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Dietary phytochemicals as adjuvants have been suggested to play important roles in enhancing chemotherapeutic potential owing to multitargeted chemopreventive properties and lack of substantial toxicity. Here, we investigated the efficacy of the combined treatment of various phytochemicals with the anticancer drug clofarabine in malignant mesothelioma MSTO-211H cells and normal mesothelial MeT-5A cells. The combined treatment of resveratrol and clofarabine produced a synergistic antiproliferative effect in MSTO-211H cells, but not in MeT-5A cells. In MSTO-211H cells, the nuclear accumulation of Sp1 and the levels of p-Akt, Sp1, c-Met, cyclin D1, and p21 were effectively decreased by the combined treatment of them. In combination with clofarabine, the ability of resveratrol to reduce the contents of Sp1 and its target gene products was also evident in a time- and dose-dependent experiment. The inhibition of phosphoinositide 3-kinase using Ly294002 augmented a decrease in the p21 level induced by their combination, but it showed no significant effects on expression of Sp1 and cyclin D1. Taken together, the data provide evidence that the synergistic antiproliferative effect of resveratrol and clofarabine is linked to the inhibition of Akt and Sp1 activities, and suggest that this combination may have therapeutic value in treatment of malignant mesothelioma.

Cadmium is a well-known toxic metal and occupational exposure to it is associated with lung cancer. In probing the possible non-genotoxic molecular targets of cadmium-induced nasal toxicity, we performed an mRNA differential display analysis for cadmium-treated human nasal septum carcinoma RPMI-2650 cells. Cadmium (≥0.5 μM) inhibited the cell proliferation. The intracellular ROS levels were induced by cadmium treatment. In addition, cadmium elicited the AKR1C3 expression. The cadmium-induced increase in AKR1C3 protein levels was suppressed by N-acetylcysteine (NAC) and, to a lesser extent, PI3K inhibitor (Ly294002). Cells pretreated with Ly294002 were more resistant to cadmium toxicity than control. The increase in AKR1C3 protein level was accompanied by an increase in the nuclear transcription factor Nrf2. Overall, our data suggest that cadmium-induced ROS cause up-regulation of AKR1C3 expression, at least partially via the activation of PI3K-related intracellular signaling pathways, and Nrf2 activation, thereby contributing to an adaptive intracellular response to cadmium toxicity.

N-Acetylcysteine (NAC), sulfidryl-containing thiol antioxidant, has been heralded as chemopreventive agent, generally because of its ability to scavenge free radicals. It also suppresses the proliferation of many cancer cells; however, the antiproliferative mechanism(s) remain to be fully elucidated. In this study, we investigated a growth-suppressive mechanism of NAC action in androgen-independent prostate carcinoma PC-3 cells. NAC (≥ 1mM) inhibited the proliferation of PC-3 cells in a dose- and time-dependent manner. Moreover, NAC treatment suppressed the activation of NF-κB induced by IKK-β as detected by the NF-κB reporter gene assay. NAC exerted a biphasic effect on the intracellular ROS levels depending on incubation time; the antioxidant effect was seen within 2h after NAC treatment, however, a pro-oxidant effect was evident after 48 h treatment. In addition to these effects, NAC treatment elicited a dose- and time-dependent increase in the Cyr61 expression that was accompanied by an increase in its mRNA and blocked by cycloheximide pretreatment. Importantly, NAC treatment caused an early but transient activation of Akt and Erk1/2. The NAC-induced increase in Cyr61 protein levels was suppressed by the PI3K inhibitor (Ly294002) and, to a lesser extent, MEK/Erk1/2 inhibitor (PD98059). Taken together, our data suggest that the antiproliferative effect of NAC is partially mediated by intracellular ROS production, the inhibition of NF-κB activity, and the activation of PI3K- and/or MEK/Erk-related intracellular signaling pathways, which lead to up-regulation of Cyr61 expression.

Malignant mesothelioma is highly resistant to apoptosis. Hence, new strategies to enhance the apoptotic signal and overcome resistance to therapeutic drugs are necessary to improve the therapeutic efficacy of malignant mesothelioma. Here, we investigated the effects of the combined treatment of various phytochemicals as a chemo-potentiator in combination with the chemotherapeutic agent clofarabine in malignant mesothelioma MSTO-211H cells and normal mesothelial Met-5A cells. Treatment with resveratrol in combination with clofarabine at a subtoxic concentration produced a synergistic antiproliferative effect and induced apoptotic cell death, as evidenced by increased subG1 peak on flow cytometric analysis, chromatin condensation and nuclear fragmentation on DAPI staining, and DNA laddering on agarose gel electrophoresis, in MSTO-211H cells, but not in Met-5A cells. In MSTO-211H cells, endogenous expression of the transcription factors Nrf2 and Sp1 proteins, several Nrf2 and Sp1-regulated gene products (HO-1, c-Met, and cyclin D1), and Akt phosphorylation, were effectively suppressed by the combined treatment of clofarabine and resveratrol. Furthermore, the nuclear accumulations of Nrf2 and Sp1 were inhibited by the combination treatment. In combination with clofarabine, the ability of resveratrol to increase the contents of the phosphorylated p53 and the apoptotic molecules, PARP and cleaved caspase 3, was also evident in a time- and dose-dependent experiment. Taken together, the data provide evidence that the synergistic antiproliferative effect of resveratrol and clofarabine is linked to simultaneous suppression of multi-target molecules, such as Nrf2, Sp1, and Akt activities, and suggest that this combination may have therapeutic value in treatment of malignant mesothelioma. Citation Format: David M. Lee, Yoon-Jin Lee, Jae-Hyuk Im, Seong-Youn Won, Hae-Seon Nam, Sang-Han Lee. Synergistic anticancer effects of resveratrol and clofarabine in malignant mesothelioma cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3285. doi:10.1158/1538-7445.AM2013-3285