INTELLECTUAL MERIT: The goal of this proposal is to develop and investigate echogenic liposomes that will be recognized by and attach to a specific enzyme. The attached liposomes will act as contrast agents for ultrasound assay of the extent of expression of the enzyme. The enzyme will destabilize the liposome releasing encapsulated drugs as well as inhibitors for the enzyme, and the release of inhibitors will self-regulate the drug release. The investigation is directed towards optimizing ultrasound contrast and drug release. Specifically, the objectives of this proposal are to: (1) synthesize lipid-peptide conjugates containing the cleavage site for gelatinase enzymes that are over expressed in atherosclerotic plaque, (2) prepare echogenic liposomes incorporating the synthesized lipopeptides and investigate the release of liposome-encapsulated contents by gelatinases, (3) investigate stability and contrast enhancing properties of echogenic liposomes, and (4) investigate the release of liposome-encapsulated inhibitors by gelatinases in the absence and presence of ultrasonic pulses and the resultant inhibition of the enzyme.
BROADER IMPACTS: The proposed methodology, when fully developed, will find applications in the areas of diagnostics and targeted drug delivery. The area of the enzyme-triggered content release from liposomes has enormous potential to grow in the near future. The research will initiate a multi-university cross-disciplinary initiative where students will be trained in an environment where chemistry, biology and engineering will be brought together to solve an important problem. Both PIs are dedicated to teaching and training the next generation of scientists and engineers. The project will involve training undergraduate and graduate students in a cross-disciplinary environment. The proposed research will involve two Native American undergraduate students in the Mallik lab at North Dakota State. Sarkar has established a link with a collaborator in Morgan State University (an HBCU) to identify talented undergraduate research interns and to groom them for graduate study at the University of Delaware.
In this collaborative project, we have prepared lipid-based nanocarriers (liposomes) for drug delivery and ultrasound imaging of cancers. We have included commonly-used anticancer drugs, and air bubbles in the liposomes. The drugs were sequestered in the aqueous core of these carriers. However, we do not know the exact locations of the encapsulated air bubbles. Usually, the release of anticancer drugs from carriers is a slow process. In order to solve this problem, we have prepared liposomes which become unstable in the presence of enzymes overexpressed and secreted by the cancer cells. We have demonstrated that these liposomes become unstable and efficiently release the drugs outside the cancer cells. Another type of liposomes selectively enter the cancer cells, and then release the drugs (in response to increased concentrations of reducing agents or acid, as commonly observed inside cancer cells). Release from all of these carriers are increased when high frequency ultrasound pulses are applied. In addition, we have imaged the liposomes employing a medical ultrasound scanner. The released drugs selectively kills the cancer cells grown as three-dimensional spheroids. The applied ultrasound does not cause any harm to the normal cells. Four graduate students, four undergraduate students, and three high school students participated in this research project.
