PARP-1 and PTEN expression in GSC lines and sensitivity to PARPi monotherapy. Panel A. Immunoblot analysis of PARP-1 and PTEN proteins. Bars represent the mean ratios between the O.D. of PARP-1 and those of tubulin. The results are representative of one out of two experiments with similar results. Panel B. Analysis of total cellular PARP activity. Maximally stimulated PARP activity was measured in cell extracts obtained from GSC and GBM cell lines in the presence of nuclease-treated salmon testes DNA and 32P-NAD+ as described in Methods. PARP activity was expressed as fmol 32P-NAD+/μg of protein and the results are the mean (± SD) of triplicate determinations. Panel C. Sensitivity to PARPi. Tumor cells were treated with graded concentrations of GPI 15427 (0.5-50 μM) as single agent and analyzed 7 days after drug exposure. Bars represent the PARPi IC50 values and are the mean (± SD) from three independent experiments.