The results of PARP signaling Figure 2 (central bar) show that that treatment with the drug causes an over 4-fold increase of the intracellular concentration of MDA: thus PD166866 induces an oxidative stress with consequent membrane damage. However, one should not be misled by the much higher level of MDA generated by H2O2 (Figure 2 left bar) since the concentration and the power of this compound is by no means comparable with that of PD166866 in this experimental context. Finally, it is known that an uncontrolled oxidative stress may STI571 purchase lead to apoptotic cell death [20, 21]. Therefore, we analyzed an additional marker diagnostic

of apoptosis: DNA damage. Figure 2 Intracellular concentration of malonyl-dihaldehyde (MDA) after treatment with PD166866. Cells were treated with the drug (50 μM) for 24 hours and processed for the membrane lipoperoxidation test. The intracellular concentration of MDA is over 4-fold higher in cells treated with the drug (central GSI-IX datasheet bar) as compared to untreated control cells (left bar). This indicates membrane damage due to oxidative stress. DNA damage and cell death assessed by fluorescent TUNEL staining The TUNEL assay is an experimental protocol allowing the detection of DNA fragmentation. The specificity of this

assay has been disputed but modifications done to the original method Urease [21] improved its accuracy [22]. Therefore, it is generally accepted that the correct execution of the TUNEL protocol mainly labels DNA fragmentation in very advanced phases of apoptosis [23, 24] thus evidencing cells that have sustained severe DNA damage. The cells were treated with PD166866 in the usual experimental conditions (50 μM for 24 hours). Results show a very evident fluorescent staining of the cells treated with the drug (Figure 3, large panel) which

is a sign of extensive DNA rupturing. In the positive control, cells treated with H2O2 also a very diffuse fluorescence is visible (Figure 3, left small panel). On the contrary, little if any fluorescence is monitored in control plates (Figure 3, right small panel). Therefore we can conclude that in cells treated for 24 hours with PD166866 the apoptotic pathway is in progress. Figure 3 An extensive DNA damage is caused by treatment with PD166866. After treatment with the drug (50 μM for 24 hours), the cell nuclei were permeabilized. Fluorescent dUTP and terminal-deoxynucleotide-transferase were added. The enzyme conjugates the nucleotide where the sugar-phosphate backbone is interrupted. The high intensity of fluorescence (large panel) indicated of extensive DNA damage due to the exposure to the drug. This is also monitored in cells treated with H2O2 (small left panel), while it is virtually absent in untreated control cells (small right panel).