Charge Complementary Polymersomes: Advancing Stability and Delivery Efficiency in mRNA Therapeutics

There has been significant interest in the development of messenger RNA (mRNA)-based treatments lately which are uniquely is able to directly instruct cells to produce specific proteins which makes mRNA an attractive candidate for personalized medicine because it allows for tailored therapies that can be adjusted in dosage and frequency to meet individual patient needs. Despite these advantages, the clinical application of mRNA therapies still faces significant challenges. One of the primary hurdles is the inherent instability of mRNA molecules, because they are sensitive to rapid degradation by ribonucleases (RNases) present in extracellular fluids and biological environments. Another critical challenge is the efficient delivery of mRNA into the cells because naked mRNA molecules are too large and negatively charged, which make them unable to internalize. Moreover, even when mRNA enters the cells through endocytosis, it often remains trapped within endosomes, where it can be degraded before reaching the cytoplasm. For the effective mRNA therapies drug development, they must overcome these limitations. Although various delivery systems have been proposed to address these issues such as lipid-based and polymer-based carriers which showed promise in protecting mRNA from degradation and facilitating its cellular uptake. However, these systems often encounter limitations in terms of stability, efficiency of endosomal escape, and potential cytotoxicity. To this end, Professor Hyun-Ouk Kim at Kangwon National University and conducted by HakSeon Kim, Yu-Rim Ahn, Minse Kim, Jaewon Choi, SoJin Shin developed a novel mRNA delivery system termed “ChargeSomes which improved the stability and delivery efficiency of mRNA through the use of charge-complementary polymersomes. The new study is now published in the Pharmaceutics Journal.

The first step the researchers synthesized the charge-complementary polymers methoxy polyethylene glycol-block-poly-L-lysine (mPEG-b-PLL) and methoxy polyethylene glycol-block-poly-L-lysine-succinic anhydride (mPEG-b-PLL-SA) and then confirmed the successful synthesis of these copolymers using nuclear magnetic resonance and Fourier-transform infrared spectroscopy. The physicochemical properties of ChargeSomes were then analyzed using dynamic light scattering and transmission electron microscopy which demonstrated that ChargeSomes formed stable, spherical nanoparticles with a bilayer structure. These nanoparticles varied in size depending on the ratio of mPEG-b-PLL to mPEG-b-PLL-SA, with a 9:1 ratio showing optimal characteristics for mRNA delivery. Afterward, the authors assessed the stability of ChargeSomes, and they monitored the size distribution in phosphate-buffered saline at pH 7.4 over six weeks using DLS and they showed that ChargeSomes maintained consistent stability at neutral pH, indicating their robustness under physiological conditions. Furthermore, to evaluate the pH sensitivity, ChargeSomes were exposed to an acidic environment, simulating endosomal conditions. The nanoparticles exhibited significant size changes between 3 and 8 hours, confirming their pH-responsive behavior and capacity to release mRNA in acidic environments, essential for effective endosomal escape. The team also evaluated the cytotoxicity of ChargeSomes using RAW 264.7 cells and showed that ChargeSomes has minimal cytotoxicity across various concentrations and ratios of mPEG-b-PLL to mPEG-b-PLL-SA. Specifically, a 7:3 ratio showed high cell viability, confirming the safety of ChargeSomes for therapeutic applications. According to the authors, at a concentration of 0.21 mM, ChargeSomes exhibited optimal characteristics for further in vitro experiments, maintaining cell viability comparable to that of lipofectamine, a commonly used transfection reagent. Moreover, the researchers examined the efficiency of cellular uptake and endosomal escape of ChargeSomes using confocal laser-scanning microscopy (CLSM) and flow cytometry. Ovalbumin conjugated with fluorescein isothiocyanate (FITC–OVA) served as a model antigen to track cell uptake. The author’s findings indicated that OVA–FITC-encapsulated ChargeSomes showed superior cellular uptake compared to OVA–FITC alone, as evidenced by increased green fluorescence intensity in RAW 264.7 cells. Flow cytometry further corroborated these findings, with higher fluorescence levels in cells treated with ChargeSomes. To analyze endosomal escape, the authors incubated the cells with ChargeSomes over a temporal gradient and their studies demonstrated rapid transition from cell uptake to endosomal escape within 6 hours highlights the efficiency of ChargeSomes in delivering mRNA.

The researchers further tested the transfection efficiency of ChargeSomes using Enhanced Green Fluorescent Protein (EGFP) mRNA and confirmed the encapsulation and stability of EGFP mRNA within ChargeSomes, even in the presence of PBS, RNase, and fetal bovine serum. In contrast, cells treated with naked mRNA exhibited no EGFP expression, suggesting degradation or failed internalization of unencapsulated mRNA. Quantitative evaluation using flow cytometry revealed that mRNA delivery via ChargeSomes significantly improved EGFP expression efficiency compared to naked mRNA. The results indicated that ChargeSomes facilitated effective endosomal escape and cytoplasmic delivery of mRNA, with the 9:1 ratio showing the highest transfection efficiency due to its optimal physicochemical properties.

One of the major contributions of the new study is the development of a delivery system that significantly enhances the stability and protection of mRNA molecules. ChargeSomes shield mRNA from degradation by RNases and the use of charge-complementary polymers ensures that the mRNA is securely encapsulated, which is a substantial improvement over traditional delivery methods that often fail to provide adequate protection. In conclusion, Professor Hyun-Ouk Kim and his team demonstrated that ChargeSomes is a safe and efficient mRNA delivery technology that can enhance cellular uptake and promote effective endosomal escape. Additionally, the practical implications of work of Professor Hyun-Ouk Kim and colleagues extend to the development of non-viral gene therapy as well as mRNA vaccines.  Future studies should further confirm the in vivo efficacy of ChargeSomes in animal models and eventually in human trials. The versatility of the ChargeSome platform allows for the potential development of delivery systems for other types of nucleic acids, such as small interfering RNA (siRNA) or DNA which will broaden the scope of gene therapy applications.