Dendritic polymers as novel targeted anti-cancer therapeutics. Atomic force microscopy and molecular dynamics simulations.

Polyamidoamine (PAMAM) dendrimers are promising candidates for the development of targeted anti-cancer drugs. Special properties of these branched polymers make them versatile nanometer scale components for creating multifunctional macromolecules capable of detecting and killing tumor cells without harming healthy tissue. This dissertation investigates the structure and function of dendrimers in this context at length scales of only several nanometers. Using experimental and theoretical methods, this study demonstrates the link between molecular engineering at the nanoscale and biologic function at the cellular level. Molecular dynamics simulations show that dendrimers are highly flexible and capable of forming multiple interaction sites between several of their branch ends and a substrate. This opens the possibility of improved cell targeting through multivalent receptor-binding. The ability of the polymers to deform is investigated as a function of dendrimer generation (2--5). The results are in good agreement with atomic force microscopy (AFM) experiments. AFM is also employed to observe the effect of dendrimers on membranes in real time. Using phospholipid bilayers as a model system, it is shown that the effect of PAMAMs on a membrane strongly depends on the dendrimer generation, architecture, and chemical properties of the branch end-groups. The data indicates that certain dendrimers (generation ≥5) cause the formation of small holes (∼15--40 nm in diameter) in a previously intact lipid bilayer. This observation reveals a new possible mechanism leading to unwanted non-specific cell uptake and cytotoxicity. Hole formation in lipid membranes can be avoided by reducing dendrimer size (generation) and charge. In particular, charge neutral acetamide-capped generation 5 PAMAMs do not have the ability to remove lipids from the bilayers. A possible mechanism for the formation of holes in lipid bilayers is proposed. It involves the formation of vesicle-like aggregates consisting of a dendrimer surrounded by layers of lipid molecules. Dynamic light scattering measurements as well as 31P NMR data support this explanation. In addition, a theoretical framework for the self-assembly of lipid vesicles is developed and used to explain the experimental observations. The findings are also compared to recent biological studies in animal models and cell culture.PhDBiological SciencesBiophysicsHealth and Environmental SciencesPharmacologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/124267/2/3137900.pd