Arena Pharmaceuticals, Inc. Announces Anti-thrombosis Program To Be Advanced Into Preclinical Development

SAN DIEGO, Dec. 29 /PRNewswire-FirstCall/ -- Arena Pharmaceuticals, Inc. announced today that it is advancing APD791 into preclinical development from its cardiovascular research program, and expects to initiate clinical development in approximately one year. APD791 is a selective inverse agonist of the 5-HT2A serotonin receptor. By selectively inhibiting the activation of 5-HT2A serotonin receptors found on platelets and vascular smooth muscle, Arena believes that APD791 may reduce the risk of arterial thrombosis and conditions such as acute coronary syndrome, heart attack and stroke.

"APD791 represents a potential new approach to reducing the risk of arterial thromboembolic disease, a public health problem with significant mortality and morbidity," stated Jack Lief, Arena's President and Chief Executive Officer. "The advancement of this program further demonstrates Arena's ability to sustain the growth and diversification of its pipeline."

About Thrombosis

Thrombosis is the formation of a clot, or thrombus, inside a blood vessel that restricts the flow of blood. The formation of a thrombus is often caused by an injury to the wall of a blood vessel, such as the rupture of an arterial plaque. The injury to the blood vessel activates platelets which then aggregate and adhere to one another as they start to release certain platelet activating and clotting factors, including serotonin, to facilitate thrombosis. Thrombi that form in diseased atherosclerotic arteries may obstruct larger vessels or may break apart and form smaller thrombi that travel through the blood stream, or embolize, blocking blood flow in smaller vessels. Thrombi that block vessels in the heart may cause acute coronary syndrome or myocardial infarction, and those blocking the vessels of the brain may cause stroke.

About APD791

Stimulation of the 5-HT2A serotonin receptor on platelets and vascular smooth muscle is thought by Arena to play an important role in the cascade of events leading to arterial thromboembolic diseases. Normally, when a platelet is activated by one of a number of clotting and aggregating factors, such as thrombin or collagen, the platelet releases serotonin, which enhances platelet aggregation and promotes vasoconstriction and intimal hyperplasia, or thickening of the vessel wall. APD791, discovered by Arena, is a novel and orally bioavailable selective inverse agonist of the 5-HT2A serotonin receptor. By a blockade of the 5-HT2A receptor on platelets and other cardiovascular tissues, APD791 may inhibit platelet aggregation, vasoconstriction, and intimal hyperplasia, thereby reducing the risk of arterial thrombosis. Preclinical studies indicate that APD791 potentially has an improved therapeutic index over currently marketed anti-platelet drugs. Arena believes the potential improvement is due to a separation of antithrombotic activity from the increased bleeding that may be seen as a treatment effect of these currently marketed drugs.

About Arena Pharmaceuticals

Arena is a clinical-stage biopharmaceutical company focusing on the discovery, development and commercialization of small molecule drugs in four major therapeutic areas: metabolic, cardiovascular, inflammatory and central nervous system diseases. Arena is developing a broad pipeline of compounds that act on an important class of drug targets called G protein-coupled receptors, or GPCRs, using its knowledge of GPCRs and its technologies, including CART(TM) (Constitutively Activated Receptor Technology) and Melanophore. Arena has three internally discovered, clinical-stage product candidates. Arena's most advanced clinical compound, APD356, a selective 5-HT2C serotonin receptor agonist for the treatment of obesity, is expected to enter Phase 3 clinical development in the middle of 2006. Arena's lead product candidate for the treatment of insomnia, APD125, a compound with a novel mechanism of action (a selective 5-HT2A receptor inverse agonist), is expected to enter Phase 2 clinical development in early 2006. As part of Arena's collaboration with Merck & Co., Inc., an Arena product candidate for the treatment of atherosclerosis and related disorders is in a Phase 1 clinical trial. Arena also has an active collaboration with Ortho-McNeil, Inc., a Johnson & Johnson company, for the treatment of type 2 diabetes.

Arena Pharmaceuticals(R) and Arena(R) are registered service marks of the company. CART(TM) is an unregistered service mark of the company. "APD" is an abbreviation for Arena Pharmaceuticals Development.

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include statements about the initiation of clinical development of APD791, expectations related to APD791, including whether or how APD791 may be effective, Arena's ability to sustain the growth and diversification if its pipeline, the timing of the expected Phase 2 clinical trial of APD125 and the expected Phase 3 clinical trial of APD356, and other statements about Arena's strategy, technologies, preclinical and clinical programs, and ability to develop compounds and commercialize drugs. For such statements, Arena claims the protection of the Private Securities Litigation Reform Act of 1995. Actual events or results may differ materially from Arena's expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, but are not limited to, the FDA may not allow the Phase 2 clinical trial of APD125 to proceed at the time Arena expects or at all, the results of preclinical studies or clinical trials may not be predictive of future results, any unfavorable results of APD791 preclinical studies, Arena's ability to partner APD356, APD125 or other of its compounds or programs, the timing, success and cost of Arena's research, out-licensing endeavors and clinical trials, Arena's ability to obtain additional financing, Arena's ability to obtain and defend its patents, and the timing and receipt of payments and fees, if any, from Arena's collaborators. Additional factors that could cause actual results to differ materially from those stated or implied by Arena's forward-looking statements are disclosed in Arena's filings with the Securities and Exchange Commission. These forward-looking statements represent Arena's judgment as of the time of this release. Arena disclaims any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.

Contacts: Jack Lief Carin Canale President and CEO Atkins + Associates Media & Investor Relations David Walsey (858) 527-3498 Director, Corporate Communications Arena Pharmaceuticals (858) 453-7200, Ext. 1682

Arena Pharmaceuticals, Inc.

CONTACT: Jack Lief, President and CEO, or David Walsey, Director,Corporate Communications, both of Arena Pharmaceuticals, +1-858-453-7200,ext. 1682; or Media & Investor Relations, Carin Canale of Atkins +Associates, +1-858-527-3498, for Arena Pharmaceuticals, Inc.

Web site: http://www.arenapharm.com//