Microneedle delivery of plasmid DNA to living human skin: Formulation coating, skin insertion and gene expression

Abstract

Microneedle delivery of nucleic acids, in particular plasmid DNA (pDNA), to the skin represents a potential new approach for the clinical management of genetic skin diseases and cutaneous cancers, and for intracutaneous genetic immunization. In this study excised human skin explants were used to investigate and optimize key parameters that will determine stable and effective microneedle-facilitated pDNA delivery. These include (i) high dose-loading of pDNA onto microneedle surfaces, (ii) stability and functionality of the coated pDNA, (iii) skin penetration capability of pDNA-coated microneedles, and (iv) efficient gene expression in human skin. Optimization of a dip-coating method enabled significant increases in the loading capacity, up to 100 micrograms of pDNA per 5-microneedle array. Coated microneedles were able to reproducibly perforate human skin at low (<1 Newton) insertion forces. The physical stability of the coated pDNA was partially compromised on storage, although this was improved through the addition of saccharide excipients without detriment to the biological functionality of pDNA. The pDNA-coated microneedles facilitated reporter gene expression in viable human skin. The efficiency of gene expression from coated microneedles will depend upon suitable DNA loading, efficient and reproducible skin puncture and rapid in situ dissolution of the plasmid at the site of delivery.

Dissolving microneedles for DNA vaccination: Improving functionality via polymer characterization and RALA complexation

“…Given that PVP has previously been reported to form hydrogen bonds with DNA, this loss in transfection efficacy was not entirely unexpected. 26 This then prompted us in this study to examine the suitability of 4 FDA-approved polymer formulations to form dissolvable microneedles for DNA vaccination. In addition, we incorporated the amphipathic cationic peptide RALA prior to formulation to enhance the functionality of the DNA cargo.…”

“…1), which is similar to or greater than the penetration depths achieved using solid or coated needles. 26,30,43 Therefore we could be confident that a large proportion of the payload within the dissolvable polymer matrix would be deposited into the skin following microneedle insertion. The microneedle type can affect the outcomes of incomplete insertion.…”

“…For example, coated microneedles will only deliver the cargo present on the inserted part of the needle. 26 In contrast, incomplete insertion of dissolvable needles may not be as limiting as dissolution of needles creates transient pores in the SC facilitating the passage of cargo from the un-inserted needle portion and the baseplate. This can be further enhanced when the interstitial fluid is absorbed and spreads through the polymer matrix during the dissolution process.…”

“…Repeated drip-drying cycles may be used to increase the quantity of DNA present in coatings, however this is cumbersome and may affect needle conformation, and hence the ability to penetrate the SC. 21,26 Dissolvable microneedles have the potential to overcome these issues and deliver larger quantities of DNA, as cargo may be distributed throughout the whole needle as opposed to the coating. 27 Once applied, these structures swell within the interstitial fluid in the skin and undergo rapid dissolution to release their payload, thus it is essential that the needles are composed of biocompatible material and possess sufficient strength in the dry state to penetrate the SC.…”

Hydrogel Microneedle Arrays for Transdermal Drug Delivery

“…Further in vivo studies with these formulations will research the ability of these systems controlled-release pDNA expression. But the results showed that the total number of positive expression was less than solution prescription in 24 h. However, due to the design, the drug can only be loaded onto the surface of MNs, so the drug loading amount is relatively low [23][24][25]. The cost of fabrication is also another concern.…”