Gene therapy in temporal lobe epilepsy: Viral overexpression of Neuropeptides

Medicine is presently facing a high incidence of drug-resistant focal epilepsies. A subgroup of affected patients can become seizure-free after surgical removal of the epileptogenic focus. However, there remains a large cohort of patients, who cannot be treated sufficiently at present. We and others have recently demonstrated the importance of specific neuropeptides in seizure control in a pharmaco-resistant animal model of temporal lobe epilepsy (TLE). We now want to evaluate the potential of prolonged neuropeptide expression by focal application of transgene- expressing adeno-associated virus (AAV) vectors in an animal model of TLE. We will explore whether prolonged neuropeptide stimulation in selected regions of the hippocampal formation (representing the central structure in TLE) will suppress seizure activity and prevent progression of epilepsy. It is anticipated that neuropeptide over-expression driven by AAV vectors will result in reduced seizure activity, reduction of neuronal loss and conservation of brain functions. We propose to analyze the effects by means of in- vivo EEG recordings, measuring the frequency and duration of seizure related events like sharp waves, bursts and paroxysmal discharges after injection of kainic acid into the dorsal hippocampus of mice. Histochemical analyses of morphological and pathological changes in brain areas mostly affected in this model will be accompanied by behavioral tests to investigate such brain functions known to be impaired in patients suffering from temporal lobe epilepsy and reproduced in animals models of this disease. These tests will mostly focus on spatial learning abilities and emotional control. One central aspect will be the stability of beneficial effects over a long period of time, as epilepsy cannot be cured presently and patients need life-long treatment. The long-term goal of our studies is to develop the preclinical model into a gene therapy for patients suffering from refractory mesial temporal lobe epilepsy as well as other types of focal epilepsies.

Temporal lobe epilepsy is considered to be one of the most common and severe forms of focal epilepsies. Patients often develop cognitive deficits and emotional blunting along the progression of the disease. The high incidence of resistance to antiepileptic drugs (30 % on average, in some forms up to 80%) and severe side effects of pharmacological treatment poses an unmet medical challenge. Alternative treatments like surgical removal of the epileptogenic focus and deep brain stimulation are available only for a few patients and do not guarantee success at all. In the urgent quest of novel treatment strategies, neuropeptides and their receptors are interesting candidates, however, their therapeutic potential has not yet been exploited. Our novel approach is based on adeno-associated virus (AAV) vector mediated gene-therapy to transduce preprodynorphin into the epileptogenic focus in a well-accepted mouse model of chronic, drug-resistant temporal lobe epilepsy. The aim was to restore the exhausted neuronal supply of dynorphins, allowing their locally restricted release on demand. Within this project, we provided the proof of concept that AAV-mediated preprodynorphin expression in an established epileptogenic focus leads to complete suppression of seizures over months. The debilitating long-term decline of spatial learning and memory were prevented. Moreover, lost learning and memory capabilities were regained in chronic epilepsy. Neuronal preprodynorphin expression was focally restricted and its release dependent on high-frequency stimulation, as it occurs at the onset of seizures. Such local application of the AAV vector did not produce inflammatory responses or alterations to basic behavior. This suggests good safety of the application. The preclinical data collected within this project are very promising, motivating to study these vectors in other animal models. The final goal however has to be the development of a gene therapy for human temporal lobe epilepsy patients. This novel format of drug on demand delivery may be seen as key to prevent habituation and to minimize the risk of adverse effects, leading to long-term suppression of seizures and of their devastating sequelae.