T-cell intracellular antigen (TIA)-1 and TIA-1-related protein (TIAR) are mRNA-binding proteins that can aggregate within granules under specific stress conditions. In this study, we analyzed TIAR/TIA-1 aggregation under different hypoxic conditions, and studied the effects on the hypoxia-inducible factor (HIF)-1α in different cancer cell lines. Under acute and pronounced hypoxic conditions TIAR/TIA-1 co-aggregated to granules and positive co-staining with eIF3η marker suggested these to represent stress granules. In parallel, HIF-1α expression was blocked in cells displaying TIAR/TIA-1 granules. Silencing of TIAR and TIA-1 caused upregulation of HIF-1α expression, as demonstrated by western blot, immunocytochemistry and HIF-1-dependent reporter gene expression. Additionally, a critical region of the 3' end of the untranslated HIF-1α mRNA with possible adenosine-uridine-rich elements (AREs) was coupled to the luciferase reporter gene, causing downregulation of expression. Employing this reporter construct, inhibition of TIAR by siRNA attenuated the inhibitory cis-effect of this ARE-sequence. Furthermore, immunohistochemical analysis of A549 cell tumor xenografts revealed a nearly complementary expression of HIF-1α and TIAR reflecting the control of HIF-1α expression by TIAR as revealed in the cell culture studies. In sum, rapid and severe hypoxia caused co-aggregation of TIAR/TIA-1 and these proteins suppressed HIF-1α expression.

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Different routes for the in vivo administration of synthetic siRNA complexes targeting lung tumors were compared, and siRNA complexes were administered for the inhibition of hypoxia-inducible factor (HIF-1a and HIF-2a). Intravenous jugular vein injection of siRNA proved to be the most effective means of targeting lung tumor tissue in the Lewis lung carcinoma (LLC1) model. In comparison, intraperitoneal injection of siRNA was not suitable for targeting of lung tumor and intratracheal administration of siRNA exclusively targeted macrophages. Inhibition of HIF-1a and HIF-2a by siRNA injected intravenously was validated by immunohistofluorescent analysis for glucose-transporter-1 (GLUT-1), a well-established HIF target protein. The GLUT-1 signal was strongly attenuated in the lung tumors of mice treated with siRNA-targeting HIF-1a and HIF-2a, compared with mice treated with control siRNA. Interestingly, injection of siRNA directed against HIF-1a and HIF-2a into LLC1 lung tumor-bearing mice resulted in prolonged survival. Immunohistological analysis of the lung tumors from mice treated with siRNA directed against HIF-1a and HIF2a displayed reduced proliferation, angiogenesis and apoptosis, cellular responses, which are known to be affected by HIF. In conclusion, intravenous jugular vein injection of siRNA strongly targets the lung tumor and is effective in gene inhibition as demonstrated for HIF-1a and HIF-2a.

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Background: EphA2 tyrosine kinase plays an important role in tumor angiogenesis, but whether targeting this pathway can affect response to ionizing radiation (IR) remains unknown. Methods: We investigated, using a soluble EphA2-Fc chimera, whether EphA2 inhibition could sensitize A549 and MCF-7 tumor cells, as well as human umbilical vein endothelial cells (HUVEC) and dermal microvascular endothelial cells (HDMEC), to IR. Results: EphA2-Fc resulted in a greater response of endothelial cells (EC) to IR than either treatment alone. EphA2-Fc significantly increased apoptosis and decreased clonogenic survival, tube formation and migration in irradiated EC after stimulation with vascular endothelial growth factor (VEGF), without an affecting their proliferation. No difference in proliferation or survival was found in A549 and MCF-7 tumor cells. In a co-culture model, EphA2-Fc inhibited an irradiated A549 cellinduced increase in EC migration. VEGF supplementation, as well as condiotioned medium from irradiated A549 cells, phosphorylated EphA2 in EC. The latter was abrogated by EphA2-Fc. Conclusions: EC were most sensitive to a combination of EphA2 inhibition and radiotherapy. The induction of paracrine growth factors and activation of EphA2 in EC suggest a protective mechanism that tumors probably use to attenuate IR-induced antivascular effects. Our data justify further investigation to explore targeting EphA2 in tumor radiosensitivity in vivo.