Neuron-specific nanotherapeutics for spinal cord injury repair

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Due to limited intrinsic healing capacity and the absence of effective therapeutic treatment, spinal cord injury (SCI) usually results in permanent loss of motor and sensory function below the level of the lesion. SCI exhibits a complex pathophysiology that presents multiple barriers to functional recovery. These include ischemia and inflammation that cause progressive neuronal and glial cell death, as well as the presence of extracellular growth inhibitors and intrinsic deficiencies in neuronal biochemistry that limit the capacity of adult axons for plasticity/regeneration. Combination therapies using treatment modalities targeting two or more of these barriers have achieved promising preclinical results, but their application is complex and often requires multiple interventions. Thus, there is a need for the development of new technologies capable of simultaneously delivering multiple bioactive molecules. The objective of this proposal is to develop neuron-specific nanotherapeutics for SCI repair. The hypothesis is that combinatorial delivery of drugs modulating the cAMP and RhoA signaling pathways will provide neuroprotection and promote functional recovery by synergistic effect in contusion SCI model. These therapeutic targets have been chosen because of their recognition as key signaling molecules implicated in multiple aspects of SCI pathophysiology including inflammation, neuronal cell death, and both extrinsic and intrinsic barriers to axonal regeneration. Our approach is based upon a novel cationic amphiphilic co-polymer, poly (lactide-co-glycolide)-graft-polyethylenimine (PgP) developed in our lab. PgP forms polymeric micelles offering three critical features for combinatorial drug delivery: 1) a hydrophobic core for loading of rolipram (Rm), a phosphodiesterase 4 inhibitor capable of restoring cAMP levels, 2) a cationic, hydrophilic shell for electrostatic binding of siRNA targeting RhoA (siRhoA), and 3) surface functional groups that will be used for conjugation of the L1 neural cell adhesion molecule to increase neuronal targeting. In preliminary studies we show that PgP/siRhoA and PgP/Rm are each capable of achieving therapeutic effects in animal injury models. In Aim 1, we will formulate neuron-specific nanotherapeutics incorporating L1 as a targeting ligand, siRhoA in novel, designed nanostructures, and Rm (L1-PgP/siRhoA/Rm) and test their efficacy in an in vitro hypoxia SCI model. In Aim 2, we will test the most promising candidate in a rat moderate contusion injury model, incorporating studies of biodistribution and repeat and delayed administration. Therapeutic efficacy outcomes will include biochemical analysis of cAMP/RhoA, histological analysis, locomotor recovery, and neuropathic pain/allydonia. The proposed work is innovative because it uses a novel material capable of simultaneously delivering two chemically different drugs in a single formulation, cAMP/RhoA as a new combination therapy, L1 targeting and novel siRNA nanostructures. The proposed work is significant, because it addresses the critical and under-studied challenge of effective therapeutic delivery and may have widespread application to other CNS injury and disorders including traumatic brain injury, Alzheimer's disease, and stroke.