Effect of interferon on 5-fluorouracil-induced perturbations in pools of deoxynucleotide triphosphates and DNA strand breaks

A sensitive assay for dNTPs based on long synthetic oligonucleotides, EvaGreen dye and inhibitor-resistant high-fidelity DNA polymerase

Deoxyribonucleoside triphosphates (dNTPs) are vital for the biosynthesis and repair of DNA. Their cellular concentration peaks during the S phase of the cell cycle. In non-proliferating cells, dNTP concentrations are low, making their reliable quantification from tissue samples of heterogeneous cellular composition challenging. Partly because of this, the current knowledge related to the regulation of and disturbances in cellular dNTP concentrations derive mostly from cell culture experiments with little corroboration at the tissue or organismal level. Here, we fill the methodological gap by presenting a simple non-radioactive microplate assay for the quantification of dNTPs with a minimum requirement of 4-12 mg of biopsy material. In contrast to published assays, this assay is based on long synthetic single-stranded DNA templates (50-200 nucleotides), an inhibitor-resistant high-fidelity DNA polymerase, and the double-stranded-DNA-binding EvaGreen dye. The assay quantified reliably less than 50 fmol of each of the four dNTPs and discriminated well against ribonucleotides. Additionally, thermostable RNAse HII-mediated nicking of the reaction products and a subsequent shift in their melting temperature allowed near-complete elimination of the interfering ribonucleotide signal, if present. Importantly, the assay allowed measurement of minute dNTP concentrations in mouse liver, heart and skeletal muscle.

Short hairpin RNA suppression of thymidylate synthase produces DNA mismatches and results in excellent radiosensitization

PURPOSE

To determine the effect of short hairpin ribonucleic acid (shRNA)-mediated suppression of thymidylate synthase (TS) on cytotoxicity and radiosensitization and the mechanism by which these events occur.

METHODS AND MATERIALS

shRNA suppression of TS was compared with 5-fluoro-2'-deoxyuridine (FdUrd) inactivation of TS with or without ionizing radiation in HCT116 and HT29 colon cancer cells. Cytotoxicity and radiosensitization were measured by clonogenic assay. Cell cycle effects were measured by flow cytometry. The effects of FdUrd or shRNA suppression of TS on dNTP deoxynucleotide triphosphate imbalances and consequent nucleotide misincorporations into deoxyribonucleic acid (DNA) were analyzed by high-pressure liquid chromatography and as pSP189 plasmid mutations, respectively.

RESULTS

TS shRNA produced profound (≥ 90%) and prolonged (≥ 8 days) suppression of TS in HCT116 and HT29 cells, whereas FdUrd increased TS expression. TS shRNA also produced more specific and prolonged effects on dNTPs deoxynucleotide triphosphates compared with FdUrd. TS shRNA suppression allowed accumulation of cells in S-phase, although its effects were not as long-lasting as those of FdUrd. Both treatments resulted in phosphorylation of Chk1. TS shRNA alone was less cytotoxic than FdUrd but was equally effective as FdUrd in eliciting radiosensitization (radiation enhancement ratio: TS shRNA, 1.5-1.7; FdUrd, 1.4-1.6). TS shRNA and FdUrd produced a similar increase in the number and type of pSP189 mutations.

CONCLUSIONS

TS shRNA produced less cytotoxicity than FdUrd but was equally effective at radiosensitizing tumor cells. Thus, the inhibitory effect of FdUrd on TS alone is sufficient to elicit radiosensitization with FdUrd, but it only partially explains FdUrd-mediated cytotoxicity and cell cycle inhibition. The increase in DNA mismatches after TS shRNA or FdUrd supports a causal and sufficient role for the depletion of dTTP thymidine triphosphate and consequent DNA mismatches underlying radiosensitization. Importantly, shRNA suppression of TS avoids FP-mediated TS elevation and its negative prognostic role. These studies support the further exploration of TS suppression as a novel radiosensitizing strategy.

MLH1 deficiency enhances radiosensitization with 5-fluorodeoxyuridine by increasing DNA mismatches

The antitumor drug 5-fluoro-2'-deoxyuridine (FdUrd) also sensitizes tumor cells to ionizing radiation in vitro and in vivo. Although radiosensitization with FdUrd requires dTTP depletion and S-phase arrest, the exact mechanism by which these events produce radiosensitization remains unknown. We hypothesized that the depletion of dTTP produces DNA mismatches that, if not repaired before irradiation, would result in radiosensitization. We evaluated this hypothesis in mismatch repair (MMR)-deficient HCT116 0-1 cells that lack the expression of the required MMR protein MLH1 (inactive MLH1), and in MMR-proficient (wild-type MLH1) HCT116 1-2 cells. Although HCT116 0-1 cells were less sensitive to FdUrd (IC(50) = 3.5 microM) versus HCT116 1-2 cells (IC(50) = 0.75 microM), when irradiation followed FdUrd (IC(50)) the MLH1-inactivated cells exhibited greater radiosensitization compared with MMR-wild-type cells [radiation enhancement ratio (RER) = 1.8 +/- 0.28 versus 1.1 +/- 0.1, respectively] and an increase (> or =8-fold) in nucleotide misincorporations. In SW620 cells and HCT116 1-2 MLH1-wild-type cells, FdUrd (IC(50)) did not produce radiosensitization nor did it increase the mutation frequency, but after short hairpin RNA-directed suppression of MLH1 this concentration produced excellent radiosensitization (RER = 1.6 +/- 0.10 and 1.5 +/- 0.06, respectively) and an increase in nucleotide misincorporations (8-fold and 6-fold, respectively). Incubation with higher concentrations of FdUrd (IC(90)) after suppression of MLH1 produced a further increase in ionizing radiation sensitivity in both SW620 and HCT116 1-2 cells (RER = 1.8 +/- 0.03 and 1.7 +/- 0.13, respectively) and nucleotide misincorporations (>10-fold in both cell lines). These results demonstrate an important role for MLH1 and implicate mismatches in radiosensitization by FdUrd.

Combined intra-arterial 5-fluorouracil and subcutaneous interferon-alpha therapy for highly advanced hepatocellular carcinoma

Because of the difficulties of low sensitivity for anticancer agents and giving sufficient dose because of poor liver function, chemotherapy may not play a central role for treatment of hepatocellular carcinoma (HCC) patients, especially those with liver cirrhosis. However, chemotherapy must be one of the important possibilities of multimodal treatment for advanced HCC, for which hepatic resection, percutaneous ablation, transcatheter arterial embolization and other general therapies would not be effective or even possible. Also, intra-arterial perfusion chemotherapy is a common therapy for HCC and it is not difficult to maintain; but the effective rate is not sufficient. Recently, the combination therapy of s.c. interferon (IFN)-alpha and intra-arterial 5-fluorouracil (5-FU) showed an outstandingly effective rate for intractable HCC (with portal vein thrombosis). In addition,recent preclinical and clinical studies have revealed that the mechanism of combination therapy may concern direct antitumor effects (through cell-cycle arrest and induction of apoptosis) and indirect actions (through immunocompetent cells and anti-angiogenic effect). For the further advance of HCC treatment and prognosis, this therapy might be a promising treatment modality and is expected to develop. In this review, we summarize recent clinical and preclinical data regarding IFN-alpha and 5-FU combination therapy and discuss the further prospects of this therapy.

Antiproliferative effects of 5-fluorouracil and interferon-alpha in combination on a hepatocellular carcinoma cell line in vitro and in vivo

BACKGROUND AND AIM

We investigated the antiproliferative effects of interferon-alpha (IFN-alpha) and 5-fluorouracil (5-FU) in combination on a hepatocellular carcinoma (HCC) cell line.

METHOD

In the in vitro study, IFN-alpha and/or 5-FU was added to the culture of the poorly differentiated-type HCC cell line, HAK-1B, and their antiproliferative effects and additional or synergic effects in combination treatment were examined. In the in vivo study, HAK-1B cells were transplanted into nude mice and the changes in tumor volume and weight, apoptosis, BrdU and cyclin A positive cells, and artery-like blood vessels were investigated. Expressions of angiogenesis factors and IFN-alpha receptor (IFNAR-2) were examined in the developed tumors.

RESULTS

In vitro growth of HAK-1B cells was suppressed dose-dependently to 5-FU, but the addition of IFN-alpha did not induce additional or synergic effects. In vivo growth in terms of tumor diameter and weight was suppressed at most in the IFN-alpha + 5-FU (combination) group, that is, the tumor volume became 29.3% and the tumor weight became 54.7% of the control. In the combination group, numbers of BrdU-positive S-phase cells and cyclin A positive cells increased together with the increase in apoptotic cells, but there was no significant relation between the tumor shrinkage effects and angiogenesis factors or artery-like blood vessels. In the combination group, INFAR-2 decreased significantly in comparison to the other groups.

CONCLUSION

The synergic growth-suppression effects in the current in vivo study using the combination treatment are attributable to the enhanced induction of S-phase arrest and of apoptosis.

Consensus interferon enhances the anti-proliferative effect of 5-fluorouracil on human hepatoma cells via downregulation of dihydropyrimidine dehydrogenase expression

BACKGROUND/AIMS

The effectiveness of 5-fluorouracil (5-FU) treatment is influenced by the activities of pyrimidine catabolic enzymes. The aim of this study was to investigate whether interferon (IFN)-alpha influences expression of 5-FU catabolic or target-related enzymes in human hepatoma cells.

METHODS

HepG2 cells were treated with 0, 0.15, 1.5, 15, and 150 ng/ml of consensus interferon (C-IFN). Expression of mRNAs encoding dihydropyrimidine dehydrogenase (DPD), thymidine phosphorylase, and thymidylate synthase was examined by reverse transcription-polymerase chain reaction before and after C-IFN treatment. To determine the effect of pretreatment with C-IFN on 5-FU+C-IFN combination therapy, we performed WST-1 cell proliferation assays.

RESULTS

A significant reduction in the level of DPD mRNA was observed when HepG2 cells were pretreated with C-IFN (P<0.05). This reduction occurred in a time-dependent manner. Cell proliferation was reduced most significantly when HepG2 cells were treated with 5-FU and C-IFN. Furthermore, when cells were pretreated with C-IFN for 3 days, the anti-proliferative effect of 5-FU+C-IFN combination therapy was augmented significantly (P<0.05).

CONCLUSIONS

C-IFN likely improves the anti-tumor effect of 5-FU via downregulation of DPD enzyme in hepatoma cells. Pretreatment with C-IFN may increase the anti-cancer effect of 5-FU+C-IFN combination therapy.

Potential of interferon-alpha in solid tumours: part 2

The second part of this review examines the use of recombinant interferon-alpha (rIFNalpha) in the following solid tumours: superficial bladder cancer, Kaposi's sarcoma, head and neck cancer, gastrointestinal cancers, lung cancer, mesothelioma and ovarian, breast and cervical malignancies. In superficial bladder cancer, intravesical rIFNalpha has a promising role as second-line therapy in patients resistant or intolerant to intravesical bacille Calmette-Guérin (BCG). In HIV-associated Kaposi's sarcoma, rIFNalpha is active as monotherapy and in combination with antiretroviral agents, especially in patients with CD4 counts >200/mm(3), no prior opportunistic infections and nonvisceral disease. rIFNalpha has shown encouraging results when used in combination with retinoids in the chemoprevention of head and neck squamous cell cancers. It is effective in the chemoprevention of hepatocellular cancer in hepatitis C-seropositive patients. In neuroendocrine tumours, including carcinoid tumour, low-dosage (</=3 MU) or intermediate-dosage (5 to 10 MU) rIFNalpha is indicated as second-line treatment, either with octreotide or alone in patients resistant to somatostatin analogues. Intracavitary IFNalpha may be useful in malignant pleural effusions from mesothelioma. Similarly, intraperitoneal IFNalpha may have a role in the treatment of minimal residual disease in ovarian cancer. In breast cancer, the only possible role for IFNalpha appears to be intralesional administration for resistant disease. IFNalpha may have a role as a radiosensitising agent for the treatment of cervical cancer; however, this requires confirmation in randomised trials. On the basis of current evidence, the routine use of rIFNalpha is not recommended in the therapy of head and neck squamous cell cancers, upper gastrointestinal tract, colorectal and lung cancers, or mesothelioma. Pegylated IFNalpha (peginterferon-alpha) is an exciting development that offers theoretical advantages of increased efficacy, reduced toxicity and improved compliance. Further data from randomised studies in solid tumours are needed where rIFNalpha has activity, such as neuroendocrine tumours, minimal residual disease in ovarian cancer, and cervical cancer. A better understanding of the biological mechanisms that determine response to rIFNalpha is needed. Studies of IFNalpha-stimulated gene expression, which are now feasible, should help to identify molecular predictors of response and allow us to target therapy more selectively to patients with solid tumours responsive to IFNalpha.

The Escherichia coli mazEF suicide module mediates thymineless death

In 1954, Cohen and Barner discovered that a thymine auxotrophic (thyA) mutant of Escherichia coli undergoes cell death in response to thymine starvation. This phenomenon, called thymineless death (TLD), has also been found in many other organisms, including prokaryotes and eukaryotes. Though TLD has been studied intensively, its molecular mechanism has not yet been explained. Previously we reported on the E. coli mazEF system, a regulatable chromosomal suicide module that can be triggered by various stress conditions. MazF is a stable toxin, and MazE is an unstable antitoxin. Here, we show that cell death that is mediated by the mazEF module can also be activated by thymine starvation. We found that TLD depends on E. coli mazEF and that under thymine starvation, the activity of the mazEF promoter P(2) is significantly reduced. Our results, which describe thymine starvation as a trigger for a built-in death program, have implications for programmed cell death in both prokaryotes and eukaryotes.

Phase II trial of systemic continuous fluorouracil and subcutaneous recombinant interferon Alfa-2b for treatment of hepatocellular carcinoma

PURPOSE

Because cirrhosis is extremely common in hepatocellular carcinoma (HCC) in the United States, and it precludes the use of several chemotherapy agents, this phase II trial of fluorouracil (FU) and recombinant interferon alfa-2b (rIFNalpha2b) in HCC was launched with the assumption that it could be tolerated by cirrhotics.

PATIENTS AND METHODS

Forty-three patients with HCC (34), and fibrolamellar HCC (FLHCC; nine) were treated with continuous intravenous (IV) FU (200 mg/m2/d x 21 every 28 days) and subcutaneous (SC) rIFNalpha2b (4 million U/m2) three times weekly. Survival was determined in all 43 patients, and response could be assessed in 28 HCC and 8 FLHCC patients.

RESULTS

The median ages of the patients were 63.5 and 19 years among HCC and FLHCC patients, respectively. Liver cirrhosis was present among 71% of HCC patients but among none of the FLHCC patients. Nine of 36 (25%; four of 28 [14%] HCC patients; five of eight [62.5%] FLHCC patients) patients in which a response could be assessed had a complete response (CR; one patient with FLHCC and no patients with HCC) or partial response (PR; eight patients [four HCC and four FLHCC patients]). Four HCC patients underwent resection, and two had a histologic CR; one HCC patient with a PR underwent orthotopic liver transplantation. One FLHCC patient also underwent resection without clear margins. Overall median survival was 19.5 months (95% confidence interval [CI], 11.2 to 27.8 months); median survival was 15.5 months (95% CI, 8.5 to 22.5 months) among HCC patients, and that of FLHCC patients was 23.1 months (95% CI, 10.3 to 35.9 months). Overall grade 3 or 4 toxicity included stomatitis (32.6%), fatigue (4.7%), and hematologic toxicity (9.3%).

CONCLUSION

Continuous IV FU and thrice-weekly SC rIFNalpha2b are an effective treatment, especially for FLHCC, and may have a neoadjuvant role in this disease. This regimen has activity in HCC and can be tolerated even by cirrhotic patients.

A pilot trial of combination cisplatin, 5-fluorouracil and interferon-alpha in the treatment of advanced esophageal carcinoma

BACKGROUND/OBJECTIVES

Based on the synergistic effect between cisplatin and 5-fluorouracil (5-FU), and between 5-FU and interferon-alpha, we conducted a trial to assess the response rate and toxicity of the combination of cisplatin, 5-FU and interferon-alpha in patients with advanced esophageal cancer.

METHODS

Patients with locally advanced or metastatic squamous cell or adenocarcinoma of the esophagus were eligible. No prior chemotherapy or interferon were allowed. Patients received cisplatin 80 mg/m(2) on day 1, 5-FU 750 mg/m(2)/day by continuous intravenous infusion for 5 days, and interferon-alpha 5 x 10(6) units/m(2)/day by subcutaneous injection on days 1-5 of each cycle. Cycles were repeated every 21 days for a total of 6 cycles.

RESULTS

Forty patients were enrolled. Median age was 57.5 years (range 30-70). 33 had squamous carcinoma and 7 adenocarcinoma; 15 were male; the locoregional metastatic ratio was 1:39; median ECOG performance status was 2 (range 1-3). Grade 3-4 toxicities were: leukopenia (9 cases), thrombocytopenia (4), electrolyte imbalance (11), febrile neutropenia (11), vomiting (5), diarrhea (4), and mucositis (11). There were 3 early deaths, most probably related to therapy. Five patients (13%) achieved a complete response and 17 (42%) achieved a partial response, yielding an overall response rate of 55%. Response rates for squamous and adeno histology were 61% and 29%, respectively. Median survival was 6.4 months.

CONCLUSION

The combination of cisplatin, 5-FU and interferon-alpha produces a high response rate in advanced squamous cell esophageal carcinoma, but with considerable toxicity. A modified combination of the above agents is presently being evaluated at our institution.

Biochemical and molecular effects of UCN-01 in combination with 5-fluorodeoxyuridine in A431 human epidermoid cancer cells

Concurrent and pre-exposure of A431 human epidermoid cancer cells to UCN-01, an investigational anticancer drug, with 5-fluoro--2'-deoxyuridine (FdUrd), which targets thymidylate synthase, produced more than additive cytotoxicty. A 24-h exposure to 10 nM FdUrd led to inhibition of TS, a 2.5-fold increase in total thymidylate synthase protein content, profound dTTP depletion and a 6.3-fold increase in the ratio of dATP to dTTP, but did not cause single-strand breaks in DNA. However, FdUrd enhanced UCN-01-associated DNA strand breaks. Concurrent thymidine exposure led to repletion of dTTP pools, and cytoprotection against FdUrd alone and with UCN-01. UCN-01 arrested cells in G1, decreased the percentage of FdUrd-treated cells in S phase and reduced FdUrd-DNA incorporation, suggesting the latter was not important for cytotoxicity. Delayed induction of high molecular mass DNA fragmentation and poly(ADP-ribose) polymerase cleavage was observed with the combination of UCN-01 and FdUrd. These findings suggest that while FdUrd-mediated deoxynucleotide imbalance alone was insufficient to induce apoptosis in this p53-mutant cell line, it magnified UCN-01's effects, most likely by interfering with DNA repair. The clinical evaluation of UCN-01 combined with 5-fluoropyrimidines may be of interest.

Advances in the treatment of metastatic colorectal cancer

Colorectal cancer represents the third leading cause of cancer mortality in the United States. During the past four decades, 5-fluorouracil (5-FU) has served as the cornerstone of therapy for individuals with advanced colorectal cancer (ACRC). Despite numerous attempts at maximizing efficacy of 5-FU through biochemical modulation, a significant benefit in terms of survival has never been realized. The recent emergence of novel chemotherapeutic drugs employing different mechanisms of action than 5-FU has led to the incorporation of irinotecan (CPT-11) with 5-FU/leucovorin as the new standard first-line regimen for future trials. This review outlines emerging data utilizing oral fluoropyrimidines and other new agents including oxaliplatin, raltitrexed, and eniluracil. Randomized clinical trials are currently underway in an effort to define optimal combination chemotherapy regimens, scheduling of agents, duration of therapy, and choice of therapy using a variety of prognostic molecular markers.

Enhancement of sensitivity to capecitabine in human renal carcinoma cells transfected with thymidine phosphorylase cDNA

The purpose of the present study was to examine directly the role of thymidine phosphorylase (TP) in the sensitivity of renal cell carcinoma (RCC) to a novel fluoropyrimidine carbamate, capecitabine. TP cDNA-transfected RCC are used in these experiments to provide a basis for improved therapeutic benefit in chemoimmunotherapy. Human RCC line KU2 cells were transfected with pcDNA3.1/zeo(+) with or without human TP cDNA by the lipofectin method. We established a clone transfected with pcDNA3.1/zeo(+)/TP (KU2-TP15) and a clone transfected with pcDNA3.1/zeo(+) as a control (KU2-C1). TP expression levels (mean +/- SD) examined by enzyme-linked immunosorbent assay (ELISA) were 1.3 +/- 0.14 U/mg protein in KU2, 1.6 +/- 0.57 U/mg protein in KU2-C1 and 216 +/- 25.6 U/mg protein in KU2-TP15. Immunohistochemical staining of subcutaneous tumors established in Balb/c nu/nu mice showed that KU2-TP15 was strongly positive for TP expression, whereas KU2 and KU2-C1 were negative. Sensitivities in vitro to 5-fluorouracil (5FU), 5'-deoxy-5-fluorouridine (5'DFUR) and capecitabine in KU2-TP15 were significantly enhanced compared with those in KU2 or KU2-C1. A moderate but statistically significant bystander effect was observed in vitro. KU2-TP15 tumors showed significant increase in the in vivo sensitivities to 5'DFUR and capecitabine as compared with the vehicle alone while KU2-C1 tumors did not. The difference in tumor-free rate in mice bearing KU2-TP15 at 2 months after the cessation of treatment was statistically significant between the capecitabine treatment group and the controls, the 5FU treatment group and the 5'DFUR treatment group. The present study clearly provides direct evidence for the role of TP in mediating the sensitivity of RCC to capecitabine.

5-Fluorouracil: forty-plus and still ticking. A review of its preclinical and clinical development

5-Fluorouracil (5-FU) and 5-fluoro-2'-deoxyuridine (FdUrd) are pyrimidine analogs that have been part of the therapeutic armamentarium for a variety of solid tumors for over forty years. 5-FU has customarily required intravenous administration due to poor and erratic oral bioavailability, while FdUrd has generally been employed for regional administration to the liver or the peritoneal cavity. A great deal of knowledge has been gained concerning the cellular pharmacology and mechanism of action of 5-FU since it was first synthesized in the late 1950's. A more thorough understanding of the factors influencing the metabolic activation of 5-FU and its cellular effects has generated considerable interest in combining it with both modulatory agents such as leucovorin and methotrexate that enhance its metabolism or cytotoxic effects. In addition, 5-FU has also been employed to enhance the therapeutic activity of other antineoplastic agents or modalities such as cisplatin and ionizing radiation with which it can synergize. Appreciation of the clinical pharmacology of 5-FU and FdUrd have led to a variety of schedules that are clinically useful. The preclinical and clinical pharmacology of 5-FU is reviewed to provide a basis for exploring the novel approaches to permit oral administration of 5-FU or its prodrugs that will be described in other articles in this issue.

Induction of thymidine phosphorylase as a pharmacodynamic end-point in patients with advanced carcinoma treated with 5-fluorouracil, folinic acid and interferon alpha

Thymidine phosphorylase (TP) is an essential enzyme for the biochemical activation of 5-fluorouracil (5-FU). Interferon upregulates TP in vivo, although the dose and schedule of interferon for optimal biomodulation of 5-FU is not known. In this study, TP activity was measured in peripheral blood lymphocytes (PBLs) from patients with advanced carcinoma receiving treatment with 5-FU and folinic acid. Cohorts of patients were treated with interferon alpha (IFNalpha), immediately prior to 5-FU/folinic acid, at doses of 3 MIU m(-2), 9 MIU m(-2) and 18 MIUm(-2). IFNalpha was administered on day 0 cycle two, day-1 and day 0 cycle three and day-2, day-1 and day 0 cycle four. A fourth cohort was treated with IFNalpha 9 MIU m(-2) three times per week from cycle 2 onwards. Twenty-one patients were entered into the study with 19 evaluable for response. Six patients (32%) had stable disease and 13 (68%) progressive disease. There were no grade-IV toxicities. TP activity was detected in PBLs from all patients with wide interpatient variability in constitutive TP activity prior to chemotherapy, and in response to IFNalpha. 5-FU/folinic acid alone did not induce TP activity but a single dose of IFNalpha led to upregulation of TP within 2 h of administration with a further increase by 24 h (signed rank test, P = 0.006). TP activity remained elevated for at least 13 days (signed rank test, P= 0.02). There were no significant differences in TP activity between schedules or with additional doses of IFNalpha. A single dose of IFNalpha as low as 3 MIU m(-2) can cause sustained elevation of PBL TP activity in vivo indicating that biochemical markers are important pharmacodynamic endpoints for developing optimal schedules of IFNalpha for biomodulation of 5-FU.

Thymidine phosphorylase: its role in sensitivity and resistance to anticancer drugs

Thymidine phosphorylase (TP) is an angiogenic enzyme present in normal tissues. Increased levels are found in many tumors, in stromal cells, tumor cells or both. High tumor TP levels may confer a poor prognosis. Cytokines (including interferons), tissue hypoxia and low pH increase TP levels. The influence of tumor TP on fluoropyrimidine toxicity is variable, but capecitabine is a prodrug of fluorouracil that requires activation by TP and hence may have a higher therapeutic index than other fluoropyrimidines. Folate-based thymidylate synthase inhibitors may also be more effective in tumors with a high TP because of increased degradation of endogenous thymidine. Copyright 1999 Harcourt Publishers Ltd.

Tumor, normal tissue, and plasma pharmacokinetic studies of fluorouracil biomodulation with N-phosphonacetyl-L-aspartate, folinic acid, and interferon alfa

PURPOSE

To evaluate the effect of N-phosphonacetyl-L-aspartate (PALA), folinic acid (FA), and interferon alfa (IFN-alpha) biomodulation on plasma fluorouracil (5FU) pharmacokinetics and tumor and liver radioactivity uptake and retention after [18F]-fluorouracil (5-[18F]-FU) administration.

PATIENTS AND METHODS

Twenty-one paired pharmacokinetic studies were completed on patients with colorectal, gastric, and hepatocellular cancer, utilizing positron emission tomography (PET), which allowed the acquisition of tumor, normal tissue, and plasma pharmacokinetic data and tumor blood flow (TBF) measurements. The first PET study was completed when the patient was biomodulator-naive and was repeated on day 8 after the patient had been treated with either PALA, FA, or IFN-alpha in recognized schedules.

RESULTS

TBF was an important determinant of tumor radioactivity uptake (r = .90; P < .001) and retention (r = .96; P < .001), for which radioactivity represents a composite signal of 5-[18F]-FU and [18F]-labeled metabolites and catabolites. After treatment with PALA, TBF decreased (four of four patients; P = .043), as did tumor radioactivity exposure (five of five patients; P = .0437), with no change in plasma 5FU clearance. With FA treatment, there were no differences observed in whole-body metabolism, plasma 5FU clearance, or tumor and liver pharmacokinetics. IFN-alpha had measurable effects on TBF and 5-[18F]-FU metabolism but had no apparent affect on liver blood flow.

CONCLUSION

The administration of PALA and IFN-alpha produced measurable changes in plasma, tumor, and liver pharmacokinetics after 5-[18F]-FU administration. No changes were observed after FA administration. In vivo effects may negate the anticipated therapeutic advantage of 5FU biomodulation with some agents.

Thymine metabolism and thymineless death in prokaryotes and eukaryotes

For many years it has been known that thymine auxotrophic microorganisms undergo cell death in response to thymine starvation [thymineless death (TLD)]. This effect is unusual in that deprivation of many other nutritional requirements has a biostatic, but not lethal, effect. Studies of numerous microbes have indicated that thymine starvation has both direct and indirect effects. The direct effects involve both single- and double-strand DNA breaks. The former may be repaired effectively, but the latter lead to cell death. DNA damaged by thymine starvation is a substrate for DNA repair processes, in particular recombinational repair. Mutations in recBCD recombinational repair genes increase sensitivity to thymineless death, whereas mutations in RecF repair protein genes enhance the recovery process. This suggests that the RecF repair pathway may be critical to cell death, perhaps because it increases the occurrence of double-strand DNA breaks with unique DNA configurations at lesion sites. Indirect effects in bacteria include elimination of plasmids, loss of transforming ability, filamentation, changes in the pool sizes of various nucleotides and nucleosides and in their excretion, and phage induction. Yeast cells show effects similar to those of bacteria upon thymine starvation, although there are some unique features. The mode of action of certain anticancer drugs and antibiotics is based on the interruption of thymidylate metabolism and provides a major impetus for further studies on TLD. There are similarities between TLD of bacteria and death of eukaryotic cells. Also, bacteria have "survival" genes other than thy (thymidylate synthetase), and this raises the question of whether there is a relationship between the two. A model is presented for a molecular basis of TLD.

Interferon-alpha and 5-fluorouracil therapy in patients with metastatic renal cell cancer: an open multicenter trial. The Japanese Study Group Against Renal Cancer

OBJECTIVES

Recent clinical trials have implied the cytotoxic and antiproliferative effects of combining 5-fluorouracil and interferon-alpha in the treatment of metastatic renal cell cancer. We therefore conducted an open multicenter trial to test the efficacy of such a combination on this cancer.

METHODS

Human lymphoblastoid interferon (3 MIU per patient) was administered subcutaneously three times weekly for 12 weeks, while 5-fluorouracil was administered (600 mg/m2/day) as a continuous infusion for the first 5 days, followed by an intravenous bolus infusion of 600 mg/m2 once a week from the 3rd week until the 12th week.

RESULTS

Of the 63 patients entered into the trial, 55 were eligible and evaluable for systemic toxicities, and 53 were evaluable for their response. All patients had undergone a prior nephrectomy, and their European Cooperative Oncology Group (ECOG) performance status ranged from 0 to 3 (median 0). Three complete and eight partial responses were induced, with an overall response rate of 20.0%. The median time to progression and the median survival time were 11 and 33 months, respectively. World Health Organization grade 3 toxicities were observed in 8 patients; however, no grade 4 toxicities or toxicity-related deaths were noted.

CONCLUSIONS

Combination therapy of interferon-alpha plus 5-fluorouracil at the above-described dosage and schedule produced no better responses than interferon monotherapies. Prolongation of survival could be attributable to the fair performance status of the patients. This regimen has limited value for the treatment of patients with advanced renal cell cancer.

Effects of perturbations of pools of deoxyribonucleoside triphosphates on expression of ribonucleotide reductase, a G1/S transition state enzyme, in p53-mutated cells

Effects of drug treatment with antimetabolites on a human colon cancer cell line, SW480, were studied. Cells were treated with 10 microM of 5-fluorouracil (5FU), an inhibitor of pyrimidine synthesis, or 1000 microM of hydroxyurea (HU), an inhibitor of both purine and pyrimidine syntheses, or the combination. Recombinant alpha-2a-interferon (IFN), 500 U/mL, also was employed, as this augments the effects of both antimetabolites in vitro and in vivo. The predominant effect of this combination was to block cells in early S phase as measured by 5-bromo-2'-deoxyuridine (BrdUrd) incorporation. By 24 hr, 86% of the cells had accumulated in S phase, but failed to progress to G2/M. This was accompanied by an early, rapid decline in all four deoxyribonucleoside triphosphates (dNTPs) by 38-86% at 4-24 hr. Despite these effects, expression of the G1/S transition state enzyme, ribonucleotide reductase (RR), increased at 24 hr as measured by a 3 to 5-fold increase in mRNA levels for the M2 subunit, in the absence of a measurable effect on protein levels. The rise in levels of RR mRNA and the continued progression of cells into S phase were associated with a synergistic inhibition of cell cycle proliferation resulting from treatment with the three-drug combination. This suggests that in the presence of antimetabolite-induced depletion of dNTPs, SW480 cells, which lack a normal p53 gene, will proceed into S phase, and that this is associated with a rise in expression of the G1/S transition state enzyme, RR. Cells arrested in S phase by a p53-independent mechanism will undergo a synergistic enhancement of cell death.

Modulation of fluorouracil cytotoxicity by interferon-alpha and -gamma

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

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.