Angelman syndrome patient-derived neuron screen leads to clinical ASO rugonersen targeting <i>UBE3A</i>-ATS with long-lasting effect in monkeys

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by the loss of neuronal ubiquitin E3 ligase UBE3A, with no available treatment. Restoring UBE3A by downregulating the paternally cis-acting long noncoding antisense transcript (UBE3A-ATS) is a potentially disease modifying strategy. However, developing molecules targeting human UBE3A-ATS is challenging due to its selective expression in mature neurons and lack of sequence conservation across species. To overcome this, we screened a library of locked nucleic acid (LNA)-modified antisense oligonucleotides (ASOs) in AS patient-derived neurons. This let to the identification of rugonersen (RO7248824), which selectively and potently reduces UBE3A-ATS and upregulates UBE3A messenger RNA (mRNA) and protein in neurons derived from neurotypical humans, AS patients, and cynomolgus monkeys. In vivo studies with rugonersen or tool molecules in wild-type and AS mice, and cynomolgus monkeys revealed a steep relationship between Ube3a-ats knock-down and UBE3A mRNA/protein upregulation, requiring ∼90% knock-down for 50% upregulation. Two studies of up to three lumbar intrathecal (IT) rugonersen doses in monkeys showed no adverse effects and produced long-lasting paternal UBE3A mRNA/protein reactivation in key brain regions. In summary, we identified rugonersen, an ASO targeting UBE3A-ATS with excellent drug-like properties. Its sustained efficacy supports infrequent, IT dosing, and underlies its ongoing clinical development for AS.