Role of genomic factors beyond thymidylate synthase in the prediction of response to 5-fluorouracil

5-Fluorouracil (5FU) is still a major drug in combinations regimens for the treatment of colorectal cancer (CRC) both in the adjuvant and palliative setting. 5FU or its oral prodrug capecitabine is usually combined with irinotecan/oxaliplatin and the novel agents bevacizumab/cetuximab. Although this improved the outcome, the overall prognosis in patients with metastasized disease is still relatively poor. Although the target for 5FU, thymidylate synthase was shown to have a predictive value, this could only predict response in a subset of patients. Given the heterogeneous and complex nature of CRC, it is likely that other aberrations can affect therapeutic response. As an alternative, we investigated Copy number alterations using oligonucleotide-based high-throughput array-comparative-genomic-hybridization (aCGH) to obtain an unbiased screening of the whole genetic spectrum. Chromosomal aberrations have been identified in 85% of CRC patients and include genomic regions harboring copy number alterations in the DNA. These alterations may change the expression of many genes and might explain the differential response to therapy as shown in recent studies with several 5FU combinations. In order to clarify new predictive parameters for 5FU, we used aCGH in a historical cohort of patients, which received treatment with single agent 5FU, and an unsupervised clustering analysis showed a statistical (p < 0.05) difference between responding and nonresponding patients. We also find that several regions showed differences between responders/non-responders, such as losses in 12p12.3-12q15 and in 18p (where TS is located) in responding patients. Genome-wide analysis may provide an additional tool to discriminate between responders and nonresponders.

Biotransformation of 6-thioguanine in inflammatory bowel disease patients: a comparison of oral and intravenous administration of 6-thioguanine

BACKGROUND AND PURPOSE

Although 6-mercaptopurine and azathioprine are effective treatments in inflammatory bowel disease (IBD), many patients discontinue treatment because of side effects. 6-Thioguanine (6-TG) may be an alternative rescue therapy in these intolerant patients but the pharmacokinetics of 6-TG are not fully described. Here we have measured the pharmacokinetics of the biotransformation of 6-TG into the pharmacologically active metabolites, 6-thioguanine nucleotides (6-TGN), in IBD patients.

EXPERIMENTAL APPROACH

In 12 patients with IBD, levels of 6-TGN and activities of thiopurine S-methyltransferase, xanthine oxidase and hypoxanthine guanine-phosphoribosyl-transferase were measured in a two-stage (i.v. and p.o. administration of 0.3 mg·kg(-1) 6-TG), prospective study. Median exposure of 6-TGN in red blood cells (RBC) was expressed as the ratio of the area under the curve (AUC) per mg 6-TG after i.v. dosing and that after p.o. dosing.

KEY RESULTS

The median AUC per mg 6-TG was 1068 (p.o.) and 7184 (i.v.) pmol·h (8 × 10(8) RBC)(-1) . Median exposure of 6-TGN in RBC was 15% (9-28). Hypoxanthine guanine-phosphoribosyl-transferase activity correlated with peak 6-TGN and with AUC per mg (r= 0.7, P= 0.02 and r= 0.6, P= 0.03 respectively). Thiopurine S-methyltransferase activity was inversely related to AUC per mg (r=-0.8, P= 0.001), whereas that of xanthine oxidase was correlated with a lower peak 6-TGN (r=-0.7, P= 0.02).

CONCLUSIONS AND IMPLICATIONS

The great variability of the AUC per mg for 6-TG observed after p.o. and i.v. administration of 6-TG, was partly explained by variability in activities of metabolizing enzymes. Exposure of 6-TGN was low in all patients.

Induction of resistance to the lipophilic cytarabine prodrug elacytarabine (CP-4055) in CEM leukemic cells

The deoxynucleoside analogs cytarabine (Ara-C) and gemcitabine (dFdC) are widely used in the treatment of cancer. Due to their hydrophilic nature they need the equilibrative (hENT) and concentrative (hCNT) nucleoside transporters to enter the cell. To bypass drug resistance due to decreased uptake, lipophilic 5'elaidic acid esters were synthesized, elacytarabine (CP-4055, from ara-C) and CP-4126 (from gemcitabine), which are currently in clinical development for solid and hematological tumors. We investigated whether resistance can be induced in vitro, and treated the CEM leukemic cell line with weekly increasing elacytarabine concentrations, up to 0.28 microM (10 times IC(50)). The IC(50) of the resistant CEM/CP-4055 was 35 microM, about 1,000 times that of the wildtype CEM, and comparable to that of CEM/dCK- (deoxycytidine kinase deficient) (22 microM). CEM/CP-4055 was also cross-resistant to Ara-C, gemcitabine and CP-4126 (28 and 33 microM, respectively). A low level of mRNA dCK was observed, and similar to CEM/dCK-, CEM/CP-4055 did not accumulate Ara-CTP after exposure to Ara-C or elacytarabine, which is consistent with a deficiency in dCK. In conclusion, elacytarabine induced resistance similar to Ara-C. This resistance was caused by downregulation of dCK.

Limited intra-individual variability in hypoxanthine-Guanine phosphoribosyl transferase, thiopurine S-methyl transferase, and xanthine oxidase activity in inflammatory bowel disease patients during 6-thioguanine therapy

6-Thioguanine (6-TG) may be indicated in case of intolerance of or resistance to conventional thiopurines in the treatment of inflammatory bowel diseases (IBD). The aim of our study was to evaluate the intrapatient variability in the 6-TG metabolizing enzymes: hypoxanthine-guanine phosphoribosyl transferase (HGPRT), thiopurine S-methyl transferase and xanthine oxidase. We performed a pharmacokinetic study of 6-TG after oral and intravenous administration in IBD patients in remission. The enzyme activities were determined at baseline and 1 week after the initiation of 6-TG in red blood cells, peripheral blood mononuclear cells (PBMC) or plasma. From the results we conclude that HGPRT activity in erythrocytes decreases following the initiation of 6-TG therapy, which may imply that HGPRT is a rate limiting enzyme in 6-TG metabolism. Moreover, little intrapatient variability in enzyme activities was observed except for HGPRT activity in PBMC. These data may have implications in regard of future therapeutic drug monitoring.

Molecular pathways involved in the synergistic interaction of the PKC beta inhibitor enzastaurin with the antifolate pemetrexed in non-small cell lung cancer cells

Conventional regimens have limited impact against non-small cell lung cancer (NSCLC). Current research is focusing on multiple pathways as potential targets, and this study investigated molecular mechanisms underlying the combination of the PKCβ inhibitor enzastaurin with the multitargeted antifolate pemetrexed in the NSCLC cells SW1573 and A549. Pharmacologic interaction was studied using the combination-index method, while cell cycle, apoptosis induction, VEGF secretion and ERK1/2 and Akt phosphorylation were studied by flow cytometry and ELISAs. Reverse transcription–PCR, western blot and activity assays were performed to assess whether enzastaurin influenced thymidylate synthase (TS) and the expression of multiple targets involved in cancer signaling and cell cycle distribution. Enzastaurin-pemetrexed combination was highly synergistic and significantly increased apoptosis. Enzastaurin reduced both phosphoCdc25C, resulting in G2/M checkpoint abrogation and apoptosis induction in pemetrexed-damaged cells, and GSK3β and Akt phosphorylation, which was additionally reduced by drug combination (−58% in A549). Enzastaurin also significantly reduced pemetrexed-induced upregulation of TS expression, possibly through E2F-1 reduction, whereas the combination decreased TS in situ activity (>50% in both cell lines) and VEGF secretion. The effects of enzastaurin on signaling pathways involved in cell cycle control, apoptosis and angiogenesis, as well as on the expression of genes involved in pemetrexed activity provide a strong experimental basis to their evaluation as pharmacodynamic markers in clinical trials of enzastaurin-pemetrexed combination in NSCLC patients.

Micro-array analysis of resistance for gemcitabine results in increased expression of ribonucleotide reductase subunits

To study in detail the relation between gene expression and resistance against gemcitabine, a cell line was isolated from a tumor for which gemcitabine resistance was induced in vivo. Similar to the in vivo tumor, resistance in this cell line, C 26-G, was not related to deficiency of deoxycytidine kinase (dCK). Micro-array analysis showed increased expression of ribonucleotide reductase (RR) subunits M1 and M2 as confirmed by real time PCR analysis (28- and 2.7-fold, respectively). In cell culture, moderate cross-resistance (about 2-fold) was observed to 1-ss-D-arabinofuranosylcytosine (ara-C), 2-chloro-2'deoxyadenosine (CdA), LY231514 (ALIMTA), and cisplatin (CDDP), and pronounced cross-resistance (>23-fold) to 2',2'-difluorodeoxyuridine (dFdU) and 2',2'-difluorodeoxyguanosine (dFdG). Culture in the absence of gemcitabine reduced resistance as well as RRM1 RNA expression, demonstrating a direct relationship of RRM1 RNA expression with acquired resistance to gemcitabine.

Phase II study of tailored chemotherapy for advanced colorectal cancer with either 5-fluouracil and leucovorin or oxaliplatin and irinotecan based on the expression of thymidylate synthase and dihydropyrimidine dehydrogenase

BACKGROUND

Thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) are essential enzymes for 5-fluorouracil (5-FU) metabolism. In patients with advanced colorectal cancer (ACRC), retrospective studies have shown that low expression levels of TS and DPD correlated with response to 5-FU. We performed a prospective study in which the choice of first-line chemotherapy with either 5-FU or a non-5-FU containing regimen was based on TS and DPD expression.

PATIENTS AND METHODS

Fresh-frozen samples of metastases were obtained from 58 previously untreated patients with ACRC. mRNA expression of TS and DPD was quantified using an RT-PCR assay. Patients with low tumor expression of both TS and DPD received weekly bolus 5-FU/leucovorin (LV) 500 mg/m2 (group A); patients with high TS and/or DPD received 3-weekly oxaliplatin 85 mg/m2 and irinotecan 200 mg/m2 (group B). After progression, cross-over to the alternative regimen was attempted.

RESULTS

Of 53 eligible patients, 31 had tumors with both low TS and low DPD, and were treated in group A. A response was observed in 11 patients [35%; 95% confidence interval (CI) 19% to 54%]. Cross-over to second-line oxaliplatin/irinotecan resulted in a partial response in two out of 16 patients (13%; 95% CI 1% to 38%). In group B, four out of 22 patients responded (18%; 95% CI 5% to 40%), while no responses were observed in 12 patients after cross-over to 5-FU/LV (0%; 95% CI 0% to 28%).

CONCLUSIONS

Prospective selection of 5-FU/LV chemotherapy based on low TS and DPD expression in patients with ACRC did not confirm the high response rates reported in retrospective studies. The procedure of obtaining metastatic tissue and quantitation of enzymes appeared feasible but cumbersome. Before assessing the clinical utility of a predictive marker in a randomized trial, future studies should focus on prospective validation of the assay in a large and well defined population.

Comparison of mRNA expression levels determined with TaqMan and competitive template RT-PCR

Two methods for measurement of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) mRNA expression were compared. Although the relative mRNA levels compared to beta-actin measured with competitive template RT-PCR were different from the data obtained with a TaqMan based PCR, a significant correlation between the two assays was found.

Polymorphism of the thymidylate synthase gene and thymidylate synthase levels in colon cancer cell lines and different tissues of colorectal cancer patients

In a panel of 18 colon cancer cell lines we found that the thymidylate synthase (TS) genotype was related to TS enzyme activity, but not to TS protein and mRNA levels. In addition, no relation with drug sensitivity was observed. TS genotyping of different tissues from 78 colorectal cancer patients revealed a high level of homology in polymorphic status between normal and malignant tissues and the heterozygous genotype to be the most frequent.

Upregulation of platelet derived endothelial cell growth factor/thymidine phosphorylase by interferon alpha

Thymidine phosphorylase (TP) catalyzes the phosphorolytic cleavage of thymidine to thymine and deoxyribose-1-phosphate. TP, which is overexpressed in a wide variety of solid tumors, is involved in the activation and inactivation of fluoropyrimidines. TP is known to be regulated by several cytokines and interferons. In our HT29 cell line the TP mRNA and activity expression increased 2-3 fold after treatment with interferon alpha.

Role of platelet derived endothelial cell growth factor/thymidine phosphorylase in fluoropyrimidine sensitivity and potential role of deoxyribose-1-phosphate

Thymidine phosphorylase (TP) catalyzes the phosphorolytic cleavage of thymidine (TdR) to thymine and deoxyribose-1-phosphate (dR-1-P). TP, which is overexpressed in a wide variety of solid tumors, is involved in the activation and inactivation of fluoropyrimidines. We investigated the role of TP in 5'-deoxy-5-fluorouridine (5'DFUR), 5-fluorouracil (5FU) and trifluorothymidine (TFT) sensitivity. TP had no effect on TFT while it activated 5'DFUR and to a lesser extent 5FU. In order to provide an explanation for this difference in activation of 5'DFUR and 5FU, we studied the role of the 5FU co-substrate, dR-1-P, needed for its activation.

Antiproliferative activity and mechanism of action of fatty acid derivatives of gemcitabine in leukemia and solid tumor cell lines and in human xenografts

Gemcitabine is a deoxycytidine analog, which can be inactivated by deamination catalyzed by deoxycytidine deaminase (dCDA). Altered transport over the cell membrane is a mechanism of resistance to gemcitabine. To facilitate accumulation, the fatty acid derivative CP-4125 was synthesized. Since, the fatty acid is acylated at the site of action of dCDA, a decreased deamination was expected. CP-4125 was equally active as gemcitabine in a panel of rodent and human cell lines and in human melanoma xenografts bearing mice. In contrast to gemcitabine, CP-4125 was not deaminated but inhibited deamination of deoxycytidine and gemcitabine. Pools of the active triphosphate of gemcitabine increased for over 20 hr after CP-4125 exposure, while these pools decreased directly after removal of gemcitabine.

IN CONCLUSION

CP-4125 is an interesting new gemcitabine derivative.

5-Fluorouracil incorporation into RNA and DNA in relation to thymidylate synthase inhibition of human colorectal cancers

BACKGROUND

The mechanism of action of 5-fluorouracil (5-FU) has been associated with inhibition of thymidylate synthase (TS) and incorporation of 5-FU into RNA and DNA, but limited data are available in human tumor tissue for the latter. We therefore measured incorporation in human tumor biopsy specimens after administration of a test dose of 5-FU alone or with leucovorin.

PATIENTS AND METHODS

Patients received 5-FU (500 mg/m(2)) with or without high-dose leucovorin, low-dose leucovorin or l-leucovorin, and biopsy specimens were taken after approximately 2, 24 or 48 h. Tissues were pulverized and extracted for nucleic acids. 5-FU incorporation was measured using gas chromatography/mass spectrometry after complete degradation to bases of isolated RNA and DNA.

RESULTS

Maximal incorporation into RNA (1.0 pmol/micrograms RNA) and DNA (127 fmol/micrograms DNA) of 59 and 46 biopsy specimens, respectively, was found at 24 h after 5-FU administration. Incorporation into RNA but not DNA was significantly correlated with intratumoral 5-FU levels. However, DNA incorporation was significantly correlated with the RNA incorporation. Primary tumor tissue, liver metastasis and normal mucosa did not show significant differences, while leucovorin had no effect. Neither for RNA (30 patients) nor DNA (24 patients) incorporation was a significant correlation with response to 5-FU therapy found. However, in the same group of patients, response was significantly correlated to TS inhibition (mean TS in responding and non-responding groups 45 and 231 pmol/h/mg protein, respectively; P=0.001).

CONCLUSIONS

5-FU is incorporated at detectable levels into RNA and DNA of human tumor tissue, but no relation between the efficacy of 5-FU treatment and incorporation was found, in contrast to TS.

Pharmacokinetics of S-1, an oral formulation of ftorafur, oxonic acid and 5-chloro-2,4-dihydroxypyridine (molar ratio 1:0.4:1) in patients with solid tumors

S-1 is an oral formulation of ftorafur (FT), oxonic acid and 5-chloro-2,4-dihydroxypyridine (CDHP) at a molar ratio of 1:0.4:1. FT is a 5-fluorouracil (5-FU) prodrug, CDHP is a dihydropyrimidine dehydrogenase (DPD) inhibitor and oxonic acid is an inhibitor of 5-FU phosphoribosylation in the gastrointestinal mucosa and was included to prevent gastrointestinal toxicity. We determined the pharmacokinetics of S-1 in 28 patients at doses of 25, 35, 40 and 45 mg/m(2). The plasma C(max) values of FT, 5-FU, oxonic acid and CDHP increased dose-dependently and after 1-2 h were in the ranges 5.8-13 microM, 0.4-2.4 microM, 0.026-1.337 microM, and 1.1-3.6 microM, respectively. Uracil levels, indicative of DPD inhibition, also increased dose-dependently from basal levels of 0.03-0.25 microM to 3.6-9.4 microM after 2-4 h, and 0.09-0.9 microM was still present after 24 h. The pharmacokinetics of CDHP and uracil were linear over the dose range. The areas under the plasma concentration curves (AUC) for CDHP and uracil were in the ranges 418-1735 and 2281-8627 micromol x min/l, respectively. The t(1/2) values were in the ranges 213-692 and 216-354 min, respectively. Cumulative urinary excretion of FT was predominantly as 5-FU and was 2.2-11.9%; the urinary excretion of both fluoro-beta-alanine and uracil was generally maximal between 6 and 18 h. During 28-day courses with twice-daily S-1 administration, 5-FU and uracil generally increased. Before each intake of S-1, 5-FU varied between 0.5 and 1 microM and uracil was in the micromolar range (up to 7 microM), indicating that effective DPD inhibition was maintained during the course. In a biopsy of an esophageal adenocarcinoma metastasis that had regressed, thymidylate synthase, the target of 5-FU, was inhibited 50%, but increased four- to tenfold after relapse in subsequent biopsies. In conclusion, oral S-1 administration resulted in prolonged exposure to micromolar 5-FU concentrations due to DPD inhibition, and the decrease in uracil levels after 6 h followed the pattern of CDHP and indicates reversible DPD inhibition.

Rapid disappearance of deoxyribose-1-phosphate in platelet derived endothelial cell growth factor/thymidine phosphorylase overexpressing cells

Platelet derived endothelial cell growth factor/thymidine phosphorylase (PD-ECGF/TP) catalyzes the phosphorolysis of thymidine (TdR) to thymine and deoxyribose-1-phosphate (dR-1-P) and has a pro-angiogenic effect for which dR-1-P may be responsible. Using a purine nucleoside phosphorylase based assay it was found that TdR incubation did not increase dR-1-P accumulation in colon cancer cell line Colo320 and its PD-ECGF/TP transfected variant Colo320TP1. The assay was linear up to 25,000pmol dR-1-P with complete recovery of dR-1-P from cellular extracts. There was a huge discrepancy between thymine production and the measured dR-1-P level, 0.05% of the expected value for dR-1-P was found, indicating that there was a rapid disappearance of dR-1-P. However, in cellular extracts, TdR incubation increased dR-1-P, measurable by trapping, which was inhibited by a thymidine phosphorylase inhibitor. dR-1-P directly added to cellular extracts disappeared within 5-10min. In conclusion, large amounts of dR-1-P are produced by Colo320TP1 cells, which rapidly disappear thus not resulting in a net accumulation of dR-1-P in these cells.

Effect of gemcitabine and cis-platinum combinations on ribonucleotide and deoxyribonucleotide pools in ovarian cancer cell lines

Gemcitabine (dFdC) and cisplatin (CDDP) act synergistically by an increase in platinum-DNA adduct formation. Since ribonucleotide (NTP) and deoxyribonucleotide (dNTP) levels are essential for DNA-synthesis and repair of DNA damage, we investigated whether disturbances might account for differences in effects between sensitive and resistant cell lines. The human ovarian cancer cell line A2780, its CDDP-resistant variant ADDP and its dFdC-resistant variant AG6000 were exposed for 24 h to dFdC or CDDP alone, or a combination causing moderate to strong growth inhibition. In AG6000 cells UTP levels were 2-fold lower and in ADDP cells almost 2-fold higher than in A2780 cells. Levels of dTTP, dATP and dCTP were 2-5-fold lower in the resistant cell lines. Drug treatment affected NTP and dNTP levels most pronounced in A2780 cells. dFdC alone, at 1.5 nM to 1 micro M increased ATP, GTP and CTP pools 1.2 to 2.0-fold, while 10 micro M dFdC increased UTP 2.5-fold. Combination of dFdC and CDDP increased all NTP levels at low dFdC and CDDP concentrations more than 1.2-fold, but at 20 micro M CDDP only CTP increased 2.4-fold. Only 1.5 nM dFdC increased all dNTP pools more than 1.6-fold, but at 0.1 and 1 micro M dFdC, dATP and dGTP decreased down to 10-fold, while dTTP increased 3-5-fold. CDDP and the combination increased all dNTP pools over 1.4 and 1.9-fold, respectively. In AG6000 cells dFdC and CDDP hardly affected the NTP and dNTP status, except at the high concentrations, which decreased ATP, GTP and UTP levels 1.2-1.8-fold. Both CDDP alone and the combination increased dTTP, dCTP and dATP pools up to 1.6-fold. In ADDP cells NTP and most dNTP levels were hardly affected, except dGTP levels which decreased to non-detectable levels. In conclusion, both dFdC and CDDP induce concentration and combination dependent changes in NTP and dNTP pools.

Induction of thymidylate synthase as a 5-fluorouracil resistance mechanism

Thymidylate synthase (TS) is a key enzyme in the de novo synthesis of 2'-deoxythymidine-5'-monophosphate (dTMP) from 2'-deoxyuridine-5'-monophosphate (dUMP), for which 5,10-methylene-tetrahydrofolate (CH(2)-THF) is the methyl donor. TS is an important target for chemotherapy; it is inhibited by folate and nucleotide analogs, such as by 5-fluoro-dUMP (FdUMP), the active metabolite of 5-fluorouracil (5FU). FdUMP forms a relatively stable ternary complex with TS and CH(2)THF, which is further stabilized by leucovorin (LV). 5FU treatment can induce TS expression, which might bypass dTMP depletion. An improved efficacy of 5FU might be achieved by increasing and prolonging TS inhibition, a prevention of dissociation of the ternary complex, and prevention of TS induction. In a panel of 17 colon cancer cells, including several variants with acquired resistance to 5FU, sensitivity was related to TS levels, but exclusion of the resistant variants abolished this relation. For antifolates, polyglutamylation was more important than the intrinsic TS level. Cells with low p53 levels were more sensitive to 5FU and the antifolate raltitrexed (RTX) than cells with high, mutated p53. Free TS protein down-regulates its own translation, but its transcription is regulated by E2F, a cell cycle checkpoint regulator. Together, this results in low TS levels in stationary phase cells. Although cells with a low TS might theoretically be more sensitive to 5FU, the low proliferation rate prevents induction of DNA damage and 5FU toxicity. TS levels were not related to polymorphisms of the TS promoter. Treatment with 5FU or RTX rapidly induced TS levels two- to five-fold. In animal models, 5FU treatment resulted in TS inhibition followed by a two- to three-fold TS induction. Both LV and a high dose of 5FU not only enhanced TS inhibition, but also prevented TS induction and increased the antitumor effect. In patients, TS levels as determined by enzyme activity assays, immunohistochemistry and mRNA expression, were related to a response to 5FU. 5FU treatment initially decreased TS levels, but this was followed by an induction, as seen with an increased ratio of TS protein over TS-mRNA. The clear retrospective relation between TS levels and response now forms the basis for a prospective study, in which TS levels are measured before treatment in order to determine the treatment protocol.

Maintenance of ATP favours apoptosis over necrosis triggered by benzamide riboside

A new synthetic drug, benzamide riboside (BR) exhibited strong oncolytic activity against leukemic cells in the 5-10 microM range. Higher BR-concentrations (20 microM) predominantly induced necrosis which correlated with DNA strand breaks and subsequent depletion of ATP- and dATP levels. Replenishment of the ATP pool by addition of adenosine prevented necrosis and favoured apoptosis. This effect was not a pecularity of BR-treatment, but was reproduced with high concentrations of all trans-retinoic acid (120 microM) and cyanide (20 mM). Glucose was also capable to suppress necrosis and to favour apoptosis of HL-60 cells, which had been treated with necrotic doses of BR and cyanide. Apoptosis eliminates unwanted cells without affecting the microenvironment, whereas necrosis causes severe inflammation of surrounding tissues due to spillage of cell fluids into the peri-cellular space. Thus, the monitoring and maintenance of cellular energy pools during therapeutic drug treatment may help to minimize nonspecific side effects and to improve attempted drug effects.

Issues of normal tissue toxicity in patient and animal studies--effect of carbogen breathing in rats after 5-fluorouracil treatment

Non-invasive magnetic resonance spectroscopy (MRS) can be used in the clinic to monitor the pharmacokinetics of the chemotherapeutic drug 5-fluorouracil (5-FU) and the effects of modifiers. We report two studies of 5-FU toxicity in normal tissue--one with patients and the other an animal study. 1) 19F MRS signals from fluoronucleotides, cytotoxic anabolites of 5-FU metabolism, were observed in the livers of two patients treated with 5-FU for colorectal cancer, shown by computed tomography (CT) and ultrasound (US) to have no liver metastases. This is the first report of non-invasive monitoring of toxic 5-FU metabolites in normal human tissues. 2) In animals, carbogen-breathing enhances tumour uptake and the efficacy of 5-FU, and the method is under trial in patients. This study demonstrates that there were no significant effects of carbogen breathing on the levels of 5-FU and its metabolites in normal rat tissues, or on the histology of the tissues assessed after treatment.

Collateral sensitivity to gemcitabine (2',2'-difluorodeoxycytidine) and cytosine arabinoside of daunorubicin- and VM-26-resistant variants of human small cell lung cancer cell lines

Multidrug resistance (MDR), characterized by a cross-resistance to many natural toxin-related compounds, may be caused either by overexpression of a drug efflux pump such as P-glycoprotein, (P-gP), multidrug resistance proteins MRP1-3, or BCRP/MXR or, in the case of DNA topoisomerase II active drugs, by a decrease in the enzymatic activity of the target molecule termed altered topoisomerase MDR (at-MDR). However, human small cell lung carcinoma (SCLC) cell lines showed a collateral sensitivity to 2',2'-difluorodeoxycytidine (gemcitabine, dFdC) and 1-beta-D-arabinofuranosylcytosine (ara-C). H69/DAU, a daunorubicin (DAU)-resistant variant of H69 with a P-gP overexpression, and NYH/VM, a VM-26 (teniposide)-resistant variant of NYH with an at-MDR, were both 2-fold more sensitive to gemcitabine and 7- and 2-fold more sensitive to ara-C, respectively. MDR variants had a 4.3- and 2.0-fold increased activity of deoxycytidine kinase (dCK), respectively. dCK catalyzes the first rate-limiting activation step of both gemcitabine and ara-C. In addition, deoxycytidine deaminase, responsible for inactivation of dFdC and ara-C, was 9.0-fold lower in H69/DAU cells. The level of thymidine kinase 2, a mitochondrial enzyme that can also phosphorylate deoxycytidine and gemcitabine, was not significantly different between the variants. These differences most likely caused an increased accumulation of the active metabolites (dFdCTP, 2.1- and 1.6-fold in NYH/VM and H69/DAU cells, respectively) and of ara-CTP (1.3-fold in NYH/VM cells). Ara-CTP accumulation was not detectable in either H69 variant. The pools of all ribonucleoside and deoxyribonucleoside triphosphates were at least 3- to 4-fold higher in the NYH variants compared to the H69 variants; for dCTP and dGTP this difference was even larger. The higher ribonucleotide pools might explain the >10-fold higher accumulation of dFdCTP in NYH compared to H69 variants. Since dCTP is low, H69 cells might not need a high ara-CTP accumulation to inhibit DNA polymerase. This might be related to the lack of ara-CTP in H69 variants. In addition, the increased CTP, ATP, and UTP pools in the MDR variants might explain the increased ara-CTP and dFdCTP accumulation. In conclusion, the MDR variants of the human SCLC cell lines were collaterally sensitive due to an increased dCK activity, and consequently an increased ara-CTP and dFdCTP accumulation.

Modulation of both endogenous folates and thymidine enhance the therapeutic efficacy of thymidylate synthase inhibitors

Plasma levels of folates and thymidine in mice are about 10-fold higher than in humans and may influence the therapeutic efficacy of thymidylate synthase (TS) inhibitors, such as 5-fluorouracil (5FU) and the antifolates pemetrexed (MTA) and raltitrexed (RTX). Therefore, we tested their therapeutic efficacy in various murine tumor models, grown in mice on a normal and a folate-depleted diet, with high and low thymidine kinase (TK) levels. MTA and RTX were inactive against Colon-26-10 [doubling times gained by treatment; growth delay factor (GDF), 0.5 and 0.3, respectively], whereas 5FU was very active (GDF, >10; complete cures). Colon-26-10/F, grown in mice on a folate-depleted diet, was more sensitive to RTX and MTA (GDF, 2.1 and 1.3, respectively) but not to 5FU (GDF, 1.2); however, leucovorin reversed the effect leading to cures. Folate depletion did not reverse resistance of Colon-26A and Colon-26G (low TK) to MTA and RTX, whereas leucovorin only enhanced the 5FU effect in Colon-26A and Colon-26A/F. Folic acid at 15 mg/kg did not improve the therapeutic efficacy of MTA in folate-deficient mice. The folate-depleted diet decreased the reduced folates in Colon-26A/F and Colon-26-G/F tumors less (4-5-fold; P < 0.01) than in Colon-26-10/F tumors (8-fold; P < 0.001). Folate depletion increased TS levels 2-3-fold in all of the models and TK levels 6-fold (P < 0.01) in Colon-26G/F, explaining the lack of activity of MTA and RTX in Colon-26G/F. In contrast, TK-deficient FM3A/TK tumors were much more sensitive to RTX, MTA, and 5FU than parent FM3A tumors, which have comparable TS levels. The rate of thymidine phosphorylysis varied considerably in all of the tumors without a clear relation to antitumor activity. In conclusion, tumor folates may potentiate (5FU) or protect (antifolates). Murine tumor models should combine low folates and low thymidine rescue to optimize preclinical testing of antifolates.

Activation of caspases and induction of apoptosis by novel ribonucleotide reductase inhibitors amidox and didox

OBJECTIVE

Amidox and didox are two polyhydroxy-substituted benzohydroxamic acid derivatives that belong to a new class of ribonucleotide reductase (RR) inhibitors. RR is the rate-limiting enzyme for de novo deoxyribonucleotide synthesis, and its activity is significantly increased in tumor cells in proportion to the proliferation rate. Therefore, RR is a target for antitumor therapy.

MATERIALS AND METHODS

HL-60 and K562 leukemia cells were treated with increasing doses of amidox and didox. Thereafter, the mode of cytotoxic drug action was determined by Hoechst 33258/propidium iodide (HO/PI) double staining, annexin binding, DNA fragmentation, and caspase activation. This was correlated to the decrease in dNTP levels. Staining with HO/PI and binding of fluorescein isothiocyanate-conjugated annexin V to externalized phosphatidylserine were used to quantify apoptosis.

RESULTS

Low doses of amidox or didox resulted in an increase of apoptotic HL-60 cells within 48 hours. Higher doses (50 microM amidox or 250 microM didox) led to rapid induction of apoptosis, which could be detected as early as 4 hours after treatment. After 48 hours with these concentrations, almost 100% of the HL-60 cells died by apoptosis without an increase in necrosis. K562 cells were found to be resistant to amidox but not to didox. In HL-60 cells, upstream caspase 8 is processed in response to didox, whereas caspases 8 and 9 are processed upon amidox treatment. Didox-induced apoptosis, but not amidox-induced apoptosis, can be correlated with the decrease in dNTP levels. The results suggests that amidox induces several apoptosis mechanisms in HL-60 cells. In contrast, only caspase 9 is activated by didox in K562 cells, and because amidox hardly induces apoptosis in this cell line, no caspase cleavage is observed.

CONCLUSIONS

Didox triggers distinct apoptosis pathways in HL-60 and K562 cells.

End-joining deficiency and radiosensitization induced by gemcitabine

The mechanism of radiosensitization by gemcitabine (2',2'-difluoro-2'-deoxycytidine, dFdC) is not exactly known. We investigated the possible role of inhibition of the repair of DNA double-strand breaks by dFdC by measuring the extent of radiosensitization in different cell lines deficient and proficient in components of nonhomologous end-joining and in the parental cell lines. Different cell lines were incubated with 0.5 and 5 microM dFdC for 4 h. Cells deficient in DNA-dependent protein-kinase catalytic subunit (V3) showed sensitization similar to that of wild-type cells (AAS) and complemented cells (V3+YAC). Ku80-deficient cells (xrs5 and xrs6) showed even more radiosensitization by dFdC as compared with wild-type CHO-K1. However, Ku80-complemented cell lines (xrs5+huKu80 and xrs6+haKu80) did not show radiosensitization. The differences in dFdC-mediated radiosensitization were not attributable to different changes in deoxynucleotide triphosphate levels and cell cycle distribution. We conclude that a functional nonhomologous end-joining pathway is not required for dFdC-mediated radiosensitization.

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.