Redox regulation of cell proliferation by pyrrolidine dithiocarbamate in murine thymoma cells transplanted in vivo

Di-2-pyridylhydrazone Dithiocarbamate Butyric Acid Ester Exerted Its Proliferative Inhibition against Gastric Cell via ROS-Mediated Apoptosis and Autophagy

Diversified biological activities of dithiocarbamates have attracted widespread attention; improving their feature or exploring their potent action of mechanism is a hot topic in medicinal research. Herein, we presented a study on synthesis and investigation of a novel dithiocarbamate, DpdtbA (di-2-pyridylhydrazone dithiocarbamate butyric acid ester), on antitumor activity. The growth inhibition assay revealed that DpdtbA had important antitumor activity for gastric cancer (GC) cell lines (IC₅₀ = 4.2 ± 0.52 μM for SGC-7901, 3.80 ± 0.40 μM for MGC-803). The next study indicated that growth inhibition is involved in ROS generation in mechanism; accordingly, the changes in mitochondrial membrane permeability, apoptotic genes, cytochrome c, bax, and bcl-2 were observed, implying that the growth inhibition of DpdtbA is involved in ROS-mediated apoptosis. On the other hand, the upregulated p53 upon DpdtbA treatment implied that p53 could also mediate the apoptosis. Yet the excess generation of ROS induced by DpdtbA led to cathepsin D translocation and increase of autophagic vacuoles and LC3-II, demonstrating that autophagy was also a contributor to growth inhibition. Further investigation showed that DpdtbA could induce cell cycle arrest at the G1 phase. This clearly indicated the growth inhibition of DpdtbA was via triggering ROS formation and evoking p53 response, consequently leading to alteration in gene expressions that are related to cell survival.

Copper Ion Attenuated the Antiproliferative Activity of Di-2-pyridylhydrazone Dithiocarbamate Derivative; However, There Was a Lack of Correlation between ROS Generation and Antiproliferative Activity

The use of chelators for cancer treatment has been an alternative option. Dithiocarbamates have recently attracted considerable attention owning to their diverse biological activities; thus, the preparation of new dithiocarbamate derivatives with improved antitumor activity and selectivity as well as probing the underlying molecular mechanism are required. In this study, di-2-pyridylhydrazone dithiocarbamate S-propionic acid (DpdtpA) and its copper complex were prepared and characterized, and its antiproliferative activity was evaluated. The proliferation inhibition assay showed that DpdtpA exhibited excellent antiproliferative effect in hepatocellular carcinoma (IC₅₀ = 1.3 ± 0.3 μM for HepG2, and 2.5 ± 0.6 μM for Bel-7402). However, in the presence of copper ion, the antiproliferative activity of DpdtpA was dramatically attenuated (20–30 fold) owing to the formation of copper chelate. A preliminarily mechanistic study revealed that reactive oxygen species (ROS) generation mediated the antiproliferative activity of DpdtpA, and accordingly induced apoptosis, DNA cleavage, and autophagy. Surprisingly, the cytotoxicity of DpdtpA copper complex (DpdtpA–Cu) was also involved in ROS generation; however, a paradoxical relation between cellular ROS level and cytotoxicity was observed. Further investigation indicated that DpdtpA could induce cell cycle arrest at the S phase; however, DpdtpA–Cu lacked this effect, which explained the difference in their antiproliferative activity.

A Central Role for JNK/AP-1 Pathway in the Pro-Oxidant Effect of Pyrrolidine Dithiocarbamate through Superoxide Dismutase 1 Gene Repression and Reactive Oxygen Species Generation in Hematopoietic Human Cancer Cell Line U937

Pyrrolidine dithiocarbamate (PDTC) known as antioxidant and specific inhibitor of NF-κB was also described as pro-oxidant by inducing cell death and reactive oxygen species (ROS) accumulation in cancer. However, the mechanism by which PDTC indices its pro-oxidant effect is unknown. Therefore, we aimed to evaluate the effect of PDTC on the human Cu/Zn superoxide dismutase 1 (SOD1) gene transcription in hematopoietic human cancer cell line U937. We herein show for the first time that PDTC decreases SOD1 transcripts, protein and promoter activity. Furthermore, SOD1 repression by PDTC was associated with an increase in oxidative stress as evidenced by ROS production. Electrophoretic mobility-shift assays (EMSA) show that PDTC increased binding of activating protein-1 (AP-1) in dose dependent-manner suggesting that the MAPkinase up-stream of AP-1 is involved. Ectopic NF-κB p65 subunit overexpression had no effect on SOD1 transcription. In contrast, in the presence of JNK inhibitor (SP600125), p65 induced a marked increase of SOD1 promoter, suggesting that JNK pathway is up-stream of NF-κB signaling and controls negatively its activity. Indeed, using JNK deficient cells, PDTC effect was not observed nether on SOD1 transcription or enzymatic activity, nor on ROS production. Finally, PDTC represses SOD1 in U937 cells through JNK/c-Jun phosphorylation. Taken together, these results suggest that PDTC acts as pro-oxidant compound in JNK/AP-1 dependent-manner by repressing the superoxide dismutase 1 gene leading to intracellular ROS accumulation.

Protective effects of asiatic acid against D-galactosamine/lipopolysaccharide-induced hepatotoxicity in hepatocytes and kupffer cells co-cultured system via redox-regulated leukotriene C4 synthase expression pathway

Asiatic acid is a triterpenoid component possessing antioxidative, anti-inflammatory and hepatoprotective activity. In this issue, we explored the protective effects of asiatic acid and the relative mechanism in the D-galactosamine/lipopolysaccharide (D-GalN/LPS)-induced hepatotoxicity in hepatocytes and kupffer cells co-cultured system. The cultures were pretreated with asiatic acid for 12 h, followed by D-GalN/LPS exposure for 12 h. Asiatic acid reduced aspartate aminotransferase and lactate dehydrogenase generation and increased cell viability in a concentration-dependent manner. Meanwhile, the effects of asiatic acid in leukotriene C(4) synthase (LTC(4)S) expression and cellular redox status including reactive oxygen species and GSH content were detected. The results showed that D-GalN/LPS induced the increase of reactive oxygen species followed by extracellular signal-regulated kinase 1/2 (ERK 1/2) and nuclear factor-kappaB (NF-kappaB) activation. Treatment with ERK 1/2 specific inhibitor 1,4-diamino-2,3-dicyano-1,4-bis[2-aminophenylthio] butadiene (U0126) abolished the ERK1/2 protein phosphorylation and blunted LTC(4)S expression. Reactive oxygen species signaling pathway inhibitor pyrrolidine dithiocarbamate (PDTC) inhibited reactive oxygen species generation and NF-kappaB activation, which in turn blocked LTC(4)S expression and attenuated the injury. Asiatic acid can protect the hepatocytes against D-GalN/LPS-induced hepatotoxicity. During which, the cell redox was ameliorated and increased expression of LTC(4)S was reversed by the pretreatment of asiatic acid. Taken together, asiatic acid can protect against D-GalN/LPS-induced hepatotoxicity partly via redox-regulated LTC(4)S expression pathway.

Docosahexaenoic acid induces apoptosis in lung cancer cells by increasing MKP-1 and down-regulating p-ERK1/2 and p-p38 expression

Different agents able to modulate apoptosis have been shown to modify the expression of the MAP-kinase-phosphatase-1 (MKP-1). The expression of this phosphatase has been considered a potential positive prognostic factor in lung cancer, and smoke was shown to reduce the levels of MKP-1 in ferret lung. Our aim was to assess whether the n-3 polyunsaturated fatty acid docosahexaenoic acid (DHA), known to inhibit the growth of several cancer cells mainly inducing apoptosis, may exert pro-apoptotic effect in lung cancer cells by modifying MKP-1 expression. We observed that DHA increased MKP-1 protein and mRNA expression and induced apoptosis in different lung cancer cell lines (mink Mv1Lu adenocarcinoma cells, human A549 adenocarcinoma and human BEN squamous carcinoma cells). We inhibited the pro-apoptotic effect of DHA by treating the cells with the phosphatase inhibitor Na(3)VO(4) or by silencing the MKP-1 gene with the specific siRNA. This finding demonstrated that the induction of apoptosis by DHA involved a phosphatase activity, specifically that of MKP-1. DHA reduced also the levels of the phosphorylated MAP-kinases, especially ERK1/2 and p38. Such an effect was not observed when the MKP-1 gene was silenced. Altogether, the data provide evidence that the DHA-induced overexpression of MKP-1 and the resulting decrease of MAP-kinase phosphorylation by DHA may underlie the pro-apoptotic effect of this fatty acid in lung cancer cells. Moreover, they support the hypothesis that DHA may exert chemopreventive action in lung cancer.

Induction of apoptosis by d-limonene is mediated by a caspase-dependent mitochondrial death pathway in human leukemia cells

Using K562 and HL60 cell lines, we have investigated the anti-tumoral activity of d-limonene, a monocyclic monoterpene, in human leukemia cells. Apoptosis was evaluated by Hoechst staining and by the annexin V/propidium iodide binding assay. d-Limonene induced apoptosis in a dose- and time-dependent manner in both cell lines. Our findings and data, demonstrating an increase in Bax protein expression, the release of cytochrome c from mitochondria, and an increase in caspase-9 and cleaved caspase-3, but not caspase-8, after the treatment of d-limonene, all suggest that the mitochondrial death pathway is primarily involved in the development of d-limonene-induced apoptosis.

Increased stability of P21(WAF1/CIP1) mRNA is required for ROS/ERK-dependent pancreatic adenocarcinoma cell growth inhibition by pyrrolidine dithiocarbamate

We present evidence that pyrrolidine dithiocarbamate (PDTC) inhibits growth of p53-negative pancreatic adenocarcinoma cell lines via cell cycle arrest in the S-phase, while it has no effect on primary fibroblast proliferation. Growth inhibition of cancer cells is dependent on ROS and ERK1/2 induction as indicated by a significantly reduced PDTC-associated growth inhibition by the free radical scavenger N-acetyl-L-cysteine (NAC) or the MEK/ERK1/2 inhibitor (PD98059). Moreover, ERK1/2 induction is dependent on ROS production as demonstrated by a complete removal of PDTC-mediated ERK1/2 phosphorylation by NAC. p21(WAF1/CIP1) activation has a central role in growth inhibition by PDTC, as revealed by P21(WAF1/CIP1) silencing experiments with antisense oligonucleotide, and occurs via increased mRNA stability largely mediated by ROS/ERK induction. Conversely, PDTC does not affect P21(WAF1/CIP1) gene expression in primary fibroblasts, although it is able to activate p53 and the p53-regulated antioxidant SESN2. These results suggest that the resistance of fibroblasts to the cytotoxic action of PDTC may be related to the up-regulation of p53-dependent antioxidant genes. Finally, in vivo studies on PaCa44 cells subcutaneously xenografted in nude mice show that treatment with 100 or 200 mg/kg PDTC reduces of 30% or 60% the tumour volume, respectively, and does not cause any apparent form of toxicity.

Repeated exposure to pyrrolidine-dithiocarbamate induces peripheral nerve alterations in rats

Pyrrolidine-dithiocarbamate (PDTC), a synthetic compound widely used in cell biological investigations, recently attracted considerable interest as a putative anticancer agent. However, different dithiocarbamates have previously shown to cause neurological symptoms and morphological alterations in peripheral nerves. The purpose of the present study was to determine whether a 15-day oral administration with low doses of PDTC may produce adverse effects in peripheral nerves of rats. Female Wistar rats were assigned to receive PDTC [0.1, 0.5 or 1.0mmol/(kg body weight/day)] by gavage for 15 days. Reduced conduction velocity was observed by electrophysiological analysis in tibial nerves of treated animals, accompanied by a marked decrease in Shwann cell S100-protein expression determined by immunohistochemistry. Electron microscopy evaluation revealed marked myelin degeneration in the fibers of treated animals. In particular, both morphological and electrophysiological data suggested an impairment of large, fast conducting fibers, whereas the smallest and slowest ones remained intact. However, the activity of plasma and liver alkaline-phosphatase, an enzymic marker of hepatic dithiocarbamate toxicity, was not altered by the treatment. The total contents of the redox-active metal copper increased in tibial nerves of treated rats and was accompanied by raised levels of lipid peroxidation products. This finding suggests a role for oxidative stress in the development of PDTC-induced pathological and functional alterations of tibial nerves. The observation that a 15-day treatment with low doses of PDTC causes functional and morphological derangement of peripheral nerves advices against the possible use of this compound as a chemopreventive agent against cancer.

beta-Carotene downregulates the steady-state and heregulin-alpha-induced COX-2 pathways in colon cancer cells

Experimental studies have shown that beta-carotene inhibited the growth of colon cancer cells, and human trials have demonstrated that the carotenoid reduces colon cell proliferation of adenomatous polyps; however, molecular mechanisms underlying this chemopreventive activity remain unclear. Because COX-2 has been implicated as a causative factor in colon carcinogenesis, the present study was designed to investigate the relation between the growth-inhibitory effect of the carotenoid and COX-2 expression in colon cancer cells. We evaluated the effects of beta-carotene on the growth of human colon adenocarcinoma cells overexpressing (LS-174, HT-29, WiDr) or not expressing (HCT116) COX-2. We also studied COX-2 expression induced by heregulin-alpha, apoptosis induction, reactive oxygen species (ROS) production, and extracellular signal-regulated kinase 1/2 (ERK1/2) activation. beta-Carotene (0.5-2.0 micromol/L) decreased COX-2 expression (P < 0.05) and prostaglandin E(2) (PGE(2)) production (P < 0.05) in colon cancer cells. This effect was not observed in cells treated with retinoic acid or retinol. The downregulation of COX-2 by the carotenoid occurred in both untreated and heregulin-treated cells. It was accompanied by an increased ability of cells to undergo apoptosis and by a decrease in intracellular ROS production and in the activation of ERK1/2. Moreover, cells not expressing COX-2 were insensitive to the growth-inhibitory and proapoptotic effects of the carotenoid. Here, we report that the suppression of COX-2 by beta-carotene may represent a molecular mechanism by which this compound acts as an antitumor agent in colon carcinogenesis.

Docosahexaenoic acid enhances the susceptibility of human colorectal cancer cells to 5-fluorouracil

PURPOSE

Powerful growth-inhibitory action has been shown for n-3 polyunsaturated fatty acids against colon cancer cells. We have previously described their ability to inhibit proliferation of colon epithelial cells in patients at high risk of colon cancer. In the work reported here we investigated the ability of docosahexaenoic acid (DHA) to potentiate the antineoplastic activity of 5-fluorouracil (5-FU) in p53-wildtype (LS-174 and Colo 320) and p53-mutant (HT-29 and Colo 205) human colon cancer cells.

METHODS

When in combination with DHA, 5-FU was used at concentrations ranging from 0.1 to 1.0 microM, much lower than those currently found in plasma patients after infusion of this drug. Similarly, the DHA concentrations (< or =10 microM) used in combination with 5-FU were lower than those widely used in vitro and known to cause peroxidative effects in vivo.

RESULTS

Whereas the cells showed different sensitivity to the growth-inhibitory action of 5-FU, DHA reduced cell growth independently of p53 cellular status. DHA synergized with 5-FU in reducing colon cancer cell growth. The potentiating effect of DHA was attributable to the enhancement of the proapoptotic effect of 5-FU. DHA markedly increased the inhibitory effect of 5-FU on the expression of the antiapoptotic proteins BCL-2 and BCL-XL, and induced overexpression of c-MYC which has recently been shown to drive apoptosis and, when overexpressed, to sensitize cancer cells to the action of proapoptotic agents, including 5-FU.

CONCLUSION

Our results indicate that DHA strongly increases the antineoplastic effects of low concentrations of 5-FU. Overall, the results suggest that combinations of low doses of the two compounds could represent a chemotherapeutic approach with low toxicity.

n-3 PUFAs reduce VEGF expression in human colon cancer cells modulating the COX-2/PGE2 induced ERK-1 and -2 and HIF-1alpha induction pathway

n-3 Polyunsaturated fatty acids (PUFAs) inhibit the development of microvessels in mammary tumors growing in mice. Human colorectal tumors produce vascular endothelial growth factor (VEGF) whose expression is up-regulated in tumor cells by both cyclooxygenase-2 (COX-2) and PGE(2) and directly correlated to neoangiogenesis and clinical outcome. The goal of this study was to examine the capability of n-3 PUFAs to regulate VEGF expression in HT-29 human colorectal cells in vitro and in vivo. Constitutive VEGF expression was augmented in cultured HT-29 cells by serum starvation and the effects of eicosapentaenoic (EPA) or docosahexaenoic acid (DHA) on VEGF, COX-2, phosphorylated extracellular signal-regulated kinase (ERK)-1 and -2 and hypoxia-inducible-factor 1-alpha (HIF-1alpha) expression and PGE(2) levels were assessed. Tumor growth, VEGF, COX and PGE(2) analysis were carried out in tumors derived from HT-29 cells transplanted in nude mice fed with either EPA or DHA. Both EPA and DHA reduced VEGF and COX-2 expression and PGE(2) levels in HT-29 cells cultured in vitro. Moreover, they inhibited ERK-1 and -2 phosphorylation and HIF-1alpha protein over-expression, critical steps in the PGE(2)-induced signaling pathway leading to the augmented expression of VEGF in colon cancer cells. EPA always showed higher efficacy than DHA in vitro. Both fatty acids decreased the growth of the tumors obtained by inoculating HT-29 cells in nude mice, microvessel formation and the levels of VEGF, COX-2 and PGE(2) in tumors. The data provide evidence that these n-3 PUFAs are able to inhibit VEGF expression in colon cancer cells and suggest that one possible mechanism involved may be the negative regulation of the COX-2/PGE(2) pathway. Their potential clinical application as anti-angiogenic compounds in colon cancer therapy is proposed.