Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0699790 (colon cancer)
 28,837 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The effects of fluorouracil (5-FU) and interferon-gamma (IFN-gamma) on the regulation of thymidylate synthase (TS) gene expression were investigated in the human colon cancer H630 cell line. By Western immunoblot analysis, TS protein levels in H630 cells were increased 3-, 5.5-, 5-, and 2.5-fold after 8-, 16-, 24-, and 36-hr exposure to 1 microM 5-FU, respectively. When H630 cells were exposed to varying concentrations of 5-FU (0.3-10 microM) for 24 hr, increases in TS protein up to 5.5-fold were observed. A 24-hr exposure to 1 microM 5-FU resulted in a 4.5-fold increase in the level of TS protein, whereas in 5-FU/IFN-gamma-treated cells TS protein was increased by only 1.8-fold, compared with control cells. IFN-gamma treatment alone did not affect TS protein levels, relative to control. Northern blot analysis revealed no changes in TS mRNA levels when H630 cells were exposed either to 1 microM 5-FU for 8-36 hr, to varying concentrations of 5-FU (0.3-10 microM) for 24 hr, or to the combination of 5-FU and IFN-gamma. Pulse-labeling studies with [35S]methionine demonstrated a 3.5-fold increase in net synthesis of TS in cells treated with 1 microM 5-FU, whereas the level of newly synthesized TS increased only 1.5-fold in cells treated with 5-FU/IFN-gamma, compared with control cells. Pulse-chase studies revealed that the half-lives of TS protein in control and 5-FU-treated cells were equivalent. These findings demonstrate that the increase in TS protein after 5-FU exposure and the subsequent inhibitory effect of IFN-gamma on TS protein expression are both regulated at the post-transcriptional level.
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PMID:Regulation of thymidylate synthase in human colon cancer cells treated with 5-fluorouracil and interferon-gamma. 847 31

Fluoropyrimidines radiosensitize human colon cancer cells that progress into S phase in the presence of drug (M.A. Davis, H-Y. Tang, J. Maybaum, and T.S. Lawrence. Int. J. Radiat. Biol. 67. 509-512, 1995). We hypothesized that progression occurs in cells that generate elevated levels of cyclin E-dependent kinase activity despite the presence of the fluoropyrimidine. To test this hypothesis, we treated HT29 and SW620 human colon cancer cells with fluorodeoxyuridine under conditions that produced nearly complete inhibition of thymidylate synthase but which sensitized only the HT29 cells. We found that, whereas HT29 cells progressed into S phase and demonstrated increased cyclin E-dependent kinase activity, SW620 cells arrested just past the G1-S boundary and showed no change in kinase activity. Because these cell lines have the same p53 mutation, these findings suggest that there is a p53-independent G1-S checkpoint that mediates radiosensitization produced by fluorodeoxyuridine.
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PMID:Fluoropyrimidine-mediated radiosensitization depends on cyclin E-dependent kinase activation. 876 7

We developed an immunoprecipitation-RNA-random PCR (rPCR) method to isolate cellular RNA sequences that bind to the folate-dependent enzyme thymidylate synthase (TS). Using this approach, nine different cellular RNAs that formed a ribonucleoprotein (RNP) complex with thymidylate synthase (TS) in human colon cancer cells were identified. RNA binding experiments revealed that seven of these RNAs bound TS with relatively high affinity (IC50 values ranging from 1.5 to 6 nM). One of the RNAs was shown to encode the interferon (IFN)-induced 15 kDa protein. Western immunoblot analyses demonstrated that the level of IFN-induced 15 kDa protein was significantly decreased in human colon cancer H630-R10 cells compared with parent H630 cells. While the level of IFN-induced 15 kDa mRNA expression was the same in parent and TS-overexpressing cell lines, the level of IFN-induced 15 kDa RNA bound to TS in the form of a RNP complex was markedly higher in H630-R10 cells relative to parent H630 cells. These studies begin to define a number of cellular target RNA sequences with which TS interacts and suggest that these TS protein-cellular RNA interactions may have a biological role.
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PMID:Identification of in vivo target RNA sequences bound by thymidylate synthase. 877 4

Interferon (IFN) augments the anabolism of 5-fluorouracil (5FU) to its active metabolite, fluorodeoxyuridylate (FdUMP), which inhibits thymidylate synthase (TS). We sought to determine whether this resulted in greater perturbations of nucleotide pools and if so, whether this was associated with an increase in cell lethality, specifically focussing on the lethal cellular lesion, DNA double strand breaks (dsb). To determine whether combination therapy with 5FU + IFN resulted in greater depletion of thymidine nucleotide pools than 5FU alone, a highly sensitive DNA polymerase assay was used. In two human colon cancer cell lines, treatment with 5FU + IFN resulted in a rapid decrease in levels of dTTP by 95%. The addition of IFN to 5FU resulted in greater depletion of dTTP levels over treatment with 5FU alone by up to fourfold, and markedly augmented the dATP/dTTP ratio. The addition of IFN to 5FU had no effect on 5FU-induced perturbations in dCTP, dGTP or dATP pools at 8 and 12 h. Measurement of DNA dsb demonstrated that treatment of HT-29 cells with 10 microM 5FU for 24 h did not increase DNA dsb versus control. The combination of 5FU + 500 U/ml IFN, however, resulted in an increased number of dsb versus both 5FU and untreated control cells (P < 0.01), equivalent to 0.74 +/- 0.12 Gy. The addition of IFN to 5FU resulted in a selective further depletion of pools of dTTP and an increase in the number of DNA dsb versus 5FU treatment alone.
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PMID:Effect of interferon on 5-fluorouracil-induced perturbations in pools of deoxynucleotide triphosphates and DNA strand breaks. 882 94

AG337 is the recent non-classical thymidylate synthase inhibitor with promising activity and manageable toxicity in phase I clinical trials. In this study, we investigated the cytotoxic activity of AG337 alone and in combination with cisplatin in cultured human colon (HT29) and ovarian (2008) cancer cell lines and their derived counterparts selected for their resistance to 5-fluorouracil (5-FU) (HT29-5-FU) and cisplatin (2008C13). We observed that AG337 had potent cytotoxic effects in colon (IC50 = 0.17 MicroM) and ovarian cancer cells (IC50 = 0.65 microM). The cytotoxic activity of AG337 was higher than that of 5-FU in the two models. The Activity of AG337 was not significantly affected in 5-FU-resistant HT29-5-FU colon cancer cells characterized by an amplification of the thymidylate synthase gene (IC50 = 0.27 microM, p = 0.15). Combinations of cisplatin and AG337 exert synergistic activity in both ovarian and colon cancer cells. Interestingly, this synergism was maintained in 5-FU- and cisplatin-resistant cells. Therefore, our data encourage further examination of combinations of AG337 with cisplatin in cancer chemotherapy.
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PMID:Synergy between the non-classical thymidylate synthase inhibitor AG337 (Thymitaq) and cisplatin in human colon and ovarian cancer cells. 894 86

The antiproliferative effect of 5-fluorouracil (5-FU) in colon cancer can be enhanced by interferons (IFN-alpha and IFN-gamma). The mechanisms by which IFNs modulate 5-FU activity are not completely elucidated. IFN-alpha may elevate the levels of the active 5-FU metabolite 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) in the cell, possibly leading to increased inhibition of the target enzyme thymidylate synthase (TS), which might enhance DNA damage. It has been shown that IFN-gamma can prevent 5-FU induced overexpression of TS. We studied IFN modulation in three colon cancer cell lines (SW948, WiDr, human; C26-10, murine) and the sublines WiDr/F and C26-10/F, which were adapted to low folate levels. A 1.5-fold increase in 5-FU sensitivity was observed in C26-10 and C26-10/F (by murine IFN-alpha, beta); in SW948, WiDr and WiDr/F (by human IFN-gamma) and in SW948 and WiDr/ F (by human IFN-alpha). In none of the cell lines did human IFN-alpha, IFN-gamma or murine IFN-alpha, beta increase FdUMP levels after exposure to 5-FU. TS activity, indirectly measured by incorporation of [6-3H]-deoxyuridine into DNA, was inhibited by 5-FU, but the IFNs did not enhance inhibition. DNA damage was measured as a drug-induced decrease of double-stranded (dss) DNA compared to control cells. After 5-FU exposure, dss DNA decreased to 60-75% in WiDr, WiDr/F and SW948 cells. Human IFN-alpha alone caused minimal DNA damage (95% dss DNA), but increased 5-FU-induced effects to 35-50% dss DNA. IFN-gamma did not cause DNA damage and did not enhance 5-FU-mediated DNA damage. Expression of TS protein, analysed by ELISA, was increased after 5-FU exposure of SW948 cells, but this increase was not affected by addition of either IFN-alpha or IFN-gamma. It is concluded that one of the mechanisms involved in modulation of 5-FU activity is the effect of IFN-alpha on 5-FU-mediated DNA damage, but for IFN-gamma no mechanism of action was found.
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PMID:Biochemical mechanisms of interferon modulation of 5-fluorouracil activity in colon cancer cells. 915 34

Advanced colorectal cancer is generally refractory to 5-fluorouracil (5-FU) chemotherapy. This is linked to the emergence of resistant cell populations, probably due to a selection process. The identification of molecular markers and the improvement of alternative therapies thus remain important. We have used as an experimental model a rat colon cancer cell line (PROb), which exhibits features similar to those of the human situation. 5-FU treatment of rats bearing PROb tumors enhanced their survival but did not lead to cure. A PROb 5-FU-resistant subline (PRObR1) was obtained by continuous in vitro exposure to 5-FU. Resistance to 5-FU was accompanied by a 2-fold increase in thymidylate synthase activity and a substantially higher incorporation of thymidine in the presence of 5-FU, compared with parental PROb cells. Unexpectedly, in syngeneic rats, PRObR1 tumors exhibited delayed growth when compared with parental PROb tumors. This was ascribed to an increased sensitivity of PRObR1 cells to host immune response since no growth delay was observed in immunocompromised nude mice and since there was no detectable difference in proliferation rates between PROb and PRObR1 cells. 5-FU treatment was inefficient in prolonging the survival of rats bearing PRObR1 tumors. In contrast, an immunotherapeutic protocol combining sodium butyrate and recombinant interleukin-2 (NaBut/rIL-2) cured 80% of the rats bearing established PRObR1 tumors. Our results suggest that NaBut/rIL-2 treatment is efficient against 5-FU-chemoresistant rat colon cancer.
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PMID:5-Fluorouracil-resistant colonic tumors are highly responsive to sodium butyrate/interleukin-2 bitherapy in rats. 939 77

Because interferons (IFN)-alpha and -gamma individually have increased fluorouracil (FUra) cytotoxicity in several in vitro models, we studied the effects of FUra combined with IFN-alpha + gamma in HT29 colon cancer cells. A 96-hr exposure to IFN-alpha (500 units/ml) plus IFN-gamma (10 units/ml) and a 72-hr exposure to 0. 25-1 microM FUra (hr 24-96) inhibited cell growth and colony formation in an additive or more-than-additive fashion. When cells were exposed to IFN-alpha + gamma and FUra, free FdUMP levels became detectable, whereas [3H]FUra-RNA incorporation decreased. Exposure to IFN-alpha + gamma, FUra, or the combination decreased dTTP pools to 58%, 43%, and 17% of control, respectively. A marked increase in the dATP to dTTP ratio was seen with FUra with or without IFN-alpha + gamma. Thymidylate synthase catalytic activity was reduced to 28% and 24% of control with FUra with or without IFN-alpha + gamma, suggesting that the enhanced dTTP depletion must be due to another mechanism. FUra-mediated thymidylate synthase inhibition was accompanied by a 124-fold increase in total deoxyuridylate immunoreactivity and a 31-fold increase in dUTP pools, but the addition of IFN-alpha + gamma attenuated the accumulation. Treatment with IFN-alpha + gamma and FUra individually interfered with nascent DNA chain elongation, whereas the three-drug combination produced the most striking effects. IFN-alpha + gamma plus FUra produced the greatest amount of single-strand breaks in nascent DNA and dramatically decreased net DNA synthesis. IFN-alpha + gamma with or without FUra produced double-strand breaks in parental DNA. These results suggest that dTTP depletion, dATP/dTTP imbalance, pronounced inhibition of DNA synthesis, and damage to nascent and parental DNA contribute to the enhanced cytotoxicity with the triple combination.
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PMID:Modulation of fluorouracil cytotoxicity by interferon-alpha and -gamma. 946 83

After many years, during which the assumption prevailed that adjuvant chemotherapy was of no benefit in patients with resectable adenocarcinoma of the colon, findings of several large USA studies published from the late 1980s have caused a marked shift in surgical and medical opinion. Although results in patients with Dukes' B disease have not shown any clear benefit, the efficacy of adjuvant chemotherapy has nevertheless been shown in those with Dukes' C colon cancer. As a result, the Mayo regimen of 5-fluorouracil (5-FU) with low-dose leucovorin (LV) has become accepted as standard adjuvant therapy in these patients. However, the disadvantages associated with standard 5-FU-based treatment, particularly those relating to its toxicity and inconvenience of administration, have generated interest in other regimens and agents. The novel direct and specific thymidylate synthase inhibitor raltitrexed ('Tomudex') has been associated with similar objective response rates to standard therapy with 5-FU plus LV in patients with advanced colorectal cancer. In addition, raltitrexed has an attractive tolerability profile compared with that of 5-FU plus LV (specifically with respect to lower incidences of mucositis and leucopenia), and the simple 3-weekly administration schedule may be considered more convenient by many patients and may reduce healthcare resource consumption. To investigate alternatives to the Mayo regimen in the adjuvant treatment of Dukes' C adenocarcinoma of the colon, two large European trials have been set up: (1) PETACC-1 (first Pan-European Trial for Adjuvant Treatment of Colon Cancer), to compare raltitrexed with the Mayo regimen of 5-FU and low-dose LV; (2) PETACC-2 (second Pan-European Trial), to compare the Mayo regimen with three regimens in which 5-FU is given by prolonged infusion. These trials will provide valuable international data to add to those from the USA and will assess the place of raltitrexed in the adjuvant treatment of Dukes' C colon cancer. They will also compare directly for the first time infusional and bolus 5-FU regimens in the adjuvant setting.
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PMID:The establishment of a large collaborative trial programme in the adjuvant treatment of colon cancer. 957 52

A 5-fluorouracil (5-FU)-resistant subline of human colon cancer HT-29 cells was developed by repeated 1-h exposure in vitro to 5-FU. This subline (HT-29/5-FU/S) had 8-fold resistance to 5-FU in a 1-h exposure assay. However, it had rather increased sensitivity to 5-FU when assayed after a continuous 96-h exposure to it. Significantly less 5-fluorouridine-5'-triphosphate was produced in the resistant cells, leading to a lower level of 5-FU incorporation into the cellular RNA. The reduced activity of orotate phosphoribosyltransferase might explain these results. In contrast, the HT-29/5-FU/S cells were more sensitive to the inhibition of in situ thymidylate synthase (TS) by 5-FU than were the parent cells. The lower in situ TS activity may have made HT-29/5-FU/S cells more sensitive to TS inhibition by 5-FU as compared with the parent cells. The fact that HT-29/5-FU/S was more resistant to short-term 5-FU exposure but more sensitive to long-term exposure than the parent line confirmed the existence of different modes of action of 5-FU, depending on the exposure time.
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PMID:Increased sensitivity to long-term 5-fluorouracil exposure of human colon cancer HT-29 cells resistant to short-term exposure. 960 Jan 27


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