Molecular Mechanisms Underlying Effects of Epidermal Growth Factor Receptor Inhibition on Invasion, Proliferation, and Angiogenesis in Experimental Glioma

Purpose: Epidermal growth factor receptor (EGFR) signal transduction pathways are implicated in malignant glioma aggressiveness and promote tumor cell invasion, proliferation, and angiogenesis. Nevertheless, response to EGFR tyrosine kinase inhibitor gefitinib (Iressa, ZD1839) has been disappointing in clinical trials. One potential explanation may come from the diversity of molecular alterations seen in gliomas. To validate that hypothesis, we have investigated responses to gefitinib on various tumor parameters in human malignant gliomas that exhibited different molecular alterations. Experimental Design: We used a panel of six human malignant gliomas from established xenografts characterized for their genetic (EGFR, PTEN, TP53, and CDKN2A) and molecular (EGFR, PTEN, ERK, and Akt) alterations. Tumors were treated with gefitinib (1 or 10 mu mol/L) for prolonged periods (8 or 16 days) in an organotypic brain slice model that allowed quantification of invasion, proliferation, and angiogenesis. Results: In nontreated tumors, EGFR amplification was associated with profuse tumor cell invasion. After treatment, invasion was inhibited in tumors with EGFR amplification in a dose-dependent manner. Treatment had only antiproliferative effect in two of three tumors with EGFR amplification. Tumors with PTEN loss were resistant to treatment. We did not observe shrinkage of the tumors after treatment. None of the tumors had mutations of the EGFR kinase domain. Gefitinib had similar antiangiogenic effect in all of the tumors. Conclusions: Gefitinib reduces cell invasion in EGFR amplified tumors. PTEN loss of expression seems to be a determinant of resistance. Interestingly, inhibition of angiogenesis by gefitinib seems independent on the EGFR genetic status of the tumors.