Figure 1. Amplified MYCN and additional chromosomal aberrations impair drug-induced DNA damage response in neuroblastoma cells. SH-EP-MYCN cells were treated with tetracycline to suppress MYCN transgene expression. IMR5/75-C2 cells were treated with tetracycline to induce the shRNA targeting MYCN (= MYCN−). Doxo was added to the culture medium 48 h later after tetracycline addition. Cell cycle (A) and cell death (B) were analyzed using flow cytometry 48 h after doxo addition. Data are presented as mean ± SD of triplicates. (B) Also shows a western blot of MYCN knockdown 48 h after addition of tetracycline to the media. (C) Cell death was analyzed 48 h after doxo treatment using flow cytometry (sub-G₁ fractions). Shown here is the cell death enhancement (% sub-G₁ cells upon doxo treatment − % sub-G₁ cells of untreated cultures). Data are presented as mean ± SD of triplicates. (D) Cells were treated with doxo, 48 h later fixed and double stained with propidium iodide and BrdUTP to detect DNA breaks. Data shows one representative experiment.