ATM protein expression correlates with radioresistance in primary glioblastoma cells in culture

Purpose: Glioblastoma multiforme (GBM) is one of the malignancies most resi stant to radiation therapy. In contrast, cells derived from individuals wit h ataxia telangiectasia (AT) possessing mutations in the ATM gene, demonstr ate increased sensitivity to ionizing radiation, Using a collection of glio ma specimens adapted to tissue culture and several established GEM cell lin es, we investigated the relationship between ATM protein expression and rad iosensitivity. The three aims of our study were to: (1) quantify ATM protei n levels in cultured glioma cells; (2) measure the correlation between ATM protein levels and radiation sensitivity; and (3) examine the dependence of ATM on p53 status. Methods and Materials: Glioma specimens were collected, catalogued, and ada pted to grow in culture. Levels of ATM, p53, and p21 proteins were determin ed by Western blot. Radiation sensitivities were determined by clonogenic a ssays. p53 mutation status was determined by DNA sequencing. Correlations w ere identified by linear regression analysis. Results: ATM protein levels were variable in the primary gliomas, Glioma ce ll lines demonstrated significantly lower levels of ATM protein, Clonogenic assays of cell strains and cell lines yielded survival fractions (SF(2)s) consistent with the radioresistant behavior of GEM tumors in vivo. Regressi on analysis revealed a high correlation between ATM protein levels and SF, for primary glioma cell strains, but not for established GEM cell lines. p5 3 status failed to predict radiosensitivity. Conclusion: We have demonstrated that while our collection of low passage c ell cultures depends on ATM for their resistance to IR, established cell li nes may acquire adaptive characteristics which downplay the role of the ATM gene product in vitro. Therefore, attenuating ATM gene expression may be a successful strategy in the treatment of GEM tumors. (C) 2001 Elsevier Scie nce Inc.