Merck (NYSE:MRK) has agreed to acquire the biopharma Acceleron Pharma (NSDQ:XLRN) for $180 per share in cash, bringing the purchase price to roughly $11.5 billion. The companies expect the deal to close in the fourth quarter of 2021. Cambridge, Massachusetts–based Acceleron specializes in developing drugs that aim to balance transforming growth factor (TGF)-beta, which plays…