FDA Approves Avlayah for Neurologic Hunter Syndrome Manifestations

FDA Grants Accelerated Approval to Avlayah for Neurologic Hunter Syndrome

The Food and Drug Administration has granted accelerated approval to Avlayah (tividenofusp alfa-eknm), developed by Denali Therapeutics, as a treatment for neurologic manifestations of Hunter syndrome, also known as mucopolysaccharidosis type II. This marks the first new treatment option for this patient population in nearly two decades. The approval hinges on data from a phase 1/2 clinical trial and is specifically indicated for leverage in pediatric patients weighing at least 5 kg, even before the onset of advanced neurologic impairment.

Understanding Hunter Syndrome

Hunter syndrome is a rare, progressive genetic disorder stemming from a deficiency in the iduronate 2-sulfatase enzyme. This enzyme is crucial for breaking down complex sugars called glycosaminoglycans. When the enzyme is deficient, these sugars accumulate throughout the body, causing progressive damage to organs, and tissues. Symptoms can include cognitive and behavioral decline, hearing loss, and motor function impairment. The Mayo Clinic provides a comprehensive overview of Hunter syndrome, detailing its progression and impact on affected individuals.

How Avlayah Works: Enzyme Replacement and the Blood-Brain Barrier

Avlayah is an enzyme replacement therapy designed to address the underlying cause of Hunter syndrome by delivering the missing enzyme. What sets Avlayah apart is its delivery system – Denali Therapeutics’ TransportVehicle Platform – engineered to cross the blood-brain barrier. This represents a significant achievement, as delivering therapies to the brain is notoriously challenging. “This is the first FDA-approved biologic in a new class of medicines engineered to cross the blood-brain barrier, one of the most persistent challenges in medicine,” stated Ryan Watts, PhD, chief executive officer of Denali Therapeutics, during a conference call. The platform’s validation through FDA approval is a key milestone.

Clinical Trial Data: CSF and Biomarker Normalization

The FDA’s decision was based on data from an international, multicenter, open-label phase 1/2 trial involving 47 boys with Hunter syndrome, aged up to 18 years. The trial included both those who had not previously received enzyme replacement therapy (ERT) and those who had. Participants received Avlayah intravenously once a week. Researchers observed a substantial reduction in cerebrospinal fluid (CSF) heparan sulfate (HS) levels – a key biomarker of disease activity – with a 91% decrease from baseline to week 24 (95% CI, 89%-92%). Notably, 93% of patients achieved CSF HS levels within the normal range by week 24.

Beyond CSF HS, Avlayah also demonstrated an impact on other biomarkers. Neurofilament light, a marker of neuronal damage, and urine HS, indicating peripheral disease activity, both normalized following treatment. Specifically, 90% of patients showed normalized urine glycosaminoglycan levels by 12 months, compared to only two patients at baseline, according to Katie Peng, chief commercial officer of Denali Therapeutics.

Safety Profile and Ongoing Research

The most frequently reported adverse event in the trial was infusion-related reactions, experienced by 83% of patients at week 24. However, the incidence decreased over time, falling to 57% during the 80-week safety extension period and 41% during the 157-week open-label extension period. Researchers characterized the safety profile as consistent with existing ERTs and manageable for chronic therapy.

Denali Therapeutics is currently conducting a global phase 2/3 COMPASS confirmatory study, investigating Avlayah in 63 young adults with Hunter syndrome. This head-to-head, randomized controlled trial compares Avlayah to standard of care ERT, evaluating both neurologic and systemic clinical outcomes. Peter Chin, MD, chief medical officer and head of development at Denali Therapeutics, explained that the study is designed to assess a broad range of disease phenotypes and ages.

Implications and Next Steps

The approval of Avlayah represents a significant advancement in the treatment of Hunter syndrome, particularly for those experiencing neurologic complications. The ability to deliver a therapeutic enzyme across the blood-brain barrier offers a potential solution to a long-standing challenge in treating this devastating disease. The ongoing COMPASS trial will provide further evidence to confirm these initial findings and potentially expand the indications for Avlayah. Further details on the approval and ongoing research can be found in Denali Therapeutics’ press release. Patients and caregivers should consult with qualified healthcare professionals to determine if Avlayah is an appropriate treatment option. The FDA approval process involves ongoing monitoring and evaluation of the drug’s safety and effectiveness in real-world settings. The FDA’s website provides information on the device approval process and post-market surveillance.

For more information on Hunter syndrome and available resources, visit the National MPS Society website.