Drug development in Dravet Syndrome
Key Words
Epilepsy, Dravet Syndrome, seizures, drug development
Objectives
Dravet Syndrome (DS) is a catastrophic childhood epilepsy that kills ~25% of those presenting before adulthood and profoundly limits the lives of those who survive. It is untreatable.
We have discovered two drugs that are showing promise in clinical trials for the treatment of DS. However, we still do not know the mechanism(s) by which our drugs exert their beneficial effects.
Proving that they work in this mutant mouse model of DS which so closely resembles human DS will provide us with a way to determine underlying drug mechanisms of action. Understanding the mechanism of action will help us understand what makes some epilepsies resistant to drug treatment and also help us develop new treatments for drug-resistant epilepsies.
We will establish and maintain a colony of mutant DS mice. We will use behavioural and electrical (like EEG) measurement methods to find out how effective our drugs are in these mice. If the drugs work, we will use tissue from these and additional mice for ‘test tube’ experiments to determine the mechanism of action of the study drugs.
Objective 1: Establish, expand and maintain a colony of SCN1A mutant mice
Objective 2: Determine the anti-epileptic efficacy of a given study drug using behavioural and electrical monitoring methods.
Objective 3: Determine the mechanism of drug action by sampling body fluids and using ‘test tube’ methods.
Benefits
Knowing how these drugs work will help us better understand why the drug-resistant epilepsies that affect 15-20 million people worldwide occur. It will also allow us to develop better medicines to treat these resistant epilepsies.
Knowing whether our drugs work in this mouse model of DS will help regulators, industry, clinicians and patients benefit by informing and, if results are positive, speeding up the process of clinical licensing of these drugs.
Animals used
SCN1A mutant mice; ~3500 over 5 years.
Adverse effects
75% of these mice exhibit no symptoms. The remaining ~25% experience lethal seizures and, without intervention, do not survive past ~16 days old. Therefore this work is considered to be of severe severity.
We will also treat animals with our study drugs. Whilst these have been well tolerated in our long experience we cannot rule out rare reactions in a tiny proportion of animals.
We will also implant some animals with electrodes to monitor seizure activity or a small tube to sample brain fluids. This can be painful and cause suffering but we will use painkillers whenever possible.
We will need to take tissue samples from some animals in order to determine which have the disease and which do not. This can cause some pain but will be minimised by pre-treatment with a local anaesthetic.
All animals will be killed at the end of the study unless asymptomatic animals are transferred to other authorised users to establish colonies for their own research.
Replacement
Epilepsy is a disorder of the whole body (brain and periphery) and, as such, is too complex for current ‘test tube’ approaches to properly model. Moreover, regulatory (EMA) requirements demand testing in whole animal models.
Reduction Experiment sizes will be determined by statistical calculations which tell us the minimum number of animals required for a meaningful drug effect to be accurately detected in our experiments. A professional statistician will be consulted when required to ensure experimental designs are used that minimise the number of animals required yet maintain adequate precision. We will not breed more animals than we will need for our experiments.
Refinement
We will use mice which are the least sentient species possible that can be used. The mouse genome has aMice have a sufficiently high homology with that of thesimilar genetic makeup to humans and the physiology and pharmacology of the mouse nervous system is sufficiently similar to humans to accurately reflect DS.
Wherever possible, we will not use of the C57BL6 SCN1A +/- strain in order to minimise the number of animals that experience recurrent seizures over several weeks. SCN1A -/- animals which exhibit seizures by P9 and, without intervention, die by P16 will be preferred as any suffering will be limited to the shortest period of time.
We will only breed sufficient animals to meet our planned experimental needs and we will use animals as early as is scientifically possible for our experiments to minimise the time during which seizure symptoms manifest.
We will use our strong links with both the creator of these mice and the EU Dravet Syndrome Foundation which funds DS research and supports patients to gain further experience with the model to improve and maintain welfare. We have already conducted several visits to these sites and will continue during the project.