We investigated the presence of EphA2, and its ligand, ephrinA1, in glioblastoma multiforme (GBM), a malignant neoplasm of glial cells, and normal brain. We also initially examined the functional importance of the interaction between EphA2 and ephrinA1 in glioma cells. Expression and localization of EphA2 and ephrinA1 in human GBM and normal brain were examined using Western blotting, immunofluorescence, and immunohistochemistry. A functional role for EphA2 was investigated by assessing the activation status of the receptor and the effect of ephrinA1 on the anchorage-independent growth and invasiveness of GBM cells. We found EphA2 to be elevated in f90% of GBM specimens and cell lines but not in normal brain, whereas ephrinA1 was present at consistently low levels in both GBM and normal brain. EphA2 was activated and phosphorylated by ephrinA1 in GBM cells. Furthermore, ephrinA1 induced a prominent, dose-dependent inhibitory effect on the anchorage-independent growth and invasiveness of GBM cells highly overexpressing EphA2, which was not seen in cells expressing low levels of the receptor. Thus, EphA2 is both specifically overexpressed in GBM and expressed differentially with respect to its ligand, ephrinA1, which may reflect on the oncogenic processes of malignant glioma cells. EphA2 seems to be functionally important in GBM cells and thus may play an important role in GBM pathogenesis. Hence, EphA2 represents a new marker and novel target for the development of molecular therapeutics against GBM. (Mol Cancer Res 2005;3(10):541 -51)

Purpose: We investigated the expression of interleukin-13 receptor a2 (IL-13Ra2), EphA2, and Fos-related antigen 1 (Fra-1) in astrocytomas and normal brain.We sought to document whether the expression of the three factors changed with progression to higher grade malignancy and whether two or three targets in combination might be sufficient to target all patients with highgrade astrocytomas. Experimental Design: Immunohistochemistry was done for IL-13Ra2, EphA2, and Fra-1using human brain tumor tissue microarrays containing 30 specimens of WHO grades II and III astrocytomas, 46 glioblastoma multiformes (GBM), and 9 normal brain samples. Sections were scored based on frequency and intensity of expression. Western blotting was done for all three markers using GBM tumor specimens and xenograft cell lines. Two cytotoxins, IL-13.E13K.PE38QQR and ephrinA1-PE38QQR, which target IL-13Ra2 or EphA2, respectively, were tested for cytotoxicity against human GBM primary explant cells and established cells. Results: Expression of all three proteins was significantly higher in GBM compared with normal brain, low-grade, and anaplastic astrocytomas. Greater than 95% of GBM overexpressed at least two of the three markers. Importantly, every GBM overexpressed at least one marker. Human GBM primary explant cells and cell lines were potently killed by IL-13.E13K.PE38QQR and ephrinA1-PE38QQR, in accordance with their level of expression of IL-13Ra2 and EphA2, respectively. Conclusions: IL-13Ra2, EphA2, and Fra-1 are attractive therapeutic targets representing molecular denominators of high-grade astrocytomas. One hundred percent of GBM tumors overexpress at least one of these proteins, providing the basis for rational combinatorial targeted therapies/diagnostics suitable for all patients with this disease.High-grade astrocytomas, including WHO grade IV glioblastoma multiforme (GBM), are the most common adult primary malignant brain tumor and respond poorly to the current standard treatments of surgery, radiation, and chemotherapy. The mean survival rate of patients with GBM is f14 months and has improved only slightly over the past several decades. GBM tumors are highly infiltrative, resulting in residual invasive tumor cells after surgical resection and leading, in part, to the high rate of recurrence that contributes to the poor clinical outcome (1). Moreover, these tumors are often resistant to radiotherapy and chemotherapy (1, 2), the former of which is known to cause radiation-induced damage to the normal brain tissue, resulting in acute and chronic cognitive impairment (3). Molecularly targeted therapies have thus emerged as a way to increase the specificity and efficacy of antibrain tumor therapy. High-grade astrocytomas, in general, and GBM, in particular, are very heterogenous tumors, within which the tumor cells themselves often display different molecular profiles based on variables, such as the tumor microenvironment (4). Thus, a rational therapeutic approach may require more than one molecular target, which, in c...

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