Intradermal Delivery of Synthetic mRNA Using Hollow Microneedles for Efficient and Rapid Production of Exogenous Proteins in Skin

Abstract

In recent years, synthetic mRNA-based applications to produce desired exogenous proteins in cells have been gaining importance. However, systemic delivery of synthetic mRNA can result in unspecific uptake into undesired cells or organs and, thereby, fail to target desired cells. Thus, local and targeted delivery of synthetic mRNA becomes increasingly important to reach the desired cell types and tissues. In this study, intradermal delivery of synthetic mRNA using a hollow microneedle injection-based method was evaluated. Furthermore, an ex vivo porcine skin model was established to analyze synthetic mRNA-mediated protein expression in the skin following intradermal delivery. Using this model, highly efficient delivery of synthetic mRNA was demonstrated, which resulted in detection of high levels of secretable humanized Gaussia luciferase (hGLuc) protein encoded by the microinjected synthetic mRNA. Interestingly, synthetic mRNA injected without transfection reagent was also able to enter the cells and resulted in protein expression. The established ex vivo porcine skin model can be used to evaluate the successful production of desired proteins after intradermal delivery of synthetic mRNAs before starting with in vivo experiments. Furthermore, the use of microneedles enables patient-friendly, painless, and efficient delivery of synthetic mRNAs into the dermis; thus, this method could be applied for local treatment of different skin diseases as well as for vaccination and immunotherapy.

Opportunities and Challenges in the Delivery of mRNA-Based Vaccines

“…Consequently, delivery systems are imperative for intracellular delivery of mRNA to the therapeutic site of action in vitro as well as in vivo [8,74]. Different strategies have been investigated to improve RNA delivery, including improved injection strategies such as microinjections [75], RNA patches [76], gene gun-based administration [77], protamine condensation [78], RNA adjuvants [79], and encapsulation of RNA in nanoparticles consisting of lipids and/or polymers [80]. Generally, IVT mRNA for cytosolic delivery is formulated with a delivery system by mixing with a complexing agent [81], which can protect the mRNA against rapid degradation and facilitate cellular uptake.…”

“…and s.c. administration of mRNA has been shown to mediate healing of various skin diseases and to ameliorate wound healing by in situ expression of specific proteins in the skin [75,89]. Adopting this approach circumvents several obstacles otherwise associated with systemic administration of mRNA, e.g., clearance from the bloodstream via the liver, the kidneys, and the spleen [75]. Very efficient translation of the encoded protein has been shown for mRNA administered s.c. [90][91][92].…”

“…The patches/arrays provide mechanical strength needed for the needle to permeate the stratum corneum and penetrate into the viable skin layers. Following injection, depending upon the type of microneedles, the patches/arrays degrade/dissolve and the encapsulated drug is released in the interstitial fluid of the skin [75]. Administration of mRNA by using dissolvable microneedles provides an important advantage, i.e., delivery in a solid dosage form circumvents the necessity of dealing with mRNA in a liquid dosage form [110], which therefore eliminates the menace emanating from RNase contamination, along with increasing mRNA stability, and shelf life [76].…”

Nanomedicines to Deliver mRNA: State of the Art and Future Perspectives

“…This technique has shown efficient mRNA delivery for tumor antigen loading of DCs [81]; even in some studies, mRNA electroporation has been more efficient than DNA electroporation, with faster and more homogeneous protein expression in vivo [82]. The direct injection of mRNA into the target cell by the use of microneedles (namely, microinjection) [83,84], and gene gun, in which naked mRNA is pneumatically shot into the target cell, have also been used for mRNA transfection [85][86][87][88]. In in vivo applications, intravenously administered naked mRNA is rapidly degraded by ribonucleases and the innate immune system can be activated.…”

Transcutaneous delivery of DNA/mRNA for cancer therapeutic vaccination

“…Lymphatic targeting is beneficial for TCI. Preclinical studies of the delivery of synthetic long peptides, vaccine antigens, synthetic mRNA encoding model antigens or pDNA encoding antigens by hollow microneedles have been reported. Both humoral and protective cellular immune responses were successfully evoked.…”