Theranostic Nanoparticle and Drug Loaded Contrast Agents and Their Biomedical Applications

Abstract

Ultrasound contrast agents are typically microbubbles (MB) with a gas core that is stabilized by a shell made of lipids, proteins, or polymers. The high impedance mismatch between the gas core and an aqueous environment produces strong contrast in ultrasound (US). Poly(lactic acid) (PLA) MB, previously developed in our laboratory, have been shown to be highly echogenic both in vitro and in vivo. In recent years, MB have established their role in contrast enhanced medical imaging and bio-nanotechnology. We show that these microbubbles have potential in various applications including multimodal imaging and as a targeted drug delivery vehicle. Combining US with other imaging modalities such as fluorescence, magnetic resonance imaging (MRI), or computer tomography (CT) could improve the accuracy of many US applications and provide more comprehensive diagnostic information. Furthermore, our MB have the capacity to house a drug in the PLA shell and create drug-loaded nano fragments in situ when passing through an ultrasound beam. The nano-sized fragments can be taken up into the tumor via the enhanced permeability and retention (EPR) effect. To create multimodal contrast agents, we hypothesized that the polymer shell of our PLA MB platform could accommodate additional payloads. In this thesis, we therefore modified our current MB by encapsulating imaging-related nanoparticles including aqueous or organic quantum dots (QD), magnetic iron oxide nanoparticles (MNP), or gold nanoparticles (AuNP) to create bimodality platforms in a manner that minimally compromised the performance of each individual imaging technique. Controlled drug drug delivery system using microbubbles as vehicle in conjunction with ultrasound have been previously studied to reduce drug dosage, systemic toxicity, and side effects for treatment of cancer. To enhance more loading of drug on the MB for a more effective treatment, nanoparticles conjugated with drugs on the surface were used in the study. Nanopaticles are here used to take advantage of the increased surface area per volume ratio for the cancer drug to conjugate on the surface. These drug conjugated nanoaprticles have then been encapsulated inside the MB shell. AuNP and MNP were used in the study of drug delivery. The DOX-AuNP + DOX MB showed significantly higher loading than loading by the method that was previously developed in our lab, DOX-MB with drug payload ( 43.7 vs. 16.23 µg DOX / mg MB) and encpasulation effiency (48.5% vs. 22.1%). The agents achieved 19 dB of US contrast enhancement in vitro and are shown to provide visible contrast using clinical ultrasound machines. The agent also shown to be able to sustain release of DOX for more than period of 1 week, as well as to form nano polymer fragments (n-Sh) after being insonated for 20 minutes. In vitro therapeutics activity of these agents was shown with both a human breast cancer cell line (MDA-MB-231) and a hepatoma cancer cell line (Huh7). Using a model system for in situ nano-shard formation, we also demonstrated that DOX-AuNP + DOX…