LAUSR

Tumor initiation and evolution is driven by the reciprocal actions between stromal and immune cells within the tumor microenvironment (TME). Tumor-associated macrophages (TAMs) specifically M2-macrophages, a critical component of TME; participate in immune suppression, epithelial to mesenchymal transition, invasion, angiogenesis, tumor progression and subsequent metastasis foci formation. Given their prevalence in most of the human tumor tissue and correlation of their higher infiltration with lower survival, M2-macrophages represent promising targets for diagnosis, prognosis and anticancer therapy. Hence, early in vivo detection and intervention of M2-macrophages in the TME may boost the clinical outcome. Exosomes are biological nanoparticles sizing 30-150 nm, recently drawing huge attention for their potential application as therapeutic and diagnostic tool because they are more biocompatible and biodegradable with lesser toxicity than other synthetic nanoparticles and can easily percolate through the body’s barrier systems or through abnormally formed blood vessels in tumor tissue. We have generated engineered exosomes from HEK293 cells by lentiviral transfection system that carry specific peptide sequence on their external surface for targeting CD206 positive M2-macrophages. To determine the in vivo distribution of M2-macrophages, we adopted 111In-oxine based radio-labeling of the targeted exosomes and single-photon emission computed tomography (SPECT). Up to the time, among the used techniques, nuclear imaging is the foremost method to trace exosomes in vivo for better tissue penetration, sensitivity and quantitative analysis. After the labeling with 111In-oxine, we analyzed the binding efficacy and serum stability of the targeted exosome by thin layer paper chromatography (TLPC) using 100% methanol and 2M Sodium acetate solution (1:1) as eluent. More than 98% of 111In-oxine was bound to exosomes and only 5% of free 111In-oxine was dissociated from the exosomes even 24 hours after the incubation with 20% serum. When we injected these radio-labeled targeted exosomes in to 4T1 breast tumor-bearing mice, they went mostly to the periphery of the primary tumor, metastatic area in the lungs, spleen and to the liver. We performed ex vivo quantification of radioactivity from individual organ by gamma counter after final SPECT scan and observed similar distribution of the radio-labeled targeted exosomes. We also labeled the exosomes with DiI dye and injected into the same mice followed by euthanasia after 3 hours and organ collection. Fluorescent imaging from the tumor and spleen showed the adherence of exosomes to the CD206 positive macrophages confirming the targeting efficacy of the exosomes. Henceforth, we intend to utilize these exosomes as a therapeutic probe for carrying chemotherapeutic or antibody to intervene the actions of M2-macrophages in primary and distal TME. Citation Format: Mohammad H. Rashid, Thaiz F. Borin, Roxan Ara, Kartik Angara, Achyut Bhagelu, Jingwen Cai, Yutao Liu, Ali S. Arbab. CD206 positive M2-macrophage targeting engineered exosomes as a potential diagnostic and therapeutic tool [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1139.