(6e) The Design of Peptide Amphiphile Micelles for Diagnostic Applications in Atherosclerosis

Authors: 
Chung, E. J., University of Chicago
Drews, L. B., University of California, Berkeley
Tirrell, M., University of Chicago



Peptide amphiphiles self-assemble into dynamic micellar structures and provide a multivalent display of targeting peptides which can be developed for use in a wide range of diagnostic and therapeutic applications. Recently, fibrin-binding peptide amphiphile micelles were reported to be suitable for detecting blood clots, a characteristic of late staged atherosclerosis1. Although visualization of a clot within a plaque provides a powerful, molecular imaging tool, fibrin expression represents a progressed state of atherosclerotic disease, limiting the system to identifying the outcome of plaque rupture vs. diagnosing the onset of plaque vulnerability for preventative measures.

The presence of monocytes is a known marker of atherosclerotic plaque vulnerability. Specifically, activated endothelial cells secrete cytokines which recruit monocytes in large quantities. Therefore, in order to intervene before plaque rupture, we are engineering monocyte-targeting, peptide amphiphile micelles through the incorporation of the cytokine binding motif. The binding peptide sequence or Cy-7 was conjugated to a lipid tail and mixed to form fluorescently-labeled, monocyte-targeting peptide amphiphile micelles. The critical micelle concentration was determined to be approximately 1 μM with an average diameter of approximately 15 nm, confirmed via dynamic light scattering and transmission electron microscopy. These spherical micelles were stable at 37◦C in cell culture media for up to 30 minutes and bound to murine monocytes when evaluated via flow cytometry and confocal microscopy. Moreover, micelles were confirmed to be biocompatible and biofunctional using Live/Dead and chemotaxis assays, respectively.

A molecular imaging tool that binds specifically to monocytes has the potential to meet the sensitivity and accuracy standards necessary to detect vulnerable plaques and therefore provide the time and the opportunity for the patient to treat and manage them. Future studies in Apo/E knockout mice will further delineate the full potential of these novel, peptide amphiphile micelles for atherosclerosis diagnostics. Notably, since peptide micelles can be synthesized with multiple functionalities (i.e. targeting element, imaging dye, therapeutic, etc.), our investigations will lay the ground work for peptide amphiphile micelle-mediated drug delivery at the site of atherosclerotic plaques in future studies.

1. Peters, D. et al. Targeting atherosclerosis by using modular, multifunctional micelles. Proceedings of the National Academy of Sciences 106, 9815-9819, 2009.