Ary treatment but produced limited anti-tumor effects. A combination of cisplatin (CDDP) and pemetrexed is currently the first-line regimen but an average survival period with the agents is about 12 months . The clinical outcome even with the updated 22948146 combinatory chemotherapy is thus unsatisfactory and a possible second-lineagent has not yet been known. A novel therapeutics is thereby required and restoration of decreased p53 functions is one of the strategies. Bisphosphonates (BPs) are synthetic analogues of pyrophosphate and have a strong affinity for mineralized bone matrix . BPs inhibit bone absorption through interfering osteoclasts’ actions, and are currently used as a therapeutic agent for osteoporosis, malignancy-linked hypercalcemia and similar bone diseases. Recent reports demonstrated that BPs also achieved cytotoxicity on tumor cells through apoptosis induction and produced antitumor effects in vitro . The BPs-mediated effects in vivo were evidenced with osseous tumors or with bone metastasis of nonosseous tumors . Moreover, a number of studies also demonstrated the anti-tumor effects in vivo with non-osseous tumors despite BPs being readily excreted from body and accumulated in bone tissues [11,12]. The mechanism of BPsmediated cytotoxicity is dependent on BPs structures [8,9]. TheZoledronate and Cisplatin for Mesothelioma via pfirst generation of BPs is converted into non-hydrolyzable cytotoxic ATP analogues which decrease mitochondrial membrane potentials. Both the second and the third generations inhibitfarnesyl pyrophosphate synthetase and deplete isoprenoid pools, which subsequently results in decreased prenylation of small guanine-nucleotide-binding regulatory proteins (small G proteins).Figure 1. ZOL-induced cytotoxicity to mesothelioma. (A) Cells were treated with different concentrations of ZOL for 3 days and the cell viabilities were measured with the WST assay. Means of triplicated samples and the SD bars are shown. (B) Flow cytometrical analyses of cell cycle progression in ZOL-treated MSTO-211H cells. (C) Western blot analyses of unpreylated Rap1A expressions in cells treated with ZOL. Actin was used as a loading control. (D) Caspase activations in MSTO-211H cells that were treated with ZOL for 3 days were assayed with respective luminescence-based kits. The activities of untreated cells were expressed as 100 . Means of triplicated samples and the SE bars are shown. * P,0.01. doi:10.1371/journal.pone.0060297.gZoledronate and Cisplatin for Mesothelioma via pThe unprenylated form does not bind to cell membrane and the decreased membrane-bound fraction reduces functions of small G proteins since membrane binding is required for the biological activities including cell survival. It remains however uncharacterized as to the precise mechanisms of cytotoxicity induced by downregulated functions of small G proteins. In the present study, we examined cytotoxic activities of zoledronic acid (ZOL), one of the third generation of BPs, on human mesothelioma cells and investigated a possible combinatory use of CDDP with ZOL. We found that ZOL induced upregulation of p53 expression and the phosphorylation, but downregulated p53 expression had little effects on the ZOL-induced cytotoxicity. Nevertheless, the ZOL-mediated p53 activation contributed to combinatory effects with CDDP.assay, respectively, and CI,1, CI = 1 and CI.1 indicate synergistic, additive and antagonistic actions, respectively.Cell cycleCells were.