It has been recognized for decades that lipid-encapsulated cellular material is present in human blood, and that these particles can affect coagulation and stability. Although these "microparticles" have been traditionally thought to be cellular debris, more recent studies have demonstrated that a fraction of very small particles (30-100 nm) are produced by tumors and comprise a novel communication network among tumor cells. These small vesicles are termed "exosomes", and studies have shown that tumor exosomes are programmed to transfer active biomolecules (RNA, proteins) to specific sites in vivo and have been implicated in metastasis. Recent in vivo studies have reported that exosomes offer significant advantages over synthetic drug delivery systems including enhanced serum stability, low immunogenicity, and minimal clearance by lung, liver, and spleen. In addition to these beneficial characteristics, our preliminary data indicate that exosomes from tumor cells are taken up to a much greater extent by the parent tumor cell type as compared to other cell lines. This "homing" is not due to an inherently greater capacity for non-specific uptake, and the proposed studies further characterize this effect as well as investigate the protein and lipid components that are responsible for this tropism. The ability of tumor exosomes to home to the parent tumor in a mouse model will be quantified with PET imaging, and the tumor-homing behavior will be exploited by utilizing exosomes to deliver chemotherapeutics in tumor-bearing mice. Using the information gathered from proteomic and lipidomic analyses, the work also explores the potential of developing a synthetic vesicle containing the components that endow exosomes with their ability to home to tumors.
The presence of small vesicles in cancer patient serum has recently been shown to correlate with the stage of disease, which has unveiled a previously unknown network of communication and transportation among cancer cells. It follows that these same vesicles might be harnessed and exploited to deliver chemotherapeutics specifically to tumors, thereby minimizing side effects and potentially overcoming drug resistance. The proposal investigates this hypothesis in tumor-bearing mice.
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