5-Fluorouracil incorporation into human breast carcinoma RNA correlates with cytotoxicity

Integrating cell-cycle progression, drug penetration and energy metabolism to identify improved cancer therapeutic strategies

The effectiveness of chemotherapeutic drugs in tumors is reduced by multiple effects including drug diffusion and variable susceptibility of local cell populations. We hypothesized that quantifying the interactions between drugs and tumor microenvironments could be used to identify more effective anti-cancer strategies. To test this hypothesis we created a mathematical model that integrated intracellular metabolism, nutrient and drug diffusion, cell-cycle progression, cellular drug effects, and drug pharmacokinetics. To our knowledge, this is the first model that combines these elements and has coupled them to experimentally derived parameters. Drug cytotoxicity was assumed to be cell-cycle phase specific, and progression through the cell cycle was assumed to be dependent on ATP generation. The model consisted of a coupled set of nonlinear partial differential, ordinary differential and algebraic equations with an outer free boundary, which was solved using orthogonal collocation on a moving grid of finite elements. Model simulations showed the existence of an optimum drug diffusion coefficient: a low diffusivity prevents effective penetration before the drug is cleared from the blood and a high diffusivity limits drug retention. This result suggests that increasing the molecular weight of the anti-cancer drug paclitaxel from 854 to approximately 20,000 by nanoparticle conjugation would improve its efficacy. The simulations also showed that fast growing tumors are less responsive to therapy than are slower tumors with more quiescent cells, demonstrating the competing effects of regrowth and cytotoxicity. The therapeutic implications of the simulation results are that (1) monolayer cultures are inadequate for accurately determining therapeutic effects in vitro, (2) decreasing the diffusivity of paclitaxel could increase its efficacy, and (3) measuring the proliferation fraction in tumors could enhance the prediction of therapeutic efficacy.

Cytotoxic effect of a replication-incompetent adenoviral vector with cytosine deaminase gene driven by L-plastin promoter in hepatocellular carcinoma cells

Great expectations are set on gene therapy for the treatment of malignant hepatocellular carcinomas (HCC) in East Asia. Recombinant adenoviral vectors (AV) have been developed in which the L-plastin promoter (LP) regulates the expression of transgenes, in a tumor cell specific manner, resulting in an increase in the therapeutic index. The development of the AdLPCD vector, a replication-incompetent AV, containing a transcription unit of LP and E. coli cytosine deaminase (CD), was reported in our previous work. In the present study, the AdLPCD vector combined with 5-fluorocytosine (5-FC) administration was tested to see if it might have significant utility in the chemosensitization of L-plastin positive HCC. Four HCC cell lines (HepG2, Chang Liver, Huh-7 and SK-Hep-1 cells) were investigated for the expression of LacZ after infecting the cells with the AdLPLacZ vector containing a 2.4 kb fragment of LP and the LacZ gene. Relatively high levels of LP activity were detected in HepG2, followed by Chang Liver cells; whereas, no promoter activity was found in Huh-7 and SK-Hep-1 cells, as determined by AdLPLacZ infection followed by the beta-galactosidase assay. In addition, the results of RT-PCR assays for the detection of endogenous L-plastin mRNA in these cells lines correlated well with those of the beta-galactosidase activity after infection with AdLPLacZ. Based on these data, the cytotoxic effect of AdLPCD/5-FC was evaluated in HepG2 cells. These results indicate that the CD gene delivered by AV could sensitize HepG2 cells to the prodrug, 5-FC. However, the observed effects were insufficient to cause the death of most of cells. This suggests that the screening of patients for an AdLP/5-FC strategy based on AdLPLacZ data might not always guarantee a good therapeutic outcome.

Mechanisms of acquired chemoresistance to 5-fluorouracil and tomudex: thymidylate synthase dependent and independent networks

PURPOSE

Thymidylate synthase (TS) over-expression is widely accepted as a major molecular mechanism responsible for 5-fluorouracil (5-FU) and tomudex (TDX) resistance. In this study, the importance of TS in 5-FU and TDX resistance was evaluated.

METHODS

The sensitivity of TS-over-expressing 5-FU (3) and TDX (3) resistant cell lines to 5-FU and TDX was analysed. The cross-resistance between 5-FU and TDX resistant cell lines was determined. The relationship between p53 and NF-kappaB status and the sensitivity to 5-FU and TDX was evaluated.

RESULTS

Compared to relevant parental sensitive cell lines, the 5-FU resistant cell lines were highly cross-resistant to TDX (over 20,000-fold). In contrast, over-expression of TS did not significantly confer 5-FU resistance on the TDX resistant cell lines (0.8- to 1.3-fold). Thymidine (20 microM) rescue induced TDX resistance in TDX sensitive cell lines (over 10,000-fold) but only moderately influenced 5-FU sensitivity in 5-FU sensitive cell lines (1.1- to 2.4-fold). Uridine moderately protected one cancer cell line (RKO) from 5-FU-induced, but not TDX-induced, cytotoxicity. NF-kappaB transfected MCF-7 and p53 knockout HCT116 cells were resistant to 5-FU (4.4- and 2.4-fold, respectively) but not to TDX. TS protein expression in NF-kappaB transfected and p53 knockout cell lines was comparable to the relevant parental cell lines.

CONCLUSION

In some cancer cell lines, TS-independent molecular events may play a key role in 5-FU resistance. Loss of p53 function and NF-kappaB over-expression may be involved in TS-independent 5-FU chemoresistance in some cancer cell lines.

Chk1-dependent slowing of S-phase progression protects DT40 B-lymphoma cells against killing by the nucleoside analogue 5-fluorouracil

Chk1 plays a crucial role in the DNA damage and replication checkpoints in vertebrates and may therefore be an important determinant of tumour cell responses to genotoxic anticancer drugs. To evaluate this concept we compared the effects of the nucleoside analogue 5-fluorouracil (5FU) on cell cycle progression and clonogenic survival in DT40 B-lymphoma cells with an isogenic mutant derivative in which Chk1 function was ablated by gene targeting. We show that 5FU activates Chk1 in wild-type DT40 cells and that 5FU-treated cells accumulate in the S phase of the cell cycle due to slowing of the overall rate of DNA replication. In marked contrast, Chk1-deficient DT40 cells fail to slow DNA replication upon initial exposure to 5FU, despite equivalent inhibition of the target enzyme thymidylate synthase, and instead accumulate progressively in the G1 phase of the following cell cycle. This G1 accumulation cannot be reversed rapidly by exogenous thymidine or removal of 5FU, and is associated with increased incorporation of 5FU into genomic DNA and severely diminished clonogenic survival. Taken together, these results demonstrate that a Chk1-dependent replication checkpoint which slows S phase progression can protect tumour cells against the cytotoxic effects of 5FU.

Modulation of uridine phosphorylase gene expression by tumor necrosis factor-alpha enhances the antiproliferative activity of the capecitabine intermediate 5'-deoxy-5-fluorouridine in breast cancer cells

Uridine phosphorylase (UPase) has been shown to play an important role in the antineoplastic activity of 5-fluorouracil (5-FU) and in the anabolism of its oral prodrug, capecitabine, through the conversion of 5'-deoxy-5-fluorouridine (5'-DFUR) into 5-FU. In this study, we investigated the effect of tumor necrosis factor-alpha (TNF-alpha) on UPase gene expression and 5'-DFUR antiproliferative activity and elucidated the involved signal transduction pathway. Our data indicate that TNF-alpha significantly induced UPase mRNA expression and its enzymatic activity in EMT6 murine breast cancer cells, leading to an enhanced cytotoxicity of 5'-DFUR. This is further confirmed by an increased incorporation of 5'-DFUR-originated 5-FU nucleotides into nucleic acids. To clarify the mechanism of TNF-alpha-induced UPase expression, we first observed the effect of TNF-alpha on the UPase promoter activity with a series of 5'-deleted promoter-luciferase constructs. Transient transfection analysis showed that the TNF-alpha-inductive pattern in EMT6 cells was consistent with the presence of a nuclear factor-kappaB (NF-kappaB) binding element (-1332/-1312 bp) in the UPase promoter region. Furthermore, electrophoretic mobility shift assays, supershift, and cotransfection assays revealed that the activation of p65 was responsible for UPase induction by TNF-alpha. Finally, the induction of UPase by TNF-alpha could be suppressed by PS-341, a NF-kappaB inhibitor. In summary, TNF-alpha efficiently induces UPase gene expression through a NF-kappaB subunit p65-dependent pathway enhancing cell sensitivity to 5'-DFUR. The elucidation of this regulation mechanism may aid in the clinical use of 5-FU-based chemotherapy.

5-fluorouracil interferes with actin organization, stress fiber formation and cell migration in corneal endothelial cells during wound repair along the natural basement membrane

Corneal endothelial cells respond to a circular freeze wound by undergoing actin cytoskeletal reorganization that is mainly characterized by the disappearance of circumferential microfilament bundles (CMBs) and the subsequent appearance of distinct stress fibers. This cytoskeletal rearrangement is associated with changes in cell shape as migrating cells lose their polyhedral appearance, spread out, and assume a stellate morphology with cell processes extending outward into the injured area. We report here that in the presence of low concentrations (0.01-0.l mM) of the anti-metabolite 5-fluorouracil (5-FU), characteristic actin organization becomes disrupted and migrating cells do not display elongated processes typical of control tissues and translocation into the injury zone is retarded, but not inhibited. Rhodamine phalloidin staining revealed no evidence of stress fiber formation. A higher concentration of 5-FU (1.0 mM) not only prevented formation of discernible stress fibers but also resulted in a more restricted cell movement during wound repair. That this was not a cytotoxic effect was demonstrated by transferring tissues back into standard medium allowing endothelia to reinitiate migration and undergo complete wound healing by 72 h post-transfer. Overnight incubation of endothelia in 4 muM phallacidin resulted in limited CMB disruption the extent of which was dependent on the 5-FU concentration. The effects of 5-FU on the actin cytoskeleton are reversible and by 24 h after placing treated endothelia into medium without 5-FU, actin begins to become re-established and by 48 h microfilament patterns in the tissue resemble those of non-treated endothelia. Similarly, when non-injured tissues are cultured in the presence of 5-FU for 24 h, subsequently injured and returned to standard medium, they exhibit no stress fibers when observed at 24 h post-wounding. However, by 48 h post-injury these cells now display stress fibers and extend processes into the wound area. Biochemical studies on isolated muscle actin demonstrated that actin polymerization is unaffected in the presence of either 0.01 or 1 mM 5-FU as determined by the F-actin sedimentation and falling ball viscosity techniques. Thus, the mechanism(s) by which 5-FU exerts its actions on the actin cytoskeleton appears to be one of an indirect nature.

Genotoxicity test system based on p53R2 gene expression in human cells: examination with 80 chemicals

p53R2, which encodes a subunit of ribonucleotide reductase, is activated by DNA damage induced by gamma-ray and ultraviolet irradiation, and also by genotoxic chemicals such as adriamycin. For the purpose of constructing an easy-operating genotoxicity test system using human cell lines, we developed a p53R2-dependent luciferase reporter gene assay, and demonstrated dose-dependent luminescence caused by adriamycin in two human cell lines that express wild-type p53, MCF-7 and HepG2. The performance of this assay system was evaluated with 80 chemicals including those known in the Ames test as genotoxic or non-genotoxic. When the luciferase activity of cells treated with the test sample was over 200% to that of control cells in a dose-dependent increasing manner, the sample was judged positive as a genotoxic chemical. Forty of 43 Ames-positive chemicals induced luciferase activity in this assay system. Eight Ames-negative chemicals also induced luciferase activity. These eight chemicals are genotoxic in other in vitro test systems using mammalian cells. It is suggested that this assay system can be applied to rapid screening of chemicals for potential human genotoxicity.

A novel polypyrimidine antitumor agent FdUMP[10] induces thymineless death with topoisomerase I-DNA complexes

FdUMP[10], a 10mer of 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP), the thymidylate synthase inhibitory metabolite of 5-fluorouracil (FU), is most closely correlated with the DNA topoisomerase I (Top1) inhibitor camptothecin in the National Cancer Institute COMPARE analysis, but not with FU. FdUMP[10] exhibits more potent antiproliferative activity than FdUMP or 5-fluoro-2'-deoxyuridine (FdU) and is markedly more active than FU. Camptothecin-resistant P388/CPT45 cells lacking Top1 are cross-resistant to FdUMP[10] as well as to FdUMP, FdU, and the thymidylate synthase inhibitor raltitrexed (Tomudex). FdUMP[10] induces DNA single-strand breaks and cellular Top1-DNA complexes. Such complexes are also observed in response to FdUMP, FdU, raltitrexed, and FU. The FdUMP[10]-induced Top1-DNA complexes are not inhibited by the caspase inhibitor z-VAD-fmk and form independently of apoptotic DNA fragmentation, indicating that they do not correspond to apoptotic Top1-DNA complexes. In biochemical assay, Top1 is directly trapped at uracil and FdU misincorporation sites. We propose that FdUMP[10] damages DNA by trapping Top1 at uracil and FdU misincorporation sites resulting from thymidylate synthase inhibition and thymine depletion.

Recombinant adenoviral vector containing tumor-specific L-plastin promoter fused to cytosine deaminase gene as a transcription unit: generation and functional test

The expression of therapeutic transgenes in recombinant adenoviral vectors is a major cause of toxicity in dividing cancer cells as well as non dividing normal cells. To solve the problem of toxicity to normal cells, we have reported on a recombinant adenoviral vector system (AdLP-) in which the expression of the transgene is directed by the tumor-specific L-plastin promoter (LP) (Chung et al., 1999). The object of this study was to generate a recombinant adenoviral vector system which would generate tumor cell specific expression of cytosine deaminase (CD) gene. We report the construction of a replication-incompetent adenoviral vector in which CD is driven by the L-plastin promoter (AdLPCD). Infection of 293 cells by AdLPCD generated the functional CD protein as measured by HPLC analysis for the conversion of 5-Fluorocytosine (5-FC) to 5-Fluorouracil (5-FU). HPLC analysis in conjunction with counting radioactivity for [6-3H]-5FC and [6-3H]-5FU demonstrated vector dose-dependent conversion of 5-FC to 5-FU in AdLPCD infected ovarian cancer cells. The results from present and previous studies (Peng et al., 2001; Akbulut et al., 2003) suggest that the use of the AdLPCD/5-FC system may be of value in the treatment of cancer including microscopic ovarian cancer in the peritoneal cavity.

A role for DNA mismatch repair in sensing and responding to fluoropyrimidine damage

The phenomenon of damage tolerance, whereby cells incur DNA lesions that are nonlethal, largely ignored, but highly mutagenic, appears to play a key role in carcinogenesis. Typically, these lesions are generated by alkylation of DNA or incorporation of base analogues. This tolerance is usually a result of the loss of specific DNA repair processes, most often DNA mismatch repair (MMR). The availability of genetically matched MMR-deficient and -corrected cell systems allows dissection of the consequences of this unrepaired damage in carcinogenesis as well as the elucidation of cell cycle checkpoint responses and cell death consequences. Recent data indicate that MMR plays an important role in detecting damage caused by fluorinated pyrimidines (FPs) and represents a repair system that is probably not the primary system for detecting damage caused by these agents, but may be an important system for correcting key mutagenic lesions that could initiate carcinogenesis. In fact, clinical studies have shown that there is no benefit of FP-based adjuvant chemotherapy in colon cancer patients exhibiting microsatellite instability, a hallmark of MMR deficiency. MMR-mediated damage tolerance and futile cycle repair processes are discussed, as well as possible strategies using FPs to exploit these systems for improved anticancer therapy.

5-fluorouracil: mechanisms of action and clinical strategies

5-fluorouracil (5-FU) is widely used in the treatment of cancer. Over the past 20 years, increased understanding of the mechanism of action of 5-FU has led to the development of strategies that increase its anticancer activity. Despite these advances, drug resistance remains a significant limitation to the clinical use of 5-FU. Emerging technologies, such as DNA microarray profiling, have the potential to identify novel genes that are involved in mediating resistance to 5-FU. Such target genes might prove to be therapeutically valuable as new targets for chemotherapy, or as predictive biomarkers of response to 5-FU-based chemotherapy.

Differential growth inhibition by 5-fluorouracil in human colorectal carcinoma cell lines

The effects of 5-fluorouracil (5-FU) on cell growth were investigated using a primary culture of human fibroblasts, MRC-5, and three established human colon cancer cell lines, DLD-1, LoVo and SW620. Detailed flow cytometric analyses revealed differential growth inhibition among these cell lines including three modes of cell growth modulation: (a) loss or accumulation of S phase cells; (b) G2/M block; and (c) G1-S arrest. From analyses on the amount of 5-FU incorporated into cellular RNA and the activity of thymidylate synthase (TS), suppression of TS and depletion of dTTP, a possible consequence of the former, was considered to be the major action of 5-FU in these cells. Differences in the cellular responses to the nucleotide pool imbalance appeared to make the cell growth modulation diverse. Loss of S phase cells and G1-S phase arrest were evident in p53 wild-type cells, MRC-5 and LoVo. Cells proficient in DNA mismatch repair, SW620 and MRC-5, showed marked modulations in S-G2/M progression. These findings suggest that multiple factors, including p53 and DNA mismatch repair, participate in diverse cell growth modulations in cells treated with 5-FU. Cellular resistance to 5-FU correlated well with a loss of modulations in S-G2/M progression, rather than with a defect of G1-S arrest, which suggests the significance of DNA mismatch repair as a factor affecting the sensitivity of cells to 5-FU.

Severe cardiotoxicity during 5-fluorouracil chemotherapy: a case and literature report

The chemotherapeutic agent 5-fluorouracil (5-FU) is a widely accepted part of many cancer treatment protocols. Its cardiotoxic potential is known, but considered uncommon and usually not life threatening, although some cases of severe cardiotoxicity related to 5-FU have been reported. The pathogenesis of cardiotoxicity caused by 5-FU is not clear. We report a case of sudden onset of severe cardiac failure, without ischemic symptoms or signs, during 5-FU treatment with serious consequences, in a previously healthy 23-year-old patient with squamous cell carcinoma of the tongue. Endomyocardial biopsy showed proliferation of the sarcoplasmic reticulum with marked vacuolization, similar to that found with doxorubicin cardiotoxicity. Because 5-FU cardiotoxicity is unpredictable and can have potentially fatal consequences, it requires, in our opinion, further clarification. With this well-documented case, including an endomyocardial biopsy, we hope to encourage additional efforts to investigate the pathophysiologic mechanisms of 5-FU cardiotoxicity.

Treatment of colorectal cancer: hepatic metastasis

Almost one-third of patients dying from colorectal cancer have tumor limited to the liver. Systemic chemotherapy is the appropriate palliative management of patients with metastases to the liver and other sites. For many patients with isolated hepatic metastases, systemic chemotherapy is also the most appropriate treatment. However, results with systemic chemotherapy indicate that one-third or less of patients will respond to such treatments, and long-term survival is rare. In this report we provide information concerning the natural history of colorectal hepatic metastases, followed by the expected benefits with systemic chemotherapy. This information provides background for the regional therapeutic strategies of surgical resection, cryosurgery, and hepatic artery chemotherapy. We discuss the selection factors appropriate for such treatments, morbidity and mortality, and the potential long-term benefits of such approaches. The last section focuses on surgical considerations in hepatic resection and hepatic artery chemotherapy.

In vivo replication-deficient adenovirus vector-mediated transduction of the cytosine deaminase gene sensitizes glioma cells to 5-fluorocytosine

Viral vector-mediated transfer of chemosensitization genes represents a promising new approach to the treatment of cancer. Previous reports have demonstrated that transfection of the bacterial cytosine deaminase (cd) gene into mammalian cells can sensitize them to the otherwise nontoxic nucleoside, 5-fluorocytosine (5-FC). We now report that a replication-deficient adenovirus vector that transduces the cd gene (Ad.CMV-cd) highly sensitizes 9L gliosarcoma cells to 5-FC, and that gene transduction is associated with a potent bystander effect that is not dependent on direct cell-to-cell contact. Stereotactic injection of Ad.CMV-cd into established rat gliomas, followed by systemic administration of 5-FC in vivo, results in prolongation of survival.

Antifolates: current developments

In summary, the problem of MTX resistance has been approached in a mechanistic fashion, based on the wealth of information generated over the years. To date, these strategies have produced several new classes of anticancer drugs, with a variety of anticipated and unanticipated mechanisms of action. Several of these have shown promising preclinical activity, and these are moving into more stringent testing in the clinic.

Aberrant cell cycle inhibition pattern in human colon carcinoma cell lines after exposure to 5-fluorouracil

In this report, we describe the use of two human colon carcinoma cell lines, HCT-8 and HT-29, as potential models to study DNA- and RNA-directed cytotoxicity due to 5-fluorouracil (FUra) exposure by flow microfluorimetric analysis of DNA cell content. The sensitivity of the HT-29 line (EC50 = 0.9 microM) to FUra was somewhat greater than that of the HCT-8 line (EC50 = 4 microM), but each presented a dramatically different DNA histogram after exposure to FUra. In HCT-8, an unexpected and nearly complete disappearance of cells in S-phase occurred, whereas in HT-29 the expected accumulation of cells at the G1-S border was observed. The absence of HCT-8 cells in S-phase also occurred as a result of two RNA polymerase inhibitors: actinomycin D and dichloro-D-ribofuranosylbenzimidazole. However, an accumulation of cells in S-phase was observed in the presence of 5-fluorodeoxyuridine. These results suggest that in the HCT-8 cell line, FUra predominantly causes an RNA-related toxicity. By comparison, the rate of formation of 5-fluorodeoxyuridine monophosphate, the increased dUMP pool size, and low thymidylate synthase activity in the HT-29 line are consistent with its greater susceptibility to DNA-directed toxicity. Further evidence was seen in the prevention of FUra cytotoxicity by thymidine in HT-29, but not in HCT-8 cells. Similarly, Leucovorin synergized the action of FUra in HT-29 but not in HCT-8. Enzymatic correlates supporting these observations are seen in the greater activity of uridine kinase than thymidine kinase (20:1) in HCT-8 cells compared with that in HT-29 cells (4:1).

The cell cycle effects and induction of apoptosis by 5-bromouridine in cultures of human leukaemic MOLT-4 and HL-60 cell lines and mitogen-stimulated normal lymphocytes

5-Bromouridine (BrUrd) and several analogues of this antimetabolite exhibit antiviral activity and are potent inhibitors of the human immunodeficiency virus. The antitumour activity of BrUrd, however, in comparison with 5-fluorouridine or 5-fluorouracil, is less pronounced. Because BrUrd is incorporated into RNA and can be detected immunocytochemically and analysed by cytometry, it may prove useful as an RNA precursor to assay cell transcriptional activity. The aim of the present study was to evaluate the cell cycle effects of BrUrd incorporation in human lymphocytic leukaemic MOLT-4 and HL-60 cells and mitogenically stimulated normal peripheral blood lymphocytes. BrUrd suppressed cell proliferation and induced cell death; when measured after 72 h of treatment, the LD50 was 10 and 20 microM for HL-60 and MOLT-4, respectively, and LD90 was 100 microM, for both cell lines. BrUrd was maximally incorporated by the cells progressing through S phase of the cycle and the S phase cells were most severely perturbed by the drug, which was detected in RNA but not in DNA. Suppression of the S phase traverse of MOLT-4, HL-60 and normal lymphocytes was seen at > or = 30 microM BrUrd concentration. Also sensitive was the cell traverse through G2+M which, in the case of lymphocytes, HL-60 and MOLT-4 cells, was perturbed at > or = 30, > or = 200 and 500 microM BrUrd concentrations, respectively. Transition of lymphocytes from G0 to G1 was little affected at < 100 microM, and, although suppressed, was still observed even at 500 microM BrUrd concentration. Apoptosis of HL-60 cells and lymphocytes was observed at > or = 50 microM BrUrd after 24 h of incubation; death of MOLT-4 cells had mixed features of apoptosis and necrosis and resembled the 'mitotic' or 'reproductive cell death' as described in other cell systems. The cytostatic and cytotoxic effects of BrUrd should be taken into consideration when using this antimetabolite as an antiviral agent in the clinic or as an RNA precursor in assays of cell transcriptional activity.

Enhancement of antineoplastic activity of 5-fluorouracil in mice bearing colon 38 tumor by (6R)5,10-dideazatetrahydrofolic acid

(6R)5,10-Dideazatetrahydrofolic acid (DDATHF, Lometrexol), a potent antitumor drug in vivo and in vitro, is an inhibitor of the two folate-dependent enzymes in the de novo purine biosynthesis pathway: glycinamide ribonucleotide (GAR) and amino imidazole carboxamide (AICAR) transformylases. A single dose of DDATHF (50 mg/kg, i.p.) in C57/BL6 mice caused a prolonged depletion of purine nucleotides (ATP and GTP) in colon 38 tumor and only a temporary effect in liver. GAR transformylase activity was higher in colon 38 tumor than in liver, but a kinetic analysis on the purified enzyme showed no differences in Ki values for DDATHF or Km values for the folate substrate. As a consequence of de novo purine synthesis inhibition, there was a 2- to 3-fold elevation of 5-phosphoribosyl-1-pyrophosphate pools in colon 38 tumor between 4 and 12 hr after DDATHF administration. When DDATHF (50 mg/kg) was administered 4 or 8 hr prior to 5-fluorouracil (5-FU; 85 mg/kg, i.p., weekly), these biochemical effects significantly increased the antitumor activity of 5-FU, with a modest increase in toxicity. Lower doses of DDATHF (25 and 37.5 mg/kg) when combined with 5-FU also resulted in an improved antitumor activity without additional toxicity. The two different schedules of administration for DDATHF, 4 and 8 hr prior to 5-FU, showed no differences in antitumor activity or toxicity.

Hepatic arterial floxuridine and leucovorin for unresectable liver metastases from colorectal carcinoma. New dose schedules and survival update

BACKGROUND

We studied three new dose schedules of hepatic arterial infusion of floxuridine (FUDR) and leucovorin and update survival analysis of a previously reported trial using these drugs by hepatic arterial infusion for patients with hepatic metastases from colorectal carcinoma.

METHODS

Untreated patients with hepatic metastases from colorectal cancer were treated with three dose schedules: Group D, FUDR (0.3 mg/kg/day) and leucovorin (30 mg/m2/day) as a 14-day continuous infusion through an implantable hepatic arterial pump alternating with a 4-week rest period; Group E, a lower dose of FUDR (0.25 mg/kg/day) and leucovorin (30 mg/m2/day) as a 14-day infusion alternating with 2 weeks of saline; and Group F, FUDR (0.3 mg/kg/day) with a lower leucovorin dose (15 mg/m2/day) for 2 weeks followed by a 2-week rest.

RESULTS

In 42 patients with unresectable hepatic metastases, the complete-plus-partial response rate was 56%, with a median survival of 24.2 months. Complete-plus-partial response rates for groups D, E, and F were 30%, 54%, and 75%, respectively. Twelve percent of the 42 patients developed biliary sclerosis; the percentages of patients per group were 17%, 15%, and 6%, respectively. Updated median survival of the original 24 patients treated with FUDR and leucovorin by hepatic arterial infusion and these 42 new patients (66 total) was 28.8 months. One-, two-, three-, four-, and five-year survival rates were 86%, 62%, 31%, 15%, and 7%, respectively.

CONCLUSIONS

Hepatic arterial chemotherapy with FUDR and leucovorin for patients with hepatic metastases from colorectal carcinoma yields a high response rate and 1- and 2-year survivals of 86% and 62%, respectively. Although a lower dose of leucovorin (15 mg/m2) with FUDR produces a high response rate with less toxicity, before larger scale trials are initiated, further investigation is needed to reduce toxicity. A study of hepatic arterial dexamethasone with FUDR and leucovorin has been initiated for this purpose.

Relation between the incorporation of 5-fluorouracil into liver carcinoma and normal tissue RNA at hepatic arterial administration in the rat is altered by overnight starvation

The cytotoxicity of 5-FUra has been related to its incorporation into RNA. In a model of secondary liver cancer in the rat, the incorporation of 5-FUra into the acid-soluble fraction, RNA and DNA of several normal tissues and an adenocarcinoma of the colon transplanted to the liver was determined. A therapeutic labelled dose of the drug was infused via the hepatic artery for 2 hr and the rats killed 1 hr later. Half of the rats were starved overnight before treatment. The incorporation of 5-FUra into liver and intestinal RNA increased at starvation. It was unchanged in kidney and bone marrow. The incorporation into tumor RNA decreased insignificantly. The incorporation into tumor RNA was significantly higher than in hepatic, intestinal, and renal RNA at ad libitum feeding. This difference disappeared at overnight starvation.

Cytotoxic mechanisms of 5-fluoropyrimidines. Relationships with poly(ADP-ribose) polymerase activity, DNA strand breakage and incorporation into nucleic acids

A comparative study of the cytotoxic mechanisms of 5-fluorouracil (FU) and 5-fluoro-2'-deoxyuridine (FdUrd) was carried out in Chinese hamster ovary K1 (CHO-K1) cells. The poly(ADP-ribose) polymerase (PADPRP) inhibitor, 3-aminobenzamide (3AB, 3 mM) enhanced the cytotoxicity of FU with a dose enhancement factor at 10% survival of 2. This enhancement was also evident when cells were grown in dThd-free medium, but the IC50 for FU was reduced from 50 to 35 microM. In contrast, 3AB did not enhance the cytotoxicity of FdUrd but exerted a small protective effect. The IC50 for FdUrd was reduced from 35 to 1.25 microM in dThd-free medium. A 55% reduction in NAD levels was seen within 6 hr of 5.0 microM FdUrd treatment in dThd-free medium, and this reduction persisted over 24 hr. This drop was prevented by co-incubation with 3AB, indicating that PADPRP activation was the cause of the NAD depletion. In contrast, FU treatment had little or no effect on NAD levels. Alkaline elution analysis of cells treated with up to 150 microM FU revealed no DNA strand breaks in mature DNA, but an increase in breaks in nascent DNA. Co-incubation with 3AB had little or no effect on strand break levels. FdUrd (up to 40 microM) produced a dose-dependent increase in both mature and nascent DNA strand breaks. Analysis using a "relative elution" formula demonstrated that 3AB increased the amount of FdUrd-induced strand breaks (at doses < or = 5-100 microM) in mature DNA. Whereas FU elution profiles for nascent DNA were biphasic, those for FdUrd were linear. Co-incubation with 3AB increased [3H]FU incorporation into both RNA (by 50%) and DNA (45%). 3AB also enhanced [3H]FdUrd incorporation (by 40%) into RNA but had no effect on incorporation into DNA. These data indicate that in addition to acting as an inhibitor of PADPRP, 3AB exerts other metabolic effects.

Tauromustine is more effective than conventional chemotherapy in the treatment of colonic tumors

Despite recent advances in chemotherapy, the prognosis of advanced colorectal cancer remains poor. Although the taurine-based nitrosourea tauromustine (TCNU) has demonstrated schedule-dependent synergism with 5-fluorouracil (5-FU) and leucovorin (LV) against a variety of tumors in vitro, its efficacy relative to and in combination with these drugs in vivo remains unknown. To study this, BALB/C mice had C26 tumor implanted subcutaneously five days prior to the following treatment (doses and route of administration being the same in all groups): Group 1--no treatment; Group 2--TCNU (30 mg/kg by gavage); Group 3--LV (100 mg/kg intraperitoneally [IP]) and, one hour later, LV plus 5-FU (100 mg/kg IP); Group 4--LV and, one hour later, LV plus 5-FU and TCNU; and Group 5--TCNU and, on the following day, LV and, one hour later, LV plus 5-FU. All treatments were repeated seven days later. Body weight and tumor weight were measured twice weekly, and survival was noted. Postmortems were performed in all animals, and evidence of primary or secondary tumor was recorded. All surviving animals were sacrificed at 60 days. We found that 1) 87 percent of animals receiving TCNU and 60 percent of animals receiving LV, 5-FU, and TCNU survived to day 60; none of these animals had evidence of tumor when sacrificed; 2) animals in all other groups died by day 34; 3) evidence of metastases was found in five animals in Group 1 and one each in Groups 2 and 5; and 4) administering TCNU 24 hours prior to 5-FU plus LV resulted in death from toxicity in all animals. Thus, while synergism between TCNU and 5-FU plus LV was not seen, the antitumor properties of TCNU are significantly greater than those of conventional chemotherapy.

The syndrome of 5-fluorouracil cardiotoxicity. An elusive cardiopathy

BACKGROUND

A case of reversible cardiogenic shock linked to 5-fluorouracil (5-FU) was observed. Recognizing the increasing use of 5-FU, the authors tried to map this syndrome.

METHODS

They reviewed 134 additional case reports, retrieved information from literature searches, focused on clinical features, and discussed possible pathophysiologic findings and prevention of this syndrome.

RESULTS

Although angina and electrocardiographic changes were common and reproducible (approximately 90% each), coronary artery disease was found in a few patients. A total of 33 patients had severe left ventricular dysfunction, 28 without evidence of myocardial infarction. The symptoms were responsive to conservative management (90%).

CONCLUSIONS

Cardiac toxicity is a little known complication of 5-FU therapy, with an unknown but significant incidence. It is highly treatable.

Stimulation of 5-fluorouracil metabolic activation by interferon-alpha in human colon carcinoma cells

Interferon-alpha (IFN alpha) increases the cytotoxicity of 5-fluorouracil (FUra) in vitro, and the combination has clinical efficacy against advanced colorectal cancer. IFN alpha treatment of HT-29 colon carcinoma cells induced a greater than two-fold increase in the intracellular levels of the active metabolite of FUra, FdUMP. Using cell extracts from HT-29 cells and FUra as substrate, IFN alpha produced a 1.9- and 8.7-fold increase, respectively, in the activities of uridine phosphorylase and pyrimidine nucleoside phosphorylase (PyNP). Furthermore, the effect was selective for the conversion of FUra to FdUMP, as IFN alpha did not increase the cellular levels of FUTP, nor did it change the extent of incorporation of FUra into RNA (or DNA). IFN alpha also had no effect on thymidine kinase activity, the second step in the activation of FUra. Hence the effect of IFN alpha on PyNP activity is likely a critical biochemical event that modulates the cytotoxicity of FUra.

Preliminary evidence that incorporation of 5-fluorouracil into RNA correlates with antitumor response

A comparative study of two different species of a fluorouracil assay was conducted on 11 patients who had carcinoma that was deemed unresectable after the surgical operation. For these patients FU at a dose of 10 mg/kg was intravenously administered before operation, and portions of the tumors were resected within 120-150 min to assay both the (FU)RNA/RNA and FU/protein. After surgery, all patients were given FU alone either intravenously or orally. The FU, which was in an acid-soluble material (FU/protein), was not related to the antitumor effect of FU. However, the FU in RNA [(FU)RNA/RNA)] was found to be related to the antitumor effect of FU. When the concentration of (FU)RNA/RNA was above approximately 200 ng/mg, FU was effectual in unresectable carcinomas. It is probable that the (FU)RNA/RNA may be more suitable than FU/protein for predicting the antitumor effect of FU.

Biochemical pharmacology and analysis of fluoropyrimidines alone and in combination with modulators

After more than three decades since their introduction, fluoropyrimidines, especially FUra, are still a mainstay in the treatment of various solid malignancies. The antitumor effects of fluoropyrimidines are dependent upon metabolic activation. FdUMP, FUTP and FdUTP were identified as the key cytotoxic metabolites that interfere with the proper function of thymidylate synthase and nucleic acids. The relevance of these metabolites is cell-type specific. Recently, fluorouridine diphospho sugars have been detected, but the precise function of this class of metabolites is currently unknown. In mammalian systems fluoropyrimidines and their natural counterparts share the same metabolic pathways since the substrate properties in enzyme-catalyzed reactions are frequently comparable. Ongoing studies indicate that the metabolism and action of fluoropyrimidines exhibit circadian rhythms, which appear to be due to variations in the activity of metabolizing enzymes. Essential for the expanding knowledge of the pathways and effects of fluoropyrimidines has been the constant improvement of analytical methods. These include ligand binding techniques, numerous dedicated HPLC systems and 19F-NMR. Because the overall response rates achieved with fluoropyrimidines are modest, strategies based on biochemical modulation have been devised to enhance their therapeutic index. Biochemical modulators include a wide range of various compounds with different modes of action. In recently completed clinical trials, combinations of FUra with leucovorin, a precursor for 5,10-methylene tetrahydrofolate, or with levamisole, an anthelminthic with immunomodulatory activity, appeared to be superior to FUra alone. At the preclinical level combinations of fluoropyrimidines with, e.g. interferons or L-histidinol were demonstrated to be interesting candidates for further testing. The future therapeutic utility of fluoropyrimidines will depend on both the improvement of combination regimens currently used in the treatment of cancer patients and the judicious clinical implementation of promising experimental modulation strategies. Moreover, novel fluoropyrimidines with superior pharmacological properties may become important as part of or instead of modulation approaches.

Kinetic analysis of 5-fluorouracil action against various cancer cells

Based on our recent kinetic analysis, which made it possible to distinguish between the cell-killing actions of cell cycle phase-specific and non-specific agents, we attempted to elucidate the actions of 5-fluorouracil (FUra) on three different cancer cell lines. By colony-forming assay, the concentrations of fluorouridine (FUrd), fluorodeoxyuridine (FdUrd) or FUra giving 90% cell kill (IC90) at various exposure times (texps) were obtained. With P388 cells, the curve of texps-IC90 for FUrd on a log-log scale was linear with a slope of -1, which is typical for cell cycle phase-nonspecific agents. In contrast, the curve for FdUrd showed a much steeper slope than -1, which is characteristic for cell cycle phase-specific agents. We found that the curve for FUra was exactly the same as that for FUrd, indicating that the mode of FUra action on P388 leukemia is analogous to that of FUrd. Similar results were observed with human colon and renal cancer cell lines, HT-29 and KU-2, although when the cells were exposed to relatively low concentrations of FUra for a long time, a cell cycle phase-specific action became evident.

The effect of structural modifications of 5-fluorouracil derivatives on their transport and biodegradation by isolated rat jejunum

The continuous-perfusion technique was used in an isolated segment of everted rat jejunum to study transport and biotransformation processes in a series of cancerostatic derivatives of 5-fluorouracil. Metabolic alterations during penetration of the intestinal wall were assessed by high-performance liquid chromatography (HPLC). Octanol-buffer partition coefficients were measured, and the lipophilicity of the study compounds and fragmental constants for their sugar moieties were assessed. In the present series of 5-fluorouracil derivatives, there was no correlation between lipophilicity and metabolic cleavage to 5-fluorouracil, but a correlation was found between lipophilicity and the transport rate. Remarkable stability of the nucleoside bond and high biotransport were observed with 5'-chloro-5-fluorouridine, suggesting a different mode of activation for this derivative.

Evidence of a new metabolic pathway of 5-fluorouracil in Escherichia coli from in vivo 19F-NMR spectroscopy

Two distinct metabolic pathways of 5-fluorouracil are proposed in Escherichia coli. The first metabolic pathway is a reductive degradation with the formation of dihydrofluorouracil as the first metabolite. The second metabolic pathway is shown to be a hydroxylating degradation, possibly with the formation of 5-hydro-6-hydroxy-5-fluorouracil as the first metabolite. The metabolites of both pathways undergo subsequent hydrolytic degradation with fluoride ion as the common final product. The chemical structures of these metabolites were partially identified by 19F-NMR. The results show a close resemblance between these two metabolic pathways with in vivo pyrimidine biodegradation. The reductive degradation has been proposed by several laboratories, whereas the hydroxy degradation has not been reported before. Both the reductive and hydroxy pathways are demonstrated in this report, to be independent reactions.

Interaction of deoxyuridine with fluorouracil and dipyridamole in a human colon cancer cell line

We have reported previously that dipyridamole increases the toxicity of 5-fluorouracil and alters fluorouracil metabolism in HCT 116 cells, producing a selective increase in fluorodeoxyuridine monophosphate (FdUMP) levels by blocking the efflux of fluorodeoxyuridine. Dipyridamole also blocks deoxyuridine efflux and prolongs the intracellular half-life of deoxyuridine monophosphate (dUMP). The significance of the effect of dipyridamole on FdUMP and dUMP levels was explored further. In cell growth experiments, 1-50 microM deoxyuridine enhanced the cytotoxicity of 5 microM fluorouracil in a dose-dependent manner, and greater than or equal to 10 microM deoxyuridine increased the augmentation of fluorouracil toxicity produced by 0.5 microM dipyridamole. The effect of deoxyuridine on [6-3H]fluorouracil metabolism was studied. After 4 hr, 25 microM deoxyuridine increased the amount of [3H]FdUMP formed 2- to 4-fold relative to that of fluorouracil +/- dipyridamole alone. The mechanism by which deoxyuridine increased FdUMP was examined by measuring the distribution of [2'-3H]deoxyuridine metabolites following exposure of 25 microM deoxyuridine +/- 5 microM fluorouracil. Tritium appeared in the FdUMP peak at 4 and 24 hr in cells exposed to fluorouracil and deoxyuridine, indicating that [3H]deoxyribose was transferred to fluorouracil. A large buildup of [3H]dUMP was seen in cells exposed to fluorouracil plus deoxyuridine for 4 and 24 hr compared to exposure to [3H]deoxyuridine alone, suggesting that dUMP may also inhibit catabolism of FdUMP. Since the increased FdUMP levels produced by dipyridamole did not appear to correlate with further depletion of thymidine triphosphate pools, the incorporation of [3H]fluorouracil metabolites into nucleic acids was monitored by cesium sulfate density centrifugation. Fluorouracil-RNA increased as a function of time (1, 2 and 13 pmol/10(6) cells after 4, 8 and 24 hr), but fluorouracil-DNA was detected only after 24 hr (0.5 pmol/10(6) cells). Dipyridamole however, did not appear to alter the pattern of incorporation of fluorouracil into either RNA or DNA. Perturbations of endogenous dUMP levels by fluorouracil and dipyridamole were then studied. In cells exposed to fluorouracil alone, dUMP pools were unchanged from control at 2 hr, but they had increased 9-fold by 4 hr (3362 pmol/10(6) cells). Simultaneous exposure to fluorouracil and dipyridamole resulted in a 1.5-fold (566 pmol/10(6) cells) and 13.6-fold (5049 pmol/10(6) cells) increase over control dUMP levels after 2 and 4 hr respectively. The dUMP pools continued to enlarge through 24 hr. The effect of fluorouracil on DNA fragility was examined.(ABSTRACT TRUNCATED AT 400 WORDS)

Thymidylate synthase: a target for anticancer drug design

N10-Propargyl-5,8-dideazafolic acid (CB3717) has proved to be an interesting recent addition to the spectrum of antifolate drugs. Its sole biochemical locus of action appears to be thymidylate synthase, an inhibitory effect which is potentiated by intracellular polyglutamation. The drug has shown a spectrum of clinical activity and toxicity which is unusual for an antimetabolite. It seems likely that the former is attributable to its inhibition of TS, whilst the latter relates to the drug's poor aqueous solubility at physiological pH. Seminal to the discovery of a new generation of more selective thymidylate synthase inhibitors has been the observation that the C2 desamino derivative (CB3804) retains the useful TS-inhibitory and cytotoxic properties of CB3717. It is some two orders of magnitude more water soluble than CB3717 at physiological pH and appears not to produce, in the mouse, the liver and kidney toxicities which have restricted the wider use of CB3717. Thus, in desamino CB3717, it has proved possible to separate the structural features determining antitumor activity from those which are responsible for its systemic toxicities. These encouraging results prompted systematic structure-activity studies of other C2-modified quinazolines, which revealed that the desirable properties of the desamino compound are not unique. Results with two other CB3717 analogues, the C2-methyl (CB3819) and C2-methoxy (CB3828), have been discussed in the present paper. All three CB3717 analogues exhibit TS-inhibitory activities which are broadly comparable to those of the parent drug. In continuous culture CB3828 is as cytotoxic as CB3717, while CB3804 and CB3819 are at least an order of magnitude more potent. As with the desamino derivative (CB3804), so CB3819 is substantially more water soluble than CB3717 and is apparently devoid of its major toxicities. However, the effects of CB3828 on whole cell TS inhibition, both in vitro and in vivo, are rapidly reversible upon removal of exogenous compound, while the inhibition is sustained in similar experiments with the other three compounds. It is likely that these effects relate to the extent to which the various derivatives are converted to polyglutamate species and retained intracellularly. With the exception of CB3828, all are good substrates for FPGS, and the polyglutamate derivatives of CB3717, CB3804 and CB3819 are better TS inhibitors than the corresponding monoglutamates. CB3804 and CB3819 are less toxic and are cleared from the plasma much more rapidly than CB3717, so that the rate and extent of their polyglutamation may be an essential prerequisite of pharmacological activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of dosage and infusion time on the incorporation of 5-fluorouracil into DNA and RNA of normal tissues and an adenocarcinoma transplanted to rat liver

In a model of secondary liver cancer in Wistar rats the incorporation of 5-FUra into the acid soluble fraction, RNA, and DNA of several normal tissues and of an adenocarcinoma of the colon transplanted to the liver was determined; 300, 1,200 or 24,000 nmoles of 5-FUra were infused via the gastroduodenal artery for 0.5, 2, or 24 hr. The rats were killed 1.5, 3, or 24 hr after the beginning of the infusions. In general, higher doses resulted in a higher labelling. However, the ratio of incorporation into tumor RNA compared to normal tissue RNA was higher at the 1,200 than at the 24,000 nmole dosage. There was a decreased RNA/DNA ratio in the tumor at 24 hr after 24,000 nmoles of 5-FUra had been infused over 0.5 or 2 hr, indicating decreased synthesis and/or increased breakdown of RNA.

Correlation between ribosomal RNA production and RNA-directed fluoropyrimidine cytotoxicity

The relationship between cytotoxicity and fluoropyrimidine effects on the production of mature cytoplasmic 28S and 18S ribosomal RNA was studied in S-180 cells for the fluoropyrimidines: 5-fluorouracil (FUra), 5-fluorouridine (FUrd), 5-fluorodeoxyuridine (FdUrd), and 5'-deoxy-5-fluorouridine (5'-dFUrd). After a 6-hr drug exposure, the total cytotoxicity in the absence of added thymidine (dThd) was determined by soft-agar cloning and resulted in LC90 (lethal concentration to 90% of cells) values of 0.6 microM FdUrd, 0.7 microM FUrd, 5.3 microM FUra and 93 microM 5'-dFUrd. The RNA-directed (dThd-nonreversible) cytotoxicity was assessed by cloning the cells in the presence of 10 microM dThd. This resulted in an altered order of potency and increased LC90 values to 5.5 microM FUrd, 20 microM FUra, 265 microM FdUrd and 870 microM 5'-dFUrd. The production of mature cytoplasmic rRNA was determined by measuring the amount of [3H]cytidine incorporated into the 28S and 18S rANA species following their separation by agarose gel electrophoresis, compared with the level of [3H]cytidine incorporated into the nuclear rRNA. When all four fluoropyrimidines were compared together, the degree of inhibition of cytoplasmic rRNA production was poorly predictive of the total cytotoxicity in the absence of dThd (correlation coefficient, r = 0.77). FdUrd, in particular, had a very minor effect on rRNA production even at very toxic drug concentrations. When toxicity was assessed in the presence of dThd, however, there was a strong and significant correlation between rRNA production and RNA-directed cytotoxicity (r = 0.95, P less than 0.001), for all the fluoropyrimidines tested, including FdUrd. Thus, when the inhibition of thymidylate formation was eliminated as a site of drug action and only RNA-directed cytotoxicity was assessed, the impaired production of cytoplasmic rRNA was strongly associated with cytotoxicity. These results demonstrate that the inhibition of mature cytoplasmic rRNA production may be an important common mechanism of RNA-directed cytotoxicity for all the fluoropyrimidines, and not limited to FUrd or FUra.

Potentiation of the chemotherapeutic action of 5'-deoxy-5-fluorouridine in combination with guanosine and related compounds

The effect of inosine, guanosine, and guanosine 5'-monophosphate (GMP) on the antitumor activity of 5'-deoxy-5-fluorouridine (5'-DFUR) was investigated using P388 leukemia and P815 mastocytoma. The antitumor activity of 5'-DFUR was markedly enhanced by coadministration of inosine or guanosine. The increase in lifespan (ILS) of mice treated with 5'-DFUR was augmented by the combination with guanosine or inosine in a dose-dependent fashion, and the maximum ILS was about 160% with the combination, while that in the case of 5'-DFUR alone was only 48% in the P388 leukemia system. The therapeutic ratio (dose at ILSmax/dose at ILS30) of the combination with guanosine or inosine was 333 and 136, respectively, whereas that of 5'-DFUR alone was 3.6. GMP also markedly potentiated the antitumor activity of 5'-DFUR in both P388 leukemia and P815 mastocytoma systems, just as it potentiated the activity of 5-fluorouracil in the latter system. The uric acid level in the serum was elevated after IP injection of guanosine or inosine but the value was much lower in the case of guanosine than in inosine.

Effect of 5-fluorouracil on the cell growth and cell cycle kinetics of a mouse ascites tumor growing in vivo

The effect of 12, 24 and 36 mg/kg body weight doses of fluorouracil (5-FU) on the Bp 8 ascites sarcoma growing in vivo was studied. From sequential studies of the total number of cells together with the composition of cells in the cell cycle, the cell cycle flow was calculated and correlated to the pharmacokinetics, which was determined by using 3H-5-FU. The dose of 12 mg/kg 5-FU affected cell growth between 24 and 72 hours, while the effect of higher doses was immediate. An early block in outflow of cells from G1 was followed by an increased outflow, indicating an early inhibition followed by an enhancement of the initiation of the DNA synthesis. This increased outflow from G1 together with the decrease in outflow from the early S-phase, i.e. decreased DNA synthesis, resulted in an accumulation of cells in the early part of the S-phase. The prolonged effects on the cell growth and the cell cycle flow despite the very fast decline in the drug concentration both in the ascites fluid and within the cells, together with a constant level of the drug in the macromolecular fraction, suggest an interaction between 5-FU and RNA/DNA at later times rather than an inhibition of the thymidylate synthetase activity.

Concurrent allopurinol and 5-fluorouracil: 5-fluoro-2'-deoxyuridylate formation and thymidylate synthase inhibition in rat colon carcinoma and in regenerating rat liver

The formation of FdUMP and the inhibition of TS were studied in a subcutaneously growing transplantable rat colon carcinoma and in regenerating rat liver following bolus administration of 5-FU, with or without HPP pretreatment. In tumor, peak levels of FdUMP at 30 min following bolus 5-FU, 100 mg/kg, averaged 4931 +/- 587 pmol/g. Pretreatment with HPP, 50 mg/kg, 24 h and 1 h before 5-FU, reduced the peak FdUMP level to 2085 +/- 387 pmol/g. The inhibition of TS by 5-FU treatment was greater than 95% by 30 min, and after 48 h residual enzyme inhibition averaged 40%. No effect on TS inhibition by 5-FU treatment could be observed as a result of HPP pretreatment. The levels of TStot increased linearly after 5-FU treatment and doubled within 48 h. In regenerating rat liver, neither FdUMP levels nor TS inhibition, studied at 1 h after bolus 5-FU, were affected by HPP pretreatment.

Effects of administration routes on the uptake of uridine and 5-fluorouridine into an adenocarcinoma transplanted to rat liver

In a model of secondary liver cancer in Wistar rats, the effect of different administration routes on the uptake of 3H-uridine into tumor and several normal tissues was studied. The rats were inoculated with a tumor cell suspension in the central liver lobe. Ten days later, they were distributed into four groups with a catheter placed in the gastroduodenal artery, the portal vein, one of the femoral veins, or in the peritoneal cavity. 3H-uridine was injected 46 h later and after an additional 90 minutes the animals were anesthetised and pieces of liver tumor and normal tissues were removed and frozen. The incorporation into the acid-soluble fraction and RNA was analyzed. In a separate experiment, 3H-fluorouridine was administered by the gastroduodenal artery and a comparison was made with the uptake of 3H-uridine. A significantly higher amount of uridine was incorporated into the tumor by the arterial route. The intraportal and intraperitoneal routes were comparable, while a somewhat higher incorporation was found by the systemic route. The consequences of using the different routes upon the incorporation into RNA of tumor and dose-limiting organs are demonstrated. With the aid of this experimental model, it is possible to evaluate further the effect by different manipulations on different drugs regarding the administration route.