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PubMed2004

[CHL prevent colon neoplasms in mice and its selective inhibition on COX-2].

BACKGROUND & OBJECTIVE: Chlorophyllin (CHL) was proved to have strong anti-inducement effect toward many mutagens and epicarcinogens. This study was to explore effect of CHL in preventing colon neoplasms in mice induced by dimethylhydrazine (DMH), and the selective inhibition on cyclooxygenase 2(COX-2). METHODS: The colorectal neoplasms were induced with DMH in mice and the different dose of CHL were administered in different phases, then the prevention of colorectal neoplasms by CHL was examined; The IC50 and growth curve of HT29 cells were measured with MTT method after treated with CHL; The effect of CHL on the expression of COX-1 mRNA and COX-2 mRNA in HT29 cells were measured with RT-PCR method; The effect of CHL on the expression of COX-2 protein and NF-kappaB protein were measured with western blot and immunohistochemistry methods. RESULTS: The incidence of colon cancer, average tumor amount, and percentage of carcinoma in CHL group were significantly lower than those in DMH group (P< .05); CHL could inhibit the growth of HT29 cells. The effects were dose dependent; CHL could selectively inhibit the expression of COX-2mRNA in HT29 cells,the expression of COX-2 protein in colon neoplasms and HT29 cells, and the expression of NF-kappaB protein in colon neoplasms. CONCLUSIONS: CHL could prevent colon neoplasms in mice induced by DMH and the preventive effect related to selective inhibition on COX-2, furthermore, the inhibition of CHL on COX-2 was realized by inhibiting NF-kappaB protein.

Animals↗
PubMed1990

T-cell recognition of HLA class II molecules induced by gamma-interferon on a colonic adenocarcinoma cell line (HT29).

HLA class II molecules may be induced on non-lymphoid cells by gamma-interferon (IFN-gamma). We investigated if HLA class II molecules induced by IFN-gamma on the HT29 colonic carcinoma cell line are functional, i.e. if they may be recognized by allogeneic T cells. We found that IFN-gamma-treated HT29 (HT29IFN) cells could not induce primary proliferative responses of peripheral blood T lymphocytes, nor were they able to induce proliferation in T-lymphocyte clones (TLC) specific for HLA class II molecules found on HT29IFN. However, in the presence of exogenous interleukin 2 (IL-2), 1 of 5 DQw8-specific TLC proliferated when restimulated with HT29IFN, and 3 of these 5 TLC could very effectively inhibit the growth of HT29IFN, probably due to a cytotoxic effect. Both the proliferative response and the cytotoxicity were inhibited by anti-DQ MoAb. We conclude that T cells may recognize HLA-DQ molecules on non-lymphoid cells, which may be of relevance for autoimmune diseases, graft-versus-host disease, and possibly for the recognition of malignant cells.

Adenocarcinoma↗
PubMed1984

Dopamine receptors in a human colonic cancer cell line (HT29). Some receptor-related biological effects of dopamine.

The presence of dopamine receptors in normal colonic cells has been postulated from physiological studies. The existence of such receptors in human colonic tumor cells and their role in tumor progression are still unknown. The aim of the present work was to characterize the dopaminergic receptors in a human colonic adenocarcinoma cell line (HT29) and to evaluate the effect of dopamine on cAMP, protein and DNA synthesis. The binding characteristics of 3H-dopamine on the tumor cells were rapid, reversible, specific, saturable and stereospecific. The first site characterized corresponds to a D3 subtype:KD 3.09 nM, insensitive to sulpiride, unrelated to adenylate cyclase. Competitive inhibitions of 3H-dopamine binding by different drugs showed the existence of a second binding site, D1, with an apparent affinity for dopamine of 6,700 nM. The rank order of potency of inhibitors of 3H-dopamine binding was: haloperidol greater than dopamine greater than cis flupenthixol greater than (+) butaclamol greater than (-) butaclamol greater than trans flupenthixol greater than isoproterenol greater than clonidine greater than prazosin. D3 binding sites are modulated with age, Bmax was 116 fmol/10(6) cells on the 5th day and decreased to 8.2 fmol/10(6) cells on the 15th day of culture. Cell culture in serum-deprived medium allowed an increase in the number of high-affinity receptor sites. D1 sites are coupled to adenylate cyclase as shown by a dose-dependent cAMP accumulation from 10(-8) M to 10(-5) M dopamine concentrations. Interacting with D1 sites, dopamine evokes an increase in protein synthesis with no modification of 3H thymidine incorporation. The present results indicate that the human colonic cancer cell line HT29 exhibits dopamine receptors and that stimulation may induce metabolic modifications in the tumor cells.

Binding, Competitive↗
PubMed1990

Transforming growth factor beta 1 acts as an autocrine-negative growth regulator in colon enterocytic differentiation but not in goblet cell maturation.

Previous studies from this laboratory (Schroy, P., Rifkin, J., Coffey, R.J., Winawer, S., and Friedman, E. (Cancer Res., 50: 261-265, 1990; Schroy, P.C., Winawer, S., and Friedman, E. Cancer Lett., 48: 53-58, 1989) found that a 7-day treatment of the human colon carcinoma cell line HT29 with the differentiation agent hexamethylene bisacetamide (HMBA) induces both a 4-5-fold increase in transforming growth factor beta 1 (TGF beta 1) mRNA levels and reduced tumorigenicity in vivo. A series of 15 cloned lines with different commitments to differentiation has been isolated from 20-day HMBA-treated HT29 cells, maintained without HMBA, and utilized to study the role of TGF beta 1 in colon carcinoma differentiation. Two such lines, HD6 and HD8, differentiate to 97 and 76% mucus-secreting goblet cells, respectively, in columnar monolayers in postconfluent culture. Both HD6 and HD8 cells exhibit low TGF beta 1 mRNA levels, little different from the undifferentiated HT29 parental line, and exhibit no growth modulation in response to exogenous TGF beta 1. In contrast, two other lines, HD3 and HD4, differentiate to fluid-transporting enterocytic cells with functional brush borders and exhibit autocrine-negative growth response to TGF beta 1. Both lines express TGF beta 1 mRNA at levels 11-12-fold higher than the parental line and respond to exogenous TGF beta 1 by growth inhibition. HD3 cells secrete biologically active TGF beta 1 into conditioned media, which inhibited growth of a TGF beta 1-sensitive mink cell line. This inhibition was blocked by antisera to TGF beta 1, proving the specificity of the inhibition. A range of concentrations of this TGF beta 1 antiserum stimulated HD3 cell growth in a dose-dependent manner, further documenting the autocrine-negative response of the cells to TGF beta 1. Another cell line, HI1, was blocked in enterocytic differentiation. HI1 cells synthesized as much TGF beta 1 mRNA as HD3 and HD4 cells, yet they responded to exogenous TGF beta 1 with less growth inhibition, suggesting some impairment in their response to TGF beta 1. A third class of response to TGF beta 1 was exhibited by the HP1 cell line, which was resistant to HMBA-induced differentiation, remaining undifferentiated with a multilayered growth pattern. HP1 cells synthesized TGF beta 1 mRNA at levels over 20 times the parental level but were stimulated to divide by TGF beta 1, exhibiting autocrine-positive response to this growth factor.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetamides↗
PubMed1992

Bile acids, non-phorbol-ester-type tumor promoters, stimulate the phosphorylation of protein kinase C substrates in human platelets and colon cell line HT29.

Protein kinase C (PKC) is the target for a number of tumor promoters. The mechanism underlying the promoting effects of bile acids in colorectal cancer is not understood. We report that sodium deoxycholate (DOC) triggered activation of PKC in physiological conditions. The biphasic effects of DOC upon PKC activation were Ca(2+)-stimulated and did not require phosphatidylserine (PtdSer) as phospholipid co-factor. The optimal rate of activation was obtained at 0.4 mM DOC and reached approximately half the maximal rate of activation obtained in the presence of PtdSer. Similarly to PtdSer, DOC supported diacylglycerol- as well as phorbol-ester-mediated PKC activation. The reciprocal effects of PtdSer and DOC upon PKC in either 0.5 mM CaCl2 or 0.5 mM EGTA suggest that DOC interacts with the phospholipid-binding domain to elicit PKC activation. DOC-supported enzyme activation exhibited substrate specificity different from that of PtdSer-supported enzyme activation. All tested primary and secondary bile acids activated PKC to various extents, with DOC being the most potent. We suggest that amphipathic bile acids acting in a PtdSer-like manner provide the hydrophobic environment required for PKC activation. Treatment of 32P-labeled platelets and colonic cells HT29 Cl.19A with DOC enhanced the phosphorylation of endogenous substrates for PKC. Colonic cells responsive at 50 microM DOC, appeared to be 10-fold more sensitive than platelets. We suggest that direct or indirect activation of PKC by bile acids may account for the promoting effects of these non-phorbol-ester-type tumor promoters.

Bile Acids and Salts↗
PubMed1987

Cycloheximide induces accumulation of vasoactive intestinal peptide (VIP) binding sites at the cell surface of a human colonic adenocarcinoma cell line (HT29-D4). Evidence for the presence of an intracellular pool of VIP receptors.

Incubation of monolayers of HT29-D4 cells (a clone of the human colonic adenocarcinoma cell line HT29) in the presence of 17.5 microM cycloheximide resulted in an increase in the number of vasoactive intestinal peptide (VIP) binding sites at the cell surface without any change in the affinity of receptor for its ligand. The increase in 125I-VIP-binding capacity was dose-dependent between 0.35 microM and 17.5 microM cycloheximide and was correlated with the inhibition of protein biosynthesis. At higher concentrations of drug (17.5-100 microM) a plateau corresponding to a twofold increase in VIP-binding capacity was reached independently of the extent of protein synthesis inhibition. We found that VIP receptors of HT29-D4 cells with such an enhanced binding capacity behaved like those of control cells with respect to receptor internalization and recycling (i.e. the cycle of occupied receptors was insensitive to cycloheximide). After inactivation of 90% of cell-surface VIP receptors by alpha-chymotrypsin, we observed a biphasic kinetic of reappearance of VIP-binding sites. 40% of VIP-binding sites reappeared very quickly (less than 5 min) and 100% within 17 h. The fast recovery of VIP receptors was probably due to the deployment of new binding sites from an intracellular pool. The rate and extent of recovery of these receptors were similar in control cells and in cycloheximide-treated cells. However, the slow recovery was inhibited in cycloheximide-treated cells probably because a pool of immature receptors was depleted by the drug before the alpha-chymotrypsin treatment. Our data are consistent with the existence of two different intracellular pathways of occupied and unoccupied VIP receptors.

Adenocarcinoma↗
PubMed1999

A Fas-dependent component in 5-fluorouracil/leucovorin-induced cytotoxicity in colon carcinoma cells.

We have shown previously (J. A. Houghton et al., Proc. Natl. Acad. Sci. USA, 94: 8144-8149, 1997) that thymineless death in thymidylate synthase-deficient (TS-) colon carcinoma cells is mediated via Fas/FasL interactions after deoxythymidine (dThd) deprivation, and that Fas-dependent sensitivity of human colon carcinoma cell lines may be dependent upon the level of Fas expressed. The objective of this study was to elucidate whether a Fas-dependent component exists in 5-fluorouracil (FUra)/leucovorin (LV)-induced cytotoxicity of colon carcinoma cells, and whether this may be potentiated by IFN-gamma-induced elevation in Fas expression, using the HT29 cell line as a model. The cytotoxic activity of FUra/LV was inhibited by dThd in HT29 cells and also, in part, by NOK-1+NOK-2 MoAbs that prevent Fas/FasL interactions. FUra/LV-induced cytotoxicity was significantly potentiated by IFN-gamma, reversed by exposure to NOK-1+NOK-2 antibodies, and correlated with a 4-fold induction of Fas expression in the presence of IFN-gamma and significant elevation in expression of FasL. Using five additional human colon carcinoma cell lines, FUra/LV-induced cytotoxicity was dThd-dependent in GC3/c1, VRC5/c1, and Caco2 but not in HCT8 or HCT116 cells. Like HT29 cells, this cytotoxicity was potentiated by IFN-gamma in GC3/c1 and VRC5/c1 but not in Caco2, which fails to express Fas, nor in HCT8 and HCT116, in which no dThd-dependent FUra-induced cytotoxicity was demonstrated. Data suggest that a Fas-dependent component, potentiated by IFN-gamma, exists in FUra/LV-induced cytotoxicity but requires FUra/LV-induced DNA damage for IFN-gamma-induced potentiation to occur.

Cell Division↗
PubMed2004

Differential effects of monastrol in two human cell lines.

The kinesin-related protein HsEg5 plays essential roles in mitotic spindle dynamics. Although inhibition of HsEg5 has been suggested as an aid in cancer treatment, the effects of such inhibition on human cells have not been characterized. Here we studied the effects of monastrol, an allosteric HsEg5 inhibitor, on AGS and HT29 cell lines and compared them to those of taxol. While both cell lines were similarly sensitive to taxol, AGS cells were more sensitive to monastrol. The differences in sensitivity were determined by the degree of inhibitory effect on cell proliferation, reversibility of monastrol-induced G2/M arrest, intracellular phenotypes and induction of apoptosis. In both cell lines, monastrol-induced apoptosis was accompanied by mitochondrial membrane depolarization and poly-ADP-ribose polymerase 1 cleavage. In AGS, but not HT29 cells, monastrol-induced apoptosis involved a prominent cleavage of procaspases 8 and 3. While in AGS cells, monastrol induced the formation of symmetric microtubule asters only, in HT29 cells, asymmetric asters were also formed, which may be related to specific HsEg5 functions in HT29 cells.

Antineoplastic Agents, Phytogenic↗
PubMed1991

Acyl-CoA: cholesterol acyltransferase in HT 29 cell subpopulations. Defect of activity in the undifferentiated cells.

The ACAT activity was studied on different subpopulations deriving from HT29 cells, a human colon carcinoma cell line. Grown on standard medium (25 mM glucose), about 95% of these cells are undifferentiated (G + cells). From this heterogeneous population, differentiated cells were selected by glucose deprivation and grown either on medium without glucose (G - cells) or in standard medium containing 25 mM glucose (G-Rev cells). The G- and G-Rev cells have the features of differentiated small intestine cells. The two types of differentiated cells (G- and G-Rev) exhibited similar ACAT activities and the kinetic characteristics of the enzyme were also similar. A time-course study showed increasing activity during the exponential phase and a decrease just after confluency. It was possible to stimulate the enzyme by micellar or lipoprotein cholesterol. In contrast, the ACAT activity was hardly detectable in undifferentiated G + cells. In addition, all the experimental conditions known to stimulate ACAT activity, and confirmed in the differentiated HT29 cells, were inefficient in the undifferentiated G + cells. Therefore, the different models derived from HT29 cells provide the opportunity to study cholesterol esterification as well as the consequences of its aberrances in intestinal cells.

Adenocarcinoma↗
PubMed2000

CD44s expression in human colon carcinomas influences growth of liver metastases.

CD44 is a family of cell-surface adhesion molecules which exist in several isoforms arising from mRNA alternative. Malignant transformation of colonic mucosa is associated with alterations in CD44 expression, which result in up-regulation of high-molecular-weight CD44 isoforms and down-regulation of CD44s. We have demonstrated that stable transfection of CD44s into colon-carcinoma cell lines reduces their tumorigenicity. To understand the influence of CD44s expression on the metastatic potential of human colon carcinomas, we measured the ability of several different CD44s-transfected colon carcinomas to establish experimental liver metastases following splenic inoculation in mice. We observed that introduction of CD44s into 2 different human colon carcinoma cell lines, HT29 and KM12C6, resulted in reduced growth of liver metastases by as much as 75%. To explore the relationship between hyaluronate adhesion and metastasis, we transfected HT29 cells with cDNA encoding a mutant CD44s that does not bind to hyaluronate. HT29 transfectants expressing this mutant CD44s demonstrate an 84% reduction in growth of liver metastases, despite minimal binding to hyaluronate by the mutant CD44s. In concert, these results indicate that CD44s down-regulation, which occurs with malignant transformation of colonic mucosa, is associated with enhanced growth of experimental liver metastases. Consequently, the functional consequences of CD44s down-regulation in colon carcinomas may be just as significant as the consequences of up-regulation of other CD44 isoforms.

Alternative Splicing↗
PubMed2003

Extracellular MUC3 mucin secretion follows adherence of Lactobacillus strains to intestinal epithelial cells in vitro.

BACKGROUND: Mucins are large complex glycoproteins that protect intestinal mucosal surfaces by limiting access of environmental matter to their epithelial cells. Several mucin genes have been described, including MUC3 that is a membrane associated mucin of the small intestine. Increased MUC3 mRNA transcription is induced by incubation of intestinal epithelial cells with a Lactobacillus strain known to be adherent to them. AIMS: To determine whether increased epithelial cell MUC3 mucin expression in response to Lactobacillus strains results in increased extracellular secretion of MUC3 mucins and the importance of epithelial cell adherence in modulation of MUC3 mucin expression. METHODS: HT29 cells grown to enhance expression of MUC3 mucins were incubated with selected Lactobacillus strains. Spent cell culture medium was collected for detection of secreted MUC3 mucins using dot blot immunoassay with a generated MUC3 antibody. Post-incubation HT29 cell RNA was collected for analysis of MUC3 expression by northern blot analysis using a MUC3 cDNA probe. In vitro binding studies using Lactobacillus strains incubated alone or coincubated with enteropathogenic Escherichia coli strain E2348/69 were used for adherence and inhibition of adherence studies, respectively. RESULTS: Lactobacillus strains with minimal ability to adhere to HT29 cells failed to induce upregulation of mucin gene expression. There was a direct correlation between upregulation of MUC3 mucin mRNA expression and extracellular secretion of MUC3 mucin. The same Lactobacillus strains that increased extracellular secretion of MUC3 mucin led to reduced adherence of enteropathogen E coli E2348/69 during coincubation experiments. CONCLUSION: Probiotic microbes induce MUC3 mucin transcription and translation with extracellular secretion of the MUC3 mucins. Epithelial cell adherence enhances the effects of probiotics on eukaryotic mucin expression.

Bacterial Adhesion↗
PubMed2004

[Activation of nuclear factor-kappa B and expression of cytokine in intestinal epithelia stimulated by TNF-alpha].

OBJECTIVE: To investigate the effect of nuclear factor-kappa B activation on proinflammatory cytokine expression in intestinal epithelia when intestinal epithelia are in inflammatory condition. METHODS: Colonic adenocarcinoma HT29 cells were cultured in wells and TNF-alpha (10 ng/ml) was added into half of the wells. The supernatants were collected and measured for IL-8 after 3 hours, nuclear factor-kappaB (NF-kappaB) P65 and IL-8 mRNA were also examined by Western blotting and RT-PCR respectively. RESULTS: It was found that in the condition of no stimuli, there is little IL-8 mRNA expression of HT29 cells, P65 is seldom in HT29 cells' nuclei, and the concentration of IL-8 in supernatant is just 172 ng/L. However, after being stimulated by TNF-alpha, a lot of P65 expression in nuclei and a large number of IL-8 mRNA expression of HT29 cells are shown and the concentration of IL-8 in supernatant (639 ng/L) is significantly higher than that of control (P<0.01). CONCLUSION: The activation of nuclear factor-kappa B modulates the expression of some proinflammatory cytokine in intestinal epithelia, and regulates epithelia function in inflammatory reaction.

Epithelial Cells↗
PubMed2004

Time- and dose-dependent effects of curcumin on gene expression in human colon cancer cells.

BACKGROUND: Curcumin is a spice and a coloring food compound with a promising role in colon cancer prevention. Curcumin protects against development of colon tumors in rats treated with a colon carcinogen, in colon cancer cells curcumin can inhibit cell proliferation and induce apoptosis, it is an anti-oxidant and it can act as an anti-inflammatory agent. The aim of this study was to elucidate mechanisms and effect of curcumin in colon cancer cells using gene expression profiling. METHODS: Gene expression changes in response to curcumin exposure were studied in two human colon cancer cell lines, using cDNA microarrays with four thousand human genes. HT29 cells were exposed to two different concentrations of curcumin and gene expression changes were followed in time (3, 6, 12, 24 and 48 hours). Gene expression changes after short-term exposure (3 or 6 hours) to curcumin were also studied in a second cell type, Caco-2 cells. RESULTS: Gene expression changes (>1.5-fold) were found at all time points. HT29 cells were more sensitive to curcumin than Caco-2 cells. Early response genes were involved in cell cycle, signal transduction, DNA repair, gene transcription, cell adhesion and xenobiotic metabolism. In HT29 cells curcumin modulated a number of cell cycle genes of which several have a role in transition through the G2/M phase. This corresponded to a cell cycle arrest in the G2/M phase as was observed by flow cytometry. Functional groups with a similar expression profile included genes involved in phase-II metabolism that were induced by curcumin after 12 and 24 hours. Expression of some cytochrome P450 genes was downregulated by curcumin in HT29 and Caco-2 cells. In addition, curcumin affected expression of metallothionein genes, tubulin genes, p53 and other genes involved in colon carcinogenesis. CONCLUSIONS: This study has extended knowledge on pathways or processes already reported to be affected by curcumin (cell cycle arrest, phase-II genes). Moreover, potential new leads to genes and pathways that could play a role in colon cancer prevention by curcumin were identified.

Journal Article↗
PubMed1995

Down-regulation of CFTR expression in an HT29-derived cell line by stable antisense RNA production.

In order to examine the interactions of the cAMP activated CFTR chloride ion channel with other chloride ion channels present in epithelial cells we have generated a model based on antisense mRNA down regulation of CFTR expression. The HT29-derived epithelial cell line CJC4-1 has integrated a plasmid that is constitutively expressing CFTR exons 1-6 in the antisense orientation, from the MoMULV LTR. This cell line shows a reduction in cAMP-activated chloride efflux, as measured by iodide efflux assay, in comparison to the parental HT29 cell line and a sense transfected control.

Cell Line↗
PubMed2003

Interferon-gamma pharmacokinetics and pharmacodynamics in patients with colorectal cancer.

PURPOSE: The study objectives were to define subcutaneous (s.c.) interferon gamma (IFN-gamma) disposition in patients with gastrointestinal malignancies receiving 5-fluorouracil (5-FU) and leucovorin (LV) and to examine the relationship between IFN-gamma exposures and Fas upregulation in vivo and in vitro. METHODS: Patients received IFN-gamma (10, 25, 50, 75, and 100 microg/m(2)) with LV and 5-FU, and serial samples were collected after the first dose. IFN-gamma concentrations were measured by ELISA. A linear one-compartment model with a lag was fitted to the IFN-gamma plasma concentration-time data. To examine the relationship between IFN-gamma systemic exposure and biological activity in vivo, cell surface Fas upregulation was assessed in peripheral blood mononuclear cell (PBMC) subcompartments. RESULTS: The median (range) apparent IFN-gamma clearance was 46 l/m(2) per hour (2.6-92 l/m(2) per hour). With increasing IFN-gamma dosages, the area under the concentration-time curve (AUC(0--> infinity )) and C(max) increased; however, significant interpatient variability was observed. IFN-gamma AUC(0--> infinity ) and time above 33.3 pg/ml significantly correlated with Fas upregulation in several PBMC compartments, but dosage was significantly correlated with this pharmacodynamic marker only in CD4(+) and CD56(+) cells. In vitro studies in HT29 cells demonstrated that clinically relevant IFN-gamma concentrations (1 to 10 U/ml for 6.5 h) with 5-FU/LV upregulated Fas expression 3.5-fold, similar to that in PBMC in vivo. CONCLUSIONS: We characterized IFN-gamma disposition and developed a limited sampling model for use in future pharmacokinetic studies. Our results showed that IFN-gamma upregulates Fas in PBMC in vivo and in HT29 cells in vitro at tolerable, clinically relevant exposures and that monitoring IFN-gamma pharmacokinetics/pharmacodynamics may be warranted in IFN-gamma clinical use.

Adult↗
PubMed1993

Effect of sodium butyrate on the expression of retinoblastoma (RB1) and P53 gene and phosphorylation of retinoblastoma protein in human colon tumor cell line HT29.

Sodium butyrate is known to induce morphological and biochemical changes associated with cell differentiation in some colon tumor cell lines including HT29. In our present study we observed that sodium butyrate treatment caused a decrease in the level of expression of RB1 gene on day seven of butyrate treatment but a gradual six to sevenfold decrease in the level of expression of p53 gene. Western blot analysis revealed a decrease in the level of the phosphorylated form of Rb protein (pRb) and an increase in the level of underphosphorylated pRb as compared to the control cells. These changes in the phosphorylation level were observed from day three of sodium butyrate treatment. In addition, the flat foci forming large differentiated cells also began to appear after 3 days of sodium butyrate treatment. In this study, we are able to show that, besides induction of differentiation, sodium butyrate treatment can also cause a reversal in the phosphorylation status of the pRb in colon tumor cell line HT29. These results suggest that the phosphorylation level of pRb could be associated with the cell differentiation process in human colonic epithelium and as a consequence in its neoplastic development.

Adenocarcinoma↗
PubMed1999

pH-dependent uptake of irinotecan and its active metabolite, SN-38, by intestinal cells.

Irinotecan (CPT-11) and its active metabolite, 7-ethyl-10-hydroxycamptothecin (SN-38), are believed to be reabsorbed by intestinal cells and to enter the entero-hepatic circulation, but there is little information to date. Our objective was to investigate the intestinal transport of CPT-11 and SN-38 in correlation with their associated cytotoxicity. Using either isolated hamster intestinal epithelial cells or/and human colon carcinoma HT29 cells, the uptake rates of [(14)C]CPT-11 and [(14)C]SN-38, both as respective non-ionic lactone form at acidic pH and anionic carboxylate form at basic pH, were investigated by the rapid vacuum filtration technique. The effect of physiologic intestinal luminal pH (6.2-8.0) on the uptake rate and cytotoxicity of SN-38 were estimated by the above method and the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay, respectively. The lactone forms of CPT-11 and SN-38 were transported passively, while the respective carboxylate form was absorbed actively. Uptake rates of both lactones were significantly higher than those of their carboxylates. Under physiologic pH, the respective uptake rates of CPT-11 and SN-38 were pH sensitive and decreased significantly by around 65%, at pH greater than 6.8. Furthermore, with decreasing pH, a higher uptake rate of SN-38 into HT29 cells correlates with a greater cytotoxic effect (r = 0.987). CPT-11 and SN-38 have absorption characteristics of weakly basic drugs such as short-chain fatty acids, suggesting that alkalization of the intestinal lumen may be critical to reduce their reabsorption and associated side effects.

2,4-Dinitrophenol↗
PubMed1990

Metabolism of low-density lipoprotein in differentiated and undifferentiated HT29 colon cancer cells.

The metabolism of human low-density lipoproteins was studied in 2 subpopulations deriving from cells of HT29, a human colon carcinoma cell line. When grown on standard medium (25 mM glucose), about 95% of these cells are undifferentiated (G+ cells). From this heterogeneous population, a subpopulation with features of differentiated small-intestinal cells was selected by glucose deprivation (G- cells). The characteristics of the LDL receptor were first investigated. The results showed that the binding of 125I-LDL to G+ and G- cells performed at 4 degrees C was saturable and specific. The Kd values were not statistically different in the 2 cell subpopulations. The Bmax of G+ cells was 55 +/- 6 ng 125I-LDL/mg cell protein and showed no changes whatever the phase of culture. In G- cells, the Bmax was higher during the exponential phase of culture and decreased in the post-confluent phase (82 +/- 5 versus 15 +/- 6.8 ng 125I-LDL/mg cell protein). Cellular degradation of 125I-LDL was effective in both cell subpopulations but time-course studies showed that, in post-confluent G- cells, degradation was slowed as compared to G+ cells (4 hr vs. 2 hr to reach maximal degradation). The rate of LDL processing at 37 degrees C was enhanced by pre-incubation with FCS-supplemented medium, suggesting the existence of a serum component which stimulates the total degradation of 125I-LDL. Concerning regulation of the LDL receptor activity, we demonstrated that pre-incubation of G+ cells with LDL induced 80% down-regulation of receptor number in both phases of culture. This was also observed in G- cells during the exponential phase while only a 20% decrease of the receptor number was observed in post-confluent G- cells. The LDL degradation of G+ cells resulted in an inhibition of the cholesterogenic activity by 30% and 60% depending on the phase of culture. In G- cells, LDL pre-incubation inhibited cholesterol synthesis to the same extent (45%) in the exponential phase but did not affect the rate of cholesterol synthesis when cells were confluent. The defective regulatory role of LDL on receptor number and cholesterol synthesis suggests that, in the post-confluent differentiated cells, cholesterol derived from LDL does not reach the regulatory pool. Taken together, our findings indicate the existence of functional LDL receptors in the HT29 cell line, either in the differentiated or in the undifferentiated form.

Adenocarcinoma↗