(Reuters) - U.S. private equity firm Blackstone Group Inc has secured $3.4 billion from investors for its first fund dedicated to investments in the life sciences sector, targeting $4.6 billion in total, a regulatory filing showed on Thursday. At its target fundraising amount, the fund would be one of the biggest in the sector. The raise underscores investors' strong appetite for the lucrative returns associated with the development of high-impact drugs, as well as their tolerance for risk, given that a therapy's success is far from certain.