Arena Pharmaceuticals and Aristea Therapeutics Establish Collaboration for Development of RIST4721 for Treatment of Serious Immune-Mediated Inflammatory Diseases

Agreement Provides Arena with Exclusive Option to Acquire Aristea and its CXCR2 Programs post-Phase 2

Arena Pharmaceuticals, Inc. (NASDAQ:ARNA) and Aristea Therapeutics, Inc. today announced a strategic collaboration to advance the clinical development of RIST4721, an oral CXCR2 antagonist being developed by Aristea for the treatment of palmoplantar pustulosis (PPP) and other neutrophil-mediated diseases.

Under the terms of the agreement, Arena will provide a $60 million upfront payment to Aristea and a $10 million equity investment in Aristea's Series B financing. In return, Aristea has granted Arena an exclusive option to acquire Aristea, including rights to all CXCR2 programs, upon completion of the Phase 2b study of RIST4721 in PPP. The agreement also provides a framework during the option period for the companies to jointly explore the development of additional neutrophil-mediated diseases, including hidradenitis suppurativa (HS) and inflammatory bowel disease (IBD), potentially generating multiple data readouts during the option period.

Separately, Aristea announced today the closing of a $63 million Series B financing led by Fidelity Management & Research Company, LLC, with participation by existing investor Novo Holdings A/S and new investors Arena Pharmaceuticals and funds managed by Tekla Capital Management, LLC.

"The collaboration and option agreement with Aristea provides Arena with an opportunity to bolster our early- to mid-stage immunology pipeline in two of our core therapeutic areas, dermatology and gastroenterology," said Amit D. Munshi, President and Chief Executive Officer of Arena Pharmaceuticals. "We look forward to working closely with the Aristea team with the goal of bringing a novel therapy to patients with neutrophilic diseases."

"This collaboration reflects Arena's commitment to Aristea's highly innovative science, the significant progress we have made in exploring best-in-class therapeutics for serious and rare inflammatory diseases, and the value of our clinical pipeline," said James M. Mackay, Ph.D., Chief Executive Officer of Aristea Therapeutics. "There are currently no approved therapies for PPP in U.S. or EU. Our lead candidate product, RIST4721, has completed a Phase 2a study and it is on track to initiate Phase 2b. We look forward to our productive collaboration with Arena and to accelerating the development of RIST4721 to bring this therapy to patients."

Conference Call & Webcast Information

Arena will host a conference call and live webcast to discuss the announcement with the investment community today, Tuesday, July 27, 2021, at 4:45 PM ET. Conference call will be broadcast live in listen-only mode on the company's investor relations website at https://invest.arenapharm.com/events-presentations. To ask questions, please use the dial-in information below:

Dial-in: (877) 643-7155 (United States) or (914) 495-8552 (International)

Conference ID: 7026617

About RIST4721 and Palmoplantar Pustulosis (PPP)

RIST4721 is an oral CXCR2 antagonist being developed for the treatment of PPP with results reported from its Phase 2a clinical trial in 2020. PPP is a debilitating condition that is characterized by repeated flares of sterile neutrophil-filled pustules that lead to redness and thickening on the palms of the hands and/or the soles of the feet and associated pain, itching and burning sensations. CXCR2 plays important roles in neutrophil recruitment to inflammatory sites and represents a promising therapeutic target for the treatment of neutrophil-mediated inflammatory diseases. Later this year, Aristea is initiating a Phase 2b study to investigate RIST4721 in PPP and plans to expand development into two additional orphan indications, familial Mediterranean fever (FMF) and Behcet's disease.

About Arena Pharmaceuticals

ARENA Pharmaceuticals is a team with a singular purpose – deliver important medicines to patients. In a rapidly changing global market, we work with a sense of urgency every day to understand the needs of all our stakeholders, identify bold, sometimes disruptive, ideas to get medicines to patients, and relentlessly execute until it's done.

We are developing a richly diversified portfolio of therapeutic candidates targeting gastroenterology, dermatology and cardiology. Our pipeline includes four investigational medicines in eight indications and eleven ongoing or planned clinical trials. To fuel our growth, we are unlocking the value of our historical GPCR research with a sustainable discovery engine for broad portfolio expansion.

Arena's lead investigational compound in dermatology, etrasimod, is a highly selective, once-daily, oral sphingosine 1-phosphate (S1P) receptor modulator intended to provide systemic and local effects on specific immune cell types with the potential to treat multiple immune-mediated inflammatory diseases, including ulcerative colitis, Crohn's disease, eosinophilic esophagitis, atopic dermatitis, and alopecia areata.

ARENA - Care More. Act Differently.

About Aristea Therapeutics

Aristea Therapeutics (Air-iss-tay-uh) is a clinical-stage immunology focused drug development company developing novel therapies to treat serious inflammatory orphan diseases. The Aristea team is leveraging its broad industry expertise and proven success in drug development to form synergistic partnerships and build a pipeline of novel drugs. Aristea's lead program, RIST4721, is currently in Phase 2 clinical development. Aristea is headquartered in San Diego, CA.

To learn more, please visit www.aristeatx.com and follow us on social media @Aristeatx

Forward-Looking Statements

Certain statements in this press release are forward-looking statements that involve a number of risks and uncertainties. These forward-looking statements may be identified by introductory words such as "development," "option," "will," "opportunity," "potentially," "goal," "look forward to," "promising," "later this year," "investigate," "targeting," "intended to," "plans," "potential," or words of similar meaning, or by the fact that they do not relate strictly to historical or current facts. Such forward-looking statements include, without limitation, statements about the collaboration between Arena and Aristea, including its effectiveness and focus, Arena's exclusive option to acquire Aristea, including rights to all CXCR2 programs, potential data readouts, potential payments to Aristea, and the opportunity and commitment that the collaboration represents; Aristea's science, progress, and pipeline, including the potential to be best-in-class; the potential of Aristea's CXCR2 programs, including the potential development, FDA approval and commercialization of RIST4721 and the potential for RIST4721 to serve as a treatment for PPP, HS, IBD, or other neutrophil mediated diseases; Arena's purpose, work, ideas, execution, portfolio, pipeline, ongoing and planned trials, research, and discovery engine; etrasimod, including its design and potential; and Aristea's focus, partnerships, and pipeline. 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 and Aristea's expectations. Factors that could cause actual results to differ materially from the forward-looking statements include, without limitation, the following: the collaboration is subject to closing conditions, including regulatory approval, which may not be satisfied or occur; Arena may never exercise its exclusive option to acquire Aristea, including rights to all CXCR2 programs; clinical trials and other studies may not proceed at the time or in the manner expected or at all; enrolling patients in ongoing and intended clinical trials is competitive and challenging; risks related to unexpected or unfavorable new data; results of clinical trials and other studies are subject to different interpretations and may not be predictive of future results; nonclinical and clinical data are voluminous and detailed, and regulatory agencies may interpret or weigh the importance of data differently and reach different conclusions than Arena, Aristea, or others, request additional information, have additional recommendations or change their guidance or requirements before or after approval; the timing and outcome of research, development and regulatory review is uncertain; Arena's and Aristea's ability to obtain financing on favorable terms; Arena's and Aristea's expectations regarding the need to raise additional funds to advance all of their programs; you and others may not agree with the manner in which Arena and Aristea allocate their resources; drug candidates may not advance in development or be approved for marketing; risks related to developing and commercializing drugs, including regulatory, manufacturing and supply issues and the availability and use of RIST4721; risks and uncertainties relating to cash and revenues that may be generated from product sales or other sources, including the impact of competition; risks related to relying on partner performance; risks related to government and other third party actions, including decisions and other actions relating to approval, reimbursement and pricing; our and third parties' intellectual property rights; and satisfactory resolution of litigation or other disagreements with others. With respect to Arena, additional factors that could cause actual results to differ materially from those stated or implied by forward-looking statements are disclosed in Arena's filings with the Securities and Exchange Commission (SEC), including but not limited to Arena's most recent Annual Report on Form 10-K and Quarterly Report on Form 10-Q. Arena and Aristea are providing this information as of the date of this press release, and Arena and Aristea disclaim any intent or obligation to update these forward-looking statements, other than as may be required under applicable law.

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