BOSTON, April 4 (Reuters) - Sarissa Capital Management LP, the activist hedge fund run by Alexander Denner that invests in pharmaceutical and healthcare companies, has hired asset management veteran Eric Vincent as president, according to his LinkedIn profile and two people familiar with the matter. Sarissa is seeking to cross the $1 billion mark in assets under management by attracting new investors at a time when demand for hedge funds is picking up again. Scale is important for firms like Sarissa, which pressure companies to adopt their proposals and give them board seats.