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New advances in biomaterials and nanotechnology impact on the next generation of drug delivery liposomes.

Posted by on in Pharmaceutical Sciences
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At the Centre for Drug Research (CDR), University of Helsinki, Dr. Alex Bunker leads the Computational Nanomedicine Group. In his research, he applies molecular modelling as a tool in nanoscale drug delivery research, known as "nanomedicine". A particular focus of his group is the PEGylated liposome, and he has modelled its surface in the bloodstream with molecular dynamics simulation. The same way that a map can be used to represent a country, he and his team have simulated a flat slab of the membrane of the liposome.


Coating of the liposomal surface with polyethylene glycol (i.e., PEGylation) suppresses the uptake of drug by the reticuloendothelial system, thereby prolonging the half-life of the drug in the plasma. For example, a liposome-PEG formulation of doxirubicin is currently marketed by Janssen Products under the brand names Doxil or Caelyx. It is an approved therapeutic for treating Kaposi's sarcoma, ovarian cancer, and multiple myeloma.


Animations from the Computational Nanomedicine Group show liposome-PEG membranes in gel (movie1 & movie2) and liquid crystalline phase (movie3 & movie4) interacting with salt ions in the bloodstream. From these simulations, his team has determined that when the PEG layer density is too high, the Cl- ions (cyan) are expelled from the layer, negating the desired effect of a neutral protective layer. Also, in the looser liquid crystalline phase, some PEG actually enters the membrane core.

His team has also studied the PEGylated liposome surface with a new targeting ligand, the AETP moiety. Their simulations demonstrate that the cause of failure of this new targeting moiety is increased coverage by the PEG polymer, due to its hydrophobic nature (movie5). Compare this to the PEGylated liposome with RGD moiety simulation (movie6).


New advances in biomaterials and nanotechnology will no doubt impact the next generation of drug delivery liposomes. Dr. Bunker's work in this area is important given that many of the most basic scientific questions (e.g., how is a liposome interacting with components in the bloodstream?) are not easily addressed using standard physico-chemical methods. Dr. Bunker hopes that his work will lead to a more thorough understanding of how PEG-liposomes perform in vivo, but also lay the groundwork for computational testing and ultimate development of new polymer coatings.

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