Walgreens, the largest U.S. drugstore chain, said it will close the stores amid plans to boost its previously announced cost-cutting initiative by $500 million. Walgreens expects to reduce costs by a projected $1.5 billion by the end of fiscal 2017, the company said. “After a rigorous analysis, the company has identified additional opportunities for cost savings, primarily in its Retail Pharmacy USA division,” the company said Thursday.