INTERVIEW-UPDATE 1-Arena to sell weight drug alone or with help

* Expects 2010 spending of up to $114 million

* Spending assumes Arena pays for pre-launch activities

* Shares fall 2.9 percent (Adds analyst comment, share price)

By Deena Beasley

LOS ANGELES, March 12 (Reuters) - Arena Pharmaceuticals Inc expects to launch sales of its weight loss drug -- alone or with a partner -- within 12 weeks of U.S. regulatory approval, according to the company.

Arena's shares fell almost 3 percent in Friday trading.

The U.S. Food and Drug Administration's deadline for review of the experimental drug, called lorcaserin, is Oct. 22.

Arena Chief Executive Officer Jack Lief told Reuters that the company aims to secure a commercial partner for lorcaserin before then, but is prepared to hire a contract sales team on its own if needed.

"We will certainly be ready to launch either with a commercialization organization or on our own within 12 weeks of hitting the go button," he said.

Arena and its rivals Vivus Inc and Orexigen Therapeutics Inc are each working to develop the first new prescription weight loss drug in a decade.

Lief said he expects the FDA to convene a panel of outside experts to review lorcaserin several weeks before the deadline.

"We are becoming increasingly concerned that given lorcaserin's (FDA review) date of Oct. 22, Arena has yet to secure a commercial partner," BMO Capital Markets analyst Jason Zhang said in research note.

Vivus and Orexigen are also seeking, but have yet to secure, partnerships for their potential weight loss drugs.

Obesity has become a full-fledged epidemic in the United States, but many drug treatments have failed while others have been abandoned due to safety issues.

Arena said on Friday that it expects to use cash and short-term investments of $97 million to $107 million for operations and interest expense in 2010, and another $7 million for capital expenditures, mainly related to a manufacturing facility in Switzerland.

Those spending figures assume that Arena, and not another pharmaceutical company, pays for the lorcaserin pre-commercial launch activities, but do not include costs for hiring a contract sales force.

"We plan to put in place an agreement with a contract sales organization to build a targeted sales force. If we need to, we can trigger that at any time," he said.

The CEO said that Arena, based in San Diego, is manufacturing lorcaserin at its Swiss facility and completing the build-out of its commercial supply chain.

The company is also taking steps to lay the groundwork for lorcaserin's entry into the market, such as working on a formulary access plan for managed care companies.

Lorcaserin works in a way similar to fenfluramine, which was part of the fen-phen diet cocktail that was withdrawn in 1997 after being linked to heart valve damage.

Arena's drug is designed to block appetite signals in the brain, but by being much more selective than fenfluramine in the receptors it affects. Fenfluramine also binds to a separate cell receptor in the heart. In clinical trials, lorcaserin was not associated with heart valve problems.

Arena also reported on Friday that its fourth-quarter net loss narrowed to $29.8 million, or 32 cents a share, from a loss of $62.5 million, or 84 cents a share, in the year-earlier quarter, due to lower research and development costs.

The company held cash and short-term investments of just over $115 million at the end of last year.

Shares of Arena were down 9 cents, or 2.9 percent, at $3.02 in afternoon trading on Nasdaq. (Editing by Gerald E. McCormick)