Recent Advancement in mRNA Vaccine Development and Applications

Messenger RNA (mRNA) vaccine development for preventive and therapeutic applications has evolved rapidly over the last decade. The mRVNA vaccine has proven therapeutic efficacy in various applications, including infectious disease, immunotherapy, genetic disorders, regenerative medicine, and cancer. Many mRNA vaccines have made it to clinical trials, and a couple have obtained FDA approval. This emerging therapeutic approach has several advantages over conventional methods: safety; efficacy; adaptability; bulk production; and cost-effectiveness. However, it is worth mentioning that the delivery to the target site and in vivo degradation and thermal stability are boundaries that can alter their efficacy and outcomes. In this review, we shed light on different types of mRNA vaccines, their mode of action, and the process to optimize their development and overcome their limitations. We also have explored various delivery systems focusing on the nanoparticle-mediated delivery of the mRNA vaccine. Generally, the delivery system plays a vital role in enhancing mRNA vaccine stability, biocompatibility, and homing to the desired cells and tissues. In addition to their function as a delivery vehicle, they serve as a compartment that shields and protects the mRNA molecules against physical, chemical, and biological activities that can alter their efficiency. Finally, we focused on the future considerations that should be attained for safer and more efficient mRNA application underlining the advantages and disadvantages of the current mRNA vaccines.

Hepatocyte-targeted delivery of imiquimod reduces hepatitis B virus surface antigen

Hepatitis B virus (HBV) can rapidly replicate in the hepatocytes after transmission, leading to chronic hepatitis, liver cirrhosis and eventually hepatocellular carcinoma. Interferon-α (IFN-α) is included in the standard treatment for chronic hepatitis B (CHB). However, this therapy causes serious side effects. Delivering IFN-α selectively to the liver may enhance its efficacy and safety. Imiquimod (IMQ), a Toll-Like Receptor (TLR) 7 agonist, stimulates the release of IFN-α that exhibits potent antiviral activity. However, the poor solubility and tissue selectivity of IMQ limits its clinical use. Here, we demonstrated the use of lipid-based nanoparticles (LNPs) to deliver IMQ and increase the production of IFN-α in the liver. We encapsulated IMQ in two liver-targeted LNP formulations: phospholipid-free small unilamellar vesicles (PFSUVs) and DSPG-liposomes targeting the hepatocytes and the Kupffer cells, respectively. In vitro drug release/retention, in vivo pharmacokinetics, intrahepatic distribution, IFN-α production, and suppression of serum HBV surface antigen (HBsAg) were evaluated and compared for these two formulations. PFSUVs provided >95% encapsulation efficiency for IMQ at a drug-to-lipid ratio (D/L) of 1/20 (w/w) and displayed stable drug retention in the presence of serum. DSPG-IMQ showed 79% encapsulation of IMQ at 1/20 (D/L) and exhibited ∼30% burst release when incubated with serum. Within the liver, PFSUVs showed high selectivity for the hepatocytes while DSPG-liposomes targeted the Kupffer cells. Finally, in an experimental HBV mouse model, PFSUVs significantly reduced serum levels of HBsAg by 12-, 6.3- and 2.2-fold compared to the control, IFN-α, and DSPG-IMQ groups, respectively. The results suggest that the hepatocyte-targeted PFSUVs loaded with IMQ exhibit significant potential for enhancing therapy of CHB.

Development of a child-friendly oral drug formulation using liposomal multilamellar vesicle technology

Many medicines are only available in solid dosage forms suitable for adults, and extemporaneous compounding is required to prepare formulations for children. However, this common practice often results in inaccurate dosing and unpleasant taste, reducing the medication adherence. Here, we report the development of a new method to prepare and compound child-friendly oral formulations based on a liposomal multilamellar vesicle (MLV) platform. MLVs composed of a phospholipid (DSPC) and cholesterol (55/45, molar ratio) were prepared using the standard thin film hydration method with 300 mM citric acid (pH 2), followed by an addition of aqueous sodium carbonate to adjust the exterior pH to 8-10 for creating a transmembrane pH gradient. Weak-base drugs, such as chloroquine (CQ) and hydroxychloroquine (HCQ), could be actively and completely loaded into the MLVs at a drug-to-lipid ratio of 15-20 wt%. This technique formulated weak-base drugs from the powder or tablet form into a liquid preparation, and the complete drug encapsulation would prevent contact between the drug molecules and the taste buds. The gradient MLV formulation could be preserved by lyophilization and stored at room temperature for at least 8 weeks. Upon reconstitution with water, the MLV formulation could completely encapsulate CQ at 20 wt%, which was comparable to the freshly prepared MLVs. The CQ-loaded MLV formulation could be stored at 4 °C for 2 weeks without drug leakage. In vitro release studies indicated that MLV could retain CQ in the simulated saliva, but released up to 50% and 30% of the drug in the simulated gastric and intestinal fluids, respectively. The orally delivered MLV-CQ formulation displayed higher CQ absorption in mice, with a 2-fold increase in the area under the curve (AUC) of the plasma profile compared to CQ solution. Our data suggest that the new MLV method could serve as a platform to prepare child-friendly oral formulation for weak-base drugs.

Simultaneous Chromatographic Quantitation of Drug Substance and Excipients in Nanoformulations Using a Combination of Evaporative Light Scattering and Absorbance Detectors

Nanomedicines including lipid- and polymer-based nanoparticles and polymer-drug conjugates enable targeted drug delivery for the treatment of numerous diseases. Quantitative analysis of components in nanomedicines is routinely performed to characterize the products to ensure quality and property consistency but has been mainly focused on the active pharmaceutical ingredients (APIs) in academic publications. It has been increasingly recognized that excipients in nanomedicines are critical in determining the product quality, stability, consistency, and safety. APIs are often analyzed by high-performance liquid chromatography (HPLC), and it would be convenient if the same method can be applied to excipients to robustly quantify all components in nanomedicines. Here, we report the development of a HPLC method that combined an evaporative light scattering (ELS) detector with an UV-vis detector to simultaneously analyze drugs and excipients in nanomedicines. This method was tested on diverse nanodrug delivery systems, including a niosomal nanoparticle encapsulating a phytotherapeutic, a liposome encapsulating an immune boosting agent, and a PEGylated peptide. This method can be utilized for a variety of applications, such as monitoring drug loading, studying drug release, and storage stability. The information obtained from the analyses is of importance for nanomedicine formulation development.

Improved Liver Delivery of Primaquine by Phospholipid-Free Small Unilamellar Vesicles with Reduced Hemolytic Toxicity

Hemolytic toxicity caused by primaquine (PQ) is a high-risk condition that hampers the wide use of PQ to treat liver-stage malaria. This study demonstrated that phospholipid-free small unilamellar vesicles (PFSUVs) composed of Tween80 and cholesterol could encapsulate and deliver PQ to the hepatocytes with reduced exposure to the red blood cells (RBCs). Nonionic surfactant (Tween80) and cholesterol-forming SUVs with a mean diameter of 50 nm were fabricated for delivering PQ. Drug release/retention, drug uptake by RBCs, pharmacokinetics, and liver uptake of PFSUVs-PQ were evaluated in in vitro and in vivo models in comparison to free drugs. Additionally, the stress effect on RBCs induced by free PQ and PFSUVs-PQ was evaluated by examining RBC morphology. PFSUVs provided >95% encapsulation efficiency for PQ at a drug-to-lipid ratio of 1:20 (w/w) and stably retained the drug in the presence of serum. When incubated with RBCs, PQ uptake in the PFSUVs group was reduced by 4- to 8-folds compared to free PQ. As a result, free PQ induced significant RBC morphology changes, while PFSUVs-PQ showed no such adverse effect. Intravenously (i.v.) delivered PFSUVs-PQ produced a comparable plasma profile as free PQ, given i.v. and orally, while the liver uptake was increased by 4.8 and 1.6-folds, respectively, in mice. Within the liver, PFSUVs selectively targeted the hepatocytes, with no significant blood or liver toxicity in mice. PFSUVs effectively targeted PQ to the liver and reduced RBC uptake compared to free PQ, leading to reduced RBC toxicity. PFSUVs exhibited potential in improving the efficacy of PQ for treating liver-stage malaria.

Altering the intra-liver distribution of phospholipid-free small unilamellar vesicles using temperature-dependent size-tunability

We demonstrated that phospholipid-free small unilamellar vesicles (PFSUVs) composed of TWEEN 80 and cholesterol (25/75, mol%) could be fabricated using a staggered herringbone micromixer with precise controlling of their mean size between 54 nm and 147 nm. Increasing the temperature or decreasing the flow rate led to an increase in the resulting particle diameter. In zebrafish embryos, 120-nm PFSUVs showed 3-fold higher macrophage clearance compared to the 60-nm particles, which exhibited prolonged blood circulation. In mice, the 60-nm particles showed dominant accumulation in the liver hepatocytes (66% hepatocytes positive), while the 120-nm particles were delivered equally to the liver and spleen macrophages. Accordingly, in a murine model of acetaminophen-induced hepatotoxicity the 60-nm particles loaded with chlorpromazine reduced the serum alanine aminotransferase level and liver necrosis 2- to 4-fold more efficiently than their 120-nm counterparts and the free drug, respectively. This work showed that the intra-liver distribution of PFSUVs was largely determined by the size. Most other nanoparticles published to date are predominantly cleared by the liver Kupffer cells. The 60-nm PFSUVs, on the other hand, focused the delivery to the hepatocytes with significant advantages for the therapy of liver diseases.