Exosomes play pivotal roles in intercellular communication and cancer progression. Recent findings have shown exosomes to incite proangiogenesis and prepare lymph nodes as remote niches for accumulation and migration of melanoma cells. Exosomes present a highly curved morphology with a size range of ∼30-100 nm that is distinct from other lipid vesicles. Furthermore, exosomes have the potential as a general metastasis biomarker since their increased secretion in the peripheral blood has been correlated with cancer metastasis. Since aqueous suspensions of exosomes cannot be seen by conventional optical methods, we hypothesized that a molecular probe that binds to exosomes could be a novel tool for detecting these vesicles. We aim to develop a minimally-invasive diagnostic tool to detect and measure secreted exosomes as biomarkers of cancer metastasis that may help clinicians and patients decide on an appropriate therapeutic action. Taking a cue from nature and using solid phase ‘Click’ chemistry as a technique for peptide modification, we created a fluorophore-tagged cyclic peptide based on the membrane penetrating C2B domain of Synaptotagmin I. We investigated the peptide-lipid interactions using synthetic liposomes as preliminary models of exosomes through a combination of spectroscopic techniques. We found that the peptide probe was selective for highly curved liposomes (d <100 nm) and does not bind to low curvature liposomes (d >100 nm). We tested blood plasma samples from rat models to find out if our preliminary findings would translate to the detection of exosomes. Our results showed that blood plasma treated with the peptide probe showed fluorescence intensity that was remarkably higher than the untreated peptide, which indicated binding to exosomes. Furthermore, we used a real time nanoparticle tracking analysis system to visualize the exosomes in a dynamic and physiologically-relevant medium. The peptide-treated exosomes were detected as fast-moving, fluorescent particles even in the complex matrix of blood plasma. This technique provided us with a platform to study the size distribution and concentration of exosomes in blood plasma. We have created a peptide probe that selectively binds to exosomes from an animal model. The investigation of the exosome binding property of this probe on clinically relevant samples is ongoing.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4743. doi:1538-7445.AM2012-4743