U.S. RESEARCH ROUNDUP-Alkermes, Chesapeake Energy Corp, Latam Airlines

Oct 21 (Reuters) - Wall Street securities analysts revised their ratings and price targets on several U.S.-listed companies, including Alkermes, Benchmark Electronics and Copa Holdings on Friday. HIGHLIGHTS * Chesapeake Energy Corp : Nomura raises to neutral from reduce * Latam Airlines : Santander raises to buy from hold * Proofpoint Inc : Piper Jaffray raises target price to $90 from $85; overweight Following is a sum