services company's stock to its "franchise pick" list, based on projected recovery in demand growth.

Yahoo — Pivotal Research downgraded Yahoo to "hold" from "buy," based in part on declining market share in digital advertising.

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