5-Fluorouracil induced Fas upregulation associated with apoptosis in liver metastases of colorectal cancer patients

BACKGROUND

In vitro, thymidylate synthase (TS) inhibition by 5-fluorouracil (5-FU) induces thymineless apoptosis possibly via Fas receptor Fas ligand interactions and cell-cycle arrest. In colorectal cancer patients we evaluated whether 5-FU administration also resulted in apoptosis and cell-cycle arrest and which proteins might be involved.

PATIENTS AND METHODS

Biopsy specimens were taken from 36 patients 2, 22 or 46 hours after administration of 500 mg/m2 5-FU, and from 12 control patients who did not receive 5-FU. In frozen tissue-sections from liver metastases immunohistochemistry was performed with antibodies directed against p53, p21, E2F2, Rb, Ki67 and TS (cell-cycle related) and bax, BCL-2, BCL-x, mcl-1, PARP, caspase-3, Fas receptor and Fas ligand (apoptosis related). Apoptosis was determined by M30 immunostaining, which recognises a cleavage product of cytokeratin 18.

RESULTS

Fas receptor expression was 50% higher (P = 0.036) 46 hours after 5-FU administration compared to the control group. This was associated with a 12% increase (P < 0.02) in M30 positive tumour cells and with elevation of caspase-3 and PARP expression. The expression of Ki67 and E2F2 was 30% lower after 46 hours compared to the control group, whereas TS was 56% lower after 2 hours and 32% higher again after 46 hours. No differences in the expression of the other proteins were found.

CONCLUSIONS

These results suggest that 5-FU decreases proliferation status and induces apoptosis possibly via the Fas pathway. Since Fas mediated cell killing is important for cytotoxic T cells this indicates that clinical studies combining immunotherapy for activation of T cells and chemotherapy using 5-FU might be very effective.

Schedule-dependent pharmacodynamic effects of gemcitabine and cisplatin in mice bearing Lewis lung murine non-small cell lung tumours

The combination of 2',2'-difluorodeoxycytidine (gemcitabine, dFdC) and cis-diammine-dichloroplatinum(II) (cisplatin, CDDP) is increasingly applied in clinical oncology. We studied the underlying mechanisms of the in vivo schedule dependency and supraadditive interaction between dFdC and CDDP in C57/B16 mice bearing Lewis lung (LL) tumours. Mice were treated with CDDP (6 mg/kg) and dFdC (60 mg/kg) either simultaneously or in a 4 or 24 h interval with dFdC preceding CDDP or vice versa. Four, 8 (in some cases 12) and 24 h after treatment mice were sacrificed and tumours, kidneys, blood and bone marrow (BM) were collected. Since CDDP acts by formation of Platinum (Pt)-DNA adducts and dFdC by incorporation of its triphosphate (dFdCTP) into DNA, we measured total Pt levels, dFdCTP accumulation and Pt-DNA adducts by atomic absorption spectrometry (AAS), high performance liquid chromatography (HPLC) and 2P-postlabelling, respectively. These levels were related to the previously determined antitumour efficacy and toxicity of the dFdC/CDDP combination. Peak dFdCTP accumulation in tumours (11 pmol/mg) was found 4 h after dFdC treatment, while CDDP tended to reduce this in a time-dependent way. Peak levels of total Pt in tumours were found 4 h after CDDP treatment (581 fmol/mg) and dropped 1.8-fold after simultaneous treatment with dFdC (P = 0.04). Treatment with dFdC 4 h after or simultaneously with CDDP increased Pt retention (level 24 h after CDDP treatment) 1.4- and 1.6-fold (P = 0.04 and P = 0.03, respectively). Peak Pt-DNA adduct levels in tumours were also found 4 h after CDDP treatment (7 fmol/microg DNA) and were decreased 3-fold by dFdC treatment 24 h prior to CDDP (P = 0.04). Pt-DNA adduct retention was only decreased when dFdC was given 4 h before CDDP (8-fold (P < 0.01)). The retention and the area-under the concentration time curve of Pt-DNA adducts were related to decreased tumour doubling time (linear regression coefficient (R) = 0.95; P < 0.05, 0.96 P = 0.04 and 0.90; P = 0.04. Pt-DNA adduct levels in the BM cells reached a plateau level 4-24 h after CDDP treatment (approximately 10 fmol/microg DNA), which was increased by dFdC when given either simultaneously with, 4 h before or 4 h after CDDP (6-, 3- and 5-fold at 28 h, 8 h and 28 h, respectively (P < or = 0.04)). Peak Pt-DNA adduct formation (24 h: 8 fmol/microg DNA) in kidneys was enhanced by dFdC when given simultaneously with or 4 h before CDDP (4 h timepoint) (P < 0.01). However, retention was 4- and 6-fold decreased when dFdC was given 4 or 24 h after CDDP, respectively (P < or = 0.01). dFdC given 24 h before CDDP decreased all Pt-DNA adduct levels in kidneys 3-fold or more (P < or = 0.03). Pt-DNA adduct levels were inversely related to kidney toxicity when the most toxic schedule was excluded from the analysis. Peak levels of total Pt in kidneys were reached 24 h after CDDP treatment (4.3 fmol/mg) and the 8 h levels were increased 2-fold by dFdC when given 4 h after CDDP (P = 0.07).

The ribonucleotide reductase inhibitor trimidox induces c-myc and apoptosis of human ovarian carcinoma cells

Trimidox (3,4,5-trihydroxybenzohydroxamidoxime), a recently synthesized inhibitor of ribonucleotide reductase (RR), was shown to exert anti-proliferative activities in HL-60 and K562 human leukemia cell lines and to prolong the life span of mice inoculated with L1210 mouse leukemia cells. Here we test whether trimidox also exhibits anti-neoplastic properties in ovarian carcinoma cells. Since the mode of action of trimidox on cell fate has not been investigated so far, we addressed this unresolved item and find that this polyhydroxybenzoic acid derivative induces apoptosis of N.1 human ovarian carcinoma cells when tested in growth factor deprived medium. Utilizing an improved analysis, based on Hoechst 33258/propidium iodide double staining, apoptosis is quantified and discriminated from necrosis. Trimidox induces c-myc expression, which is indispensible for apoptosis of N.1 cells, and expression of plasminogen activator/urokinase type (upa), which supports the apoptotic process under more physiological conditions. Surprisingly, trimidox does not block dNTP synthesis in N.1 cells at the concentrations tested and, therefore, trimidox induces apoptosis independent of RR-inhibition. Like TNFalpha or benzamide riboside, which are also inducers of apoptosis of N.1 cells, trimidox also down-regulates the G1 cell cycle phosphatase cdc25A, whereas cyclin D1 becomes up-regulated. This report shows that trimidox destroys human ovarian carcinoma cells by inducing them to undergo apoptosis as well as corroborating previous investigations which demonstrated that apoptosis of these cells depends on c-myc over-expression when survival factors are withdrawn.

The multilayered postconfluent cell culture as a model for drug screening

New drug development requires simple in vitro models that resemble the in vivo situation more in order to select active drugs against solid tumours and to decrease the use of experimental animals. In this paper, we review the characteristics and scope of a relatively simple cell-culture system with a three-dimensional organisation pattern - the multilayered postconfluent cell culture model. Solid tumour cell lines from diverse origins when grown in V-bottomed microtiter plates reach confluence in 3-5 days and then start to form multilayers. The initial exponential growth of the culture is followed by a plateau phase when cells reach confluence. This produces changes in the morphology of the cells. For some cell lines, it is possible to observe cell differentiation. A substantial advantage of the system is the use of the sulforodamine B (SRB) assay to determine relative cell growth or viability, which allows semiautomation of the experiments. Several experiments were performed to assess the differences and similarities between cells cultured as monolayers and multilayers, and eventually, compared with the results for solid tumours and some other models such as spheroids. Cell-cycle analysis for multilayers showed a lower S-phase arrest, which is accompanied by a decrease in the expression of cell-cycle-related proteins and a decrease in cellular nucleotide pools. Gene and protein expression of topoisomerase I, topoisomerase II and thymidylate synthase expression were lower for multilayers, but no substantial changes were observed for the expression of DT-diaphorase. P53 expression increased. Multilayer cultures present distinctive properties for drug transport across the membrane, drug accumulation and retention. In fact, the transport of antifolates across the membrane, accumulation of topotecan and gemcitabine-triphosphate are reduced in multilayers when compared with monolayers, which may be related to a decrease in drug penetration to the inner regions of the multilayers. Alteration of these pharmacodynamic parameters is directly related to a decrease in drug activity. The most powerful application of multilayers is in the assessment of cytotoxicity. Solid tumour cell lines from different origins have been treated with several conventional and investigational anticancer drugs. The data show that multilayers are more resistant to the drugs than the corresponding monolayers, but there are substantial differences between the drugs depending on culture conditions, e.g. the difference was rather small for a drug such as cisplatin, miltefosine and EO9, a drug, which is activated under hypoxic conditions. Gemcitabine was active against ovarian cancer but not against colon cancer, resembling the in vivo situation. This observation was not evident with monolayer experiments. Another interesting application is the possibility to perform drug combination studies. The combination of gemcitabine and cisplatin proved to produce selective cell kill in H322 cells (non-small cell lung cancer cell line). Neither of the drugs was independently able to produce similar effects. In summary, multilayer cultures are relatively simple three-dimensional systems to study the effect of microenvironmental conditions on anticancer drug activity. The model might serve as a base for a more rigorous secondary in vitro screening.

Prognostic role of thymidylate synthase, thymidine phosphorylase/platelet-derived endothelial cell growth factor, and proliferation markers in colorectal cancer

5-Fluorouracil (5FU)-based therapy is given to patients with advanced colorectal cancer and as adjuvant treatment. Thymidylate synthase (TS) is the target for 5FU, and may have a prognostic role for the outcome of 5FU-based therapy together with proliferation markers such as p53 and Ki67. Thymidine phosphorylase (TP, also known as platelet-derived endothelial cell growth factor) may be of importance both in the 5FU drug activation pathway and in tumor angiogenesis, similar to vascular endothelial growth factor (VEGF). TS and TP levels were determined biochemically in fresh-frozen tumor specimens of 32 untreated patients with colorectal cancer, whereas in paraffin-embedded tissue samples, immunohistochemistry was performed for TS, TP, and additional prognostic markers such as p53, Ki67, and VEGF as well as microvessel density. All factors were correlated with patient characteristics such as age, gender, Dukes' stage, angio-invasion, and differentiation grade. TS and TP as measured by various assays were correlated with overall and disease-free survival in this patient group. TP enzyme activity and protein expression correlated with each other. A significant correlation was found between TP enzyme activity and 5-fluoro-2'-deoxyuridine-5'-monophosphate binding activity. VEGF expression correlated significantly with TP immunostaining and Ki67 index. Survival analysis revealed a significant relation of TS levels to the overall survival in this small patient group and a significant correlation between TP activity and disease-free survival. TS and TP both were of prognostic significance in these patients with colorectal cancer. The interesting relationship of TS and TP with angiogenesis and proliferation needs further investigation.

Determinants of activity of the antifolate thymidylate synthase inhibitors Tomudex (ZD1694) and GW1843U89 against mono- and multilayered colon cancer cell lines under folate-restricted conditions

The cytotoxicity and metabolic effects of two thymidylate synthase (TS) inhibitors, Tomudex (Raltitrexed, ZD1694) and GW1843U89, were studied in WiDr colon cancer cells under four different growth conditions: as standard monolayers and as postconfluent multilayers grown under either high (WiDr, 8.8 microM folic acid) or low (WiDr/F, 1 nM leucovorin) folate conditions. Both GW1843U89 and ZD1694 were 13-15-fold more active against WiDr/F than WiDr cells when cultured as monolayers (IC50s in WiDr/F cells were 0.22 and 0.39 nM, respectively). WiDr cells were markedly less sensitive to the drugs when grown as multilayers (4-15-fold), in contrast to the WiDr/F cells, which were equally sensitive. However, total growth inhibition could not be achieved in WiDr multilayers (concentration causing total growth inhibition > 10,000 nM), whereas in WiDr/F multilayers, it could be achieved at 0.42 nM ZD1694 and 150 nM GW1843U89. Growth conditions markedly affected the TS levels when using different enzyme assays. At nonsaturating substrate concentrations, the catalytic activity of TS was similar in mono- and multilayers grown under high folate conditions but lower in multilayers at saturating concentrations. In cells grown under low folate conditions, TS catalytic activity was 3-6-fold lower in multilayers than in monolayers. This was consistent with a decrease in the number of S-phase cells in multilayers. Western blotting revealed less pronounced (2-3-fold) differences in the TS protein content. Exposure of the cells for 24 h to the drugs increased the TS levels by 4-fold. Because this increase in TS levels might explain the decrease in sensitivity to the TS inhibitors, we measured TS inhibition (TSI) by the drugs in intact cells using the TS in situ assay. GW1843U89 was more active than ZD1694. However, after 4 h of exposure in WiDr/F mono- and multilayers, TSI was in the same range for both drugs [50% TSI (TSI50), 0.5-1.7 nM]. In WiDr cells, the TSI50 for ZD1694, but not GW1843U89, was 10 times higher in the multilayers as compared to the monolayers. Despite the increase in TS protein levels, the extent of TSI was similar or even more pronounced in both cell lines grown as either multi- or monolayers. Because the cells were grown under depleted and folate-rich conditions that may affect folate uptake, we measured folate transport using methotrexate (MTX) as the reference drug for the activity of the reduced folate carrier. MTX uptake was 4-fold lower in multilayers compared to monolayers in both WiDr and WiDr/F cells. Uptake of MTX was 5-fold more effective in WiDr/F cells than in WiDr cells in both mono-and multilayers. In conclusion, the resistance of WiDr multilayers to the novel antifolates ZD1694 and GW1843U89 may be due to the high folate medium concentrations, which may be responsible for impaired drug uptake along with less effective TSI. In contrast, WiDr/F monolayers and multilayers were very sensitive to these antifolates. These effects of folate homeostasis may explain some of the variable results seen in treatment of solid tumors with new antifolate TS inhibitors.

Cell specific cytotoxicity and structure-activity relationship of lipophilic 1-B-D-arabinofuranosylcytosine (ara-C) derivatives

Lipophilic derivatives of ara-C were developed with the aim to improve drug penetration and retention in solid tumors. Ara-C was esterified at the 5'-position with fatty acids (16-22 C-atoms, 0-3 double bonds). The derivatives were inactive in cell lines with various forms of ara-C and 2',2'-difluorodeoxycytidine (dFdC, gemcitabine) resistance, including deoxycytidine kinase (dCK) deficiency. The activity in the parent cell lines correlated negatively with chain length and positively with double bonds.

Thymidylate synthase level as the main predictive parameter for sensitivity to 5-fluorouracil, but not for folate-based thymidylate synthase inhibitors, in 13 nonselected colon cancer cell lines

Thymidylate synthase (TS), a critical enzyme in the de novo synthesis of thymidylate, is an important target for fluoropyrimidines and folate-based TS inhibitors. In a panel of 13 nonselected human colon cancer cell lines, we evaluated the role of TS levels in sensitivity to 5-fluorouracil (5FU) and four folate-based TS inhibitors that have been introduced recently into the clinic: ZD1694 (Tomudex, Raltitrexed, TDX), GW1843U89 (GW), LY231514 (LY), and AG337 (Thymitaq, AG). Because the latter compounds have different transport and polyglutamylation characteristics, we also related these parameters with drug sensitivity, measured by the sulforhodamine B assay after 72 h of drug exposure. For 5FU, the IC50s varied from 0.8 to 43.0 microM. Leucovorin (LV) potentiated the activity of 5FU in only 4 of 13 cell lines. Sensitivity to folate-based TS inhibitors was variable; IC50s were in the range of: 5.3-59.0 nM TDX; 11.0-1570 nM LY; and 0.5-8.9 nM GW. Eleven of 13 cell lines had an IC50 for AG between 1.3 and 5.3 microM. Two cell lines were resistant to AG, Colo201 and SW1116, with IC50s of 27 and 29 microM, respectively. TS catalytic activity (conversion of dUMP to dTMP) varied from 62 to 777 pmol/h/10(6) cells. The number of FdUMP binding sites varied from 32 to 231 fmol/10(6) cells. Regression analysis showed a significant relation between TS catalytic activity and IC50s for 5FU and 5FU/LV. Kis for FdUMP showed a significant Spearman rank correlation with the IC50s of AG and GW. The role of antifolate transport, accumulation, and polyglutamylation was determined with [3H]methotrexate (MTX) as a reference compound. [3H]MTX influx via the reduced folate carrier varied from 18.6 to 150 fmol/10(6) cells/min. Folylpolyglutamate synthetase (FPGS) activity showed a range from 47 to 429 pmol/10(6) cells/h. A total of 24 h of [3H]MTX accumulation showed a 20-fold variation, from 1.2 to 21.8 pmol/10(6) cells. FPGS levels showed a Spearman rank positive correlation with cytotoxicity to TDX. In conclusion, in a heterogeneous nonselected human colon cancer cell line panel, the best predictor for sensitivity to 5FU and 5FU/LV was TS activity. Multiple sensitivity determinants were of importance for antifolate TS inhibitors, including FPGS activity and TS enzyme kinetics.

Combination chemotherapy studies with gemcitabine and etoposide in non-small cell lung and ovarian cancer cell lines

Gemcitabine (2',2'-difluorodeoxycytidine, dFdC) and etoposide (4'-demethylepipodo-phyllo-toxin-9-4,6-O-ethylidene-beta-D-g lucopyranoside, VP-16) are antineoplastic agents with clinical activity against various types of solid tumors. Because of the low toxicity profile of dFdC and the differences in mechanisms of cytotoxicity, combinations of both drugs were studied in vitro. For this purpose, we used the human ovarian cancer cell line A2780, its cis-diammine-dichloroplatinum-resistant and VP-16 cross-resistant variant ADDP, and two non-small cell lung cancer cell lines, Lewis Lung (LL, murine) and H322 (human). The interaction between the drugs was determined with the multiple drug effect analysis (fixed molar ratio) and with a variable drug ratio. In the LL cell line, the combination of dFdC and VP-16 at a constant molar ratio (dFdC:VP-16 = 1:4 or 1:0.125 after 4- or 24-hr exposure, respectively) was synergistic (combination index [CI], calculated at 50% growth inhibition = 0.7 and 0.8, respectively; CI <1 indicating synergism). After 24- and 72-hr exposure to both drugs at a constant ratio, additivity was found in the A2780, ADDP, and H322 cell lines (dFdC:VP-16 = 1:500 for both exposure times in these cell lines). When cells were exposed to a combination of dFdC and VP-16 for 24 or 72 hr, with VP-16 at its IC25 and dFdC in a concentration range, additivity was found in both the LL and H322 cells; synergism was observed in the A2780 and ADDP cells, which are the least sensitive to VP-16. Schedule dependency was found in the LL cell line; when cells were exposed to dFdC 4 hr prior to VP-16 (constant molar ratio, total exposure 24 hr), synergism was found (CI = 0.5), whereas additivity was found when cells were exposed to VP-16 prior to dFdC (CI = 1.6). The mechanism of interaction between the drugs was studied in more detail in the LL cell line; dFdCTP accumulation was 1.2-fold enhanced by co-incubation with VP-16, and was even more pronounced (1.4-fold) when cells were exposed to VP-16 prior to dFdC. dCTP levels were decreased by VP-16 alone as well as by the combination of both compounds, which may favor phosphorylation of dFdC, thereby increasing dFdCTP accumulation. DNA strand break (DSB) formation was increased for exposure to both compounds together compared to exposure to each compound separately, this effect being most pronounced when cells were exposed to VP-16 prior to dFdC (38% and 0% DSB for dFdC and VP-16 alone, respectively and 97% DSB for the combination). The potentiation in DSB formation might be a result of the inhibition of DNA repair by dFdC. Provided the right schedule is used, VP-16 is certainly a compound eligible for combination with dFdC.

5-fluorouracil/leucovorin-induced inhibition of thymidylate synthase in normal tissues of mouse and man

We evaluated the effects of 5-fluorouracil (5FU) and leucovorin (LV) on thymidylate synthase (TS) in normal rapidly dividing tissues, which may contribute to toxic side-effects of treatment with 5FU and LV. TS levels were determined in biopsies of human liver and colon mucosa and murine bone marrow, liver and intestinal mucosa at several time points after administration of therapeutic doses of 5FU or LV/5FU. In murine liver, after treatment with 100 mg/kg 5FU, TS inhibition was significantly higher than after LV/5FU administration (P < 0.001). A similar trend was observed in human liver tissue. Murine intestinal mucosa had TS levels below the limit of detection after 5FU or LV/5FU treatment. In human colon mucosa samples, administration of 500 mg/m2 5FU resulted in a large extent of TS inhibition but the small number of samples did not allow a time- or 5FU-LV/5FU-related evaluation. TS activity in murine bone marrow cells was strongly inhibited to 10% of the control value during 48 h. LV/5FU administration resulted in a slightly higher inhibition. No human bone marrow was available to measure TS levels. Both in mice and humans the most pronounced TS inhibition occurred in the tissue that was involved in dose-limiting toxicity. Therefore it is very likely that TS inhibition in normal tissues contributes to the toxic side-effects of 5FU treatment.

Similar changes were induced by Cladribine and by gemcitabine, in the deoxypyrimidine salvage, during short-term treatments

Short term treatments (1-2 hrs) of human tonsillar lymphocytes by Cladribine (2-Chloro-deoxyadenosine, CdA) have suggested a new target for CdA, the inhibition of dCMP deaminase (Sasvári et al. 1994; BBRC 203, 1378). Further investigations have shown, that the dCMP-deaminase activity could be inhibited by 2-Cl-dAMP in cell free extracts of lymphocytes. The pool size of dUMP (measured by an antibody against dUMP) was also decreased in WiDr colon cancer cells by CdA. The new antimetabolite against solid tumours, Gemcitabine (2',2'-difluoro-deoxycytidine, dFdC), had similar effects on the salvage of thymidine (dThd) and deoxycytidine (dCyd) as CdA. The Ki values for 3H-dThd and 3H-dCyd incorporation into DNA were 0.16 uM and 1.0 uM dFdC, respectively. The labeling of the TTP pool increased 6-7 times, while of dCTP pool only 1.5-1.7 times, suggesting a decrease of the size of corresponding pools. Similarly to CdA, the labeling as well as the concentration of dUMP was also decreased by dFdC. Both analogues are able to increase the deoxycytidine kinase activity, necessary for their phosphorylation and therapeutic action in cells. The target(s) for the two different drugs seems to be common.

Biochemical mechanisms of interferon modulation of 5-fluorouracil activity in colon cancer cells

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.

Tumor size and origin determine the antitumor activity of cisplatin or 5-fluorouracil and its modulation by leucovorin in murine colon carcinomas

5-Fluorouracil (FUra) is one of the few effective agents in the treatment of patients with colorectal cancer. Its effects on the target enzyme thymidylate synthase (TS) can be modulated by leucovorin (LV) or cisplatin (CDDP). Tumor size and differentiation of tumor characteristics can influence therapeutic efficacy. We therefore studied the relationship between tumor size (cutoff point 200 mm3) and the antitumor activity of FUra and its modulation by LV in murine Colon 26 and Colon 38 tumors. The doubling time of tumors measuring > 200 mm3 was about 160% longer. The antitumor effect of FUra in these large tumors was decreased and could not be modulated by LV. In addition, three subtypes of Colon 26 (Colon 26-A, Colon 26-B, and Colon 26-10) were identified and characterized for tumor-induced weight loss, TS activity, response to chemotherapy, and histological features. Mice bearing Colon 38 and Colon 26-10 did not lose weight as a result of tumor growth. Colon 26-A caused a weight loss of up to 19%, whereas mice with Colon 26-B tumors remained within 10% of their initial weight and tolerated at least 2.5 times more tumor load than did mice bearing Colon 26-A, which induces cachexia. Among untreated tumors, TS catalytic activity was highest in Colon 26-B (5536 pmol mg protein(-1) h(-1)) and lowest in Colon 38 (799 pmol mg protein(-1) h(-1)); Colon 26-A and Colon 26-10 had intermediate activities (about 2500 pmol mg protein(-1) h(-1)). 5-Fluoro-2'-deoxyuridine monophosphate (FdUMP) binding was comparable in the three Colon 26 subtypes but was lower in Colon 38. The antitumor activity of FUra could be modulated by LV in Colon 38, Colon 26-10, and Colon 26-A but could not in Colon 26-B, with complete responses (CR) being obtained in Colon 26-10 and Colon 38. The latter two were highly sensitive to CDDP, followed by Colon 26-A and Colon 26-B (CRs: 50%, 40%, 25%, and 0, respectively). Furthermore, necrosis was noted in Colon 26-B and Colon 38 but not in Colon 26-A. In conclusion, (1) the antitumor activity of FUra in large tumors is decreased and cannot be modulated by LV and (2) characteristics and sensitivity to chemotherapeutics can vary substantially in closely related tumors of the same origin.

Therapeutic efficacy of fluoropyrimidines depends on the duration of thymidylate synthase inhibition in the murine colon 26-B carcinoma tumor model

5-Fluorouracil (FUra) and 5-fluoro-2'-deoxyuridine (FdUrd) are common chemotherapeutic drugs for the treatment of advanced colorectal cancer. Two recognized mechanisms of action of these agents are inhibition of thymidylate synthase (TS) and incorporation of fluorinated UTP into cellular RNA. In previous studies on drug scheduling of both fluoropyrimidines, we observed the highest therapeutic efficacy by using a weekly i.v. push schedule. Furthermore, weekly 400-mg/kg FdUrd is superior to equitoxic weekly 80-mg/kg FUra in murine Colon 26-B carcinoma. We evaluated the most important pharmacokinetic and pharmacodynamic effects of both fluoropyrimidines to delineate the biochemical mechanisms underlying their differences in therapeutic activity in this tumor model. FUra concentrations and elimination in tumors after FdUrd or FUra administration were comparable, and the level of FUra incorporation into cellular RNA following treatment with FUra or FdUrd was similar. Free tumoral 5-fluoro-dUMP levels were initially 3-fold higher after FdUrd but diminished rapidly thereafter. The number of free [3H]5-fluoro-dUMP-binding sites decreased to about 25 and 15% of control values within 2 h after treatment with equitoxic doses of FUra and FdUrd and remained low for 72 h. The duration of TS inhibition was significantly longer following treatment with FdUrd compared with FUra, 168 and 72 h, respectively. The superiority of the antitumor activity of an i.v. push of FdUrd over FUra in the treatment of Colon 26-B tumors correlates with maintenance of TS inhibition and repeated drug administration when TS remains low, whereas FUra incorporation into RNA does not appear to distinguish the antitumor response of FdUrd from that of FUra in this tumor model.

Addition of leucovorin in modulation of 5-fluorouracil with methotrexate: potentiating or reversing effect?

Potentiation of the anti-tumor activity of 5-fluorouracil (5FU) by methotrexate (MTX) and leucovorin (LV) requires careful scheduling to achieve the most favorable interactions between these 3 drugs. In vitro the triple combination of MTX/5FU/LV was tested at 4 time intervals and with 3 MTX concentrations in 3 cell lines. MTX/5FU/LV was never superior to both 5FU/LV and MTX/5FU, moreover LV reduced growth inhibition by MTX/5FU in 2 cell lines. MTX/5FU was associated with only moderately increased levels of the 5FU metabolite FdUMP, while LV/5FU reduced the free FdUMP levels. MTX/LV/5FU had a dual effect and FdUMP levels gave no clear indication regarding the anti-proliferative effect that could be expected. In vivo the time-dependent potentiation of MTX on the 5FU anti-tumor activity was confirmed for the treatment of HNX-14C-bearing mice. Addition of LV to the MTX/5FU combination failed to cause a gain in anti-tumor efficacy. For the treatment of Colon-26-bearing mice, MTX/5FU was comparable to LV/5FU, but the triple combination of MTX/LV/5FU seemed to have a better anti-tumor effect. However, the toxicity of the latter treatment was greater than that of LV/5FU. The data from both in vitro and in vivo experiments failed to support the addition of LV to MTX/5FU therapy, possibly due to a reversing effect of LV.

The effect of different routes of administration of 5-fluorouracil on thymidylate synthase inhibition in the rat

A rat colon tumour model of liver metastases was used to administer 5-fluorouracil (5FU) by intraperitoneal (i.p.) bolus injection (50 mg/kg), isolated liver perfusion (ILP, 150 mg/kg) and hepatic artery infusion (HAI, 50 mg/kg). The biochemical effect of 5FU, delivered by different routes, on its target enzyme thymidylate synthase (TS) was studied in both tumour and normal tissues of the rat. In tumour tissue, only small differences were observed in the extent of TS inhibition. A pronounced inhibition of TS was observed 3 h after 5FU administration by all routes, but was followed by a recovery of TS activity within 24 and 48 h. Effects of 5FU on normal tissues were diverse. In liver, TS activity increased 6-fold after ILP and HAI administration of 5FU, and a 2-fold increase of FdUMP binding to TS was seen for all routes of administration. In intestinal mucosa, both induction of TS activity (by ILP) and inhibition of TS activity (by HAI) were observed, while i.p. injection did not cause major changes. TS activity and FdUMP binding to TS in bone marrow was strongly inhibited after administration of 5FU by all routes, but administration by ILP seemed slightly advantageous, since a smaller extent of TS inhibition was observed compared to the other routes of administration. 5FU given by ILP had a small antitumour effect in this colon tumour model, while HAI administration had no antitumour activity. Since this difference in antitumour activity could not be related to differences in TS inhibition in the tumour, the RNA-directed mechanism of action of 5FU could be involved. Focusing on the effects of TS, we may conclude that the ILP administration of 5FU offered the important advantage of a lack of severe TS inhibition in normal tissues, which corresponds with the low systemic toxicity observed.

Thymidylate synthase inhibition after administration of fluorouracil with or without leucovorin in colon cancer patients: implications for treatment with fluorouracil

PURPOSE

To determine the time-dependence of fluorouracil (5FU)-induced thymidylate synthase (TS) inhibition in colon cancer patients, the effect of leucovorin (LV), and the relation to response.

PATIENTS AND METHODS

A 5FU injection (500 mg/m2) was given to 47 patients with advanced colorectal cancer; tumor biopsy specimens were obtained 1 to 72 hours after laparotomy. Eleven patients received LV (2-hour infusion of 500 mg/m2) with 5FU midinfusion; biopsies were obtained after 45 hours. TS inhibition was evaluated by comparing the number of total and free 5-fluoro-2'-deoxy-uridine-5'- monophosphate (UMP) (FdUMP) binding sites and the total and residual catalytic activity of TS.

RESULTS

The total catalytic TS activity varied from 0 to 621 pmol/h/mg protein and the total number of FdUMP binding sites varied from 0 to 976 fmol/mg protein. The residual catalytic TS activity after 2, 23, and 45 hours was 41%, 65%, and 74% of the total catalytic activity; the number of free FdUMP binding sites was 12%, 27%, and 49% of the total number, respectively. LV enhanced TS inhibition after 45 hours; the residual catalytic activity decreased from 74% to 49%, and the number of free FdUMP binding sites from 49% to 24%. Eleven of 19 patients treated with hepatic arterial infusion of 5FU had a partial response (PR). In the nonresponding patients, total TS activity was significantly higher (P < .05) than in responding patients. A high TS activity with a poor inhibition correlated with no response.

CONCLUSION

Residual and total TS activity are predictive for response to 5FU. The findings may be applicable for treatment of patients with advanced disease and TS should be evaluated as a prognostic factor in adjuvant chemotherapy studies.

In vitro antitumour activity of cis- and trans-5-fluoro-5,6-dihydro-6-alkoxy-uracils; effects on thymidylate synthesis

A class of new 5-fluorouracil (FU) analogues, the 5-fluoro-5,6-dihydro-6- alkoxy-uracils was synthesised with a modification at the 6-position of the pyrimidine ring. At this position the analogues have a hydroxy or alkoxy group of different chain lengths either in the cis- or trans-configuration. The antiproliferative effect of these compounds was tested on five cell lines of different origin. Generally, the analogues with a cis-configuration had a higher activity than those with a trans-configuration. The growth inhibitory effect of the compounds decreased with increasing alkoxy chain length, but the compound with a hydroxy group had the lowest growth inhibitory effect. One analogue, cis-5-F-5,6-dihydro-6-methoxy-uracil had a higher antiproliferative effect than FU in one of the cell lines. Effects on thymidylate synthase (TS), the possible target of these analogues, were evaluated by thymidine rescue of growth inhibition and incorporation of tritiated deoxyuridine (3H-UdR) into DNA. In solid tumour cell lines addition of TdR reversed the antiproliferative effect. Inhibition of TS in intact cells was determined by measuring 3H-UdR incorporation in two cell lines. The effect of cis-5-F-5,6-dihydro-6-methoxy-uracil on incorporation of 3H-UdR was 2- to 5-fold stronger than that of FU in both cell lines. All other compounds produced a higher 3H-UdR incorporation than FU both at equimolar and equi-toxic concentration. Concluding from these results we regard cis-5-F-5,6-dihydro-6-methoxy-uracil as the most promising FU analogue of this series, because of its higher antiproliferative activity than FU and marked inhibition of TS in intact cells.

Development, characterization and application of an antibody against 5-fluoro-2'deoxyuridine-5'monophosphate, the active metabolite of 5-fluorouracil

5-Fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) is the active metabolite of the anticancer agent 5-fluorouracil (5FU). Antibodies against a conjugate of thyroglobulin with acetylated FdUMP were raised in 4 rabbits. The maximal titer was reached after 3-5 boosters. Subsequently, the antisera were collected and partially purified. In a competition assay a 100-fold excess of the natural nucleotide dUMP could displace tritiated FdUMP (20 pmol per assay) by about 50% in all antisera. However, tritiated dUMP itself did not bind to the antibody. No cross-reactivity was observed with the FdUMP precursor 5FU and with the natural nucleoside uridine and the nucleotides dTMP, dTTP and UTP. A considerable cross-reactivity was observed with the monophosphate of bromodeoxyuridine (Br-dUMP). Radio-immuno assays for FdUMP and dUMP were developed, for which a 100-fold dilution could be used. The FdUMP assay was linear in a range of 0.1 to 5 pmol FdUMP in aqueous solutions. Tumour samples contained a non-identified interfering factor; a similar interference was observed in an enzyme based assay for FdUMP. The dUMP assay was performed by competition of unlabeled dUMP with tritiated FdUMP and was linear from 50 to 2000 pmol dUMP per assay. The antibody recognized FdUMP bound in a ternary complex synthesized in a cell-free system between FdUMP, its target enzyme thymidylate synthase and the folate co-factor. Immunohistochemical staining for demonstration of the ternary complex in 5FU treated cells and tumours from patients and animals was not yet successful, neither with peroxidase nor with immunofluorescence staining. Possibly the amount of bound FdUMP is below the detection limit or FdUMP bound to TS is masked. The antibody may prove to be useful in studies on modulation of FdUMP and dUMP after treatment with thymidylate synthase inhibitors.