Figure 1. ZnCl₂ reactivates p53 in chemoresistant glioblastoma cells. (A) Semi-quantitative RT-PCR analyses of p53 target genes in human glioblastoma ADF cells pre-treated with 100 μM ZnCl₂ for 6 h before the addition of 4 μg/ml cisplatin (cisp) for 16 h. When appropriate, the p53 inhibitor pifithryn α (PFT) (30 μM) was added to ZnCl₂ before the administration of chemotherapy. β-actin levels were monitored as an internal standard. (B) 20000 ADF cells were plated in 60-mm dished and - 24 h later - treated with 100 μM ZnCl₂ for 16 h, followed by the addition of 4 μg/mL cisp for 2 h. Cells were then washed with PBS and placed in fresh medium. ZnCl₂ was replaced in the culture medium every two days. Colonies were stained with crystal violet 14 d after seeding and quantified. Data are presented as means ± SD *p = 0.034, as compared with cells treated with cispl plus ZnCl₂.