UPDATE 1-Arena to cut 25 pct jobs to focus on obesity pill

* Plans to cut 66 jobs by March 28

* Sees related charge of $3.8 mln

* Says job cut to reduce annual expense by $13.5 mln

* Shares down 4 pct

Jan 27 (Reuters) - Arena Pharmaceuticals Inc (ARNA.O) said it will cut about 25 percent of its U.S. jobs, or about 66 employees, to conserve cash and focus its resources on getting regulatory approval for its obesity drug.

Arena expects the job cut, to be completed around March 28, to reduce annual cash expense by about $13.5 million, and sees restructuring charges of about $3.8 million, mainly in the first quarter of 2011.

Lorcaserin, the company's experimental obesity pill, was rejected by U.S. health regulators last October citing cancer risks.

Arena said it still expects to resubmit the new drug application by the end of 2011, and is in talks with the regulator to finalize the protocols for activities designed to address the issues raised by the Food and Drug Administration.

Shares of the company were down 4 percent at $1.91 in after-hours trade. They closed at $2 on Thursday on Nasdaq. (Reporting by Esha Dey in Bangalore; Editing by Vyas Mohan)