Background: Tumor-derived exosomes (TDEs) are small membrane bound extracellular vesicles (EVs) that have the ability to alter their immediate microenvironment (ME) through cell-cell interaction and are known to be critical modulators of pre-metastatic niche. Lung cancer is a highly metastatic disease, with metastases often occurring when the tumor is in a clinically early stage. It is known to metastasize to the liver in the Asian population, but the underlying mechanism still remains unclear. Thus, understanding the role of TDEs in development of liver metastasis and its contributions to improvise the prognostic and therapeutic implications is of great importance.
Methodology: Exosomes isolated from serum of lung cancer liver metastasis patients were characterized by nanoparticle tracking analysis, electron microscopy and flow cytometry with antibody directed at CD63. These exosomes were further co-cultured with A549 cells to check for their uptake at various time intervals. Moreover, effect of isolated exosomes was tested on: 1. Cell motility and invasiveness of A549 cells determined by transwell chamber migration assay and scratch assay; 2. Gene expression profiles and cell cycle regulation studies; and 3. Histopathological changes and liver function tests after exosome were intraperitoneally injected in Wistar rats to investigate the early events involved in the metastatic spread.
Results: We found that CD63 - FITC labelled exosomes isolated from serum of liver metastatic patients were actively incorporated by A549 cells. The exosome uptake by A549 cells induced migratory/invasive phenotypic and morphologic changes in a concentration and time- dependent manner. Moreover, on further evaluating the effect of TDEs on different phases of cell cycle it was observed that cellular uptake of exosomes was increased during G2/M phase stimulating the cells to enter these cell cycle phases leading to cell proliferation. Further, we observed that E-cadherin, beta catenin, VEGFA, CDKN2A and TGFBR2 were differentially expressed when A549 cells were treated with exosomes demonstrating an important role of these TDEs in altering the tumor microenvironment. Liver function test demonstrated an increase in serum SGPT and SGOT levels whereas when histopathological examination was done the lungs showed patches of pneumonitis and the liver was highly inflamed.
Conclusion: Collectively this study indicated that metastatic tumor derived exosomes are capable of increasing the migratory and invasive property of the primary lung cancer cells. Furthermore, our results depict an undisputable role of these exosomes as key modulators in the formation of the pre-metastatic niche required for the colonization of circulating tumor cells (CTCs) ultimately leading to distant metastasis. Thus understanding and targeting tumor derived exosomes could lead to better and novel therapeutic strategies.
Citation Format: Kanisha Shah, Dr. Rakesh M. Rawal. Metastatic lung cancer-derived exosomes stimulate premetastatic niche in liver: Beyond seed soil hypothesis [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 5187.