Angelman syndrome patient neuron screen identifies a potent and selective clinical ASO targeting UBE3A-ATS

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by the loss of neuronal E3 ligase UBE3A with no available treatment. Restoring UBE3A levels via downregulation of the paternally cis-acting long non-coding antisense transcript (UBE3A-ATS) is a potentially disease modifying.Developing molecules targeting human UBE3A-ATS is challenging because its expression and function is restricted to neurons and lacks species sequence conservation. To overcome this, we performed a library screen of locked-nucleic acid (LNA)-modified antisense oligonucleotides (ASOs) on AS patient-derived neurons.Rounds of optimization led to the identification of RO7248824, which selectively and potently reduces UBE3A-ATS, while concomitantly upregulating UBE3A mRNA and protein. These properties held true in both human AS patient- and neurotypical-, as well as cynomolgus monkey-derived neurons. Tool molecules targeting murine UBE3A-ATS , revealed a steep relationship between UBE3A-ATS knock-down and UBE3A mRNA/protein upregulation in both wild-type (WT) and AS Ube3am-/p+ mice, whereby an almost 90% downregulation was required to achieve a 50% reactivation, respectively. This relationship was confirmed in cynomolgus monkeys. Repeated lumbar intrathecal administrations of RO7248824 was well tolerated without adverse in-life effects and produced a robust, long lasting (> 3 months) paternal UBE3A reactivation in multiple monkey brain regions.Our results demonstrate that AS induced pluripotent stem cell derived neurons serve as an excellent translational tool leading to the identification of LNA-modified ASOs with excellent drug-like properties translating to infrequent, intrathecal dosing and serves as the basis for the ongoing clinical development of RO7248824 for AS.