(Reuters) -Biogen beat Wall Street estimates for third-quarter profit, helped by better-than-expected sales of some of its multiple sclerosis treatments. The company, however, cut its annual profit forecast as it expects to take a hit of $1.25 per share from research and development charges related to certain acquisitions in the fourth quarter. Biogen said it is pursuing deals to build its early-stage pipeline amid declining sales of its once top-selling multiple sclerosis medicines in the face of stiff ...