Exosomal circRNA-100338 Promotes Hepatocellular Carcinoma Metastasis via Enhancing Invasiveness and Angiogenesis

Background &amp; Aims: Exosomes play crucial roles in regulating the crosstalk between normal and cancer cells in the tumor microenvironment, and regulating cancer proliferation, migration and invasion through their cargo molecules. In the present study, we aim to investigate the pro-invasive role of exosomal circRNA-100338 in HCC metastasis.<br><br>Methods: We analyzed the pro-invasiveness of exosomal circRNA-100338 in HCC using the transwell invasion assay. The co-culture of human umbilical vein endothelial cells (HUVEC) and exosomes derived from HCC cell lines were used to evaluate the impact of HCC derived exosomes on HUVEC. Nude mice models were used to validate the findings by<i> in vitro</i>. Clinically, quantitative RT-PCR was used to quantify the expression of serum exosomal circRNA-100338 in HCC patients at both pre-surgery within one week, and post-surgery within three weeks.<br><br>Results: We for the first time showed that circRNA-100338 was highly expressed in both high metastatic HCC cells and their secreted exosomes. The transwell invasion assay showed that the overexpression or knockdown of exosomal circRNA-100338 significantly enhanced or reduced the invasive abilities of HCC cells. Subsequently,<i> in vitro</i> and <i>in vivo</i> assays showed that exosomal circRNA-100338 affected the cell proliferation, angiogenesis, permeability, and vasculogenic mimicry (VM) formation ability of human umbilical vein endothelial cells (HUVEC), and tumor metastasis. Furthermore, we also observed that the persistent high expression of exosomal circRNA-100338 in serum of HCC patients who underwent curative hepatectomy may be a risk indicator of pulmonary metastasis.<br><br>Conclusions: Our findings indicated that metastatic ability of HCC cells could be enhanced by transferring exosomal circRNA-100338 to recipient HUVECs, which could affect proangiogenic activity by regulating angiogenesis.<br><br>Funding Statement: This study was supported by grants from the medical-engineering cross fund of Shanghai Jiao Tong University (No. YG2017MS13), the pre-research fund of Shanghai sixth People’s Hospital (LYZY-0229), the International Foundation of Translational Medicine for abroad Scholars and Students, U.S. and China (No. UCTMP2015-03C001), and the National Natural Science Foundation of China (No. 81272401).<br><br>Declaration of Interests: The authors declare that they have no conflicts of interests.<br><br>Ethics Approval Statement: This study was approved by the Research Ethics Committee of Shanghai Jiaotong University affiliated Sixth People’s Hospital, and informed consent was obtained from each patient. All mice were handled according to the recommendations of the National Institutes of Health Guidelines for Care and Use of Laboratory Animals. The experimental protocol was approved by the Shanghai Medical Experimental Animal Care Committee.