(512c) Influence of Process Parameters and Composition on Long-Term Stability of Lipid Nanocarrier Formulations

Novel therapies, such as mRNA- vaccines, gene therapies and personalized medicines have shown an enormous potential within recent years. In order to unfold their full potential it is important to deliver the active pharmaceutical ingredient (API) or its blueprint (e.g. mRNA) to a specific target site in the human body. To protect the API or blueprint from degradation and instabilities on its way to this site, nanocarriers such as liposomes or lipid nanoparticles (LNPs) are increasingly used for encapsulation. Classically, these nanocarriers are produced by mixing a (liquid) organic phase containing different lipids (building blocks), with a second (liquid) aqueous phase containing the API or blueprint. Although these carriers are already used industrially (e.g. Covid-19 vaccines), their formulation mechanism (process parameters and composition) is not well understood and thus production is still based on trial-and-error principles. This can result in the formulation not being in thermodynamic equilibrium, which potentially reduces its long-term stability and requires storage at ultra-low temperatures (e.g. -80°C).

To address this challenge, we developed a systematical method for nanocarrier formulation taking thermodynamic equilibrium into account. Model systems containing DOPC-/DPPC-liposomes, as well as KC2-LNPs were used within this work. For a thorough characterization, we investigated both the influence of process parameters (e.g., flow rate ratios) and feed compositions (e.g., lipid content and ethanol concentration) on size, molecular mass and polydispersity of the nanocarriers. Characterization of the nanocarriers was performed using light scattering techniques. All nanocarriers were then analyzed towards phase behavior and long-term stability. Results show that varying the process parameters lead to liposomes of different size (radius 30 to 300 nm) and molecular weight. Changes in the composition of the liposomes and LNPs have a minor influence on the size, but can significantly affect the thermodynamic equilibrium and thus the long-term stability. Based on the results, we could thus create a nanocarrier formulation at their equilibrium size, being stable at room temperature for several months. Concluding, these investigations will contribute to a mechanistic understanding of the long-term stability of lipid nanocarrier formulations, which can pave the way for an optimized production process.