Directed Evolution of Adeno-Associated Virus Vectors for Seizure Gene Therapy

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DESCRIPTION (provided by applicant): Epilepsy afflicts approximately 2.5 million people in the U.S., making epilepsy one of the most prevalent neurological disorders (Hauser and Hesdorffer, 1990). Although current, anti-epileptic medication effectively controls the seizures in approximately 70% of this population, for the remaining 30% medications do not adequately control the seizures (Kwan and Brodie, 2000). In these intractable cases, surgical resection offers a final option, and for those patients that qualify for surgery, up to 66% remain seizure free for 2 years post- surgery (Spencer et al., 2005). However, longer term prognosis is more uncertain, and if the site of seizure genesis impinges upon brain sites associated with critical functions, resective surgery is not a viable option (McIntosh et al., 2004; Ojemann, 1997). Recently, several studies have established gene therapy approaches that significantly influence seizure sensitivity in vivo. Using adeno-associated virus (AAV) vectors, the expression and constitutive secretion of the neuroactive peptide, galanin, can prevent seizure activity in vivo (Haberman et al., 2003; McCown, 2006), while the expression of prepro-neuropeptide Y also significantly attenuates seizure activity in vivo (Richichi et al., 2004). At present, though, the clinical application of these viral vector gene therapies will require direct neurosurgical injection into the brain. Recent developments in AAV directed evolution provide a potential means to circumvent neurosurgical intervention. Maheshri et al. (2006) showed that by introducing random changes in the AAV 2 capsid by error prone PCR, subsequent directed evolution resulted in AAV mutants that lacked heparin binding or evaded the in vivo immune response to AAV 2. In preliminary studies, the Samulski laboratory has shown that the combination of DNA shuffling techniques with directed evolution produces novel mutant AAV vectors with unique in vivo tropisms. Because seizures compromise the blood-brain barrier in areas of seizure activity, we propose to develop a mutant AAV library through DNA shuffling of AAV capsid 1-9 sequences. Then after kainic acid-induced seizures, the mutant library will be administered i.v. and through directed evolution techniques, novel mutant AAV vectors will be identified that following seizure activity, cross the compromised BBB and transduce neurons. The successful creation of such mutant AAV vectors could revolutionize the treatment of intractable seizure disorders. The proposed studies focus upon developing a novel gene therapy method for the treatment of neurological disorders. Using directed evolution techniques, we will select specific gene delivery vehicles that can access a seizure-impaired brain after peripheral intravenous administration. If successful, this novel approach could greatly advance the application of gene therapy to the treatment of neurological disorders.