Authors :
Presenting Author: Natalia Rodriguez, PhD – UCB
Yana Van den herrewegen, PhD – UCB
Jérôme Clasadonte, PhD – UCB
Ana Rita Gomez, PhD – UCB
Geroges Mairet-Coello, PhD – UCB
Hazel Poyntz-Farminer, PhD – UCB
Denis Goosen, PhD – UCB
Rocio Lledo-Garcia, PhD – UCB
Miranda Cornet, PhD – UCB
Onur Kas, PhD – UCB
Brittany Vallette, PhD – UCB
Christian Wolff, PhD – UCB
Rationale:
STXBP1 haploinsufficiency is a severe developmental epileptic encephalopathy (DEE) characterized by a loss of function of the syntaxin-binding-protein-1 (STXBP1) and is associated with severe neuronal development delay, intellectual disability and seizures. STXBP1 is an early onset disease and rapid treatment is needed after diagnosis to impact the disease progression. There are currently no efficacious treatments for the disease, and we explored the potential of a gene therapy (GT) to modulate STXBP1 haploinsufficiency in a STXBP1 KO mouse model. In this study we evaluated the efficacy and safety of a GT administered intracerebrally in the striatum of STXBP1 KO mice at juvenile age and measured the impact on multiple disease symptoms.
Methods:
STXBP1 heterozygous (HET) KO mice have been licensed from the University of Amsterdam. AAV constructs have been produced at UCB and encode the long splice variant human STXBP1 under the control of a neuronal promoter. Animals have been injected at PND 24-28 using a bilateral intra-striatal administration with either vehicle or AAV treatment (low dose of 2.6E10 and high dose of 1.3E11 vgc). EEG electrodes were implanted at the prefrontal cortex and cerebellum levels in parallel to the AAV injection, and the spike wave discharges (SWD) were recorded in group housing video-EEG wireless telemetry platform (24 hours/day) for several weeks. A battery of behavioral tests was performed to evaluate motor and cognitive performances. Analysis of transgene expression was performed in isocortex tissue using qPCR, Western Blot, LC-MS and Immunohistochemistry.
Results:
STXBP1 HET mice have reduced mouse STXBP1 protein levels and present a robust disease phenotype with reduced body weight, frequent absence seizures, motor and cognitive deficits. We confirmed transgene expression by qPCR in the isocortex of all transduced mice with the two doses. Analysis of protein levels by Western Blot and LC-MS in the isocortex indicated a significant increase in the long variant hSTXBP1 levels with both doses although the total STXBP1 levels were only significantly increased with the high dose. The high dose led to a rapid suppression of SWD already one week after GT injection and almost complete reduction of SWD after 5 weeks of treatment. The low dose translated into a reduction of SWD frequency of 60-70% which was maintained until 10 weeks after treatment. GT did not affect body weight, hindlimb clasping and fear conditioning. We observed unexpected death in mice treated with the high dose 3-6 weeks after administration and EEG analysis confirmed the presence of convulsive seizures in these mice. No convulsive seizures have been observed with the low dose.
Conclusions:
Our study shows that the intra-striatal administration of an AAV GT in juvenile STXBP1 HET mice is able to rescue the SWD but not the overall disease symptoms. Although the treatment with a low dose is tolerated and safe, the use of higher doses of AAV translates into convulsive seizures in this model.
Funding: UCB Pharma