Using the Epigenetic Code
To Promote the Unpackaging
and Transcriptional Activation of DNA Polyplexes for Gene Delivery
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Abstract
Nonviral gene delivery has seen limited clinical application
due
in part to the inefficiency with which most nonviral vehicles navigate
the intracellular gene delivery pathway. One key problem is the inability
of most DNA-packaging materials to release DNA and enable its efficient
transcription. Thus, our aim was to develop gene delivery polyplexes
capable of initiating their own transcription upon arrival in the
nucleus. We created nuclease-resistant polyplexes with plasmid DNA
(pDNA) and post-translationally modified histone 3 (H3K4Me3) tail
peptides known to signal transcriptional activation on chromosomal
DNA. When the H3K4Me3–pDNA polyplexes were directly microinjected
into the nuclei of NIH/3T3 mouse fibroblasts, protein expression occurred
earlier and in a greater fraction of cells than when polyethylenimine–pDNA
polyplexes were microinjected. The rate of protein expression initiated
by the H3K4Me3–pDNA polyplexes was also significantly accelerated
in comparison with the rate initiated by non-trimethylated H3–pDNA
polyplexes. These differences in protein expression rates were quantified
by the development of a noncompartmentalized cellular kinetics model.
These results highlight the importance of polyplex unpackaging as
a gene delivery barrier, and demonstrate for the first time that the
epigenetic code can be utilized in nonviral gene delivery