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Arena Pharmaceuticals Granted Patent for Drug Screening Methods Related to Ortho McNeil, Inc. Collaboration
via COMTEX

August 11, 2005

SAN DIEGO, Aug 11, 2005 /PRNewswire-FirstCall via COMTEX/ --

Arena Pharmaceuticals, Inc. (Nasdaq: ARNA) announced today that it was granted patent number 1133559, entitled "HUMAN ORPHAN G PROTEIN-COUPLED RECEPTOR RUP3," by the European Patent Office. The patent relates to certain drug screening methods utilizing the 19AJ receptor, an orphan G protein-coupled receptor, or GPCR, which was discovered by Arena and is active in regulating blood glucose levels in a glucose-dependent manner. The invention set forth in the patent was utilized to identify the orally bioavailable compounds that Ortho-McNeil, Inc., a Johnson & Johnson company, and Arena are developing to treat diabetes as part of the collaboration they initiated in December 2004.

"This patent highlights the value of Arena's approach to the discovery and development of potential drugs that target orphan GPCRs, where the natural ligand is unknown," commented Jack Lief, Arena's President and Chief Executive Officer. "In partnership with Ortho-McNeil, Inc., the 19AJ program is making good progress towards its goal of developing an orally bioavailable drug that can effectively regulate blood glucose levels in a glucose-dependent manner, avoiding the potential for hypoglycemia."

19AJ is an orphan GPCR preferentially expressed in beta cells, the cells in the pancreas responsible for producing insulin in response to increases in blood glucose. Preclinical results indicate that stimulating the 19AJ receptor allows beta cells to produce insulin more efficiently in response to changes in blood glucose levels. In addition, stimulation of the 19AJ receptor has been found to increase levels and activity of intracellular factors thought to be involved in the preservation of beta cells.

Unlike the GLP-1 receptor, another beta-cell receptor responsible for secreting insulin in a glucose-dependent manner, the 19AJ receptor is amenable to small molecule, orally bioavailable drug development. Arena has discovered potent, selective and orally available small molecule agonists of the 19AJ receptor that improve glucose tolerance and lower blood glucose levels in animal models of diabetes. The 19AJ mechanism is glucose dependent: in animal studies, 19AJ agonists only lowered blood glucose when it rose above normal levels, such as after a meal. Therefore, unlike the glucose-insensitive sulphonylureas, 19AJ agonists neither lowered normal fasting blood glucose nor caused hypoglycemia.

About Diabetes

The International Diabetes Foundation has estimated that in 2001 there were 177 million adults with diabetes worldwide, an increase of 17% over the number in 2000. This estimate includes 21.4 million in the United States and 32.2 million in the European Union. Approximately 90%, or 160 million, of diabetics suffer from type 2 diabetes, the adult-onset form of the disease. Type 2 diabetes is characterized by inadequate response to insulin and/or inadequate secretion of insulin as blood glucose levels rise. Therapies for type 2 diabetes are directed toward correcting the body's inadequate response with oral and injectable medications, or directly modifying insulin levels through direct injection of insulin or insulin analogs.

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 proprietary 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 in Phase 2b. 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 scheduled to begin a Phase 2 clinical trial by the end of 2005. As part of Arena's partnership 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.

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 progress of, and expectations relating to, Arena's collaboration with Ortho-McNeil, Inc. and related compounds and other statements about Arena's strategy, goals, expectations, technologies, preclinical and clinical programs, and ability to develop compounds. 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, Ortho-McNeil's and Arena's success in developing compounds under the collaboration with Arena, the timing, success and cost of Arena's research, out-licensing endeavors and clinical studies, Arena's ability to obtain additional financing, and the timing and receipt of payments and fees, if any, from Arena's collaborators, including Merck and Ortho-McNeil. 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
President and CEO

David Walsey
Director, Corporate Communications

Arena Pharmaceuticals
(858) 453-7200, ext. 1682

Susan Neath
Atkins + Associates
Media & Investor Relations
(858) 527-3486

SOURCE Arena Pharmaceuticals, Inc.

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, Susan Neath of Atkins + Associates, +1-858-527-3486, for Arena
Pharmaceuticals

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