Moreover, it is also possible that various previously identified WFA-induced molecular effects

,22,40]. In our study, the highest resistance was observed for the anti-metabolite 5-FU, which can be an S-phase dependent cytostatic. Its cytotoxic efficacy declined in Rbknockdown clones by 10%0% as in comparison to the nonsense handle, irrespective of the Rb-knockdown extent (IC50 = 41 mM), which might be explained by the slower growth in the modulated cell populations (data not shown) and by presumably increased levels of thymidilate synthase (TS), the cellular target of 5-FU, as described for cells with no Rb [41]. A study performed on adult somatic cells These outcomes suggest that ROS remarkably mediates the mitochondria-related apoptosis in vitamin K2-taken care of T24 cells revealed that following spontaneous immortalization and loss of functional p53, 5-FU failed to induce cell cycle arrest regardless of the presence of Rb [42]. Therefore, lower levels of p53 in our Rb-deficient cell clones possibly contributed also towards the diminished activity of 5-FU. The antineoplastic efficacies of cytosine arabinoside and doxorubicin have been slightly decreased by total Rb-knockdown (shRNA1) only. Ara C also incorporates into DNA, which include 5-FU, and retards chain elongation, nevertheless it differs in its mode of action from 5-FU in its potential to inhibit DNA polymerase, both in replication and repair [39]. The resistance to Ara C in cells with complete Rb-knockdown was related to lowered levels of p53, mutations of which have been found to be causal for resistance to Ara C therapy in patients with acute myeloid leukemia (AML) as a result of impaired apoptosis induction [43]. Doxorubicin, which is a DNA damaging agent, was much less productive in cells with full Rb-knockdown but not in the setting with 17% residual Rb-expression. As located by Jackson et al. [44], it induces a senescence-like phenotype in breast cancer cells that entails p53-p21 responses early soon after drug therapy followed by p130 recruitment to crucial promoters regulating cell cycle transition. Knockdown of all 3 Rb family members members (Rb, p107 and p130) was needed to bypass the downregulation of cell cycle genes due to compensatory roles of p107 and Rb [44]. In line with this study, 83% Rb-knockdown in our experiments was not enough to alter the sensitivity from the treated cell population towards doxorubicin. In variance towards the other drugs, exposure to cisplatin was connected with improved sensitivity on the clone showing 17% Rb-expression, but no difference of the cell clone with comprehensive Rb-knockdown. Cisplatin is active in all phases on the cell cycle, causes DNA breaks and activates as a consequence the p53 signaling pathway, followed by apoptosis involving the Rb/c-Abl pathway. The activation of p53 is determined by the phosphorylation status of Rb, suggesting that larger levels of Rb and c-Abl (as mediator of apoptosis) in cells with 17% Rb expression could possibly be a cause for their enhanced sensitivity. Reed et al. reported that cisplatin causes significantly decreased cellular viability in Rb-deficient lung cancer cell lines because it deregulates specific Rb/E2F target genes as well as the G1 checkpoint mechanism [41]. Similarly, Seely et al. [45] treated Schwann cells, proficient and deficient in Rb, with cisplatin and observed that a significant fraction of Rb-deficient cells entered the S-phase with the cell cycle at very low concentrations of the drug, in contrast to cells proficient for Rb, which have been inhibited in their capability to proliferate.