Nonviral gene delivery to the liver

Abstract

Diseases of the liver have a large impact on human health. Genetic disorders, metabolic disorders, alcoholism, cancer, or infections can all impair liver function. If serious enough, a liver transplant may be necessary, a major surgical procedure which requires lifelong immune suppression and relies on the availability of donor livers. Gene therapy is being intensively studied as a potential method to treat many disorders, including disorders of the liver. While viral gene therapy has seen some success, possible side effects make it risky, so nonviral gene delivery vectors are being developed. Unfortunately, these nonviral vectors do not yet have the efficiency of the viral vectors. Nonviral gene delivery vectors face many challenges in vivo. The vectors must protect DNA from nucleases while it moves through the bloodstream, they must avoid nonspecific uptake, they must be enter the correct cells, and must enter the nucleus before the DNA can be expressed. If any step of this process fails, there will be very little, if any, expression, and it may be impossible to determine what went wrong. One impediment to nonviral gene delivery research is the transition from in vitro studies to in vivo studies. The cancer derived cell lines most often used for in vitro transfections are rapidly dividing, which makes nuclear entry much easier than in the whole animal. While primary cells would be a more accurate model of the in vivo environment, the number of cells that can be obtained from tissues is small, and primary cells usually cannot be cultured for long. This limits the number of experiments that can be done with each preparation of cells. To overcome this, we have miniaturized transfection assays, including the transfection of mouse primary hepatocytes with luciferase in 384 well plates. Because fewer cells are needed, more experiments can be performed with each liver preparation. Another issue introduced by the differences between in vitro and in vivo research is circulatory stability. In vitro, large particles with strong positive charges are desired, because they sink down onto the cells and are attracted to the negatively charged cellular membranes. However, in vivo these particles will aggregate serum proteins and become lodged in narrow capillary beds in the lungs or other organs, often causing toxicity. While this behavior can usually be overcome through PEGylation, improving a particle's circulatory half-life will still improve its chances of finding the correct target. Scavenger receptors found on liver nonparenchymal cells are very efficient at removing negatively charged particles from the bloodstream. We have shown that dosing large amounts of PEGylated polyacridine DNA polyplex can saturate the scavenger receptors and improve circulatory half-life. We have also shown that large doses of PEGylated peptide, with or without acridine groups, can inhibit scavenger receptor uptake through the formation of peptide-protein nanoparticles. By inhibiting scavenger receptor uptake, DNA can be successfully hydrodynami...

Metabolic stability and persistence of expression of mRNA for nonviral gene delivery

“…RNase H cleavage is the dominant mechanism of antisense oligonucleotide (ASO) therapies, in which a DNA or modified DNA oligonucleotide is delivered that represses translation of a target mRNA through sequence-specific hybridization and subsequent RNase H cleavage and inactivation201 . Previous data from our lab had demonstrated that hydrodynamic dosing of a DNA oligo(T) hybridized to the mRNA poly(A) tail gave equivalent level of expression as dosing mRNA with no poly(A) tail86 , indicating that RNase H was active in vivo after hydrodynamic dosing, in this case to cleave off the poly(A) tail.To prove that RNase H was able to cleave off the tail extensions, SphI (+239) RNA and LU (+5,000) RNA were hybridized with the DNA oligo and incubated with E.coli RNase H. This resulted in distinct bands indicative of RNase H-specific cleavage(Figure 3-7B). The LU (+5,000) mRNA likely had multiple annealing and cleavage points.…”

“…Delivery regarding DNA have been reviewed by members of our lab elsewhere 85,86 . This section focuses on the current state of mRNA delivery in the field and how those barriers are overcome (see Figure 1-9 for a summary).…”