Complexation Between DNA and Hydrophilic-Cationic Diblock Copolymers

Abstract

DNA-polycation complexes (polyplexes) are gene delivery vehicles that offer a number of advantages over viral vehicles: high genetic payload capacity, low toxicity, and low cost. Among the many polycation architectures, hydrophilic-cationic diblock copolymers are particularly promising due to their versatility. Compared to the emphasis on biological evaluation of polyplexes, however, in-depth understanding of the polyplex formation process (and the parameters involved) is rather sparse. Thus, this thesis discusses the physics of polyplex formation. First, a collection of solution-state techniques are employed to elucidate the effects of diblock composition, ionic strength, DNA morphology, and pH on DNA-diblock binding. Specifically, the binding thermodynamics and strength - measured using isothermal calorimetry and circular dichroism spectroscopy, respectively - turn out to show a strong dependence on the cationic content in the diblock, leading to wide ranges of polyplex size, dispersity, and stability. Second, the effects of hydrophilic block structure, charge density, and polyplex formation route are investigated. It is found that bulkier hydrophilic blocks translate to larger polyplexes when DNA is in excess and that hydrophilic block solubility controls polyplex stability when the diblock is in excess. With fixed material and concentration, different polyplex sizes and dispersities can be achieved by varying solution ionic strength or DNA-polycation mixing route. To this end, the analysis of polyplex formation presented in this thesis provides original insights into physical variables that can be adjusted to tune the DNA-polycation binding behavior and resulting polyplex properties, which can aid in the guided development of polymeric DNA delivery systems.