Lamar Advertising Co. (NasdaqGS:LAMR) is in advanced talks to buy billboard assets in five U.S. cities from Clear Channel Outdoor Holdings Inc. (NYSE:CCO) worth roughly $450 million, according to people familiar with the matter. Lamar is close to a deal to purchase Clear Channel Outdoor's billboard assets in Cleveland, Des Moines, Memphis, Reno and Seattle, the sources said, adding that the negotiations have not been finalized.