Brain Delivery of Nanomedicines: Trojan Horse Liposomes for Plasmid DNA Gene Therapy of the Brain.

William M. Pardridge

doi:10.3389/fmedt.2020.602236

Abstract

Non-viral gene therapy of the brain is enabled by the development of plasmid DNA brain delivery technology, which requires the engineering and manufacturing of nanomedicines that cross the blood-brain barrier (BBB). The development of such nanomedicines is a multi-faceted problem that requires progress at multiple levels. First, the type of nanocontainer, e.g., nanoparticle or liposome, which encapsulates the plasmid DNA, must be developed. Second, the type of molecular Trojan horse, e.g., peptide or receptor-specific monoclonal antibody (MAb), must be selected for incorporation on the surface of the nanomedicine, as this Trojan horse engages specific receptors expressed on the BBB, and the brain cell membrane, to trigger transport of the nanomedicine from blood into brain cells beyond the BBB. Third, the plasmid DNA must be engineered without bacterial elements, such as antibiotic resistance genes, to enable administration to humans; the plasmid DNA must also be engineered with tissue-specific gene promoters upstream of the therapeutic gene, to insure gene expression in the target organ with minimal off-target expression. Fourth, upstream manufacturing of the nanomedicine must be developed and scalable so as to meet market demand for the target disease, e.g., annual long-term treatment of 1,000 patients with an orphan disease, short term treatment of 10,000 patients with malignant glioma, or 100,000 patients with new onset Parkinson's disease. Fifth, downstream manufacturing problems, such as nanomedicine lyophilization, must be solved to ensure the nanomedicine has a commercially viable shelf-life for treatment of CNS disease in humans.

Highlights

Intravenous AAV9-based viral gene therapy is FDA approved as a one-time treatment for juvenile spinal muscular atrophy [10]
The strong immune response against the viral coat protein prevents a second injection of the virus, which limits AAV treatment to a single administration [303]
Gene expression in brain in vivo is demonstrated following the IV administration of THLs encapsulating plasmid DNA >20 kb (Table 4). These limitations of viral gene therapy provide the rationale for the parallel development of nonviral targeted nanomedicines that deliver plasmid DNA across the blood-brain barrier (BBB) following IV administration

Summary

INTRODUCTION

DNA in the interior of pegylated liposomes that have a net anionic charge, and the tips of 1–2% of the surface PEG strands are conjugated with a MAb that targets an endogenous receptor expressed on both the BBB endothelium and on brain cells [44]. Affinity cross-linking of [125I]IGF1 or [125I]-IGF2 to human brain microvessel membranes showed the only saturable binding site had a MW of 141 kDa for either peptide [101], which is identical to the size of the alpha subunit of the IGF1R in peripheral tissues Both IGF1 and IGF2 produce high affinity binding to the IGF1R with KD values of 0.3 and 2.3 nM, respectively [102, 103]. Support for the BBB TfR transcytosis model was produced with an electron microscopic study of rat brain following a 10 min carotid arterial infusion of a conjugate of 5 nm gold (Au) and the OX26 TfRMAb [109]. As the TfRMAb exits the intra-endothelial volume and enters into the post-vascular space, the concentration of the TfRMAb undergoes a dilution of ∼1,000-fold, which produces a TfRMAb concentration in the post-vascular compartment that is too dilute to detect with light microscopic immune-histochemistry or immune-gold silver staining

Methodology for Demonstration of

Findings

CONCLUSIONS