P2-425: Systemic mannitol administration with convection enhanced delivery of rAAV increases area of gene distribution and uptake in mouse hippocampus

Recombinant Adeno-associated viral (rAAV) vectors are an effective means of gene delivery and gene transfer to the central nervous system and hold promise for the treatment of several types of degenerative brain diseases. One disadvantage of typical intracranial injections into the brain parenchyma is a limited distribution of the rAAV macromolecules to all brain regions where therapies may be needed. Convection enhanced delivery (CED) is a method of delivering clinically relevant volumes of therapeutic agents to significantly larger areas of the brain in a direct intracranial injection procedure. The CED technique is designed to utilize the phenomenon of bulk flow and positive pressure to distribute macromolecules to a large area within solid tissue. Optimizing specific parameters of the CED injection technique with the purpose of obtaining maximal gene distribution and gene uptake is an important obstacle to overcome for gene therapy studies. In the present study the CED method using the step-design cannula in addition to systemic administration of mannitol, was used to deliver rAAV vectors expressing GFP into the hippocampus of 11 month old mice. Mannitol is a blood brain barrier interruptive reagent which also induces hyperosmolarity thereby reducing intracranial pressure and facilitating the movement of particles through the interstitial space within the paranchyma. Mice were injected intracranially into the right hippocampus using the CED method with (n=8) or without (n=8) pre treatment with mannitol delivered intraperitoneally. The animals survived 8 weeks post surgery and histology was performed to assess gene distribution and expression. Animals receiving systemic injections of mannitol followed by the intracranial CED injection of rAAV into the hippocampus showed an increased area of distribution compared to animals that did not receive pre treatment with mannitol. In addition, GFP expression was also detected in regions distant from the initial site of injection in animals receiving the CED method with mannitol including significant expression in the contralateral hemisphere to the injection site. These data suggest that the CED step cannula method in conjunction with systemic mannitol induced hyperosmolarity provides an efficient means of viral vector distribution and transgene uptake.