Design of Membrane Disruptive Heteropolymers

The cell membrane is a barrier that many drugs have to overcome. One method is to ”pick the lock” by taking advantage of existing transport systems of the cell. Another is to ”break down the door” by disrupting the membrane itself until pores form for the drug to move through. This method of disrupting the membrane is the goal of this thesis, to be obtained using heteropolymers. In this project, polymers are developed and iterated upon to obtain polymers that balance membrane disruptiveness and solubility. They can be used as tools which break the cell membrane for different purposes. Two main purposes of membrane disruptive heteropolymers are presented.

The first is polymers that push and pull the membrane into pieces and extract discs from it. These nanoparticles are called ”nanodiscs”. They can extract membrane proteins to ease their study or use them as drugs. The thesis introduces poly(methacrylic acidcostyrene (MAASTY) as a polymer for this purpose. The reactivity ratios of MAASTY show that it has a higher degree of randomness in its monomer chain structure than the previously introduced poly(acrylic acidcostyrene) (AASTY). This indicated randomness being an important aspect of nanodisc forming polymers, leading to a study of variations of MAASTY synthesized with different reactivity ratios. The study demonstrates how different polymers can perform optimally in different environments. Higher randomness was beneficial when forming nanodiscs without membrane proteins, while higher order was preferred for nanodiscs with membrane proteins. This shows that testing the efficiency of nanodisc forming polymers using biomimetic membranes, without membrane proteins, is not sufficient if they are to be used to extract membrane proteins from biological cells.

The second class is polymer which form coacervates: a phase separated from water, while still being an aqueous phase. The coacervate phase is formed by amphiphilic macromolecules, such as polymers, often charged. A coacervating polymer will at its lower critical solution temperature, be pushed out of solution because of the loss of entropy of water molecules. The polymer doesn’t precipitate, because that would also lead to a large loss in entropy. Coacervates have wide uses, including as potential oral drug delivery vehicles. A drug can be stored within a coacervate in high concentration while protected from digestive enzymes by the polymers. Because coacervating polymers are amphiphilic, they can disrupt cell membranes similarly to nanodisc forming polymers, creating pores for the drug to pass through. The thesis introduces method development of an automatic synthesis setup for creation of a large library polymers and their testing for coacervating properties. The analysis of the data set is ongoing, but it does show potential to assist in future design of coacervating polymer. Additionally, one of the polymers in the library was previously shown to have potential as an oral drug delivery vehicle. This became the foundation of a spinout company: ”Vegvisir Technologies”. In this thesis experiments were performed in cooperation with the spinout to prove the effect of the coacervate in vivo in mice with semaglutide as the model drug. The experiment successfully showed a drop in blood glucose when semaglutide was delivered with the coacervate.

In summary, this thesis presents aspects of nanodisc forming and coacervating polymers that are important to their function and how use them for design of future polymers.