Polymer-enhanced endosomal escape for drug delivery: a mechanistic network of pH-triggered polymer binding, leakage, fusion, and other physical-chemical membrane behaviour

• Applicant: Dr. Maria Hoernke
• Subject Area: Biophysics
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 415894560

The main constituent of a biological membrane is a lipid bilayer, a diverse 2-dimensional mixture of lipids. Lipid membranes of cells and organelles constitute the main barriers for the transport of drugs to their site of action. Drugs that are taken up into the cell by endocytosis are engulfed by the endosomal membrane. They can act in the cytosol or in the nucleus only after endosomal escape. Otherwise, they would end up in the lysosome and be degraded. Endosomal escape is the most important barrier for transfection of genetic material for gene therapy or mRNA therapies, or protein drugs, such as enzymes. After the formation of the endosome from the plasma membrane, during the development via early and late endosome to the lysosome, the pH changes from 7.4 to 4.5. Furthermore, the membrane of early or late endosome contain a negatively charged lipid that is not present in the plasma membrane. These two aspects are combined for strategies to enhance endosomal escape: Peptides or biomimetic polymers that are only charged at the low endosomal pH are designed to selectively permeabilize only the negatively charged endosomal membrane. The currently used transfection polymers need to be improved regarding this last point, as they are toxic. For rational polymer design however, a better knowledge of the mechanisms of activity are urgently needed. This type of knowledge has been collected over the recent decades in the context of antimicrobial peptides and polymers that act very similarly. In my opinion, there is great potential in understanding the network of the different membrane effects induced by the polymers. The many different types of membrane permeabilization mechanisms are central here. However, they cannot be understood without considering their relation to various modes of membrane binding, membrane aggregation and fusion. The proposed project will reveal the mechanistic network of these membrane perturbations induced by systematically varied polymers for endosomal escape. The aim is to provide guidelines to improve (co-) polymers, combination pf polymers and polyplexes on the basis of the new understanding of the mechanistic network and polymer structure-function relations. The interplay of membrane binding, permeabilization, membrane aggregation and fusion will be examined as a function of pH-sensitive polymer charge, lipid composition of the membrane, and polymer chain length with the help of detailed, biophysical studies. This will highlight relevant options for the rational improvement of therapeutic polymers with selectivity for negatively charged membranes applied in enhanced endosomal escape but also in antimicrobial or anticancer therapy.

• DFG Programme: Research Grants