Targeted Drug Delivery for Spinal Cord Injury Using Retrograde Transport of a Nanoconjugate

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This IGNITE Project “Targeted Drug Delivery for Spinal Cord Injury Using Retrograde Transport of a Nanoconjugate” will develop nanotherapeutics for targeted delivery of drugs to the rostral ventral respiratory group (rVRG) neurons and phrenic motoneurons for the treatment of respiratory problems after spinal cord injury. The project team consists of chemical engineers, spinal cord injury researchers, a biostatistician, and an expert in pharmacology and venture development. The team has demonstrated complementary and integrated expertise to carry our all aspects of the project. Respiratory problems including pneumonia, septicemia, and pulmonary emboli are the leading causes of death in humans after spinal cord injury. Adenosine receptor antagonist drugs such as 8-cyclopentyl-1,3-diprophyxanthine (DPCPX) can induce respiratory recovery of the paralyzed hemidiaphragm by activating a latent respiratory motor pathway - the crossed phrenic pathway. However, the severe side effects of these drugs have prevented their clinical use. We have demonstrated in our previous work that it may be possible to reduce or even eliminate the side effects by delivering the drugs selectively to the respiratory neurons using nanotechnology. Nanotherapeutics promise to improve in vivo drug stability, pharmacokinetics and biodistribution, and efficacy, all of which can potentially reduce toxicity and side effects. Our nanotherapeutic design consists of a targeting/transporting protein, wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), chemically conjugated to a gold nanoparticle (AuNP), which in turn is chemically conjugated, through a biodegradable bond, to the drug DPCPX. WGA-HRP is taken up by the terminals of phrenic axons when injected into the diaphragm muscle of C2 spinal cord hemisectioned rats, and it is retrogradely transported to the phrenic motoneurons. Importantly, it is further transported transsynaptically across physiologically active synapses to neurons in the rVRG, and does not transport to any other neuron centers. By coupling the selective transporter and the drug that induces recovery with a nano-carrier, we can control the release of the drug in the two caudal neuronal populations that control diaphragm function. Our targeted drug administration can induce recovery of the paralyzed hemidiaphragm in rats by using a fraction of the systemic dosage. The IGNITE grant will support early translational efforts to demonstrate that the nanoconjugate will have sufficient biological activity (i.e., 70% respiratory function recovery at 4 weeks) while administered at a small fraction of the native drug dosage (i.e., 0.1%) to warrant further therapeutic development.