A precision medicine approach for HCN1 Developmental and Epileptic Encephalopathy

Pathogenic variants in HCN1 causing cation leak result in a severe developmental and epileptic encephalopathy (DEE). Current treatment options for patients with HCN1 -DEE are limited and are insufficient to fully address both the seizures and clinical comorbidities of this disorder. Org 34167 is a brain penetrant broad-spectrum HCN channel inhibitor that has completed phase I clinical trials. We used a range of assays at molecular, cellular, network and behavioural levels to explore the potential of Org 34167 as a precision medicine for HCN1 -DEE. Org 34167 restored the voltage sensitivity of the DEE HCN1M305L mutated channel, significantly reducing cation leak. It also restored Ih-mediated ‘sag’, hyperpolarised the resting membrane potential and reduced firing of layer V neurons from the Hcn1M294L mouse model of HCN1 -DEE, which was engineered based on the HCN1M305L pathogenic variant. Additionally, Org 34167 reduced neuronal epileptiform activity and restored retinal light sensitivity in these mice, suggesting it may improve both seizures and other clinical comorbidities. However, Org 34167-mediated tremors were noted at therapeutic doses. Org 34167 was also effective at reducing cation leak caused by five additional HCN1 pathogenic variants, suggesting broader utility. Overall, these data demonstrate that a small molecule HCN inhibitor can restore channel and consequent physiological functions, positioning it as a promising precision therapeutic approach for HCN1 -DEE. ### Competing Interest Statement The authors have declared no competing interest. * ### Abbreviations aCSF : Artificial cerebrospinal fluid AP : Action potential ASM : Anti-seizure medication AUC : Area under the curve DEE : Developmental and epileptic encephalopathy ECoG : Electrocorticography ERG : Electroretinography HCN : Hyperpolarisation-activated, Cyclic Nucleotide-gated channel HEK : Human embryonic kidney Ih : Hyperpolarisation-activated current i.p. : Intraperitoneal IV : Current-voltage SEM : Standard error of the mean V0.5 : Half-maximal activation voltage WT : Wild-type