On the Development of Analytical Methodologies to Interrogate the Lipid Dynamics and Phase Transition Resulting from the Reduction of Stimuli-responsive Vesicles

Abstract

The potential is great for liposome drug delivery systems that provide specific contents release at diseased tissue sites upon activation by upregulated enzymes; however, this potential will only come to fruition with mechanistic knowledge of the contents release process. NAD(P)H:quinone oxidoreductase type 1 (NQO1) is a target for reductively-responsive liposomes, as it is an enzyme upregulated in numerous cancer tissues and is capable of reducing quinone propionic acid (QPA) trigger groups to hydroquinones that self-cleave from dioleolylphosphatidylethanolamine (DOPE) liposome surfaces, thereby initiating contents release. This research targets the development of analytical methodologies to observe and characterize the dynamics and resulting phase change of the QPA-DOPE liposomal system. It is known that after reduction, QPA-DOPE vesicles aggregate and that the aggregation is correlated with release of their encapsulated contents. While postulated, the final phase identity of this system has not been identified as the conventional methods used to make this measurement are not capable of studying such a unique and dynamic system. Presented herein are the analytical methods, both developed and adapted, which have been used to investigate a liposomal system capable of redox stimulated contents release. The purpose of this work was to utilize these tools to (1) study the terminal phase identity of QPA-DOPE vesicles after reduction, (2) manipulate the QPA-DOPE liposomal system for triggerable inter-vesical fusion, and (3) investigate the liposome bilayer behavior post-reduction and pre-release. The findings of this work are presented and their significance discussed.