Delivery tools such as viral vectors, lipids, liposomes, polymers, polymeric micelles, inorganic nanoparticles, and extracellular vesicles have been studied for targeted therapeutic delivery. A number of these have been approved by the Food and Drug Administration for treatment of disease and many are currently being investigated in clinical trials. Extracellular vesicles (EVs) are an emerging therapeutic delivery tool based on their ability to be naturally taken up by cells, low immunogenicity, and potential for inherent targeting ability. EVs are small membrane bound particles released by cells and are considered to be a naturally occurring method of cell-to-cell communication. The targeting ability of EVs has been demonstrated using tumor cell-derived EVs that show increased uptake in tumors and tumor cells. In addition, EVs from immune cells have been used to target areas of inflammation, and one potential benefit of using EVs is that tracking studies have shown that EVs cross tissue barriers in vivo. EVs have been tracked by common imaging modalities, all of which rely on labeling the EV with a modality-specific tracer, such as inorganic nanoparticles, fluorescent dyes, bioluminescent or fluorescent proteins, or radioactive tags. One of the emerging imaging methods for tracking EVs in vivo is magnetic particle imaging (MPI), which uses superparamagnetic iron oxide nanoparticles (SPIOs) as the tracer. Once labeled with SPIOs, EVs can be tracked in vivo with MPI, which offers the significant advantages of being sensitive and directly quantitative. Development of EVs as a therapeutic delivery tool can be enhanced through imaging, and here I evaluate this for primary cancer and metastasis as well as cardiovascular disease. I initially evaluated EV delivery to primary breast cancer in a mouse model because of disease prevalence and importance. Women in the United States have a 12.8% chance of developing breast cancer during their lifetime. This study labels breast cancer-derived EVs with SPIOs (iron-labeled 3EVs referred to as FeEVs) to measure retention in primary breast cancer tumors with MPI. These FeEVs were retained for longer and in greater amounts compared to SPIOs in vivo when injected intratumorally. Further analysis of the tumors revealed that FeEVs were taken up by tumor cells and were found around tumor-associated macrophages (TAMs). Breast cancer may metastasize to the brain which is often deadly, as it is very difficult to treat because of the blood brain barrier (BBB). Treatment options for brain metastasize include surgical resection, stereotactic radiosurgery, whole brain radiation therapy, and systemic chemoor endocrine therapies, which are limited by the BBB. EVs have been shown to cross the BBB, offering the potential for use as a therapeutic delivery tool for metastatic tumors in the brain. For this reason, FeEVs from metastatic breast cancer cells with a predilection to going to the brain (brain-seeking) were injected into the left ventricle of the heart (intracardiac, i.c.) in mice with brain metastasis as well as healthy control mice. Unmodified SPIOs alone were also injected into mice with brain metastasis as a control to show EV targeting. Only mice with brain metastasis injected with FeEVs had detected iron signal in the head, indicating their possible use as a therapeutic delivery tool.The third study involved EVs isolated from immune cells for targeting of myocardial infarction (MI). Human monocyte-like cells (THP-1) were transfected with firefly luciferase, and EVs from these cells were isolated and delivered to recipient cardiac organoids in vitro. Bioluminescence was detected in the recipient cells suggesting directed delivery. Assessing the difference in delivery to normal organoids and hypoxic organoids could be an indicator of effective targeting to diseased tissues. EVs isolated from specific donor cells demonstrated the ability to target damaged cardiac tissue.
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