U.S. drugmaker Pfizer (PFE.N) pressed the scientific case for its controversial plan to acquire AstraZeneca (AZN.L) on Monday as its chief executive prepared for a grilling from British lawmakers. In the latest phase of Pfizer’s campaign to counter critics of its proposed $106 billion deal, research head Mikael Dolsten said he had been through five different mergers and acquisitions and denied such big transactions disrupted drug research.