Business Description

Overview We are a clinical-stage biotechnology company developing novel small molecule therapeutics to treat unmet needs in immune-mediated diseases. In October 2025, we announced plans to explore strategic alternatives focused on maximizing stockholder value after being unable to align with the U.S. Food and Drug Administration, or FDA, on a potential registrational clinical trial of zetomipzomib, a novel, selective inhibitor of the immunoproteasome in patients with relapsed and refractory autoimmune hepatitis, or AIH. Following this announcement, we have been implementing a restructuring plan and wind-down of our business operations to focus on strategic alternatives for zetomipzomib development. In January 2026, we announced that the FDA Division of Hepatology and Nutrition granted us a new Type C meeting to discuss the development of zetomipzomib in patients with AIH. This Type C meeting would involve a review of a potential global, randomized Phase 2b clinical study of zetomipzomib in patients with relapsed and refractory AIH. As part of the briefing package submitted to the FDA, Kezar submitted pharmacokinetic and hepatic safety data analyses from previously conducted clinical trials to support a proposal for parallel AIH and hepatic impairment studies. Kezar also submitted additional safety data and an updated risk-mitigation plan aimed to modify the previous requirement issued from the FDA to require 48-hour in-unit patient monitoring in future AIH studies. In March 2026, we completed a successful Type C with the FDA during which the FDA provided constructive feedback and critical guidance on the regulatory pathway for development of zetomipzomib in AIH, including agreement with us on treatment duration, endpoints and enrollment criteria. In addition, the FDA provided additional guidance around safety monitoring that we believe will enable a technically feasible clinical trial of zetomipzomib in AIH. Zetomipzomib is currently the only investigative agent to have demonstrated steroid sparing clinical activity in AIH patients who are refractory or intolerant to standard of care therapies. Our product candidate, zetomipzomib, is a first-in-class selective immunoproteasome inhibitor in development for the treatment of severe autoimmune diseases of high unmet medical need. We believe that the immunoproteasome is a validated target for the treatment of a wide variety of immune-mediated diseases given its ability to regulate multiple drivers of the inflammatory disease process. Many inflammatory disorders are currently treated one cytokine or cell type at a time, but the immunoproteasome affects a broad spectrum of immune regulators. Based on clinical data generated to date, we believe that zetomipzomib has the potential to address multiple chronic immune-mediated diseases. We previously studied an oncology product candidate, KZR-261, in an open-label Phase 1 clinical trial designed to evaluate safety and tolerability, pharmacokinetics and pharmacodynamics, as well to explore preliminary anti-tumor activity. KZR-261 was discovered as part of our Sec61-based research program. In August 2024, we announced that we had stopped enrollment in the KZR-261 Phase 1 clinical trial and ceased our Sec-61 research program, and we reallocated clinical resources toward development of zetomipzomib. On March 6, 2026, we entered into an asset purchase agreement with Enodia Therapeutics SAS, or Enodia, pursuant to which Enodia (i) acquired all of our rights, title and interest in our Sec61-based discovery and development program assets, including KZR-261; and (ii) assumed liabilities from us related to certain transferred contracts and from the ownership, use, operation or maintenance of such assets under the asset purchase agreement. Clinical Development of Zetomipzomib Zetomipzomib is a clinical development candidate for AIH, a rare, chronic disease in which the immune system attacks the liver and causes inflammation and tissue damage, severely impacting patients’ health and quality of life. Lifelong maintenance therapy is required to avoid relapse and burdensome adverse effects. If left untreated, AIH can lead to cirrhosis, liver failure and hepatocellular carcinoma. Standard of care treatment for AIH involves daily corticosteroid use and/or chronic treatment with broad-based immunosuppressants, which together are associated with significant toxicities and often result in inadequate response or relapse after treatment withdrawal.…