mRNA gene therapy has recently emerged as a candidate to enable multiple therapeutic applications including protein replacement therapy, vaccine immunology, and regenerative medicine. Despite the extensive therapeutic potential, the successful clinical translation of mRNA gene therapies has been very limited in practice due to the inadequate understanding of how to target various organs or cell type for protein expression. Multiple studies in the past decade have demonstrated carrier material properties and routes of administration as significant parameters influencing the expression profile of mRNA therapeutics. However, the disparate nature of these reports has prevented critical and global understanding of how these factors contribute to organ targeting for mRNA delivery. Elucidation of trends and commonalities in materials achieving tissue specific mRNA delivery may enable the realization of the medical and commercial promise of therapeutic mRNA medicines. The purpose of this review is to provide a thorough and robust meta-analysis of the various materials that have been successfully used to target different organs for mRNA delivery. The article summarizes the distinct properties of the materials used as well as evaluates various routes of administration of mRNA therapeutics and the applications that can be achieved. This review will therefore serve as useful guide for the community in the development of future materials for mRNA delivery to enable the full potential of this nucleic acid modality for gene therapy.
The insulin-transport enhancing effects of a pH-sensitive poly((methacrylic acid)-grafted-poly(ethylene glycol)) hydrogel system were studied using Caco-2 monolayers as an in vitro model of intestinal transport. Further, the ability of the hydrogel system to protect entrapped proteins through the upper gastrointestinal tract via digestion in simulated gastric and simulated intestinal fluids with digestive enzymes was confirmed. Caco-2 cell monolayers were exposed to a series of formulations including insulin alone, the polymer in insulin solution, insulin-loaded polymer (ILP) and ILP previously subjected to simulated digestive fluids with enzymes. These studies demonstrated greatly increased insulin transport for the ILP samples when compared with insulin alone and insulin in the presence of polymer, P app = 12.7 × 10−8 cm/s and 6.61 × 10−8 cm/s versus 0.07 × 10−8 cm/s and 0.06 × 10−8 cm/s, respectively. While enhanced transport with the ILP was observed, the largest changes in TEER values did not coincide with the highest amounts of insulin transport, this suggests that the paracellular route may not be the sole mechanism of transport. Further, as the Caco-2 cell line has been demonstrated to possess the insulin receptor, active transport or a mixed mechanism cannot be ruled out.
Therapeutic proteins and peptides represent a major area of research in current pharmaceutical and biotechnology companies. Due to their inherent instability, the vast majority of these drugs require parenteral administration. Such is the case for as many as 6 million patients in the United States who use insulin in the treatment of diabetes mellitus. Oral insulin delivery would is a highly desirable alternative method of administration, though it continues to be an elusive target due the enzymatic digestion of insulin and low levels of absorption from the gastrointestinal tract. Hydrogel polymers have shown promise as potential carriers for oral insulin delivery. In particular, a pH responsive hydrogel composed of poly(methacrylic acid-g-polyethylene glycol), P(MAAg- EG), has shown the ability to protect insulin from enzymes in the gastric environment and release in small intestines. It was also able to induce a hypoglycemic effect in vivo when delivered to isolated ileal segments in rats. However, this material has not shown similar potential for oral protein delivery of other model drugs. To date, the unique interaction between P(MAA-g-EG) and insulin, which give it such potential for oral delivery, are not completely understood.The focus of this research is to investigate how P(MAA-g-EG) hydrogels interact with insulin and to improve upon current designs for oral insulin delivery. An attempt is made to correlate the structure and chemistry of the hydrogel to its interaction with insulin over the pH range exhibited by the gastrointestinal tract in vitro. Further insight is gained by observing the interaction of the hydrogel with insulin-like proteins including insulin glargine, an insulin analog, and polyethylene glycol (PEG) modified insulin. The PEG-insulin conjugate is synthesized and characterized to maintain the bioactivity of the protein, which is confirmed in vivo using intravenous and subcutaneous administration in rats. Finally, the proposed system is tested using an in vivo model in Sprague Dawley rats and related to the potential application of P(MAA-g-EG) to deliver insulin and PEG modified insulin for the treatment of diabetes.%%%%Ph.D., Biochemical Engineering – Drexel University, 2008
Abstract Controlling the biodistribution of nanoparticles upon intravenous injection is the key to achieving target specificity. One of the impediments in nanoparticle-based tumor targeting is the inability to limit the trafficking of nanoparticles to liver and other organs leading to smaller accumulated amounts in tumor tissues, particularly via passive targeting. Here we overcome both these challenges by designing nanoparticles that combine the specificity of antibodies with favorable particle biodistribution profiles, while not exceeding the threshold for renal filtration as a combined vehicle. To that end, ultrasmall silica nanoparticles are functionalized with anti-human epidermal growth factor receptor 2 (HER2) single-chain variable fragments to exhibit high tumor-targeting efficiency and efficient renal clearance. This ultrasmall targeted nanotheranostics/nanotherapeutic platform has broad utility, both for imaging a variety of tumor tissues by suitably adopting the targeting fragment and as a potentially useful drug delivery vehicle.
Abstract Summary: Environmentally responsive hydrogels composed of poly(methacrylic acid‐g‐ethylene glycol) (P(MAA‐g‐EG)) have shown promise for oral insulin delivery due to their pH responsive complexation behavior. A series of hydrogel formulations were polymerized with varying amounts of crosslinker and varying monomer volume fraction. The mesh size of the network depended primarily on pH, varying from 8.0 to 27.2 nm. Insulin loading efficiency varied directly with crosslink density, ranging from 42.7 to 84.9% of available insulin loaded into the hydrogels. The release of insulin was performed with each polymer formulation at 5 pH levels ranging from 2.7 to 6.8. Insulin release was less than 20% for all formulations tested with insulin for the duration of the 3 hour release study for all pH levels considered except when the pH was 6.8, at which point the release occurred as a burst. Loading studies performed with insulin glargine, an insulin analog with an increased pI, showed the same trends as native insulin. However, the release of insulin glargine only occurred at a pH level above that of the pI of the protein. These results indicate that hydrogen bonds and ionic interactions between the protein and P(MAA‐g‐EG) may strongly influence its loading and release behavior in vitro .
