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BP: Fachverband Biologische Physik

BP 12: Poster 2

BP 12.56: Poster

Dienstag, 6. September 2022, 17:30–19:30, P4

The pH dependent phase transition in lipid nanoparticle cores leads to changes of protein expression in single cells — •Julian Philipp¹, Lennart Lindfors², and Joachim Rädler¹ — ¹LMU, Munich, Germany — ²AstraZeneca, Mölndal, Sweden

Lipid nanoparticles developed into the most powerful delivery platform for mRNA based vaccination and therapies. In general LNPs are core/shell particles exhibiting PEG-lipid and DSPC at the surface and ionizable lipid, cholesterol and mRNA in the core. However, the pH dependent changes induced by ionizable lipids in the context of endosomal release are little understood. Here we study the ionizable lipids MC3, KC2, DLin-DMA as model systems as they exhibit different efficacy despite similar pK values. Using synchrotron X-ray scattering we study the structure of bulk phases containing ionizable lipid/cholesterol with and without polyA as mRNA surrogate. The bulk phases exhibit ordered mesophases at low pH and a transition into isotropic swollen phases at higher pH. We find inverse hexagonal H_II lipid phases in case of MC3 and KC2 and cubic Pn3m and H_II phases in case of DLin. Bulk phases with polyA show coexistence of pure lipid phases and condensed nucleic acid lipid phases. We show that the observed bulk structures are consistent with the SAXS scattering profile of mRNA containing LNPs. The difference in structural features is also consistant with the delayed onset and reduced level of GFP expression observed in single cell time courses after transfection with DLin LNPs compared to MC3 and KC2. We conclude that pH dependent bulk phase transitions trigger endosomal release.