Authors :
Presenting Author: Christopher Reid, PhD – Florey Institute of Neuroscience
Bang Bui, PhD – University of Melbourne; Ian Forster, PhD – Florey Institute of Neuroscience; Chaseley McKenzie, BSci – Florey Institute of Neuroscience; Ming Soh, PhD – Florey Institute of Neuroscience; James Spyrou, BSci – Florey Institute of Neuroscience; Da Zhao, PhD – University of Melbourne; Lauren Bleakley, PhD – Florey Institute of Neuroscience
Rationale: Pathogenic variation in
HCN1 is an established cause of epilepsy with a subset of
HCN1 pathogenic variants causing Developmental and Epileptic Encephalopathies (DEEs), a syndrome that is characterised by drug resistant epilepsy and significant developmental delay. Although a full genotype-phenotype relationship is yet to be established,
HCN1 pathogenic variants that cause cation leak associate strongly with DEE. Therapeutic strategies that target HCN1 channel cation leak are therefore expected to improve outcomes for a high proportion of
HCN1-DEEs. Org 34167 is a propyl-1,2 benzisoxazole derivative that is a brain penetrant broad-spectrum HCN channel inhibitor. Here we explore the utility of this small molecule precision approach in a mouse model of
HCN1-DEE.
Methods: The biophysical properties of human HCN1 channels were recorded using 2-electrode voltage clamp from Xenopus oocytes. Whole-cell current-clamp recordings were made from L5 pyramidal neurons from the Hcn1
M294L mouse model of DEE. Electrocorticography and electroretinography recording were made from the Hcn1
M294L model to monitor brain and retinal function. A range of assays were used to monitor behavioural changes. Org 34167 was injected IP one hour prior to tests in the Hcn1
M294L mouse.
Results: Org 34167 restored the voltage sensitivity of the DEE HCN1
M305L mutated channel, significantly reducing cation leak. It also restored I
h-mediated ‘sag’, hyperpolarised the resting membrane potential and reduced firing of layer V neurons from an
HCN1-DEE mouse model based on the same variant. Additionally, Org 34167 reduced neuronal epileptiform activity and restored retinal light sensitivity, suggesting it may improve both seizures and other clinical comorbidities. However, Org 34167-mediated tremors were noted at therapeutic doses, possibly due to HCN2 channel inhibition. Org 34167 was also effective at restoring biophysical function in five additional
HCN1 variants suggesting broader utility.
Conclusions: Overall, these data demonstrate that a small molecule HCN inhibitor can restore channel and consequent physiological functions, positioning it as a potential precision therapeutic approach in
HCN1-DEE.
Funding: NHMRC Ideas grant