Delivery of therapeutic peptides and proteins across the blood-brain barrier (BBB) into the central nervous system has proven to be a major obstacle in treating neurological diseases. The selective neuronal loss observed in ALS, Alzheimer's, Parkinson's, cerebral ischemia, and other neurodegenerative diseases, coupled with the growing body of evidence that neurotrophic factors have a protective effect against various degenerative lesions, has supported a therapeutic role for a large variety of neurotrophic factors and their derivatives in treating these diseases (e.g., NGF, BDNF, NT-3,4/5,CNTF, GDNF, IGF-1 PNT-1, etc.). Similarly, SOD, BDNF, and FGF have been suggested to have a role in preventing hippocampal neuronal damage following cerebral ischemia. The risk of infection, catheter clotting, neurosurgical costs, diffusional limitations beyond the ventricular surface to the parenchyma of the brain where these factors are needed to affect discrete populations of degenerating neurons, and rapid clearance by the CSF emphasize the considerable need to develop novel forms of non-invasive drug delivery to the nervous system for treatment of neurological diseases in humans. We have developed methodologies to quantify the permeability of the BBB to peptides and proteins with appropriate correction for the residual plasma volume occupied by the protein in the capillary bed of brain with a second radioactive tracer of the same protein. This technology has allowed our development of strategies to facilitate targeted nervous system delivery of therapeutic proteins after parenteral a ministration. These strategies include the identification of proteins with high permeabilities which could be used as carriers for the delivery of therapeutic compounds. A second strategy is the chemical or biochemical modification of therapeutic proteins to increase permeability while still preserving their bioactivity. Crucial to the treatment of neurological disease is not only the enhanced permeability at the BBB after parenteral administration of the therapeutic protein but also: 1) the bioactivity of the protein must be preserved after modification or coupling to a carrier, 2) the protein must be delivered to a discrete population of affected neurons or glia within the nervous system, 3) the protein must retain its bioactivity after delivery, and 4) most importantly, it must be capable of soliciting a bioresponse in this population of cells. In this grant proposal, we plan to test the efficacy of our strategies for increasing the permeability of NGF at the BBB compared to the native protein after parenteral administration. The strategy that produces the highest permeability will then be evaluated in three animal models to test the effectiveness of the delivered modified NGF in soliciting a bioresponse in cholinergic neurons in discrete brain regions after parenteral administration compared to the native NGF. These results will have direct implications for treating human neurological disease.
