The effect of irradiation on the Eph family of receptor tyrosine kinases in lung adenocarcinoma
Lung cancer is the most lethal form of malignancy and prognosis remains poor despite recent advances in diagnostic and therapeutic modalities. The phenomenon of new blood vessel formation in tumors is one of the key events in lung cancer pathogenesis and metastasis. During embryonic development and...
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|Zusammenfassung:||Lung cancer is the most lethal form of malignancy and prognosis remains poor despite recent advances in diagnostic and therapeutic modalities. The phenomenon of new blood vessel formation in tumors is one of the key events in lung cancer pathogenesis and metastasis. During embryonic development and angiogenesis, there is an impressive interplay between Eph receptors and Ephrin ligands expressed in EC and associated tissues that greatly affect the structure of new blood and lymphatic vessels. The Eph family of receptor tyrosine kinases (RTKs) and their ligands, ephrins, are dysregulated in different malignancies and play an important role in tumor blood vessel formation, remodelling and metastasis. The response of tumor to ionizing radiation (IR) is highly-dependent on tumor microenvironment and involves a series of complex biological interactions between tumor and vascular compartment. However, the influence of IR on the Eph family of RTKs remains unknown. During the last decades, radiobiological research has focused primarily on the cancer cell compartment. Indeed, much less is known about the effect of ionizing radiation on the endothelial cell (EC) compartment and the complex interaction between tumor cells and their microenvironment, consisting of extracellular matrix and ECs. In the present study, the effect of IR on the key members of the Eph family of RTKs in both A549 and Ecs was analysed both in vitro and in vivo. Moreover, the way the two-compartment system, consisting of tumor and ECs, intercommunicates in response to IR and the impact of Eph on this interaction was analysed. The primary aim of this study was to elucidate the mechanisms of the combination of novel antiangiogenic agents, such as Eph-blocking agents, and IR for effective treatment of lung cancer. In this thesis, a critical review of angiogenesis and the biology of Eph and Ephrins was performed. Furthermore, the interrelation between IR and Eph family of RTKs was investigated. The experimental results suggested that IR can transmit a proangiogenic stimulus to tumor associated vascular compartment through inducing different members of Eph/ephrins in tumor cells. IR promoted transcriptional activation of EphA2 and its ligand ephrinA1 but not EphB4/ephrinB2 in lung adenocarcinoma cells in vitro, while none of these members analysed was induced in irradiated ECs. Immunofluorescence detection of EphA2 revealed astronger membranous staining in irradiated lung adenocarcinoma xenografts. Immunohistochemical studies revealed in irradiated A549 xenografts revealed stronger expression for EphA2 and ephrinA1, as compared to unirradiated tissues. Furthermore, no difference was observed in the viability of lung adenocarcinoma cells in vitro after IR and EphA2 blockade using a soluble EphA2-Fc receptor chimera as analysed by an WST assay. IR of lung adenocarcinoma cells and immediate co-culture with ECs increased endothelial cell migration in vitro. EphA2 blockade significantly suppressed irradiated tumor-induced endothelial cell migration in vitro. This is the first demonstration to show the involvement of different members of the Eph/Ephrins in IR induced tumor angiogenesis both in vitro and in vivo. These data propose a new mechanism that tumor cells probably use to protect their vascular compartment from the cytotoxic effect of IR and rationalise the use of EphA2 inhibitors in combination with radiation therapy for the treatment of lung adenocarcinoma.|