Omeros Corporation Announces Upcoming Presentations at ASH Annual Meeting

-- New and Updated Data from Ongoing Phase 2 Study of OMS906 in Paroxysmal Nocturnal Hemoglobinuria Selected for Podium Presentation --

Omeros Corporation (Nasdaq: OMER) today announced that two abstracts directed to OMS906, Omeros’ investigational inhibitor of MASP-3, the key activator of the alternative pathway of complement, will be presented at the 65th Annual Meeting of the American Society of Hematology (ASH), to be held December 9-12, 2023 in San Diego.

Both abstracts were published today and are now available on the ASH website at www.hematology.org. Details of the congress presentations are found below.

OMS906, a Novel Alternative Pathway MASP-3 Inhibitor, Normalizes Hemoglobin Levels and Increases Clone Size in Treatment-Naïve PNH Patients (Abstract #573) Session Name: 508. Bone Marrow Failure: Acquired: Unraveling the Future of PNH Therapy from Clinical Trials Date: Sunday, December 10, 2023 Podium Presentation Time: 5:00 p.m. PT Location: San Diego Convention Center, Room 7

Alternative Pathway MASP-3 Inhibitor OMS906 Effectively and Potently Inhibits Complement-Mediated Hemolysis in Preclinical Models Mechanistically Similar to Paroxysmal Nocturnal Hemoglobinuria (Abstract #4082) Session Name: 508. Bone Marrow Failure: Acquired: Poster III Date: Monday, December 11, 2023 Presentation Time: 6:00 p.m. - 8:00 p.m. PT Location: San Diego Convention Center, Halls G-H

The presentation materials associated with each abstract will be made available on Omeros’ website at www.omeros.com following the congress presentations.

About OMS906

OMS906 is an investigational human monoclonal antibody targeting mannan-binding lectin-associated serine protease-3 (MASP-3), the key activator of the complement system’s alternative pathway. The complement system plays a central role in inflammation and becomes activated as a result of tissue damage or microbial infection. Responsible for the conversion of pro-complement factor D to complement factor D, MASP-3 is believed to be the premier target in the alternative pathway – it has the lowest native circulating level and low relative clearance compared to the other alternative pathway proteins and, unlike C5 and C3 blockers, MASP-3 inhibition leaves intact the lytic arm of the classical pathway, important for fighting infection. Also, unlike other components of the alternative pathway, MASP-3 is believed not to be an acute phase reactant, which could provide a significant advantage to MASP-3 inhibitors, like OMS906, over other alternative pathway inhibitors. MASP-3 inhibitors are thought to have preventive or therapeutic effects across a broad range of diseases including paroxysmal nocturnal hemoglobinuria (PNH), hemolytic uremic syndrome (HUS), atypical HUS, traumatic brain injury, arthritis, wet age-related macular degeneration, ischemia-reperfusion injury, transplant-related complications and other immune-related disorders.

About Omeros Corporation

Omeros is an innovative biopharmaceutical company committed to discovering, developing and commercializing small-molecule and protein therapeutics for large-market and orphan indications targeting immunologic disorders including complement-mediated diseases, cancers, and addictive and compulsive disorders. Omeros’ lead MASP-2 inhibitor narsoplimab targets the lectin pathway of complement and is the subject of a biologics license application (BLA) pending before FDA for the treatment of hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA). Omeros’ long-acting MASP-2 inhibitor OMS1029 is currently in a Phase 1 clinical trial. OMS906, Omeros’ inhibitor of MASP-3, the key activator of the alternative pathway of complement, is advancing in clinical programs for paroxysmal nocturnal hemoglobinuria (PNH), complement 3 (C3) glomerulopathy. Funded by the National Institute on Drug Abuse, Omeros’ lead phosphodiesterase 7 (PDE7) inhibitor OMS527 is in clinical development for the treatment of cocaine use disorder (CUD) and is also being developed as a therapeutic for other addictions as well as for a major complication of treatment for movement disorders. Omeros also is advancing a broad portfolio of novel immuno-oncology programs comprised of two cellular and three molecular platforms. For more information about Omeros and its programs, visit www.omeros.com

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Jennifer Cook Williams Cook Williams Communications, Inc. Investor and Media Relations [e-mail]