[Establishment and biological characterization of 5-fluorouracil-resistant human colon cancer HT-29/5-FU cell line].

OBJECTIVE: To establish 5-fluorouracil (5-FU)-resistant human colon cancer HT-29 cell line (HT-29/5-FU) in vitro and observe its biological properties. METHODS: The HT-29/5-FU cell line was established by continuously exposing the HT-29 cells to ascending doses of 5-FU. The morphology and colony formation rate were detected. The growth curve and the chemosensitivity of HT-29/5-FU cell line were determined by MTT assay. Western blotting was used to analyze the expressions of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD). Cell cycle and apoptosis were measured by flow cytometry. RESULTS: The resistance of HT-29/5-FU cells to 5-FU was 3.59-fold greater than that of HT-29 cells. The morphology of HT-29/5-FU cells differed from that of HT-29 cells. Compared with HT-29 cells, HT-29/5-FU cells showed remarkable reduction of cell proliferation and colony formation, higher expressions of TS and DPD, higher percentage of cells in the S phase, and stronger ability of resistance to apoptosis induced by 5-FU. CONCLUSION: The biological characters of HT-29/5-FU cell line may play an important role in 5-FU-resistant mechanisms, which may also contribute to elucidate the potential mechanisms of tumor drug resistance as well as resistance reversal.

Pseudolaric acid B inhibits inducible cyclooxygenase-2 expression via downregulation of the NF-κB pathway in HT-29 cells.

PURPOSE: Pseudolaric acid B (PAB) is a diterpene acid isolated from the root and trunk bark of Pseudolaric kaempferi Gordon. Previous work has found that PAB has anti-inflammatory and anti-tumor effects in xenograft models of human hepatocellular carcinoma. The aim of this study is to evaluate the correlation between anti-cancer and anti-inflammatory effects of PAB and its molecular mechanisms on HT-29 cells. METHODS: Production of prostaglandin E2 (PGE2) in HT-29 cells was evaluated by ELISA. mRNA of cyclooxygenase-2 (COX-2) was analyzed by RT-PCR assay. High-content screening (HCS) method was adopted to detect the cytokine mixture (CM)-induced transcription activity of NF-κB and STAT3. Western blotting was used to evaluate the protein expression levels of inflammatory mediators induced by CM. After treatment with PAB in various concentrations, the inhibition rate of cell proliferation was measured with sulforhodamine B assays. For the in vivo studies, tumor-bearing models xenografted with HT-29 cells were developed in nude mice, and following oral administration with PAB, tumor inhibition rate was calculated. RESULTS: PAB inhibited the PGE2 production in HT-29 cells significantly (P < 0.05) with similar results detected at the COX-2 mRNA level. Furthermore, PAB suppressed the COX-2 protein expression and significant nuclear translocation of NF-κB and STAT3 induced by CM, which correlated with a concomitant degradation of I-κB and a decrease in constitutive STAT3 phosphorylation (P < 0.05). Moreover, various concentrations of PAB inhibited the proliferation of HT-29 cells in a dose- and time-dependent manner. In vivo, after treatment with PAB for 17 days, the tumor weight of the 50 and 100 mg/kg treated groups was 0.62 ± 0.15 and 0.54 ± 0.06 g, respectively. When compared to the control group (0.82 ± 0.16 g), the inhibition rate of tumor weight was 24.2% at 50 mg/kg (P < 0.05) and 34.7% at 100 mg/kg (P < 0.001). CONCLUSIONS: PAB shows potential anti-cancer activity in HT-29 cells, and its molecular mechanisms are related to the anti-inflammatory action.

Oncogenic Ras, but not (V600E)B-RAF, protects from cholesterol depletion-induced apoptosis through the PI3K/AKT pathway in colorectal cancer cells.

Cholesterol is necessary for proliferation and survival of transformed cells. Here we analyse the effect of cholesterol depletion on apoptosis and the mechanisms underlying this effect in colorectal cancer cells carrying oncogenic Ras or (V600E)B-RAF mutations. We show that chronic cholesterol depletion achieved with lipoprotein-deficient serum (LPDS) and 25-hydroxycholesterol (25-HC) treatment results in a significant increase in apoptosis in HT-29 and Colo-205 cells containing the (V600E)B-RAF mutation, but not in HCT-116 and LoVo cells harbouring the (G13D)Ras mutation, or BE cells, which possess two mutations, (G13D)Ras and (G463V)B-RAF. We also demonstrate that oncogenic Ras protects from apoptosis induced by cholesterol depletion through constitutive activation of the phosphatidylinositol-3 kinase (PI3K)/AKT pathway. The specific activation of the PI3K/AKT pathway by overexpression of the (V12)RasC40 mutant or a constitutively active AKT decreases the LPDS plus 25-HC-induced apoptosis in HT-29 cells, whereas PI3K inhibition or abrogation of AKT expression renders HCT-116 sensitive to cholesterol depletion-induced apoptosis. Moreover, our data show that LPDS plus 25-HC increases the activity of c-Jun N-terminal kinase proteins only in HT-29 cells and that the inhibition of this kinase blocks the apoptosis induced by LPDS plus 25-HC. Finally, we demonstrate that AKT hyperactivation by oncogenic Ras protects from apoptosis, preventing the activation of c-Jun N-terminal kinase by cholesterol depletion. Thus, our data demonstrate that low levels of cholesterol induce apoptosis in colorectal cancer cells without oncogenic Ras mutations. These results reveal a novel molecular characteristic of colon tumours containing Ras or B-RAF mutations and should help in defining new targets for cancer therapy.

Radiation-induced thymidine phosphorylase upregulation in rectal cancer is mediated by tumor-associated macrophages by monocyte chemoattractant protein-1 from cancer cells.

PURPOSE: The mechanisms of thymidine phosphorylase (TP) regulation induced by radiation therapy (XRT) in various tumors are poorly understood. We investigated the effect and mechanisms of preoperative XRT on TP expression in rectal cancer tissues. METHODS AND MATERIALS: TP expression and CD68 and monocyte chemoattractant protein-1 (MCP-1) levels in rectal cancer tissues and cancer cell lines were evaluated before and after XRT in Western blotting, immunohistochemistry, enzyme-linked immunoassay, and reverse transcription-polymerase chain reaction studies. Isolated peripheral blood monocytes were used in the study of chemotaxis under the influence of MCP-1 released by irradiated colon cancer cells. RESULTS: Expression of TP was significantly elevated by 9 Gy of XRT in most rectal cancer tissues but not by higher doses of XRT. In keeping with the close correlation of the increase in both TP expression and the number of tumor-associated macrophages (TAMs), anti-TP immunoreactivity was found in the CD68-positive TAMs and not the neoplastic cells. Expression of MCP-1 was increased in most cases after XRT, and this increase was strongly correlated with TP expression. However, this increase in MCP-1 expression occurred in tumor cells and not stromal cells. The XRT upregulated MCP-1 mRNA and also triggered the release of MCP-1 protein from cultured colon cancer cells. The supernatant of irradiated colon cancer cells showed strong chemotactic activity for monocyte migration, but this activity was completely abolished by neutralizing antibody. CONCLUSIONS: Use of XRT induces MCP-1 expression in cancer cells, which causes circulating monocytes to be recruited into TAMs, which then upregulate TP expression in rectal cancer tissues.

Chemopreventive effect of chitosan oligosaccharide against colon carcinogenesis.

Chitosan oligosaccharide (COS, 3 kDa

A novel cell type-specific role of p38alpha in the control of autophagy and cell death in colorectal cancer cells.

Cancer develops when molecular pathways that control the fine balance between proliferation, differentiation, autophagy and cell death undergo genetic deregulation. The prospects for further substantial advances in the management of colorectal cancer reside in a systematic genetic and functional dissection of these pathways in tumor cells. In an effort to evaluate the impact of p38 signaling on colorectal cancer cell fate, we treated HT29, Caco2, Hct116, LS174T and SW480 cell lines with the inhibitor SB202190 specific for p38alpha/beta kinases. We report that p38alpha is required for colorectal cancer cell homeostasis as the inhibition of its kinase function by pharmacological blockade or genetic inactivation causes cell cycle arrest, autophagy and cell death in a cell type-specific manner. Deficiency of p38alpha activity induces a tissue-restricted upregulation of the GABARAP gene, an essential component of autophagic vacuoles and autophagosomes, whereas simultaneous inhibition of autophagy significantly increases cell death by triggering apoptosis. These data identify p38alpha as a central mediator of colorectal cancer cell homeostasis and establish a rationale for the evaluation of the pharmacological manipulation of the p38alpha pathway in the treatment of colorectal cancer.

Therapeutic potential of antisense oligodeoxynucleotides to down-regulate thymidylate synthase in mesothelioma.

Malignant mesothelioma is an aggressive tumor of the serosal surfaces of the lungs, heart, and abdomen. Survival rates are poor and effective treatments are not available. However, recent therapeutic regimens targeting thymidylate synthase (TS) in malignant mesothelioma patients have shown promise. We have reported the use of an antisense oligodeoxynucleotide targeting TS mRNA (antisense TS ODN 83) to inhibit growth of human tumor cells. To test the potential for antisense targeting of TS mRNA in treatment of malignant mesothelioma, we assessed and compared the effects of antisense TS ODN 83 on three human malignant mesothelioma cell lines (211H, H2052, and H28) and human nonmalignant mesothelioma cells (HT29 colorectal adenocarcinoma, HeLa cervical carcinoma, and MCF7 breast tumor cell lines). We report that ODN 83 applied as a single agent effectively reduced TS mRNA and protein in malignant mesothelioma cell lines. Furthermore, it inhibited malignant mesothelioma growth significantly more effectively than it inhibited growth of nonmalignant mesothelioma human tumor cell lines: a difference in susceptibility was not observed in response to treatment with TS protein-targeting drugs. In malignant mesothelioma cells, antisense TS both induced apoptotic cell death and reduced proliferation. In nonmalignant mesothelioma cells, only reduced proliferation was observed. Thus, antisense TS-mediated induction of apoptosis may be the basis for the high malignant mesothelioma sensitivity to antisense targeting of TS. Further preclinical and clinical study of TS antisense oligodeoxynucleotides, alone and in combination with TS-targeting chemotherapy drugs, in mesothelioma is warranted.

Chemopreventive effect of protein extract of Asterina pectinifera in HT-29 human colon adenocarcinoma cells.

We investigated the effect of protein extract of Asterina pectinifera on the activity of 4 enzymes that may play a role in adenocarcinoma of the colon: quinone reductase (QR), glutathione S-transferase (GST), ornithine decarboxylase (ODC), and cyclooxygenase (COX)-2. QR and GST activity increased in HT-29 human colon adenocarcinoma cells increased that had been exposed to 4 concentrations of the protein extract (80, 160, 200, and 240 microg/mL). Additionally, 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ODC activity decreased significantly in cells exposed to the extract in concentrations of 160 microg/mL (p<0.05), 200 microg/mL (p<0.005), and 240 microg/mL (p<0.005). TPA-induced COX-2 activity also decreased in cells exposed to extract concentrations of 10, 20, 40, and 60 microg/mL. COX-2 expression was also inhibited in cells exposed to this extract. These results suggest that this protein extract of A pectinifera has chemopreventive activity in HT-29 human colon adenocarcinoma cells, and therefore, may have the potential to function as a chemopreventive agent in human colorectal cancer.

Multiple sampling in single-cell enzyme assays using CE-laser-induced fluorescence to monitor reaction progress.

A novel method for assaying enzymes from a single cell or small cell populations is described. The key advantage of this method is the ability to repeatedly sample a single cell enzyme reaction. Whereas multiple sampling has been achieved for larger cell types with a diameter of 1 mm, we report a technique by which single cell enzyme assays of small cells (15 microm in diameter) can be repeatedly carried out. Individual cells were isolated using an in-house-built micromanipulator and placed in nanoliter-scale reaction vessels. The cells were lysed with solution containing substrate, and enzyme activity was assayed by removing 5-nL aliquots with a recently developed nanopipettor. The reaction aliquot was then analyzed using capillary electrophoresis with laser-induced fluorescence detection to quantitate enzyme activity. Sf9 cells were assayed at the single cell level and found to be highly heterogeneous with respect to alpha-glucosidase II activity. Since only 5 nL of the single cell reaction was removed, multiple sampling was possible, allowing triplicate analysis of enzyme activity for each individual cell. Multiple sampling also permitted a single cell reaction to be monitored over time. The sensitivity of this method was demonstrated in the analysis of a low-abundance enzyme, alpha1,3-N-acetylgalactosaminyltransferase, from single HT29 cells. Detecting the product of this enzyme reaction required minimizing the dilution of cellular contents. To demonstrate the potential applications of this methodology in small scale biochemical analyses, single Arabidopsis knf embryos lacking the alpha-glucosidase I encoding KNOPF gene were assayed. Mutant embryos demonstrated insignificant conversion of a triglucose substrate, as compared to wild type, confirming the deletion of alpha-glucosidase I. Embryos were simultaneously assayed for a second enzyme, beta-galactosidase, illustrating that the mutants were viable except for their lack of alpha-glucosidase I activity.

Butyrate-induced differentiation of colon cancer cells is PKC and JNK dependent.

Butyric acid, a short-chain fatty acid physiologically present in human large gut, is derived from bacterial fermentation of complex carbohydrates. It has been shown to reduce the growth and motility of colon cancer cell lines and to induce cell differentiation and apoptosis. Apoptosis is considered a result of normal colonocyte terminal differentiation in vivo. The aim of this study was to characterize the cellular mechanisms regulating differentiation of colon cancer cells stimulated with sodium butyrate (NaB). The two human colon cancer cell lines Caco-2 and HT-29 were treated with NaB at physiologically relevant concentrations. Alkaline phosphatase (ALP) activity, a marker of colonocyte differentiation, was increased 48 hr after treatment with 1 mM NaB. Higher doses of NaB (5 and 10 mM) induced apoptosis of the cells and failed to stimulate the colonocyte differentiation. Therefore, we assumed that butyrate augments cell differentiation and induces apoptosis, acting via various intracellular mechanisms, and butyrate-mediated programmed cell death cannot be considered a consequence of colonocyte terminal differentiation. The effect of NaB on ALP activity was significantly attenuated in the presence of inhibitors of protein kinase C and JNK. Inhibition of MEK-ERK signal transduction pathways augmented the impact of butyrate on colonocyte differentiation. These results suggest that butyrate could influence the colonocyte differentiation via modulation of the activity of cellular protein kinases and signal transduction.

[Influence of sodium butyrate on growth of HT-29 colon carcinoma cells and expression of inducible nitric oxide synthase (iNOS)].

BACKGROUND & OBJECTIVE: Sodium butyrate could inhibit several cancer cell lines in vitro. This study was designed to investigate the effects of sodium butyrate on the growth of HT-29 colon carcinoma cells, the expression of iNOS, and the excretion of NO. METHODS: The HT-29 cells were co-incubated with sodium butyrate at various concentration. The cell proliferation was determined by MTT test, and the iNOS protein of HT-29 cells was stained by immunochemical SP method. The absorbance value (A value) of iNOS was measured by automatic image analysis system. Griess's technique was used to examine the excretion of nitric oxide (NO). RESULTS: The survival rates of HT-29 cells treated by sodium butyrate decreased in a time-dependent and dose-dependent manner. IC(50) value of sodium butyrate was decreased with prolonged incubation time (15.4 mmol/L at 12 hours, 5.7 mmol/L at 24 hours, 2.5 mmol/L at 36 hours, 0.9 mmol/L at 48 hours). Simultaneously sodium butyrate decreased the expression of iNOS in the cytoplasm and the excretion of NO in a similar manner. CONCLUSION: Sodium butyrate could inhibit the expression of iNOS, consequently reduce the excretion of NO. It may play an important role in the mechanism that sodium butyrate inhibits the growth of HT-29 colon carcinoma cells.

Telomerase inhibition using azidothymidine in the HT-29 colon cancer cell line.

BACKGROUND: We investigated the effects of telomerase inhibition by using the reverse transcriptase inhibitor azidothymidine (AZT) in the human colorectal cancer cell line HT-29 in the presence and absence of 5-fluorouracil (5-FU). METHODS: HT-29 cells were cultured in the presence of AZT. Telomerase activity was measured by using the telomerase repeat amplification protocol. Telomere length was determined by Southern analysis. The colorimetric microtiter assay was performed to determine the cytotoxic effects of AZT, alone and in combination with 5-FU. RESULTS: The presence of 3'-azido-3'-deoxythymidine triphosphate (AZT-TP) effectively inhibited telomerase extracted from HT-29 cells. HT-29 cells cultured with 125 microM of AZT underwent fewer total population doublings over 91 days. Southern analysis revealed that telomere attrition occurred within this period. Exposure to 125 microM of AZT resulted in slightly reduced viability (10%) of HT-29 cells. However, the presence of AZT increased 5-FU cytotoxicity, suggesting that the effects of these two drugs are synergistic. CONCLUSIONS: The data are consistent with telomerase inhibition having growth-inhibitory effects in addition to those predicted to accompany loss of telomere function. Further studies using specific small-molecule inhibitors will confirm whether the growth-inhibitory and 5-FU-sensitivity effects seen here are a direct result of telomerase inhibition.

Apoptosis induced by cryo-injury in human colorectal cancer cells is associated with mitochondrial dysfunction.

Cryotherapy, a method of in situ ablation, is used in the treatment of colorectal liver metastases with variable results. During the treatment, the central area of treated tumor undergoes necrotic destruction by lethal cryo-injury; however, the cellular response of tumor exposed to sublethal cryo-injury at the peripheral zone is unclear. In our study, we have identified the induction of apoptosis by cryo-injury at -10 degrees C in 4 colorectal cancer cell lines (HT29, HCT116, KM12C and KM12SM). The apoptosis was characterized by chromatin condensation, transferase-mediated dUTP nick end-labeling (TUNEL) staining, proteolytic cleavage of poly(ADP-ribose) polymerase (PARP) and cytokeratin 18, and activation of caspase-3. The occurrence and intensity of cryo-induced apoptosis did not correlate with the functional status of p53 in the cell lines studied. The expression of anti-apoptotic proteins (Bcl-2, Bcl-X(L)) and pro-apoptotic proteins (Bax, Bcl-X(S), Bad, and Bak) in response to cryo-injury varied in this cell line panel. The basal level of Bcl-2/Bax protein ratio correlated inversely to the apoptotic rate. We further demonstrated that Bax level decreased in cytosol and increased in mitochondria, followed by a loss of mitochondrial membrane potential after cryo-injury in HT29 cells. These findings indicate that cryo-injury induces apoptosis in colorectal cancer cells via disruption of mitochondrial integrity. The cryo-induced apoptosis was also identified in a nude mouse tumor xenograft model. Our elucidation of the apoptosis pathway induced by cryo-injury implies that synergistic combination of cryosurgery with pharmacological agents that augment of apoptosis induction may have clinical relevance in treating colorectal liver metastasis.

Activated SRC protein tyrosine kinase is overexpressed in late-stage human ovarian cancers.

OBJECTIVE: The objective of this study was to determine if the Src tyrosine kinase is overexpressed and activated in late-stage human ovarian cancers. METHODS: Western analysis and immune complex kinase assays were performed on a panel of human ovarian cancer cell lines and normal ovarian epithelial cell cultures, and immunohistochemical analysis for Src and activated Src were performed on a panel of late-stage human ovarian tumors. RESULTS AND CONCLUSIONS: Src is overexpressed and activated in a majority of late-stage ovarian tumors as well as in a panel of cultured malignant human ovarian epithelium grown in vitro, but not in normal ovarian epithelium (NOE) or immortalized NOE. Src overexpression was found to be frequently, but not always, associated with HER-2/neu overexpression, but no statistical association between Src and Her-2/neu overexpression could be demonstrated.

Red wine polyphenols inhibit the growth of colon carcinoma cells and modulate the activation pattern of mitogen-activated protein kinases.

Red wine is a rich source of polyphenols, which exhibit a number of biological effects in different in vitro and in vivo systems. The bioavailability of polyphenols is poor and the plasma concentrations of major red wine polyphenols are usually low after consumption of dietary relevant amounts of red wine. In contrast to most organ systems, the gastrointestinal tract (particularly the epithelial cells of this organ system) is exposed to high concentrations of polyphenols. Here, we show that the total polyphenol pool isolated from a red wine (varity Lemberger, vintage 1998) at micromolar concentrations inhibited the proliferation of transformed colon epithelial cells HT 29 clone 19A induced by epidermal growth factor (EGF). Inhibition of proliferation was also associated with modulation of activation of mitogen-activated protein kinases (MAPK). Stress activated c-Jun N-terminal kinases 1/2 (JNK) and p38 MAPK were significantly activated by red wine polyphenols (6 mmol/L). Maximum phosphorylation of both MAPK was observed after a 1-h treatment with red wine polyphenols. In contrast, activation of extracellular signal regulated kinase (ERK) 1/2 by EGF (1 nmol/L) was significantly inhibited by red wine polyphenols (6 mmol/L). This signaling pattern, activation of JNK 1/2 and p38 MAPK and inhibition of ERK 1/2, is typical for antiproliferative compounds, indicating that red wine polyphenols may inhibit the proliferation of colon carcinoma cells by modulating MAPK intracellular signal transduction pathways.

Tumor necrosis factor-alpha induces apoptosis associated with poly(ADP-ribose) polymerase cleavage in HT-29 colon cancer cells.

BACKGROUND: Tumor necrosis factor-alpha (TNF-alpha) is known for its selective cytotoxic activity on tumour cells. We analysed the response of HT-29 human colon carcinoma cells to this cytokine. MATERIALS AND METHODS: After TNF-alpha treatment, cell proliferation, cell cycle, reactive oxygen species (ROS) production (flow cytometry), the amount of apoptotic cells (flow cytometry, fluorescence microscopy), cleavage of poly (ADP-ribose) polymerase (PARP) and caspase-3 activity (Western blotting) were detected. RESULTS: TNF-alpha induced a decrease of cell growth and viability, an accumulation of cells in the S-phase of the cell cycle, an increase of subdiploid cell population and nuclear chromatin condensation and fragmentation, but not sooner than 96-120 hours. However, earlier events characteristic of apoptosis occurred, such as caspase-3 activation, PARP cleavage to 89 kDa fragment and changes in ROS production. CONCLUSION: We demonstrated that, in addition to being an early marker of apoptosis, activation of caspase-3 and degradation of PARP may play a causative role in HT-29 cell death induced by TNF-alpha.

Atypical protein kinase C zeta as a target for chemosensitization of tumor cells.

Exposure of tumor cells to cytotoxic agents simultaneously activates a variety of intracellular signaling pathways. Some of these pathways involve enzymes from the protein kinase C (PKC) family of serine/threonine kinases. This family includes isoenzymes that negatively influence cell death, whereas other demonstrate an opposite effect. The present study analyzes the role of the zeta atypical PKC isoform in tumor cell response to cytotoxic agents. Using a histone H1 phosphorylation assay, we showed that both tumor necrosis factor alpha and etoposide activate PKCzeta in U937 human leukemic cells. Stable transfection of a kinase-dead, dominant-negative PKCzeta mutant in U937 cells decreases Bcl-2 expression while increasing the expression of Bax and several procaspases. This transfection also prevents etoposide-induced nuclear factor-kappaB nuclear translocation and accumulation of X-linked inhibitor of apoptosis protein. PKCzeta inhibition accelerates the occurrence of apoptosis in leukemic cells exposed to etoposide and tumor necrosis factor alpha. This sensitization was confirmed in vitro by use of a clonogenic assay. In addition, PKCzeta inhibition sensitized tumor cells grown in nude mice to etoposide. These results indicate that PKCzeta isoform is a protective signals that is activated in tumor cells exposed to a cytotoxic agent. This inducible resistance factor thus appears an attractive target for chemosensitization of tumor cells.

Effects of deoxycholate on human colon cancer cells: apoptosis or proliferation.

BACKGROUND: Deoxycholic acid has long been attributed as a tumour promoter in the colon. It exerts its growth-related actions in a phorbol ester-like manner, by stimulating protein kinase C. The aim of this study was to investigate the effect of deoxycholic acid on proliferation and apoptosis in the colon, by exposing colon cancer cells to it in increasing concentrations. METHODS: Human colon cancer cells (Caco-2 and HT-29) were treated with deoxycholate or its two structural isomers, 3-beta-12-alpha-dihydroxy-5-beta-cholan-24-oic acid and 3-alpha-12-beta-dihydroxy-5-beta-cholan-24-oic acid. Proliferation was evaluated by cell counting, and apoptosis by estimating percentage cell survival and assessment of nuclear morphology. RESULTS: Within the concentration range of up to 20 microM, deoxycholate stimulated growth of both human colon cancer cell lines. Its growth-promoting effect was abolished after inhibition of protein kinase C. At concentrations above 100 microM, deoxycholate induced apoptosis in both cell lines. Epimers of deoxycholate were significantly less potent in stimulating growth. CONCLUSION: Low-dose deoxycholate stimulates colon cancer cell proliferation while > 100 micromol L(-1) of this secondary bile acid induces apoptosis in colon cancer cells. Deoxycholate might promote the likelihood of malignant transformation by increasing epithelial cell turnover in the colon.

Induction of multidrug resistance proteins MRP1 and MRP3 and gamma-glutamylcysteine synthetase gene expression by nonsteroidal anti-inflammatory drugs in human colon cancer cells.

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been demonstrated to suppress colorectal tumorigenesis. NSAIDs have also been used to treat inflammatory illnesses. However, the underlying mechanisms of action by NSAIDs have not been completely elucidated. In this study, we reported that among the six members of the multidrug resistance protein gene (MRP1 to MRP6) family which encode membrane transporters for a diverse group of antitumor agents, expression of MRP1 and MRP3 but not the others in human colorectal cancer cell lines was induced by sulindac. This induction profile is consistent with the results using prooxidants which produce reactive oxygen species (ROS) and generate oxidative stress as previously reported. Moreover, treatment of colorectal cancer cells with sulindac induced ROS. Suppression of ROS formation by antioxidant N-acetylcysteine (NAC) downregulated the induction of MRP1 and MRP3 expression. Expression of another oxidative stress-sensitive gene, gamma-glutamylcysteine synthetase heavy subunit gene (gamma-GCSh), which encodes the rate-limiting enzyme in glutathione biosynthesis, was also induced by sulindac. However, the suppression of sulindac-induced gamma-GCSh expression by NAC was less sensitive compared with that of MRP1 and MRP3. We also demonstrated that induction of MRP3 and gamma-GCSh was independent of intracellular COX-2 levels. These results, collectively, suggest a ROS-related, COX-2-independent mechanism for the induction of drug resistance gene expression that bears important implications to the roles of NSAIDs in colorectal carcinogenesis and inflammatory response.

Glutathione-S-transferase-pi expression regulates sensitivity to glutathione-doxorubicin conjugate.

We have reported that glutathione-doxorubicin conjugate (GSH-DXR) exhibited potent cytotoxicity against tumor cells and inhibited glutathione-S-transferase (GST) enzyme activity. In order to determine whether or not the expression of GST-pi lowered the cytotoxicity of GSH-DXR, cytocidal activity of the conjugate was examined using tumor cells in which the level of GST-pi expression was regulated by transfecting GST-pi cDNA in the correct or reverse direction and comparing with that of DXR. Enhancement of GST-pi expression by transfecting GST-pi sense cDNA into human hepatoblastoma HepG2 cells in which GST-pi expression was extremely low caused an increase in GST activity from 0.26 to 55.0 nmol/mg/min and a marked reduction in transfectant sensitivity to GSH-DXR to 1/120 (0.15-18 nM IC50) although the sensitivity to DXR was slightly decreased to 1/2.6 (380-990 nM IC50). By contrast, a high GST-pi-expressing human colon cancer cell line, HT29, showed a decrease in GST enzyme activity from 72.0 to 45.9 nmol/mg/min after transfecting GST-pi antisense cDNA and a marked improvement in transfectant sensitivity to GSH-DXR was observed (28-2.9 nM IC50) compared with the transfectant sensitivity to DXR (1020-320 nM IC50). Additionally, the expression of GST-pi in HepG2 cells caused a decrease in GSH-DXR-induced activation of caspase-3, which was an apoptotic marker, whereas the suppression of GST-pi in HT29 cells showed an increase in caspase-3 activation. These results suggested that the cytocidal efficacy of GSH-DXR, but not that of DXR, was controlled by the level of GST-pi expression in the cells.