|AUDENTES THERAPEUTICS, INC. filed this Form 10-K on 03/13/2017|
Overview of Crigler-Najjar
Crigler-Najjar is a rare, congenital autosomal recessive monogenic disease characterized by severely high levels of bilirubin in the blood and risk of irreversible neurological damage and death. Crigler-Najjar is caused by mutations in the gene encoding the UGT1A1 (uridine-diphosphate (UDP)-glucuronosyltransferase (UGT) 1A1) enzyme resulting in an inability to convert unconjugated bilirubin to a water-soluble form that can be excreted from the body. Unconjugated bilirubin can cross the blood brain barrier, and the accumulation of unconjugated bilirubin in the central nervous system can lead to irreversible neurological damage and death.
Infants with Crigler-Najjar develop severe jaundice shortly after birth resulting in rapid presentation and diagnosis. Clinical diagnosis can be confirmed via genetic testing of the UGT1A1 gene. The current standard of care for Crigler-Najjar is aggressive management of high bilirubin levels with persistent, daily phototherapy, usually for longer than 12 hours per day, for the rest of a patient’s life. Exchange transfusion or plasmapheresis are sometimes required in order to lower bilirubin levels rapidly. Phototherapy becomes less effective as a child ages, beginning around the age of four years. Average life expectancy is reported as being 30 years of age with phototherapy, and there is an ongoing lifelong risk of a catastrophic cerebral event. Crigler-Najjar is estimated to affect approximately one in 1,000,000 newborns.
Limitations of Current Therapy for Crigler-Najjar
There are currently no products approved specifically for the treatment of Crigler-Najjar. The current standard of care for Crigler-Najjar is aggressive management of high bilirubin levels, with persistent, daily phototherapy, usually for longer than 12 hours per day using intense fluorescent light focused on the bare skin, while the eyes are shielded. The impact on quality of life is substantial. Phototherapy speeds bilirubin decomposition and excretion, lowering serum bilirubin levels. However, the effectiveness of phototherapy typically wanes beginning around four years of age due to thickening of the skin and a reduction in the surface area to body mass ratio. As children get older, compliance with phototherapy becomes challenging. As Crigler-Najjar infants and children begin to experience progression of neurological symptoms and increasing risk of a catastrophic cerebral event, a liver transplant is often required for survival. However, limited donor organ availability, the risks associated with the transplant procedure itself and potential for organ rejection limit the utility of a transplant as a widespread treatment modality for Crigler-Najjar.
AT342 consists of an AAV8 vector capsid designed to deliver a functional UGT1A1 gene and increase UGT1A1 protein expression in the liver and other tissues. Importantly, AAV8 has high affinity for liver cells allowing for the efficient introduction of therapeutic genes into liver cells. We believe that AT342 has the potential to provide long-term clinical benefit to Crigler-Najjar patients through persistent expression of the protein following a single administration, resulting in significant reduction in bilirubin levels, reduction or elimination of the need for lengthy daily phototherapy treatment and elimination of the need for a liver transplant.
Preclinical Proof-of-Concept for AT342
We conducted a dose ranging study of AT342 in a Crigler-Najjar knockout mouse model. In this study, a single tail vein injection at doses of 2.5 x 1012 vg/kg and 2.5 x 1013 vg/kg of AT342 rapidly reduced and normalized bilirubin levels for the duration of the study.