Epilepsy afflicts approximately 3 million people in the U.S., and although current, anti-epileptic medication effectively controls the seizures in approximately 70% of this population, medications do not adequately control seizures for the remaining 30% (Kwan and Brodie, 2000). Because fewer than 10% of patients with drug refractory epilepsy are considered for surgical resection, a substantial number of epilepsy patients essentially have no effective therapeutic options (Engel et al.;1992, Siegel, 2004). Even with the introduction of many new drugs, the number of drug resistant epilepsies has not decreased, prompting Loscher and Schmidt (2011) to state that """"""""the available evidence indicates that the efficacy and tolerability of drug treatment of epilepsy has not substantially improved"""""""". Recent studies by Gray et al (2010) have provided a potential solution to this problem. Using an acute limbic seizure model Gray et al. (2010) showed that capsid DNA shuffling and directed evolution could identify a novel, chimeric adeno-associated virus (AAV) clone (#83) which upon intravenous administration selectively crossed the acute seizure compromised blood-brain barrier and transduced cells in the CNS. In order to realize the full potential of this approach we hypothesize that additional DNA shuffling and directed evolution in a chronic limbic seizure model will produce safe, therapeutically effective, chimeric vectors. Two new brain specific AAV capsid libraries will be constructed, one based upon error prone PCR of clone 83 and the other composed of unique, multiple clones that cross the seizure compromised blood-brain barrier. The libraries will be injected intravenously into rats with documented chronic, spontaneous seizure activity. Subsequently, neurons will be dissociated from the hippocampus and the piriform cortex, and the mutant clones will be rescued. After in vivo validation of both transduction efficacy and peripheral biodistribution, the most effective clones will be packaged with proven therapeutic neuropeptide cassettes and recombinant virus will be produced. These novel vectors will be administered intravenously to rats with documented spontaneous seizure activity in order to assess the ability to attenuate spontaneous limbic seizure activity, as well as after acute seizures to test for anti-epileptogenic actions. If successful the findings would dramatically shift current epilepsy treatment paradigms and significantly impact the treatment refractory epileptic population.
Approximately 30% of the epileptic population proves resistant to drug therapy, yet the introduction of many new anti-seizure drugs over the last 20 years has not impacted this refractory population. The proposed research will identify novel adeno-associated viral vectors that exhibit the ability to selectively cross the seizure compromised blood-brain barrier and transduce cells after intravenous administration. These vectors would provide the ability to deliver anti-epileptic therapy to the entire extent of those brain areas involved in the seizure, yet simultaneously avoid normally functioning brain areas. Thus, a positive outcome from these studies could directly translate to novel therapeutic approaches for the treatment of intractable epilepsy.