Hydroxyurea accelerates the loss of epidermal growth factor receptor genes amplified as double-minute chromosomes in human glioblastoma multiforme

OBJECTIVE: We sought to determine whether hydroxyurea could accelerate the loss of amplified epidermal growth factor receptor (EGFR) genes from glioblastoma multiforme (GEM). There is good reason to think that elimination of amplified EGFR genes from GBMs will negatively impact tumor growth. Hydroxyurea has previously been shown to induce the loss of amplified genes from extrachromosomal double minutes (dmin) but not from chromosomal homogeneously staining regions. METHODS: Pulsed-field gel electrophoresis and Southern blot hybridization were used to demonstrate EGFR genes amplified as dmin. Giemsa-stained metaphase spreads were prepared in an attempt to visualize dmin. A GBM cell line containing amplified EGFR genes was treated continuously in vitro with 0 to 150 mu mol/L hydroxyurea, and slot blot analysis was used to show the loss of amplified EGFR genes. RESULTS: Amplified EGFR genes were found on dmin in 4 of 11 (36%) fresh human GBM biopsy specimens. None of the GBMs contained EGFR genes amplified as homogeneously staining regions. Amplified dmin were not microscopically visible when stained with Giemsa because of their small size. Slot blot analysis showed that these low doses of hydroxyurea accelerated the loss of amplified EGFR genes in a dose- and time-dependent fashion. Pulsed-field gel electrophoresis and Southern blot analysis confirmed that EGFR gene loss was accompanied by amplified dmin loss in a dose-dependent fashion. CONCLUSION: These studies suggest the potential use of low-dose hydroxyurea in the treatment of GBMs.