The protection by the bone-structured skull, the lack of targeting or retention specificity, and the presence of the impermeable blood brain barrier (BBB) render the brain the least promising territory for drug intervention. In this R21 application, we propose an innovative brain drug delivery approach by utilizing the biodegradable clinical MR imaging agent, the superpara-magnetic iron oxide nanoparticles (MION), as the drug carrier and a clinical magnetic field as the tool for overcoming the skull barrier thereby achieving the specific brain-site targeting. Transferrin ligands will be immobilized onto the dextran coating of the MION particles for localization and retention of the targeted MION onto brain capillaries. TAT, a potent cell transduction peptide derived from the HIV protein, will also be linked to the dextran coating to serve as the contrivance for overriding the BBB and cell membrane barriers. It has been demonstrated in animal studies that via covalent linkage, TAT was able to transduce MION into organ tissues including the brain. To attenuate the non-specific uptake of MION by normal tissues, the trans-membrane activity of TAT will be masked via the binding with heparin. It has been confirmed that heparin can completely inhibit TAT-mediated cell transduction in vivo. A pharmacokinetic study will be conducted to determine the time required for MION to reach the maximum localization at the brain site but minimum systemic distribution. Protamine, a clinical heparin antidote, will be administered at this pre-determined time frame to dissociate heparin from its electrostatic binding to TAT. Once relieved from heparin inhibition, TAT will resume its potent trans-membrane activity, enabling MION to cross BBB and enter brain cells. Inside the brain, drug molecules, which will be linked to the dextran coating via hydrolysable bonds, will be slowly released from MION, sustaining a therapeutic concentration of the drug over an extended period of time. Parkinson's disease (PD) will be selected as the disease model to assess the feasibility of this approach in delivering dopamine into the brain. This is primarily because that PD offers a sensitive and clinically relevant animal model (i.e. the 6-OHDA rat model) that produces both physical (e.g. kinesic) and chemical (e.g. TH immunohistochemistry) responses in a direct correlation to the brain dopamine concentration and activity. Therefore, the success or failure of this brain drug delivery approach can be unquestionably confirmed from the experimental results. Since the 6-OHDA rat PD model can be applied in a reverse manner to examine the neuroprotective effects of peroxidase, a potent H202 scavenger that can protect neurons from attack by free radicals, delivery of peroxidase will also be attempted to see if this can retard PD progression. Because of the restricted budget and short duration of the R21 grant, this application plans to take a shotgun approach to achieve the proof-of-concept of this project, by conducting primarily in vivo animal studies. However, if the approach proves feasible in delivering both the hydrophilic dopamine and large peroxidase protein (two drugs that cannot cross BBB), a greatly extended R01 application basing on brain delivery of neurotrophic factors for promoting neuronal survival, stimulating axonal growth, and altering the course of the underlying 9 disease, will be followed to achieve the ultimate PD treatment.
