FDA Gives GSK’s Nucala the Greenlight for Hypereosinophilic Syndrome


GlaxoSmithKline has been given the greenlight by the FDA to market its Nucala (mepolizumab) humanized monoclonal antibody for the treatment of hypereosinophilic syndrome (HES) without an identifiable non-blood-related cause of the disease in adults and children 12 years of age and older.

The pharma giant’s drug is already approved as an add-on maintenance treatment for severe eosinophilic asthma and eosinophilic granulomatosis with polyangiitis. The new approval makes it the first FDA-approved therapy in over a decade to treat HES and the third indication for the therapy overall.

"Today's approval marks the first time in over a decade that there is a new FDA-approved treatment option for patients with hypereosinophilic syndrome," said Ann Farrell, M.D., director of the Division of Nonmalignant Hematology in the FDA's Center for Drug Evaluation and Research, in a statement. "FDA is committed to helping develop safe and effective treatment options for this group of rare and debilitating blood diseases and other rare conditions."

HES represents a heterogeneous group of rare disorders characterized by persistent eosinophilia (abnormally elevated white blood cells) with corresponding evidence of organ damage. The skin, central nervous system, respiratory tract and heart are the most commonly affected organ systems in this disease. While HES affects only around 5,000 patients in the U.S. each year, it’s a debilitating disease which currently lacks a cure or robust management options.

The FDA approval granted to GSK’s mepolizumab for the treatment of HES was based on an agency review of the company’s pivotal Phase III trial data released last November. In this trial, a total of 108 patients with severe HES were randomized to either mepolizumab or placebo injections administered every four weeks. A significantly lower proportion of patients treated with mepolizumab experienced flares of their disease (28%) compared with patients who were assigned the placebo (56%). Overall, there was a 50% relative reduction in HES flares with mepolizumab versus placebo over a 32-week treatment period.

Additionally, the study showed that treatment with mepolizumab resulted in a 66% lower risk of a first HES flare compared with placebo. Also, patients who received mepolizumab had lower fatigue scores over the duration of treatment.

“Mepolizumab has the potential to change the treatment landscape for patients with HES which is a complex and debilitating disease with limited therapeutic options today,” GSK’s chief scientific officer and R&D head, Hal Barron, said in a statement.

GSK’s approval for HES is a small victory over AstraZeneca’s rival Fasenra (benralizumab) drug, which is also seeking approval for the disease following its 2019 approval for the drug as an asthma treatment contained in a self-administered auto-inject pen. In their own recent trial of 20 patients with HES, AstraZeneca found their drug reduced blood eosinophil counts by up to half in 90% of their patients after 12 weeks. Only 30% of patients who received placebo in this study experienced this same reduction.

Within a year after this approval, GSK will likely submit an additional approval application for mepolizumab in chronic rhinosinusitis with nasal polyps, an indication already conquered by Sanofi and Regeneron’s IL-4/13 inhibitor Dupixent (dupilumab), which was granted breakthrough therapy designation on Sept. 14 based on positive long-term efficacy and safety Phase III data.

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