Theoretically, gene therapy techniques offer an attractive alternative treatment option for intractable,
focal epilepsies. Although logical gene therapy targets include excitatory and inhibitory receptors, variable viral vector tropism interjects an uncertainty as to the direction of change, seizure suppression, or seizure sensitization. To circumvent this therapeutic liability, adeno-associated virus (AAV) vectors have been constructed where the gene product is constitutively secreted from the transduced cell. Using AAV vectors, the
fibronectin secretory
signal sequence (FIB) was placed in front of the coding sequence for
green fluorescent protein or the active portion of the neuroactive
peptide galanin (GAL). Subsequent studies showed that these vectors supported expression and constitutive secretion of these gene products from transfected cells in vitro. More importantly, upon transduction in vivo, AAV-FIB-GAL vectors significantly attenuated
focal seizure sensitivity, and this seizure attenuation could be controlled in vivo by using a
tetracycline-regulated promoter. The expression and constitutive secretion of
green fluorescent protein, or the expression of GAL alone, exerted no effect on
focal seizure sensitivity. Moreover, unilateral infusion of the AAV-FIB-GAL vectors into the hippocampus prevented
kainic acid-induced hilar cell death. With regard to limbic
seizures, bilateral infusion of AAV-FIB-GAL vectors into the piriform cortex prevented both behavioral and localized electrographic seizure activity after the peripheral administration of
kainic acid. Also, when rats were electrically kindled to class V seizure activity, subsequent infusion of AAV-FIB-GAL proved capable of significantly elevating the seizure initiation threshold. Thus, these studies clearly demonstrate the anti-seizure effectiveness of AAV vector-mediated expression and constitutive secretion of
galanin.