Novel AAV mediated RNA editing treatment for Dravet Syndrome.

Dravet syndrome (DS) is a severe childhood epilepsy which leads to life-long disability. The disease becomes apparent in the first year of life, where babies present severe seizures (spontaneous & hyperthermia induced seizures), followed by developmental delay, behavioural, cognitive, and motor impairment and in some cases premature death. Approximately 90% of patients exhibit a spelling mistake, or mutation, in the genetic code of the SCN1A gene leading to loss-of-function of the voltage-gated sodium channel, Nav1.1.

This channel is present in brain cells and allow normal firing patterns between these cells. The affected brain cells which contain the mutated Nav1.1 channel, results in abnormal firing. Thus, the disease manifests. Current treatments for Dravet syndrome are inadequate and ineffective.

The process of making proteins in cells involves translating DNA (the genetic code) into RNA (the protein code) which is then made into proteins such as the Nav1.1 channel. We aim to develop a novel RNA editing therapy treatment for Dravet Syndrome, altering the protein code so more protein is made. Our approach involved delivering our RNA editing therapy using a virus called adeno-associated virus (AAV), to increase the healthy SCN1A gene expression and therefore restore the Nav1.1 function.

We aimed to test this novel treatment in a DS mouse model. The DS mouse model, like the human DS patients, contain one functional gene and one-non-functional gene and show clinically relevant phenotypes such as, spontaneous seizures, hyperthermia induced seizures, behavioural abnormalities, and premature death.

We developed 21 novel RNA editing sequences, of which 5 sequences showed to significantly increase healthy Scn1a (mouse gene equivalent) expression in cells. We selected two novel RNA editing sequences and produced AAV viral vector to test in the DS mouse model. The AAV gene therapy was delivered directly to the brain and systemically in the blood stream to new-born DS mice.

The results showed that the first candidate AAV-mediated RNA editing treatment showed 77% survival over 100 days, compared to 36% for untreated DS mice. The second candidate did not show an increase in survival of treated DS mice. Therefore, we proceeded with candidate 1 for the remaining animal studies.

Candidate 1 of AAV-mediated RNA editing therapy, showed a reduced tendency to hyperthermia seizures and a complete rescue of Scn1a expression in the brain region of DS treated mice.

In this proposed project we aim to expand on our current proof of concept study and develop a clinically relevant AAV-mediated RNA editing treatment. With this funding and current scientific advice from Medical and Healthcare products regulatory agency (MHRA) we aim to have a robust pre-clinical efficacy and safety data to take forward to a first in human clinical trial