Abstract 3742: Exosome-mediated EGR1 transportation controls the radiation-induced abscopal effect in head and neck cancer

Abstract

Abstract Head and neck cancer (HNC) are one of the vital types of metastatic cancer, and radiotherapy (RT) is the convincing treatment regarding its location. RT can regulate cancer growth in not only directly irradiated cells but also non-irradiated remote cells by abscopal or bystander effects. It is evident that radiation-induced Early Growth Response 1 (EGR1) is involved in the control of such type cancer progression. Also, exosomes are established carriers for biological factors basically in cell communication. In this study, we would like to identify the EGR1 as a functional molecule that carried by the radiation-induced exosome to control the HNC growth to disclose the molecular mechanism of the abscopal effect. In this case, we used FaDu cell, a hypopharyngeal cancer, for in vitro experiments. Irradiation was given to the cells in a dose-dependent manner from 0 to 12 Gy followed by exosome isolation using miRCURY Exosome Cell Kit. Characterization of the isolated exosomes was performed by Nanoparticle Tracking Analysis (NTA) for vesicle sizes and concentration, and by transmembrane markers CD63 and CD9 through western blot. We treated unirradiated FaDu cells with isolated exosomes to address the phenotypic changes. MTT assay and colony-forming assay observed the cell viability and survival. Moreover, the expression of EGR1 in both radiation-induced exosome and the exosome-treated cells were determined by western blot. To validate the causal effect of exosomal transportation of EGR1, we assessed the viability changes in EGR1-silenced FaDu cells with exosome treatment. Our results indicated that the number of exosomes was increased while the amounts of protein in each isolated exosome were also increased in a radiation dose-dependent manner. CD63 and CD9 had been identified through western blotting. Moreover, the enhanced expression of EGR1 was observed in both radiation-induced exosomes and the cells treated with isolated exosomes. The possible abscopal effect was evident by the significant decrease of the viability of unirradiated FaDu cells treated with radiation-induced exosomes. Besides, elevated expression of EGR1 was noticed in the radiation-induced exosomes comparing to non-irradiated cohorts. Notably, EGR1-containing exosomes can suppress the proliferation of the unirradiated FaDu cells. Alternatively, radiation-induced EGR1-containing exosome failed to inhibit the proliferation of EGR1 knockdown FaDu cells. In conclusion, radiation-induced EGR1 via exosome transportation contributes to the mechanism of the abscopal effect for metastatic head and neck cancer. Citation Format: Mohammady Akbor, Liang-Ting Lin. Exosome-mediated EGR1 transportation controls the radiation-induced abscopal effect in head and neck cancer [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 3742.