(ARNA) Positive Results Phase 1b of APD334 in Autoimmune Diseases

– Trial results show novel S1P1 modulator produced strong, dose-dependent lymphocyte lowering – – No clinically significant safety findings relative to heart, liver or pulmonary function –

SAN DIEGO, Jan. 7, 2015  — Arena Pharmaceuticals, Inc. (NASDAQ: ARNA) today announced top-line results from a Phase 1b multiple ascending dose clinical trial for APD334, an oral drug candidate that targets the sphingosine 1-phosphate subtype 1 (S1P₁) receptor for the potential treatment of autoimmune diseases.

In the Phase 1b clinical trial, APD334 demonstrated a dose-dependent effect on lymphocyte count lowering in blood, with mean decreases from baseline of up to 69%. Lymphocyte counts, on average, recovered to baseline within one week of conclusion of dosing. There were no clinically significant safety findings with respect to heart rate or rhythm or pulmonary function, and no clinically significant elevations in liver enzyme tests. The most common treatment-emergent adverse events were mild or moderate contact dermatitis, headache, constipation and diarrhea, with none being clearly drug related. There were no discontinuations for adverse events, and no serious adverse events were observed.

“Lymphocyte lowering at the level demonstrated in this trial has been shown to correlate with clinical efficacy in Phase 2 and Phase 3 trials of other S1P₁ modulators in multiple sclerosis, psoriasis and ulcerative colitis,” said William R. Shanahan, M.D., Arena’s Senior Vice President and Chief Medical Officer. “The results of this trial support investigation of the efficacy and safety of APD334 in patients with autoimmune diseases.”

The randomized, double-blind, placebo-controlled Phase 1b clinical trial evaluated the safety, tolerability, pharmacodynamics and pharmacokinetics of multiple-ascending doses of APD334. In five different dosing cohorts, a total of 50 healthy volunteers received APD334 and 10 received placebo for 21 days.

“Based on these impressive results, we plan to expedite APD334 into Phase 2 clinical trials for ulcerative colitis and Crohn’s disease,” said Jack Lief, Arena’s President and Chief Executive Officer. “The advancement of this promising drug candidate further demonstrates Arena’s focused expertise in discovering and developing innovative drug candidates targeting G protein-coupled receptors that have the potential to improve health.”

About Autoimmune Diseases

Autoimmune diseases, such as multiple sclerosis, psoriasis, ulcerative colitis, Crohn’s disease and rheumatoid arthritis, are characterized by an inappropriate immune response against substances and tissues that are normally present in the body. In an autoimmune reaction, a person’s antibodies and immune cells target healthy tissue, triggering an inflammatory response. Reducing the immune and/or inflammatory response is an important goal in the treatment of autoimmune diseases.

About APD334

APD334 is a potent and selective, orally available investigational drug candidate that targets the S1P₁ receptor. Discovered by Arena, APD334 has therapeutic potential in autoimmune diseases. S1P₁ receptors have been demonstrated to be involved in the modulation of several biological responses, including lymphocyte trafficking from lymph nodes to the peripheral blood. By isolating lymphocytes in lymph nodes, fewer immune cells are available in the circulating blood to effect tissue damage.

About Arena Pharmaceuticals

Arena is embracing the challenge of improving health by seeking to bring innovative medicines targeting G protein-coupled receptors to patients. Arena’s internally discovered drug, BELVIQ® (lorcaserin HCl), is approved in the United States, and Arena is focused on discovering, developing and commercializing additional drugs to address unmet medical needs. Arena’s US operations are located in San Diego, California, and its operations outside of the United States, including its commercial manufacturing facility, are located in Zofingen, Switzerland. For more information, visit Arena’s website at www.arenapharm.com.

Arena Pharmaceuticals® and Arena® are registered service marks of Arena Pharmaceuticals, Inc. BELVIQ® is a registered trademark of Arena Pharmaceuticals GmbH.

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 advancement, investigation, therapeutic indication, use, safety, efficacy, mechanism of action, and potential of APD334, including as a potential treatment for one or more autoimmune diseases; the significance of the trial results for APD334, including with respect to lymphocyte lowering and safety; the significance of lymphocyte lowering and reducing the immune and/or inflammatory response; expediting the development of APD334, including future trials and investigated indications; Arena’s expertise in discovering and developing drug candidates that have the potential to improve health; embracing the challenge of improving health; seeking to bring innovative medicines to patients; and Arena’s focus, plans, goals, strategy, expectations, research and development programs, and ability to discover and 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 following: top-line results are not comprehensive and are based on a preliminary analysis of then available data, and findings and conclusions related to the trial are subject to change following a more comprehensive review of the data; APD334 may not be developed, approved for marketing or commercialized for any disease or condition; risks related to commercializing drugs, including regulatory, manufacturing, supply and marketing issues and the availability and use of BELVIQ; cash and revenues generated from BELVIQ, including the impact of competition; Arena’s revenues will be based in part on estimates, judgment and accounting policies, and incorrect estimates or disagreement regarding estimates or accounting policies may result in changes to Arena’s guidance or previously reported results; the timing and outcome of regulatory review is uncertain, and BELVIQ may not be approved for marketing when expected or ever in combination with another drug, for another indication or using a different formulation or in any other territory for any indication; regulatory decisions in one territory may impact other regulatory decisions and Arena’s business prospects; government and commercial reimbursement and pricing decisions; risks related to relying on collaborative arrangements; the timing and receipt of payments and fees, if any, from collaborators; the entry into or modification or termination of collaborative arrangements; unexpected or unfavorable new data; nonclinical and clinical data is voluminous and detailed, and regulatory agencies may interpret or weigh the importance of data differently and reach different conclusions than Arena or others, request additional information, have additional recommendations or change their guidance or requirements before or after approval; data and other information related to any of Arena’s research and development may not meet regulatory requirements or otherwise be sufficient for (or Arena or a collaborator may not pursue) further research and development, regulatory review or approval or continued marketing; Arena’s and third parties’ intellectual property rights; the timing, success and cost of Arena’s research and development; results of clinical trials and other studies are subject to different interpretations and may not be predictive of future results; clinical trials and other studies may not proceed at the time or in the manner expected or at all; having adequate funds; and satisfactory resolution of litigation or other disagreements with others. 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.

Contact: Arena Pharmaceuticals, Inc.	Media Contact: Russo Partners
Craig M. Audet, Ph.D., Senior Vice President,	David Schull, President
Operations & Head of Global Regulatory Affairs	david.schull@russopartnersllc.com
caudet@arenapharm.com	858.717.2310
858.453.7200, ext. 1612
www.arenapharm.com