Endogenous tumor necrosis factor inhibits the cytotoxicity of exogenous tumor necrosis factor and adriamycin in pancreatic carcinoma cells

Alteration of tumor microenvironment for improved delivery and intratumor distribution of nanocarriers

Nanocarrier-based cancer chemotherapeutics are thought to increase therapeutic efficiency and reduce the side effects of associated chemotherapeutic agents by altering the agents' pharmacokinetics and tissue distribution following intravenous administration. In spite of these favorable properties, nanocarrier-based cancer chemotherapeutics are not always effective because of their heterogeneous intratumoral localization. Homogeneous distribution of nanocarriers in a tumor would improve the efficacy of nanocarrier-based cancer chemotherapeutics. In this article, we describe and discuss some trials that attempt to manipulate the barriers in the tumor microenvironment that hinder extravasation through the tumor vasculature and penetration of nanocarriers in solid tumors. Alterations of the tumor microenvironment that relate directly to the intratumoral distribution of nanocarriers may be potential strategies to improve the delivery of nanocarrier-based cancer chemotherapeutics.

Digitoflavone inhibits IκBα kinase and enhances apoptosis induced by TNFα through downregulation of expression of nuclear factor κB-regulated gene products in human pancreatic cancer cells

Tumor necrosis factor-α (TNFα) activates both cell death and cell survival pathways. The activation of survival pathway renders most cancer cells resistant to TNF-induced cytotoxicity. We found that pretreatment with digitoflavone, a plant flavonoid, greatly sensitized TNFα-induced apoptotic cell death in several human pancreatic cancer cells. In search of the molecular basis of the sensitization effect of digitoflavone, digitoflavone was found to inhibit TNFα-induced activation of nuclear transcription factor-kappa B (NF-κB) which is the main survival factor in TNFα signaling. NF-κB suppression occurred through inhibition of IκBα kinase activation, IκBα phosphorylation, IκBα degradation, and NF-κB nuclear translocation. This inhibition correlated with suppression of NF-κB-dependent genes involved in antiapoptosis (mcl-1, bcl-2, bcl-xl, c-iap1, c-iap2, flip, and survivin), proliferation (c-myc, cyclin d1), and angiogenesis (vegf, cox-2, and mmp-9). In addition, digitoflavone can activate JNK through inhibition of NF-κB signaling, provide a continuous blockade of the feed-back inhibitory mechanism by JNK-induced NF-κB activation. This study found a novel function of digitoflavone and enhanced the value of digitoflavone as an anticancer agent.

Anti-tumor necrosis factor therapy inhibits pancreatic tumor growth and metastasis

Chronic inflammation has been implicated in the pathogenesis of many severe autoimmune disorders, as well as in diabetes, pulmonary diseases, and cancer. Inflammation accompanies most solid cancers including pancreatic ductal adenocarcinoma (PDAC), one of the most fatal cancers with surgery being the only curative therapeutic approach currently available. In the present work, we investigated the role of the major proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) in the malignancy of PDAC cells in vitro and in vivo. In vitro, TNFalpha strongly increased invasiveness of Colo357, BxPc3, and PancTuI cells and showed only moderate antiproliferative effect. TNFalpha treatment of mice bearing orthotopically growing PDAC tumors led to dramatically enhanced tumor growth and metastasis. Notably, we found that PDAC cells themselves secrete TNFalpha. Although inhibition of TNFalpha with infliximab or etanercept only marginally affected proliferation and invasiveness of PDAC cells in vitro, both reagents exerted strong antitumoral effects in vivo. In severe combined immunodeficient mice with orthotopically growing Colo357, BxPc3, or PancTuI tumors, human-specific anti-TNF antibody infliximab reduced tumor growth and metastasis by about 30% and 50%, respectively. Importantly, in a PDAC resection model performed with PancTuI cells, we found an even stronger therapeutic effect for both anti-TNF compounds. Infliximab and etanercept reduced the number of liver metastases by 69% and 42%, respectively, as well as volumes of recurrent tumors by 73% and 51%. Thus, tumor cell-derived TNFalpha plays a profound role in malignancy of PDAC, and inhibition of TNFalpha represents a promising therapeutic option particularly in adjuvant therapy after subtotal pancreatectomy.

Down-regulation of molecular chaperone 78-kd glucose-regulated protein/immunoglobulin-binding protein expression involved in enhancement of human RS cell mutability

OBJECTIVES

Enhancement of cell mutability via extracellular materials of cancer cells is a crucial event leading to the development of cancers; however, the activation process of mutability is still not well understood. In this study, to identify the regulatory mechanism of cell mutability, we investigated mutability modulated in response to human pancreatic cancer cell-conditioned medium and identified the candidates for cellular molecules involved in the mutability modulation.

METHODS

To test the mutation-modulating effects of the conditioned medium, human RS cells were cultured with medium derived by culturing human pancreatic cancer KP-4 cells, followed by irradiation with UV (mainly 254 nm in wavelength). Mutations were detected by phenotypic ouabain resistance and genetic base substitution of K-ras codon 12. Messenger RNA differential display was used to identify genes that were differentially expressed between conditioned medium-treated and mock-treated RSa cells. The influence of 78-kd glucose-regulated protein/immunoglobulin-binding protein (GRP78/BiP) expression on mutability was assessed by the down-regulation of GRP78/BiP using antisense oligonucleotides or antisense complementary DNA.

RESULTS

The UV-induced mutagenicity in RS cells was strengthened by preculture with KP-4 cell-conditioned medium. Messenger RNA differential display revealed that GRP78/BiP expression was suppressed in RS cells after treatment of the conditioned medium. Furthermore, the level of UV-induced mutations was elevated significantly in GRP78/BiP down-regulated cells.

CONCLUSIONS

Culture of human RS cells with pancreatic cancer KP-4 cell-conditioned medium resulted in increased UV mutagenicity, possibly via the down-regulation of GRP78/BiP.

Tumor-suppressor function of SPARC-like protein 1/Hevin in pancreatic cancer

SPARC-like protein 1 (SPARCL1), a member of the SPARC family, is downregulated in various tumors. In the present study, the expression and localization of SPARCL1 were analyzed in a wide range of nontumorous and neoplastic pancreatic tissues by quantitative reverse transcription-polymerase chain reaction, laser capture microdissection, microarray analysis, and immunohistochemistry. For functional analysis, proliferation and invasion assays were used in cultured pancreatic cancer cells. Pancreatic ductal adenocarcinoma (PDAC) and other pancreatic neoplasms exhibited increased SPARCL1 mRNA levels compared to those of the normal pancreas. SPARCL1 mRNA levels were low to absent in microdissected and cultured pancreatic cancer cells, and promoter demethylation increased SPARCL1 levels only slightly in three of eight cell lines. SPARCL1 was observed in small capillaries in areas of inflammation/tumor growth and in some islet cells. In PDAC, 15.4% of vessels were SPARCL1-positive. In contrast, the percentage of SPARCL1-positive vessels was higher in chronic pancreatitis and benign and borderline pancreatic tumors. Recombinant SPARCL1 inhibited pancreatic cancer cell invasion and exerted moderate growth-inhibitory effects. In conclusion, SPARCL1 expression in pancreatic tissues is highly correlated with level of vascularity. Its anti-invasive effects and reduced expression in metastasis indicate tumor-suppressor function.

Improvement of cancer-targeting therapy, using nanocarriers for intractable solid tumors by inhibition of TGF-beta signaling

Transforming growth factor (TGF)-beta plays a pivotal role in regulation of progression of cancer through effects on tumor microenvironment as well as on cancer cells. TGF-beta inhibitors have recently been shown to prevent the growth and metastasis of certain cancers. However, there may be adverse effects caused by TGF-beta signaling inhibition, including the induction of cancers by the repression of TGF-beta-mediated growth inhibition. Here, we present an application of a short-acting, small-molecule TGF-beta type I receptor (TbetaR-I) inhibitor at a low dose in treating several experimental intractable solid tumors, including pancreatic adenocarcinoma and diffuse-type gastric cancer, characterized by hypovascularity and thick fibrosis in tumor microenvironments. Low-dose TbetaR-I inhibitor altered neither TGF-beta signaling in cancer cells nor the amount of fibrotic components. However, it decreased pericyte coverage of the endothelium without reducing endothelial area specifically in tumor neovasculature and promoted accumulation of macromolecules, including anticancer nanocarriers, in the tumors. Compared with the absence of TbetaR-I inhibitor, anticancer nanocarriers exhibited potent growth-inhibitory effects on these cancers in the presence of TbetaR-I inhibitor. The use of TbetaR-I inhibitor combined with nanocarriers may thus be of significant clinical and practical importance in treating intractable solid cancers.

Antioxidant enzymes and apoptosis

The role of antioxidant enzymes can be interpreted in terms of fine tuning of the concentration of reactive oxygen species which are required in the redox regulation of the cell cycle and of programmed cell death. This review summarizes findings from papers published in the last few years which deal with the relation between apoptosis and the two antioxidant enzymes, manganous superoxide dismutase (MnSOD) and catalase. With respect to MnSOD, the literature is much in favor of an inhibitory action in apoptosis. Increased MnSOD activity has been shown to prevent cell death via the receptor-mediated apoptotic pathway as well as cell death via the mitochondrial pathway. The literature on the influence of catalase activity on apoptosis is less consistent. Evidence for both an antiapoptotic and a proapoptotic role of catalase can be found. From the results reviewed here, two schemes for the involvement of MnSOD and catalase in the regulation of apoptosis can be extracted: 1) Both MnSOD and catalase inhibit apoptosis by removing superoxide anion radicals or H2O2, respectively, because these reactive oxygen species are mediators required for the apoptotic program or inhibit a survival pathway. 2) An increase in H2O2 by downregulation or inhibition of catalase activity and/or upregulation of MnSOD activity inhibits apoptosis while a decrease in H2O2 by upregulation of catalase activity and/or downregulation of MnSOD activity supports apoptosis, possibly because of a supportive role of H2O2 in a survival pathway. The data reported so far do not allow for an explanation why some cell models appear to fit the first scheme while the second scheme appears to correctly describe other cell models. The present state of the literature reveals that antioxidant enzymes play a more intricate role in cell physiology than previously assumed.

Resistance to tumor necrosis factor-alpha (TNF-alpha)-induced apoptosis in rat hepatoma cells expressing TNF-alpha is linked to low antioxidant enzyme expression

In order to study the mechanisms of resistance to tumor necrosis factor-alpha (TNF-alpha), we have constructed two stable transfectants producing TNF-alpha (Yv12-2 and Yv13-44) from the rat hepatoma H4IIE cell, which does not produce TNF-alpha. H4IIE cells were highly sensitive to apoptosis induced by TNF-alpha, whereas Yv2-12 and Yv13-44 cells were resistant. Manganous superoxide dismutase was not up-regulated in Yv2-12 and Yv13-44 cells and was unresponsive to induction by exogenous TNF-alpha and by H2O2 in H4IIE cells and in the transfectants. Catalase expression and activity were lower in Yv2-12 and Yv13-44 cells than in H4IIE cells; furthermore, the transfectants were more susceptible to H2O2. Treatment with exogenous TNF-alpha down-regulated catalase in H4IIE cells but not in Yv2-12 and Yv13-44 cells. Treatment of H4IIE cells with the catalase inhibitor 3-amino-1,2,4-triazole rendered them resistant to exogenous TNF-alpha. These data suggest a causal relationship between resistance to TNF-alpha and low catalase activity. Expression of copper and zinc containing superoxide dismutase was also decreased, whereas expression of glutathione peroxidase-1 was unchanged in Yv2-12 and Yv13-44 cells. Data from a microarray point to a down-regulation of genes in the resistant clones that code for antioxidative proteins and proteins involved in glutathione synthesis and function. We assume that a prooxidant signal linked to the down-regulation of antioxidant defense may be associated with resistance to apoptosis induced by TNF-alpha.

The role of oxygen-derived free radicals and nitric oxide in cytokine-induced antiproliferation of pancreatic cancer cells

INTRODUCTION

Pancreatic cancer cells are susceptible to antiproliferative effects of cytokines such as tumor necrosis factor-alpha (TNF-alpha). However, little is known about the mechanisms involved.

AIM

To determine the mechanisms of the antiproliferative effects of TNF-alpha on pancreatic cancer cells.

METHODOLOGY AND RESULTS

In the current study, four of five pancreatic cancer cell lines tested were responsive to the antiproliferative effects of TNF-alpha. In two cell lines, the effects of TNF-alpha were completely abolished by superoxide dismutase, suggesting that superoxide anion mediates the effects. Further, inhibition of nitric oxide (NO) synthase by L-NAME potentiated the TNF-alpha response, suggesting a protective role for endogenously produced NO in these two cell lines. MiaPaCa-2 cells, which were unresponsive to the antiproliferative effects of TNF-alpha, produced five times more nitrite than the other cell lines. Treatment of MiaPaCa-2 cells with interferon-gamma (IFN-gamma) increased inducible nitric oxide synthase mRNA as shown by reverse transcription-polymerase chain reaction. This induction was potentiated by TNF-alpha and further enhanced by a combination of three cytokines (INF-gamma, TNF-alpha, and interleukin 1-beta (IL-1beta). This combination of cytokines increased nitrite accumulation fourfold and inhibited the proliferation of this resistant cell line. These effects were prevented by L-NAME.

CONCLUSIONS

These studies suggest that TNF-alpha inhibits proliferation of pancreatic cancer cells by increasing the production of superoxide anion and that endogenously produced NO protects against this effect. In addition, there is a direct correlation between the amount of NO produced and resistance to TNF-alpha in the only resistant cell line. In contrast, treatment with a combination of IFN-gamma, TNF-alpha and IL-1beta upregulates inducible nitric oxide synthase, and the resulting markedly enhanced NO production inhibits pancreatic cancer cell growth. This pathway may provide a valuable target for therapy of this devastating disease.

Augmented adriamycin sensitivity in cells transduced with an antisense tumor necrosis factor gene is mediated by caspase-3 downstream from reactive oxygen species

While transduction of an antisense tumor necrosis factor (TNF) gene sequence can augment the cytotoxicity of adriamycin (ADM) in human cancer cells, the specific effect of introducing this sequence on the signal transduction pathway leading to cell death remains unclear. In ADM-resistant pancreatic carcinoma (PANC-1) cells, both the antioxidant N-acetyl-L-cysteine (NAC) and the caspase-3 inhibitor acetyl-L-aspartyl-L-methionyl-L-glutaminyl-L-aspartyl-aldehyde (Ac-DMQD-CHO) prevented ADM-induced cytotoxicity. NAC additionally inhibited caspase-3 activity induced by ADM treatment, while Ac-DMQD-CHO showed no suppressive effect on reactive oxygen species (ROS). Stable antisense-TNF transfectants showed higher ADM sensitivity and greater ADM-induced ROS production and caspase-3 activity than mock transfectant or parent cells. These results indicate that increased caspase-3 activity downstream from ROS production is among the mechanisms by which transduction of the antisense TNF sequence of augments ADM sensitivity of pancreatic carcinoma cells.

Telomerase reverse transcriptase and telomeric-repeat binding factor protein 1 as regulators of telomerase activity in pancreatic cancer cells

Telomerase adds hexameric repeats of 5'-TTAGGG-3' termed telomeres to ends of chromosomal DNA. This enzyme has been implicated in cellular immortalization and cellular senescence. Recently, a number of relevant genes have been cloned, including these encoding three major components of human telomerase: human telomerase RNA component (hTR), human telomerase reverse transcriptase (hTERT), and telomerase-associated protein-1 (TEP1). Also important are genes encoding human telomeric-repeat binding factor protein (TRF) 1 and 2. To clarify mechanisms regulating telomerase activity, we studied telomerase activity, the telomeric restriction fragment (TRF) length and gene expression of these telomerase components and the telomeric-repeat binding factor proteins in sequential observation following X-irradiation of cultured pancreatic cancer cells. We previously reported that PANC-1 cells are better able to tolerate thermal stress, antineoplastic drugs, and exposure to tumour necrosis factor than MIAPaCa-2 cells. MIAPaCa-2 and PANC-1 cells were exposed to X-irradiation, their telomerase activity was increased at 2 days and then decreased gradually. Of the three telomerase components, only hTERT mRNA expression showed parallel changes. TRF length was stable just before and after X-irradiation. Among binding factor proteins, TRF1 mRNA showed reciprocal changes possibly directed toward maintaining a stable telomere length. In this study, our results demonstrate that not only hTERT but also TRF1 are important regulator of telomerase activity.

Survivin as a radioresistance factor in pancreatic cancer

We examined whether survivin acts as a constitutive and inducible radioresistance factor in pancreatic cancer cells. Using a quantitative TaqMan reverse transcription-polymerase chain reaction for survivin mRNA in five pancreatic cancer cell lines, we found an inverse relationship between survivin mRNA expression and radiosensitivity. PANC-1 cells, which had the highest survivin mRNA levels, were most resistant to X-irradiation; MIAPaCa-2 cells, which showed the least survivin mRNA expression, were the most sensitive to X-irradiation. Our results suggested that survivin could act as a constitutive radioresistance factor in pancreatic cancer cells. To determine whether radioresistance is enhanced by induction of survivin expression by irradiation, PANC-1 and MIAPaCa-2 cells were subjected to sublethal doses of X-irradiation followed by a lethal dose. Survivin mRNA expression was increased significantly in both PANC-1 and MIAPaCa-2 cell lines by pretreatment with a sublethal dose of X-irradiation, as was cell survival after exposure to the lethal dose. In this system, enzymatic caspase-3 activity was significantly suppressed in cells with acquired resistance. These results suggest that survivin also acts as an inducible radioresistance factor in pancreatic cancer cells. Survivin, then, appears to enhance radioresistance in pancreatic cancer cells; inhibition of survivin mRNA expression may improve the effectiveness of radiotherapy.

The potential for monocyte-mediated immunotherapy during infection and malignancy. Part I: apoptosis induction and cytotoxic mechanisms

The mononuclear phagocyte system consists of peripheral blood monocytes and tissue macrophages that collectively play a major role in host immunity. Far from existing solely as phagocytic scavengers of cell debris and foreign matter, monocytes are highly active and responsive to inflammatory and immunological signals that activate their microbicidal and tumoricidal functions. Cytokines that are secreted as an integral component of the innate immune response such as granulocyte-macrophage colony-stimulating factor (GM-CSF) and -IFN may directly activate the functions of the monocyte system. A key mediator of the effector functions of monocytes is tumour necrosis factor (TNF) which transduces its signals upon binding to specific transmembrane receptors. TNF is highly cytotoxic to micro-organisms and susceptible malignant cells and in most cases delivers its cytotoxic signal to tumour cells by highly regulated mechanisms of programmed cell death or apoptosis. We believe that the numerous functions of the monocyte system may be harnessed for therapeutic gain both in the context of microbiological infection and malignant disease. In this review, the mechanisms by which secreted and monocyte cell-membrane-associated TNF induce apoptosis will be discussed. In addition, the cell-associated and secretory immunological mechanisms employed by monocytes in host defence will be discussed in the context of the their ability to combat infection and neoplasia.

Suppression of intracellular resistance factors by adriamycin augments heat-induced apoptosis via interleukin-1beta-converting enzyme activation in pancreatic carcinoma cells

Combination of heat and various anticancer drugs can exert a synergistic antitumor effect in vitro and in vivo, though the mechanism is not clear. We have previously shown that endogenous tumor necrosis factor (enTNF) acts as an intracellular resistance factor to inhibit the cytotoxic effect of heat by scavenging oxygen-free radicals via the induction of manganous superoxide dismutase (MnSOD). Consequently, we examined whether the suppression of these resistance factors by combining anticancer drugs and heat causes an augmentation of heat-induced cytotoxicity. The human pancreatic carcinoma cell line, PANC-1, constitutively expresses appreciable amounts of enTNF and also demonstrates heat resistance. After treatment of these cells for 15 hr with adriamycin (ADM), the expression of enTNF was decreased by 43%, and MnSOD activity was suppressed by 55%. The cytotoxic effects of the treatment of PANC-1 cells with ADM followed by heat were greater than the sum of those observed with the agents administrated individually. Heat-induced apoptosis was also augmented by pretreatment with ADM. Furthermore, the interleukin-1beta-converting enzyme inhibitor, Ac-YVAD-CMK, reversed the augmented cytotoxicity. Our results indicate that suppression of intracellular resistance factors such as enTNF and MnSOD plays an important role in apoptosis seen after heat and ADM combined therapy.

Endogenous tumour necrosis factor regulates heat-inducible heat shock protein 72 synthesis

Endogenous tumour necrosis factor (enTNF) acts as a resistant factor against cytotoxicity of heat by induction of manganous superoxide dismutase (MnSOD), thereby scavenging reactive oxygen free radicals. On the other hand, it is also well known that heat shock proteins (HSPs), which are induced by heat-stress, behave as cytoprotecting factor against this stress. However, the relationship of these two resistant factors is not yet elucidated. In the present study we would therefore propose the possibility that enTNF enhances HSP72 expression. Heat-sensitive L-M (mouse tomourigenic fibroblast) cells, which normally do not express enTNF, were transfected with a nonsecretory-type human TNF expression vector to produce enTNF. Stable transfectants showed resistance to heat treatment and an increase of HSP72 expression. Conversely, when HeLa (human uterine cervical cancer) cells, which normally produce an appreciable amount of enTNF, were transfected with an antisense TNF mRNA expression vector to inhibit enTNF synthesis, their heat sensitivity was enhanced and HSP72 expression was reduced by half. In conclusion, these findings indicate that enTNF regulates heat-inducible HSP72 synthesis.