Apoptotic cell death of human glioblastoma cells as the result of gamma-irradiation. (A) TUNEL assays of A172, GBM2, and U87MG cells following gamma-irradiation (× 200 magnification). Arrows indicate the apoptotic deaths of the tumor cells. (B) Western blot analysis of total cell extractions isolated from A172 and GBM2 at various culture passages after gamma-irradiation. Scale bars, 50 μm.