Metastatic cell responses to anticancer therapy: The possible role of cancer stem cells
Metastasis is a multistep process, by which cancer cells dissociate from the initial site and travel to form new secondary tumours at distant sites. This process has been reported to require epithelial-mesenchymal transition (EMT), by which the epithelial cancer cells convert to a mesenchymal form, associated with increasing levels of vimentin and decrease in E-cadherin markers. Cancer metastasis is also associated with aberrations in cells’ glycosylation such as Tn antigen which can be detected by Helix pomatia agglutinin (HPA) lectin extract from Helix pomatia snails. Radiotherapy could have an effect on cancer metastasis; by stimulating regulation signalling including ROS, TGF-β, E-cadherin and vimentin. This signalling can promote cancer cells to change from the epithelial to mesenchymal form. The cells behaviour could be mediated by the production of extracellular vesicles/exosomes from irradiated cells, which may have an impact on unirradiated cells. To date, the role of direct and bystander effect of ionising irradiation on the cancer cells glycosylation, EMT markers and invasiveness has not yet been investigated. Therefore, a study has been established to determine the direct effect, and if the progeny of cancer cells that survive a therapeutic dose of X-radiation show differences in aberrant glycosylation associated with metastasis, EMT markers and their ability to invade compared to unirradiated cells. The study also aims to investigate the bystander effect of extracellular vesicle/exosomes in the invasion of breast cancer cells. The molecular mechanisms that could be involved in the invasion of breast cancer cells following irradiation or exosome transfer were also investigated. In this study, both cells directly exposed to a therapeutic dose of ionising radiation and unirradiated recipient cells treated with exosomes from irradiated cells showed an increase in vimentin immunopositivity, HPA positivity, a decrease in the E-cadherin immunopositivity and a significant increase in the invasive capacity of the cells. The study also showed that breast cancer cells treated with a single dose of ionising irradiation induce invasion of breast cancer cells in vitro. The findings were further confirmed using qPCR and western blot for examination of selected genes and proteins that have an effect on the invasion of cancer cells following direct ionising irradiation or bystander effect of exosomes and may have an impact on cancer metastasis. The study also showed that exosomes isolated from irradiated cells carried a high quantity of TGF-β protein and specific miRNA which have an impact on the invasion of cancer cells. This study concludes that single therapeutic dose of ionising irradiation induces invasion of cancer cell in vitro. In addition, exosomes and its compounds that were isolated from irradiated cell condition media can promote invasion of breast cancer cells, and that could have an implication on cancer therapy in the future.
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