Determining And Characterizing Differential Biodistribution Of Tumor Derived Exosomes By Non-Invasive Nuclear Imaging

Abstract Introduction: New theory of “seeds (cancer cells) and soil (distant tissue)” transpired as scientists acquainted exosomes as seeds that cruise to distant organs and release growth factors (fertilizers) to acclimate the “foreign soil” and prepare the metastatic niche. Exosomes are nano-sized (30-150nm) spherical organelles, derived from the endosomal system for intercellular communications. Tumor derived exosomes (TDEs) play an imperative role in tumor growth, stromal reorganization, cancer stemness, neovascularization, and metastatic niche formation by providing proteins, lipids, mRNA, miRNA etc. to tumor microenvironment. Despite intense research in the field, only few studies have investigated exosome biodistribution and thus very little known about their in vivo trafficking, that is also impeding their biomedical application as diagnostic and prognostic marker and as a potential therapeutic delivery vehicle. Also, it would be of interest to investigate the biodistribution of exosomes isolated from tumor cells after different treatment. Application of nuclear imaging techniques, such as single-photon emission computed tomography (SPECT) using radio isotopically labeled exosomes have indisputable advantages over fluorescent imaging regarding tissue penetration and quantitative measurement of the biodistribution. Methods: To determine in vivo trafficking of TDEs and whether exosomes from treated cells are distributed differently, we isolated exosomes from hypoxic (1% O2) 4T1 breast cancer cells without any treatment (control), and treated with GW2580 or HET0016 drug. GW2580, a selective small molecule kinase inhibitor of colony stimulating factor 1-receptor (CSF-1R) and HET0016 that is a highly selective inhibitor of CYP4A in arachidonic acid pathway, have been shown to decrease tumor growth and metastasis. We labeled these three groups of exosomes with radio I-131 and injected them in 4T1 tumor bearing and non-tumor bearing Balb/c mice. Then, we followed up the radio I-131labeled exosome distribution for 3 consecutive days with SPECT. Results: More exosomes were localized in the lungs in tumor bearing mice compared to non-tumor bearing mice. Interestingly, control exosomes were more localized in the metastatic site that is in the lungs than the primary breast tumor. We observed TDEs from untreated cells were localized more in metastatic site than that exosomes from the GW2580 and HET0016 treated cells. Conclusion: This study demonstrates that treatment of tumor cells with drugs that inhibit tumor growth and metastasis potentially yield exosomes with less protumorigenic and less metastatic characteristics and become less homing to metastatic site. TDEs are more efficiently visualized and quantified in vivo by radio-isotope labelling of exosomes. The knowledge attained from this study will open up new horizon in exosome research and biological nanotechnology for diagnosis and prognosis and targeted treatment. Citation Format: Mohammad Harun Rashid, Thaiz Borin, Kartik Angara, Roxan Ara, Achyut Bhagelu, Ali Arbab. Determining and characterizing differential biodistribution of tumor derived exosomes by non-invasive nuclear imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-368.